Thesis (MScAgric)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Shiraz/110R grapevines, growing in a fine sandy loam soil in the Breede River Valley, were subjected to ten different drip irrigation strategies during the 2006/07, 2007/08 and 2008/09 seasons. Grapevines of the control treatment (T1) were irrigated at 30% to 40% plant available water (PAW) depletion throughout the growing season. Grapevines of three treatments were irrigated at 70% to 80% PAW depletion from bud break until véraison (i.e. when ca. 95% of grape berries have changed colour), followed by either irrigation at 30% to 40% PAW depletion (T2) or a continuous deficit irrigation (CDI) strategy (T3) or irrigation at 70% to 80% PAW depletion (T4) during ripening. The CDI strategy was obtained by applying ca. half the volume of water that was applied to the control. This allowed the soil to dry out gradually between physiological stages (i.e. bud break and véraison or véraison and harvest). Grapevines of three further treatments were irrigated at ca. 90% PAW depletion from bud break until véraison, followed by irrigation at 30% to 40% PAW depletion (T5) or a CDI strategy (T6) or irrigation at ca. 90% PAW depletion (T7) during ripening. Grapevines of two treatments were irrigated by means of a CDI strategy from bud break until véraison. For both treatments, the soil water content (SWC) was allowed to dry out gradually until ca. 90% PAW depletion was reached. After véraison, the SWC of the one treatment was maintained at ca. 90% PAW depletion by applying only four small irrigations of three hours each during ripening (T8). The soil of the other treatment, received an irrigation at véraison to refill the SWC to field capacity (T9) followed by the CDI strategy during ripening. Grapevines of the tenth treatment were irrigated at ca. 90% PAW depletion between bud break and véraison followed by a partial profile refill (PPR) strategy during ripening (T10). In order to obtain the PPR strategy, SWC was only maintained between 40% and 60% PAW depletion. Evapotranspiration varied between 3.5 mm/day and 0.1 mm/day for driest and wettest treatments, respectively, during the period between December and February. This was substantially less than the volumes required for full surface irrigation. For irrigations applied at 30% to 40% PAW depletion (T1), 70% to 80% PAW depletion (T4) and ca. 90% PAW depletion (T7) levels throughout the season, crop coefficients for the Penman-Monteith reference evapotranspiration (ETo) were 0.4, 0.2 and 0.1, respectively. Under the given conditions, the different irrigation strategies did not have any effect on root distribution and density. Shoot growth of grapevines exposed to high to severe water deficits in the pre-véraison period stopped before mid December. Shoots of grapevines that were exposed to high or severe water deficits before véraison followed by more frequent irrigation during ripening showed active re-growth. These trends occurred during all the seasons. The level of PAW depletion reflected strongly in the plant water potential in the grapevines. Leaf water potential was influenced by the prevailing atmospheric conditions, whereas stem water potential was less sensitive to atmospheric conditions, but responded more directly to soil water availability. Due to the good relationships between pre-dawn leaf, mid-day leaf, mid-day stem and total diurnal water potential, it was possible to re-classify the water status in terms of previous classifications for these water potentials based on pre-dawn measurements. Water constraints in T1, T2 and T5 grapevines were classed as experiencing no stress, whereas the T7 and T8 ones experienced strong to severe water constraints before harvest. High frequency irrigation strategies during ripening delayed sugar accumulation due to dilution of sugar in the larger berries. Except for the wettest strategy, and where grapevines were subjected to the CDI strategy throughout the season, berry mass increased during ripening, i.e. from véraison to harvest. Water deficits had a negative effect on berry mass, bunch size and yield. Where higher soil water depletion levels were allowed, irrigation strategies had a positive effect on the irrigation water productivity of grapevines compared to the frequently irrigated or CDI strategies. Higher water constraints in grapevines, particularly during ripening, improved sensorial wine colour and enhanced some of the more prominent wine aromas, e.g. spicy and berry. Grapevines that were irrigated at a high frequency during ripening produced wines with diluted character flavours and aromas and inferior overall quality. Under the given conditions, sensorial wine colour and spicy character were the dominant factors in determining overall sensorial wine quality. / AFRIKAANSE OPSOMMING: Shiraz/110R wingerdstokke in ‘n fyn sandleem grond in die Breede Rivier vallei is gedurende die 2006/07, 2007/08 en 2008/09 seisoene met tien verskillende drupbesproeiingstrategieë besproei. Wingerdstokke van die kontrole (B1) is deur die seisoen by 30% to 40% plant beskikbare water (PBW) onttrekking besproei. Drie behandelings is tussen bot en deurslaan (wanneer ca. 95% van die korrels verkleur het) by 70% tot 80% PBW onttrekking besproei, gevolg deur besproeiing by 30% tot 40% PBW onttrekking (B2), ‘n deurlopende tekort besproeiing (DTB) strategie (B3) of besproeiing by 70% tot 80% PBW onttrekking (B4) gedurende rypwording. In die geval van die DTB strategie is ongeveer die helfte van die volume water toegedien wat by die kontrole toegedien is. Laasgenoemde strategie het die grond toegelaat om geleidelik tussen fisiologiese fases (i.e. tussen bot en deurslaan of tussen deurslaan en oes) uit te droog. Drie ander behandelings is by ca. 90% PBW onttrekking tussen bot en deurslaan besproei, gevolg deur besproeiing by 30% tot 40% PBW onttrekking (B5) of ‘n DTB strategie (B6) of besproeiing by ca. 90% PBW onttrekking (B7) gedurende rypwording. Wingerdstokke van twee ander behandelings is d.m.v. ‘n DTB strategie vanaf bot tot deurslaan besproei. Beide behandelings se grondwaterinhoud (GWI) was toegelaat om geleidelik uit te droog tot ca. 90% PBW onttrekking bereik was. Na deurslaan was die GWI van die een behandeling naby ca. 90% PBW onttrekking gehandhaaf deur slegs vier klein besproeiings van drie uur elk gedurende rypwording toe te pas (B8). Die grond van die ander behandeling het tydens deurslaan ‘n besproeiing ontvang om die GWI tot by veldkapasiteit te hervul (B9) en is tydens rypwording weer d.m.v. ‘n DTB strategie besproei. Stokke van die tiende behandeling is tussen bot en deurslaan by ca. 90% PBW onttrekking besproei, gevolg deur besproeiing d.m.v. ‘n gedeeltelike profiel hervul (GPH) strategie tydens rypwording (B10). Om ‘n GPH strategie toe te kon pas, is tussen 40% en 60% PBW ontrekking gehandhaaf. Evapotranspirasie het tussen 3.5 mm/dag en 0.1 mm/dag vir onderskeidelik die natste en droogste behandelings tussen Desember en Februarie gevarieer. Dit was aansienlik laer as volumes wat vir voloppervlak besproeide wingerde benodig word. In die geval van besproeiing by 30% tot 40% PBW onttrekking (B1), 70% tot 80% PBW onttrekking (B4) en ca. 90% PBW onttrekking (B7) deur die loop van die seisoen was die gewasfaktore vir die verwysingverdamping (ETo) 0.4, 0.2 en 0.1 onderskeidelik. Onder die gegewe toestande het die verskillende besproeiingstrategië geen effek op die worteldigtheid en –verspreiding gehad nie. Lootgroei van wingerdstokke wat aan hoë tot baie hoë watertekorte blootgestel was voor deurslaan, het voor middel Desember gestop. Lote van wingerdstokke wat aan hoë tot baie hoë watertekorte voor deurslaan blootgestel is, gevolg deur besproeiing teen ’n hoë frekwensie tydens rypwording, het aktiewe hergroei getoon. Die PBW ontrekkingspeil het sterk in die plantwaterpotensiale van wingerdstokke weerspieël. Blaarwaterpotensiaal is deur heersende klimaatstoestande beïnvloed, terwyl stamwaterpotensiaal minder sensitief teenoor die klimaat was, maar meer direk deur die beskikbaarheid van grondwater beïnvloed is. Vanweë die goeie verband tussen voordagbreek blaar-, mid-dag blaar-, mid-dag stam- en totale daaglikse waterpotensiaal, was dit moontlik om water status van die stokke te her-klassifiseer in terme van vorige vir waterpotensiaalklassifikasies wat op voordagbreek waardes gebasseer is. Waterspanning in B1, B2 en B5 stokke is as geen spanning geklassifiseer, terwyl dié van B7 en B8 voor oes in die hoë tot baie hoë klasse geval het. Hoë frekwensie besproeiing strategieë gedurende rypwording kan suikertoename a.g.v. die groter korrels vertraag. Met die uitsondering van die natste strategie, asook waar stokke volgens die DTB strategie deur die seisoen besproei is, het korrelmassa gedurende rypwording toegeneem. Watertekorte het ’n negatiewe effek op korrelmassa, trosgrootte en produksie gehad. Besproeiingstrategieë waar ’n hoë mate van grondwateronttrekking voor besproeiings toegelaat is, het ’n positiewe effek op die besproeiingwaterproduktiwiteit van wingerd in vergelyking met gereelde besproeiings of ‘n DTB strategie gehad. Watertekorte, veral gedurende rypwording, het ’n verbetering in sensoriese wynkleur en meer prominente wyn aromas, tot gevolg gehad. Besproeiing teen hoë frekwensies gedurende rypwording, het wyne met ’n afgewaterde smaak en aroma karakters asook ’n swak algehele gehalte produseer. Sensoriese wynkleur en spesery karakter die dominante faktore in die bepaling van algehele kwaliteit.

Thesis (MScAgric (Soil Science))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: The sandy soils of the Riverlands Nature Reserve, near Malmesbury, and the neighbouring farm were studied to determine the effects of long term invasion of the legume Acacia saligna on the soil nutrient content of a soil previously vegetated with fynbos. The effect of the removal of this alien legume on general soil properties and groundwater quality were also studied. The changes in nitrates and nitrites (NOX) due to the invasion and removal of the alien legume were investigated in more detail than changes in other soil nutrients. In addition to that emphasis was placed on the effect of vegetation clearing on groundwater quality, specifically relating to potential contamination with nitrates. This study was initiated after Conrad et al., (1999) found increased NOX concentrations in ground water while studying the effects of pig farming on ground water nitrogen (N) near a site cleared of Acacia saligna by Working for Water (WFW). Since many sites are scheduled for removal of this alien vegetation it was deemed necessary to study the effects that clearing alone had on groundwater quality. It was suspected that there would be an increase in soil and groundwater NOX with vegetation removal due to the inputs from the legume alien invader. Soil sampling was done continuously throughout the rainy season of 2007 (From May to December) on three adjacent sites separated by some 50 m of distance, consisting of a natural fynbos site and two Acacia saligna sites. The sites were selected approximately on the same contour line to prevent interaction through lateral water flow. One of the Acacia sites was cleared by the Working for Water programme in the usual manner leaving slash on the ground. Soil samples were collected at regular intervals throughout the season from all three sites (fynbos, Acacia and cleared site) using a Jarrett soil auger. They were airdried (to achieve full oxidation of mineral N) and sieved though a 2mm sieve. Soils were analysed by atomic absorption spectroscopy for basic cations and by ion chromatography for anions, including nitrates and nitrites. Total carbon and nitrogen was determined by combustion, pH (1M KCl and H2O) and EC (1:5 H2O) were also measured. The present study was part of a wider investigation into the quality of groundwater, modelling flow and contaminant transport (Jovanovic et al., 2008). The largest changes in soil properties were observed in the top (0-5 cm) layer. The fynbos site had a lower nutrient status by comparison to the Acacia site and the cleared site. The sum of cations from the soils of the fynbos site at a soil depth of 0-5cm was 100mg/kg and soils from the cleared and Acacia sites were about 190mg/kg. The Acacia site had a higher NOX status and experienced a larger NOX fluctuation during the rainy season than the fynbos site; minimum NOX values were similar (below 10mg/kg) but the Acacia site had a maximum NOX value of near 60mg/kg and the fynbos site just below 30mg/kg. There was little difference in general soil characteristics (exchangeable cations, pH and EC, total soil C and N) during the first season after clearing, between the Acacia and the cleared sites. The effect of soluble nitrogen changes due to alien legume invasion and removal on groundwater quality, relating to NOX, during the first season after clearing, was determined. It was found that the Acacia site had higher NOX concentrations than the fynbos site. At 0-5cm the fynbos site NOX was less than 30mg/kg and the Acacia site was between 30 and 110mg/kg for most of the season, with values lower than 30mg/kg for the last four sampling dates only. N concentrations on the cleared site behaved in a similar manner to the uncleared Acacia site, but generally N values were lower on the cleared site, there were only two sampling dates where the cleared site had higher NOX values than the Acacia site at 0-5cm. The average groundwater N in NOX under the cleared site was 4.34 mg/l, and under the Acacia site 3.78mg/l, these values are both below the level determined for water contamination with nitrates. However, the increase in ground water nitrate levels after A. saligna clearing was significant. It was concluded that there is a change in the nutrient status of soil with Acacia invasion and again with removal. NOX migrates to the groundwater to a larger degree once vegetation has been removed, although during this study the nitrate pollution threshold of 10 mg/l nitrate N was not reached. / AFRIKAANSE OPSOMMING: Die sanderige gronde van die Riverlands Natuur Reservaat, naby Malmesbury, en die aangrensende plaas was bestudeer om die effek van die langtermyn indringing van die peulgewas, Acacia saligna, op die voedingswaarde van ‘n voorheen fynbos begroeide grond, sowel as die effek van die verwydering van die indringer op die algemene samestelling van die grond en grondwater kwaliteit. Oplosbare stikstof veranderings (NOX) wat plaasvind as gevolg van die indringing en verwydering van die indringer peulgewas, was in meer diepte bestudeer as die ander elemente. Klem was ook geplaas op die effek van die verwydering van plantegroei op grondwater kwaliteit, met spesifieke verwysing na potensiële nitraat besoedeling. Die studie was beplan na Conrad et al., (1999) ‘n toename van NOX konsentrasies in grondwater ontdek het, tydens ‘n studie van die effek wat vark boerdery het op grondwater N naby ‘n area waar Acacia Saligna verwyder was deur Working For Water (WFW). As gevolg van die feit dat verskeie areas in die proses is om skoongemaak te word van Acacia Saligna, is dit nodig geag om die effek daarvan of grondwater kwaliteit te ondersoek. Die hipotesis was dat daar ‘n toename in NOX konsentrasies in grond en grondwater sal wees as gevolg van die verwydering van plantegroei. Grond monsters was deurlopend geneem gedurende die reën seisoen van 2007 (Vanaf Mei tot Desember) uit nabygeleë areas wat omtrent 50 meter uitmekaar is. Die volgende tipes grond was verteenwoordig: ‘n Fynbos begroeide grond sowel as ‘n grond begroei met Acacia saligna. Die areas was geselekteer ongeveer op die selfde kontoer lyn om interaksie tussen areas te voorkom as gevolg van laterale water vloei. ’n Gedeelte van die A. saligna area was skoongemaak deur die Working for Water program op die gewone manier deur die afgesnyde plant materiaal op die grond te los. Grond monster was geneem met gereelde intervalle gedurende die seisoen op al drie areas (fynbos, A. saligna, en skoongemaakte area) deur die gebruik van ’n Jarret grondboor. Die monsters was lugdroog gemaak (om volle oksidasie van die mineraal N te verseker) en toe gesif deur ‘n 2mm sif. Die gronde was analiseer deur atoom absorpsie vir basiese katione en deur ioon chromatografie vir anione, insluitende nitriete en nitrate. Totale koolstof en stikstof was bepaal deur verbranding terwyl pH (1M KCl en H2O) en EC (1:5 H2O) ook gemeet was. Hierdie studie was deel van ‘n wyer ondersoek na die kwaliteit van grondwater, vloei modelering en vervoer van kontaminante (Jovanovic et al., 2008). Die grootste veranderinge in die grond eienskappe was in die boonste grondlaag (0-5cm) waargeneem. Die bevinding was dat die fynbos area ‘n laer voedingswaarde het as die area begroei met die indringer sowel as die die skoongemaakte area. Die som van katione onder fynbos grond by ‘n grond diepte van 0-5cm, was 100/mg/kg en die som van katione by die ander twee areas was omtrent 190mg/kg. Die Acacia area het ‘n hoër NOX inhoud en het ‘n groter NOX fluktuasie ervaar gedurende die reën seisoen as die fynbos area. Die minimum NOX waardes was soortgelyk (minder as 10/mg/kg), maar die Acacia area het ‘n maksimum NOX waarde van omtrent 60mg/kg terwyl die fynbos area se maksimum net minder as 30mg/kg gehad het. Daar nie veel verskil tussen die algemene grond eienskappe (uitruilbare katione, pH en EC, totale C en N) van die Acacia en skoongemaakte areas gedurende die eerste seisoen na die indringer verwyder is nie. Die effek van oplosbare stikstof veranderings as gevolg van die peulgewas se indringing en verwydering op grondwater kwaliteit, met verwysing na NOX, gedurende die eerste seisoen na verwydering van die indringer was bepaal. Dit was bevind dat die Acacia area ‘n hoër NOX konsentrasie as die fynbos area het. Op ‘n diepte van 0-5cm was die fynbos NOX laer as 30mg/kg terwyl die Acacia area tussen 30 en 110mg/kg vir die grootste gedeelte van die seisoen was met waardes laer as 30mg/kg vir die laaste vier datums waarop monsters geneem was. Veranderings in N op die skoongemaakte area en die Acacia area was soortgelyk, maar oor die algemeen was N waardes laer op die skoongemaakte area. Daar was slegs op twee datums gevalle gevind waar die skoongemaakte area ‘n hoër NOX inhoud as die Acacia area gehad het by ‘n diepte van 0-5cm. Die gemiddelde N in NOX in die grondwater onder die skoongemaakte area was 4.34mg/l en by die Acacia area was dit 3.78mg/l; hierdie waardes is onder die drempel vir nitraatbesoedeling in grondwater. Die nitraat inhoud van die grondwater het wel beduidend toegeneem as gevolg van verwydering van A. saligna. Die gevolgtrekking was dat daar ‘n verandering plaasvind in die voeding status van grond met Acacia saligna indringing en weer met verwydering. NOX migrasie na die grondwater verhoog met verwydering van plantegroei. In hierdie studie was die nitraat besoedeling drempel van 10mg/l nitraat N nie bereik nie.

Thesis (MScAgric (Soil Science))--University of Stellenbosch, 2007. / South Africa is a water scarce country and in certain regions the quantity of surface water is insufficient to provide communities with their domestic water needs. In many arid areas groundwater is often the sole source of water. This total dependence means that groundwater quality is of paramount importance. A high nitrate concentration in groundwater is a common cause of water being declared unfit for use and denitrification has been proposed as a potential remedy. In groundwater of the Marydale district in the Northern Cape Province, nitrate levels are high enough to be of concern for domestic and livestock consumption. A review of the literature indicates that bacterial denitrification of groundwater can be achieved in situ by using a suitable energy substrate. The technology has been tested elsewhere in the world but more certainty is needed on whether it is a feasible option for local groundwater remediation using local, cost-effective energy substrates and exploiting bacterial populations present naturally in the regolith. The objective of this study was to perform denitrification experiments by laboratory incubation using soil and groundwater samples collected in Marydale in order to determine; 1) The effectiveness of different carbon sources; 2) The effect of using soil sampled at different depths; 3) The effect of C:N ratio of the carbon substrate; and 4) The quality of resultant water. Various experiments were set up using 10 g soil and 40 mL groundwater with different concentrations of carbon sources (sawdust, glucose, maize meal and methanol). All experiments were done under a nitrogen atmosphere to exclude oxygen and temperature was kept constant at 23 °C. Indicator parameters were selected based on literature review, and major cations and anions and some metals were analysed for initially and at selected times during each experiment to evaluate whether major ion chemistry was changing over time. Parameters analysed in supernatant solutions after varying periods of time to indicate progress of denitrification and reduction included nitrate, nitrite, sulfate, alkalinity, chloride, acetate, basic cations, ammonium, pH, electrical conductivity, dissolved organic carbon, heteThe Marydale groundwater in some boreholes is of predominantly NaCl type and the nitrate concentration of 19-32 mg/L as N exceeds ideal limits for drinking water of 6mg/L as N . Two soil materials were sampled at different depths from a red sand overlying calcrete (Plooysburg form, Family Py1000). The incubation experiments showed denitrification was complete within a period of between 1 and 6 weeks depending on the carbon substrate and C:N used. Higher rates of nitrate removal were achieved where greater C:N was used. Readily degradable carbon substrates e.g. glucose showed rapid denitrification, while sawdust, a slowly degradable substrate, effected slower denitrification, hence it was concluded that intermediately degradable carbon substrates e.g. wheat straw may prove more suitable. Use of shallower soil material containing initially higher nitrate levels resulted in better denitrification rates, however, both soil materials effected denitrification.. Heterotrophic plate counts increased with time, this presence and growth of heterotrophic bacteria confirmed that conditions were optimum for growth and denitrification and that inoculation with bacteria is not a requirement for in situ denitrification. Dissolved organic carbon (DOC) concentration could be directly correlated to the initial input of carbon substrate as soil and groundwater lacked organic material. Results showed that reaction products such as acetate and nitrite, and basic cation concentrations were elevated in the supernatant solution in preliminary experiments. This was interpreted to be attributed to incomplete oxidation of organic material and excess soluble and available carbon for reaction. Cation concentrations were interpreted to have resulted from a decrease in pH brought on by organic acids produced during denitrification. The method used showed specificity, as the only parameters affected by the denitrification experiment were DOC, alkalinity, nitrite, nitrate, and the heterotrophic plate count. The DOC and HPC did not comply with acceptable levels for drinking water. Removal of HPC by boiling or chlorinating is required to ensure that the resultant water composition is of potable quality. For further research with slowly degradable carbon sources it is recommended that a C:N ratio of more than 12 should be employed, and monitoring should focus on soluble carbon nitrate, nitrite, and heterotrophic plate count. The study confirmed that denitrification of this groundwater with a range of carbon sources is possible within a short period of anaerobic contact with local soil material. With sufficient knowledge of the characteristics of the soil and groundwater in the area, establishment of a working in situ denitrification plant is probably feasible.

Thesis (MScAgric (Soil Science)--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: A number of chemical and physical features of Namibian soils in a 22 790 km2, two degree-square block between 17 – 19 oE and 22 – 23 oS in eastern central Namibia, had been investigated, and the fertility status established. In 80 % of samples the nitrate, nitrite, and sulfate concentrations of the saturated paste extract are 0 – 54.6 mg l-1 NO3 -, 0 – 24.7 mg l-1 NO2 -, and 5.4 – 20.9 mg l-1 SO4 2- respectively. In 90 % of samples the plantavailable phosphorus is below 12 mg kg-1, which is low for a soil under natural grassland, but in line with the prevailing semi-arid climate and low biomass production of the study area. In 80 % of samples the extractable calcium, magnesium, potassium, and sodium concentrations are 0.61 – 5.73 cmolckg-1 Ca (122 – 1 146 mg kg-1 Ca), 0.12 – 2.28 cmolckg-1 Mg (15 – 278 mg kg-1 Mg), 0.13 – 0.54 cmolckg-1 K (51 – 213 mg kg-1 K) and 0.05 – 0.38 cmolckg-1 Na (11 – 87 mg kg-1 Na) respectively, while the exchangeable calcium, magnesium, potassium, and sodium concentrations are 0.21 – 6.02 cmolckg-1 Ca, 0.12 – 2.01 cmolckg-1 Mg, 0.12 – 0.49 cmolckg-1 K and 0 – 0.13 cmolckg-1 Na respectively. The mean ± 1 standard deviation is 3.57 ± 3.57 cmolckg-1 for cation exchange capacity, 3.48 ± 3.61 for sum of exchangeable bases and 4.53 ± 4.39 for sum of extractable bases. The cation exchange capacity and the sum of exchangeable bases are virtually identical, which indicate the almost complete absence of exchangeable H+ and Al3+ in the soils of the study area, as expected from a semi-arid climate. None of the profiles were classified as saline or sodic. In 80 % of samples the plant-available iron, manganese, zinc and copper concentrations are 7.2 – 32.8 mg kg-1 Fe, 13.6 – 207.5 mg kg-1 Mn, 0 – 1.80 mg kg-1 Zn and 0 – 4.0 mg kg-1 Cu respectively. Soil organic matter content of the study area soils ranges between 0.05 – 2.00 %, with most (80 % of samples) containing 0.25 – 1.20 % organic matter. This is considerably lower than values reported in literature, even for other southern African countries. The reason lies with the hot, semi-arid climate. The pH distribution is close to normal, with 80 % of samples having pH (H2O) of 5.54 – 8.18, namely moderately acid to moderately alkaline. Sand, silt and clay content of most (80 %) samples varies between 60.3 – 89.7 % sand, 4.6 – 25.2 % silt and 3.5 – 19.1 % clay. The soils of the study area are mainly sandy, sandy loam and loamy sand. In 80 % of samples the coarse sand fraction ranges from 3.5 – 34.5 %, the medium sand fraction from 20.5 – 37.3 %, the fine sand fraction from 38.7 – 54.5 % and the very fine sand fraction from 0.0 – 12.9 % of all sand. The fine sand fraction, thus, dominates, with very fine sand being least abundant. The topsoil contains relatively more coarse sand and less very fine sand than the subsoil. Instances of sealing, crusting and hardening occur sporadically in the study area. Cracking is only found in pans, while self-mulching is not evident. No highly instable soils were encountered in the study area. The water-holding capacity is generally low, with depth limitations in the western highlands, the Khomas Hochland, and texture limitations in the eastern Kalahari sands. The central area has soils with a somewhat better water-holding capacity, but it is still very low when compared to arable soils of temperate, sub-humid and humid zones elsewhere in southern Africa. Soil characteristics are perceptibly correlated with climate, parent material, topography, degree of dissection of the landscape and position in the landscape. The most obvious differences are between soils formed in schistose parent material of the Khomas Hochland in the west and those of the Kalahari sands in the east. The soils of the study area are unsuitable to marginally suitable for rainfed crop production, due to low iv fertility. The study area is climatologically unsuited for rainfed crop production, so the present major land use is extensive livestock production on large farms. The natural vegetation is well adapted to the prevailing conditions. The methodology followed to delineate terrain units, with a combination of procedures involving digital elevation data and satellite imagery, seems to work well in the Namibian landscape. This study thus served as a successful proof-of-concept for the methodology, which can in future be rolled out for the remainder of the country. The site and analytical information is available in digital format as spreadsheets and in a geographical information system, as well as in a variety of digital and printed maps. / AFRIKAANSE OPSOMMING: ‘n Aantal chemiese en fisiese eienskappe van Namibiese gronde in ‘n 22 790 km2, 1o x 2o blok tussen 17 – 19 o Oos en 22– 23 o Suid in oostelike sentraal-Namibië is ondersoek en die grondvrugbaarheidstatus bepaal. In 80 % van monsters is die nitraat-, nitriet- en sulfaatkonsentrasies van die versadigde pasta ekstrak 0.0 – 54.6 mg l-1 NO3 -, 0.0 – 24.7 mg l-1 NO2 -, en 5.4 – 20.9 mg l-1 SO4 2-onderskeidelik. In 90 % van monsters is die plant-beskikbare fosfor minder as 12 mg kg-1, wat laag is vir gronde onder natuurlike grasveld, maar dit is verklaarbaar deur die heersende semi-ariede klimaat en lae biomassa produksie in die studiegebied. In 80 % van monsters is die konsentrasies van ekstraheerbare kalsium, magnesium, kalium en natrium 0.61 – 5.73 cmolckg-1 Ca (122 – 1 146 mg kg-1 Ca), 0.12 – 2.28 cmolckg-1 Mg (15 – 278 mg kg-1 Mg), 0.13 – 0.54 cmolc kg-1 K (51 – 213 mg kg-1 K) en 0.05 – 0.38 cmolckg-1 Na (11 – 87 mg kg-1 Na) onderskeidelik, terwyl die uitruilbare kalsium, magnesium, kalium en natrium konsentrasies onderskeidelik 0.21 – 6.02 cmolckg-1 Ca, 0.12 – 2.01 cmolckg-1 Mg, 0.12 – 0.49 cmolckg-1 K and 0.0 – 0.13 cmolckg-1 Na is. Die gemiddelde ± 1 standaardafwyking is 3.57 ± 3.57 cmolckg-1 vir katioonuitruilvermoë, 3.48 ± 3.61 vir die som van uitruilbare basisse en 4.53 ± 4.39 vir die som van ekstraheerbare basisse. Die katioonuitruilvermoë en som van uitruilbare basisse is feitlik identies, wat ‘n feitlik algehele afwesigheid van uitruilbare H+ and Al3+ in die gronde van die studiegebied aandui, soos verwag word weens die semi-ariede klimaat. Geeneen van die profiele is geklassifiseer as soutbrak of natriumbrak nie. In 80 % van monsters is die plant-beskikbare yster, mangaan, sink en koper konsentrasies onderskeidelik 7.2 – 32.8 mg kg-1 Fe, 13.6 – 207.5 mg kg-1 Mn, 0.0 – 1.80 mg kg-1 Zn en 0.0 – 4.0 mg kg-1 Cu. Grond organiese material inhoud in die studiegebied wissel tussen 0.05 – 2.00 %, met 80 % van monsters wat 0.25 – 1.20 % organiese material bevat. Dit is aansienlik laer as die waardes gevind in literatuur, selfs vir ander Suider-Afrikaanse lande. Die oorsaak is die warm, semiariede klimaat. Die pH verspreiding is feitlik normaal, met 80 % van monsters wat pH (H2O) van 5.54 – 8.18 het, met ander woorde matig suur tot matig alkalies. Sand, slik en klei inhoud van die meeste (80 %) monsters varieer tussen 60.3 – 89.7 % sand, 4.6 – 25.2 % slik en 3.5 – 19.1 % klei. Die gronde van die studiegebied is hoofsaaklik sand, sand-leem en leem-sand. In 80 % van monsters beslaan die growwe sandfraksie 3.5 – 34.5 %, die medium sandfraksie 20.5 – 37.3 %, die fyn sandfraksie 38.7 – 54.5 % en die baie fyn sandfraksie 0.0 – 12.9 % van die totale sandfraksie. Die fyn sandfraksie is dus dominant, terwyl die baie fyn sandfraksie die skaarsste is. Die bogronde bevat relatief meer growwe sand en minder baie fyn sand as die ondergronde. Gevalle van verseëling, korsvorming en verharding kom sporadies in die studiegebied voor. Krake kom net in panne voor en self-omkering is nie opgemerk nie. Geen hoogsonstabiele gronde is in die studiegebied gevind nie. Die waterhouvermoë is in die algemeen laag, met dieptebeperkinge in die westelike hooglande, die Khomas Hochland, en tekstuurbeperkinge in die oostelike Kalahari sande. Die sentrale gedeelte het gronde met ‘n ietwat beter waterhouvermoë, maar dis steeds baie laag in vergelyking met akkerbougronde van gematigde, sub-humiede en humiede sones elders in Suider- Afrika. Grondeienskappe is ooglopend verwant aan klimaat, moedermateriale, topografie, graad van gebrokenheid van die landskap en posisie in die landskap. Die duidelikste verskille kom voor in die gronde wat van vi skisagtige moedermateriaal van die Khomas Hochland in die weste en dié wat in die Kalahari sande in die ooste gevorm het. Die gronde van die studiegebied is ongeskik tot marginaal geskik vir droëland akkerbou, weens die lae vrugbaarheid. Aangesien die studiegebied klimatologies ongeskik is vir droëland akkerbou, is die huidige hoof landgebruik ekstensiewe veeproduksie op groot plase. Die natuurlike plantegroei is goed by die heersende omstandighede aangepas. Die metodiek wat gevolg is om terreineenhede af te baken, wat ‘n kombinasie van prosedures met digitale hoogtedata en satellietbeelde is, blyk goed te werk vir die Namibiese landskap. Hierdie studie dien dus as ‘n suksesvolle bewys-van-konsep van die metodiek, wat in die toekoms uitgebrei kan word na die res van die land. Die veld- en ontledingsinligting is beskikbaar in digitale formaat, in ‘n geografiese inligtingstelsel en ‘n verskeidenheid digitale- en gedrukte kaarte.

Thesis (MScAgric (Soil Science))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The Renosterveld of the Western Cape region is often seen as a natural occurring veld type that will very easily re-establish itself wherever land is left unattended. In this study it was firstly noted that where wheatlands of the Berg River catchment (BRC) is left bare for a number of years, the renosterbos as a pioneer is slow in its re-growth response and when it does, certain patches in the landscape are preferred. This study therefore firstly focussed on the soil restrictions that widely determined the positions in the Berg River landscape where the renosterbos will re-establish itself. Secondly we needed to know whether some of the soil restrictions encountered could be alleviated and was possibly due to cultivation of this land. Through aerial observation it was found that a general patchiness does exist in the naturally occurring Renosterveld of the Voëlvlei area and hill tops of the region and was described by others as the true nature of this veld type. Closer investigation of the soils in the Voëlvlei reserve however showed that soil type played a major role in the patchiness found here. When re-growth of the renosterbos in previously cultivated areas was investigated, it was found that the soil type played the major role in the patchiness that occurred. The most commonly found soil restriction was soil density of the lower horizons. Any soil form that prevented the renosterbos to access the perched water table, to about 15m depth could not support the renosterbos. It is however our belief that soil could be prepared for the re-growth of renosterbos and through this action; renosterbos could also be used to alleviate the salinity problems found in this region. Additionally we investigated the impact of land-use change on the soil water balance and soil salinity by comparing a mature re-established stand of Renosterveld with an adjacent wheatfield. From the results, large differences in salinity and soil water behaviour were detected between the Renosterveld and wheatfield. Modelling of soil and plant water relations was done and the results were correlated well with field observations. This research also confirmed that the renosterbos through its deep rootedness is crucial in the conservation of other species found in the Renosterveld resulting from its ability to keep the water table down and with that the salts that is so often a problem in this area. / AFRIKAANSE OPSOMMING: In die Wes-Kaap word Renosterveld gesien as 'n veld tipe wat natuurlik voorkom en maklik sal hervestig in areas waar land sonder toesig gelaat word. In hierdie studie is dit eerstens opgemerk dat waar koringlande in die Berg Rivier opvanggebied kaal gelaat word vir 'n aantal jare, is die renosterbos as pionier stadig in sy hervestiging en wanneer terug groei wel plaasvind is dit selektief. Die studie fokus dus eerstens op grondbeperkinge wat die areas bepaal waar Renosterveld sal hervestig. Tweedens wou ons vasstel of die grondbeperkings wat voorkom in die grond en wat heel moontlik die oorsaak is van landbewerking opgehef kan word. Deur lugfoto-waarneming is dit gevind dat algemene leë kolle wel opgemerk is in die natuurlik plantegroei van die Renosterveld, in die Voëlvlei area, asook teen die berg hange. Dit word beskryf as 'n algemene kenmerk van die Renosterveld. Nadere ondersoek in die verskillende grondtipes van die area het egter gewys dat die grond tipe 'n belangrike rol speel in die voorkoms en groei van die renosterbos en uiteindelik die (her-)vestiging van Renosterveld. Die terug groei van die renosterbos is ondersoek in voorheen bewerkte lande. Dit is gevind dat die grond tipe 'n belangrike rol speel in die voorkoms van die leë kolle in die Renosterveld. Die mees algemene grond beperking wat opgemerk is, was die verdigte sub-horisonte. Enige grondvorm wat toegang van die renosterboswortels tot by die grondwatertafel (tot by 'n diepte van 15m) beperk, is nie voldoende om die groei van 'n volwasse renosterbos te onderhou nie. Dit is egter ons oortuiging dat die grond voorberei kan word vir die hervestinging van die renosterbos en deur dit te bewerkstellig sal grondversouting beheer kan word. Die impak van landgebruikverandering op die grondwaterbalans en grondversouting is ook ondersoek, deur 'n volwasse stand van Renosterveld te vergelyk met 'n nabygeleë koringveld. Die resultate het getoon dat daar groot verskille in die grondwatervlakke, asook die soutinhoud tussen die Renosterveld en die koringland voorkom. Modellering van die grond-en plantwaterverhouding is uitgevoer en data het goed gekorreleer met veld waarnemings. Die studie het bevestig dat die natuurlike bewaring van die diep gewortelde renosterbos noodsaaklik is vir die voortbestaan van blom- en skilpadspesies wat slegs in die Renosterveld voorkom asook die vermoë van die renosterbos om stygende watertafels en versouting te beheer waar dit dikwels 'n probleem in hierdie area is.

Thesis (MScAgric (Soil Science))--University of Stellenbosch, 2011. / Includes bibliography. / ENGLISH ABSTRACT: The natural resource condition or health has been accepted as a valuable indicator of sustainable land use. The assessment of soil health (quality) has become a valuable tool in determining the sustainability of land management systems. This work aims to evaluate the sustainability of soil management practices in agricultural extension for vineyards in Robertson, South Africa based, on the current approach of the concept of soil health and soil quality, as well as to briefly explore the present reservations regarding the definition of the concept. The soil management treatments include a mechanical weed control, chemical weed control, annual addition of straw mulch, annual cover crop and perennial cover crop. The objective of study is to (i) identify suitable soil health (quality) indicators for vineyards in the study area; (ii) analyze the soil health (quality) indicators for different soil management treatments; (iii) evaluate the effect of various soil management treatments on the overall soil functionality, by comparing measured indicators to the soil property threshold values, for optimal vine growth; iv) establish a more consistent understanding and use of the terms health and quality, as understood and used in the general science community, with particular reference to the public health system. The soil physical, chemical and biological properties which were selected as indicators of soil health (quality) based on specific criteria similar to previous work done on the concept. The properties selected include soil texture, gravimetric water content, bulk density, soil aeration, water aggregate stability, soil pH, EC, available N,P,K , soil organic matter content, soil microbial biomass, potential mineralizable nitrogen and soil respiration. The study makes use of methods of analysis previously used for soil health and soil quality assessments, as well as soil analytical methods as accepted by experienced soil scientist within the study area. The soil was sampled on three separate events to depths of 0-200 mm for initial characterization of soil and 0-50 mm to compare soil health (quality) Between tracks and In tracks of treatment plots. The values obtained for each property were compared with the optimum for vineyards and ranked accordingly. The treatment that resulted in the most desirable soil health (quality) was the straw mulch and perennial cover crop treatments. / AFRIKAANSE OPSOMMING: Die toestand of gesondheid van natuurlike hulpbronne is aanvaar as `n waardevolle aanduiding van volhoubare grondgebruik. Die assessering van grond gesondheid (kwaliteit) is 'n waardevolle hulpmiddel in die bepaling van die volhoubaarheid van grond bestuur stelsels. Hierdie werkstuk poog om die volhoubaarheid van grond bestuurs praktyke te evalueer vir wingerde in Robertson, Suid-Afrika wat baseer is op die huidige benadering van grond gesondheid en kwaliteit. Die tesis dek ook die huidige onsekerhede oor die konsep en definisies van terme wat gebruik word in die konsep. Die grond bestuur praktyke sluit in 'n meganiese onkruidbeheer, chemiese onkruidbeheer, jaarlikse toevoeging van `n strooi deklaag, jaarlikse en meerjarige dekgewas dekgewasse. Die doel van die studie was om (i) die geskikte grond gesondheid (kwaliteit) indikators vir wingerde in die studie area te identifiseer, (ii) die grond gesondheid (kwaliteit) indikators vir verskillende bogrond bestuur praktyke te identifiseer; (iii) die effek van verskillende grond bestuur praktyke op die algehele grond funksies te evalueer, deur dit te vergelyk met die gemete indikators vir drempelwaardes vir optimale wingerd groei; iv) 'n meer konsekwente begrip en gebruik van die terme “gesondheid” en “kwaliteit” vas te stel, soos dit verstaan en gebruik word in die algemene wetenskaplike gemeenskap, met spesifieke verwysing na die openbare gesondheidsisteem. Die grond fisiese, chemiese en biologiese eienskappe wat as indikators van grond gesondheid (kwaliteit) geselekteer was, word gebaseer op spesifieke kriteria soortgelyk aan dié wat in vorige werk op die konsep gedoen was. Die eienskappe wat geselekteer is sluit in grondtekstuur, gravimetriese waterinhoud, bulk digtheid, grond deurlugting, totalle water stabiliteit, grond pH, electriese geleiding, toeganklike N, P, K, grond organiese materiaal inhoud, grond mikrobiese massa, potensiële mineraliseerbare stikstof en grond respirasie. Die studie maak gebruik van analitiese metodes wat voorheen gebruik was vir grond gesondheid en kwaliteit, sowel as die grond analitiese metodes soos gebruik deur ervare grondkundiges binne die studie gebied. Die grondmonsters was geneem op drie afsonderlike geleenthede oor dieptes van 0-200 mm vir die aanvanklike karakterisering van grond en 0-50 mm, om grond gesondheid (kwaliteit) Tussen trekkerspore en In trekkerspore van die persele te vergelyk. Die waardes verkry vir elke eienskap was vergelyk met die optimum vir wingerde en verdeel volgens kwaliteit. Die behandeling wat die mees optimale grond gesondheid (kwaliteit) getoon het, was die strooi deklaag en meerjarige dekgewas behandelings.

A greenhouse study was carried out to investigate the effectiveness of soil-applied silicon (Si) with that of foliar applications for sorghum growth. Silicon sources were soil-applied as calmasil (calcium silicate) at two rates (4 and 8t/ha) and foliar applied Si including pure K-silicate, K-humate and K-fulvate (all three foliar treatments at rates of 300 and 600 ppm). Another treatment included soil applied calmasil plus low rate of foliar applied K-humate. The soils used for the greenhouse trial were Cartref, Glenrosa, Nomanci and Fernwood. Results indicated that application of calcium silicate to the soil before planting increased sorghum yield and Si uptake in three of the four soils. Silicon uptake from different experimental treatments followed the order: Calmasil 8t/ha > calmasil 4t/ha ~ calmasil + 300 ppm K-humate> K-humate = K-fulvate = pure-K silicate = control. Foliar sprays were ineffective at increasing yield, Si content of the plant tissues or Si uptake. The concentrations of exchangeable Ca, Mg as well as soil pH were significantly increased by calmasil treatments. Extractable AI concentrations were also reduced due to the Iiming effect of calcium silicate and also possibly formation of insoluble aluminosilicates. The yield response to applied calmasil seemed to be primarily related to its Iiming effect and reductions in extractable AI in the Cartref, Glenrosa and Nomanci soils. The dry matter yield was highest in Fernwood and lowest in Cartref soil. However, there was no significant yield response to calmasil in Fernwood soil which had an initial pH of 5.8 and insignificant extractable AI concentrations. Therefore application of calcium silicate had no significant effect on extractable AI concentration in this soil. Yield response to calmasil may also have been partly due to direct positive effects of applied Si on crop growth through mechanisms such as increased photosynthetic rate and reduced transpiration rate, Addition of calmasil increased the concentrations of Si in the plant tissues and reduced those of N, P and Kin Nomanci and Fernwood soils respectively. This indicates that nutrient interactions were occurring in the plant. It was concluded that foliar-application is not an effective way of applying Si to a Siresponsive crop such as sorghum when growing in soils low in extractable soil Si. This is because Si is accumulated in plant tissues in similar amounts to macronutrients. It was also concluded that in future, studies of crop response to applied Si should include the use of non-Iiming source of Si (e.g. silicic acid) so as to separate a liming effect of calcium silicate from effect of applied Si. In a laboratory study, the effects of applied silicic acid, calcium silicate and calcium hydroxide on levels of extractable P in two Si-deficient soils were investigated. Two soils (Fernwood and Nomanci soils) were treated with two rates of P and three soil amendments (calcium silicate, calcium hydroxide and silicic acid) and incubated for six weeks at room temperature. Phosphorus was extracted using Truog, AMBIC and resin methods, and levels of exchangeable and solution AI and extractable and solution Si were also measured. Application of calcium silicate and calcium hydroxide increased soil pH in both soils while silicic acid additions had no significant effect compared with the control. The pH increase was much greater in the Fernwood than Nomanci soil because of the low buffering capacity of the sandy Fernwood soil. Exchangeable AI and concentrations of monomeric and total AI in soil solution generally followed the order: control ~ silicic acid> calcium silicate> calcium hydroxide. The lowering of soluble AI concentrations in the silicic acid treatments was attributed to formation of insoluble aluminosilicate compounds while that in the calcium silicate and calcium hydroxide treatments was attributed to their Iiming effects causing a rise in pH. Concentrations of Si in soil solution were lower in the calcium hydroxide than the control treatment suggesting the solubility of Si decreased with increased pH. Additions of both Si sources increased Si concentrations in solution and the effect was more marked for the calcium silicate treatment. This was attributed to formation of insoluble aluminosilicates in the silicic acid treatment. Concentrations of H2S04extractable Si with treatment did not closely follow the same trends as those for Si concentrations in soil solution. That is, levels of extractable Si were very much higher in the calcium silicate than silicic acid treatment in both soils. In addition, concentrations of extractable Si in the calcium hydroxide treatment were similar to control in the Nomanci soil, while for the Fernwood soil, concentrations in the calcium hydroxide treatment were exceptionally high. It was suggested that liming with calcium silicate or calcium hydroxide had rendered some Si-containing compounds in the soil acid-extractable and that the nature of acid-extractable Si fraction need further study in future. The quantities of P extracted from the two soils by the various extractants followed the order: Truog> AMBle> resin. The greatest increase in extractable P induced by additions of P was recorded for Truog P and the least for resin P. The effects of Iiming (addition of calcium silicate or calcium hydroxide) on extractable P levels differed depending on the soil and extractant used with increase, decrease or no effect being recorded. Such results confirm the complexity of lime and P interactions which occur in acid soils. Additions of silicic acid had no effect on levels of extractable P, compared to control. It was suggested that the reason for this was that phosphate is adsorbed to AI and Fe oxide surfaces much more strongly than silicate. As a result, additions of Si are ineffective at increasing extractable P levels. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.

Water treatment residues (WTRs) are the by-product from the production of potable water. They consist mainly of the precipitated hydrous oxides of the treatment chemicals, and materials removed from the raw water. This study investigated the range of treatment processes and residues produced in South Africa, and two WTRs were selected for testing on selected soils and mine materials. A questionnaire was developed and sent to water treatment authorities across South Africa. Information on the treatment chemicals, dosages, volumes and current disposal practices, and a sample of WTR from each treatment plant were requested. Eleven, of 21 authorities, returned completed questionnaires, representing 37 water treatment facilities. Organic polymers were the most commonly used treatment chemical, with most plants also using lime. Other less frequently used chemicals and additives were Alz(S04)3.14I-hO, Fe2(S04)3, FeC!), sodium aluminate, activated silica, activated charcoal, CO2 and bentonite. Information given regarding residue thickening and disposal was poor. Samples from Rand Water, Umgeni Water (Midmar), Midvaal Water Company, Amatola Water and Cape Metropolitan Council (Faure) were received or collected. An additional sample from Faure was also received, representing a change in the treatment process. These samples were analysed for a range of chemical and physical characteristics. These analyses showed that the WTRs had the potential to supply some plant nutrients (Ca, Mg, Fe, S) but that metal toxicity may be a problem, in particular Mn in the Faure WTR, and that P adsorption may be severe. The samples selected to test the potential for land disposal were from Rand Water and Faure. A pot experiment tested the growth of Eragrostis tefJ, Cenchrus ciliaris and Digitaria eriantha in mixtures of Rand WTR and material from a coal mine i.e., a sandy soil material, spoil material and coal combustion ash, at rates of 0, 50, 100, 200 and 400 g kg" with a uniform fertiliser treatment applied to all mixtures. The grass was harvested on three occasions and the mean total yield (dry mass) determined, as well as nutrient uptake. The pots were leached after each harvest and the pH and electrical conductivity determined. The soil, spoil and ash were characterised and pH, EC and water retention characteristics of the mixtures determined. Growth of the grasses in the ash treatments was poor and these were terminated. Eragrostis tefJ grown in the soil showed a decrease in mean total yield with increasing WTR application rate, but yield was good up to the 200 g kg" treatment at the first harvest, declining substantially by the second harvest. In general C. ciliaris and D. eriantha grown in the soil showed a decrease in mean total yield for all harvests with increasing WTR application. The yield of E. /ejJ, grown in the spoil, increased up to 100 g kg,l WTR addition, but decreased thereafter. Digitaria eriantha showed a decrease in yield, and C. ciliaris an increase, with increasing WTR application rate , but for all treatments the differences were non-significant. The pH and EC of the leachates generally increased with increasing WTR addition. The concentration of nutrients in the grasses did not indicate any deficiencies or toxicities. As the growth of grass was poor in the ash treatments, another pot experiment was established to test the growth of two creeping grass species grown in the Rand WTR as a cover over the ash material. Cynodon dactylon and Stenotaphrum secundatum were grown in 20, 40 and 60 mm layers of Rand WTR, with and without a fertiliser treatment. Both species performed best in the 60 mm layer with fertiliser, and C. dactylon performed better than S. secundatum. The former species was more tolerant of the high pH, but both have potential as cover vegetation on the ash dumps when these are covered with Rand WTR. A further glasshouse study investigated the effect of Faure WTR mixed with a nutrient poor sandy soil on the nutrient uptake and seed yield of common dry beans (Phaseolus vulgaris). The WTR was added to the soil at 0, 50, 100, 200 and 400 g kg" each with five levels of fertiliser (0, 25, 50, 100 (recommended optimum) and 150 %). Bean pods were harvested once the plants had senesced. The number of pods and mass and number of seeds per treatment were determined. The seeds were analysed for nutrient uptake. Interveinal chlorosis and necrotic lesions were evident on cotylendonous and new leaves in the WTR treated soils, the severity of the symptoms increasing with increasing rate of WTR. Additional pots were established at the 400 g kg" rate (without fertiliser) and leaf material collected for chemical analysis. This showed that Mn toxicity was the cause, with leaf concentrations about 12 times the recommended 100 mg kg" upper limit. However, mass of bean seed was highest in the 400 g kg" Faure WTR treatment with 150 % fertiliser. Nutrient translocation to the seed seemed to be relatively consistent regardless of treatment, with little accumulation ofMn. The data collected illustrated the range of conditions and types of WTRs produced in South Africa, and that in some instances these residues have favourable characteristics for land application. The use of the Rand WTR showed that it could be applied to the spoil medium at relatively high concentrations without severely negatively impacting on grass growth, but more caution should be used when applying this material to the soil medium. While the grass did not grow in the ash treatments, it would seem that with suitable species the Rand WTR could be beneficially applied to ash material as a cover layer. The use of the Faure WTR on a sandy soil seemed to potentially improve the yield of the indicator crop, but caution should be exercised due to the possibility of Mn toxicity. The use of additional fertiliser would seem to be essential. Further research would require that field scale investigation of both WTRs be conducted, as well as further studies of applicat ion rates and techniques in laboratory and glasshouse investigations. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2003.

The effects of irrigation-induced salinity and/or sodicity on sugarcane yield, and two growth parameters, namely stalk height and number of nodes per stalk , were investigated on a sugarcane estate in the Zimbabwean lowveld. The effects of soil salinity and/or sodicity on the size, activity and metabolic efficiency of the soil microbial community was also studied. Furrow-irrigated fields which had a gradient in soil salinity and/or sodicity which increased from the upper to lower ends of the fields were selected for this study. This gradient was recognized by decreasing sugarcane growth down from the upper to the lower ends and the appearance of salt on the soil surface at the lower ends of fields. Sugarcane growth was classified as either dead, poor, satisfactory or good; and soil samples (0-0 .15 m, 0.15-0 .3 m, 0.3-0 .6 m and 0.6-0.9 m) were taken from each of these areas. Soils from under adjacent areas of undisturbed veld were also sampled. Sugarcane growth and yields in micro-plots of the various areas of the fields were measured. Foliar samples of sugarcane were taken at 22 weeks of age and analysed for nutrient content. Soil salinity and sodicity were quantified by measuring pH(water), electrical conductivity (ECe) and cation content of saturation paste extracts and the exchangeable cation content. From this information, the sodium adsorption ratio (SARe)and exchangeable sodium percentage (ESP) were also calculated. The calcareous, vertic soils in the study area under undisturbed veld were found to have high pH values (8 to 9.5), very high exchangeable Ca and Mg concentrations and there was evidence of accumulation of soluble salts in the surface 0.15 m. Under sugarcane production, irrigation induced salinity and sodicity had developed. Under poor and dead sugarcane, high values for ECe, SARe, and ESP were generally encountered in the surface 0-0 .3 m of the profile. In addition, the pH values under sugarcane were often between 9 and 10 particularly in profiles where sugarcane grew poorly or had died. As expected, pH was positively related to ESP and SARe, but negatively related to ECe. Measurements of aggregate stability by wet sieving, the Emerson dispersion test and the Loveday dispersion score all showed that soils from the study sited tended to disperse and that dispersion was most apparent where high ESP and SARe values occurred in association with elevated pH values and relatively low ECe values. These measurements confirmed observations at the sites of low infiltration rates and restricted drainage particularly on the lower ends of fields where sugarcane had died. In addition to the above measurements it was also observed that there was a rise in the watertable under furrow irrigation and that the watertable was nearest to the surface at the lower ends of the fields. In some cases the watertable was observed to be only 0.2 to 0.3 m from the surface. Thus, death of roots due to anaerobic conditions could be occurring to a greater extent at the lower ends of the fields. Another consequence of the high watertable was that these vertic soils were observed to remain in a permanently swollen state. This limits air and water movement in the soil profile as such soils need to be allowed to dry out and crack regularly so that macroporosity can be restored. Sugarcane yield, stalk height and number of nodes per stalk were not significantly related to ECe. Sugarcane yields were, however, significantly correlated with ESP and pH while stalk height and number of nodes were negatively correlated with ESP, SARe and pH. These results suggested that sodicity was a more limiting factor for sugarcane growth than salinity. Foliar analysis of leaf tissue did not reveal substantial differences in macro- or micro-nutrient content between good and poorly-growing sugarcane. It was concluded that the gradient of decreasing sugarcane growth down the furrow-irrigated fields, with crop death at the lower ends, was the result of a combination of factors. That is, the watertable had risen due to over-irrigation and it was nearer the surface at the lower ends of the fields. Due to capillary rise of salts, this resulted in sodic and sometimes saline-sodic conditions in the surface soil. These conditions could limit plant growth through ion toxicities, plant water stress and inhibition of root growth and function and physiological processes. These would be induced by the high pH and high salt, Na and HC03- concentrations in soil solution. Poor physical conditions associated with sodicity and the continually swollen state of the soils presumably limited infiltration and aeration in the surface soil, and probably restricted root growth. In addition, it is likely that the high watertable limited effective crop rooting depth to about 0.2 m at the lower ends of the fields. The net result was that sugarcane died at the lower ends. A negative effect of soil salinity and/or sodicity was also observed on the soil microbial population. Significant negative correlations were obtained with ECe SARe and ESP with microbial biomass C and microbial activity (as measured by FDA hydrolytic activity or arginine ammonification rate). The activity of enzymes involved in C (P-glucosidase), P (phosphatase) and S (arylsulfatase) mineralization and potential nitrogen mineralization (as determined by aerobic incubation) were also negatively correlated with these factors, with the exception of arylsulfatase activity and ESP. All the above mentioned microbial population measures were also positively correlated with soil organic C content, besides potential nitrogen mineralization. The metabolic quotient, which provides an indication of stress and efficiency of the microbial community, increased considerably with increasing salinity and sodicity and decreased with soil organic C. Thus, increasing salinity and/or sodicity resulted in a smaller, more stressed, less efficient microbial community, while the turnover rate and cycling of C, N, P and S also decreased. It was concluded that salt affected soil not only causes a decline in sugarcane yield through raising the concentration of soluble salts in soil solution, but also has a detrimental effect on microbial activity and on mineralization of soil organic C, N, Sand P. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2001.

Pasture-based dairy farming is the major land use in the Tsitsikamma region of the Eastern Cape. Permanent kikuyu grass (Pennisetum clandestinum) dominates pastures in the region. Kikuyu pastures do not, however, provide adequate year-round quality feed for dairy cows. This has led to the use of annually sown pastures with perennial ryegrass (Lolium perenne) to provide winter forage. Soil degradation under this management has, however, become recognised as a major limitation. Soil quality and degradation under annual and permanent pasture in the region were evaluated in three separate studies. These were (i) an investigation of the extent of loss of soil organic matter and related soil microbial properties and aggregate stability under annual pastures, (ii) a comparison of soil physical properties under annual and permanent pastures and (iii) a survey of the nutrient status of soils and pasture herbage in the region. In the first study, four commercial dairy farms, situated on sites which represented the three main soil groups in the region were sampled, were taken from under permanent kikuyu pastures, annual ryegrass pastures and undisturbed native vegetation nearby. In comparison with undisturbed, native vegetation, soils under both annually cultivated and permanent pasture had gained soil organic matter on the sandy, low rainfall eastern end of the Tsitsikamma. By contrast, at the higher rainfall, finer-textured, western end, where the native vegetation consists of coastal forest, there was a loss of soil organic matter under both types of pasture. Despite this, soil organic C content was lower under annual ryegrass than permanent kikuyu pasture at all the sites reflecting the degrading effect of annual cultivation on soil organic matter. As a consequence, labile, K(2)S0(4) - extractable C, microbial biomass C, basal respiration, arginine ammonification, flourescein diacetate hydrolysis rates and aggregate stability were all less under annual ryegrass than permanent kikuyu pastures at all the sites. The effects of annual ryegrass and permanent kikuyu pastures on soil physical properties and root length density were compared with those of undisturbed native vegetation on the four experimental sites. Root density and the depth of rooting were much less under annual ryegrass than under kikuyu pastures or native vegetation. There was no consistent effect of improved pastures or pasture type on bulk density and total porosity or penetrometer resistance, although annual pasture soils generally had higher bulk densities and lower total porosities than those under native vegetation. There was a tendency for smaller saturated hydraulic conductivity and air permeability under ryegrass than kikuyu pastures, regardless of whether total porosity was higher or lower under ryegrass. This was attributed to annual cultivation and subsequent natural consolidation causing a decrease in pore continuity under ryegrass pastures. Penetrometer resistance values confirmed the presence of subsoil compacted layers at two annual ryegrass pasture sites. At one such site, subsoil tillage was effective in reducing penetrometer resistance and bulk density, increasing pore continuity (as evaluated by hydraulic conductivity and air permeability) and greatly increasing root density and rooting depth. The nutrient status of soil and herbage from annual ryegrass and permanent kikuyu pastures sampled from 40 dairy farms in the Tsitsikamma region were evaluated. Along with the decreased organic matter content, there was a decrease in soil pH and a loss of exchangeable cations under annual pastures. Large concentrations of extractable P and sometimes exchangeable K were measured in soils under both ryegrass and kikuyu pastures and it was concluded that the rates of applied P, and sometimes K, were often excessive (particularly under kikuyu). Various nutritional problems were also identified. These included the need for Ca supplementation, particularly under kikuyu, due to the low herbage Ca concentrations. The low Ca : P ratio measured in annual ryegrass pastures, and more particularly in kikuyu herbage, highlighted the low Ca content of herbage and also the tendency of kikuyu grass to accumulate large concentrations of P. The large K concentrations and high K : Ca +Mg ratios identified in pasture herbage suggest the potential for animal nutritional problems such as hypomagnesaemia. It was concluded that although kikuyu is an excellent pasture in terms of dry matter production it tends to be deficient in Ca (and sometimes Na) and can contain prohibitively high K levels, which are likely to induce Mg deficiencies in grazing animals. The micronutrient concentrations in herbage were generally adequate, although copper concentrations tended to be low suggesting that fertilizer applications and/or feed supplementation is required. It was concluded that annual conventional tillage results in a substantial loss of soil organic matter, soil microbial activity and aggregate stability under annual ryegrass pastures when compared to those under permanent kikuyu grass. This loss of soil organic matter can result in natural consolidation of the soil in the cultivated layer and exasperated through treading by the grazing cows. The annual cultivation can also lead to the formation of a subsoil compacted layer. Nonetheless, compaction can also occur under permanent pasture presumably due to treading damage. Careful management to avoid treading damage to pastures should be practised. In order to protect the organic matter status of annual pastures, direct drilling of such pastures should be seriously considered. In some cases, annual fertilizer P rates (and to lesser extent those of K) could be reduced considerably since the levels accumulated in the soils are excessive. / Thesis (M.Sc.Agric.)-University of Natal, Pietermaritzburg, 2002.