Gypsiferous water, i.e water containing high levels of calcium sulphate, is used to irrigate crops such as maize and wheat on a commercial scale, in some parts of South Africa due to shortage of irrigation water. Gypsiferous water is saline due to the presence of Ca2+, S042- and sometimes Mg2+ in solution. These salts may have a detrimental effect on herbicide performance. Possible herbicide injury to crops has been reported in areas irrigated with gypsiferous water, which suggested interaction between herbicides and gypsiferous water. Bioassay experiments were conducted in the greenhouse to assess whether the bioactivity and persistence of the selected herbicides were affected by the presence of gypsum in the soil. The biological activity of atrazine was significantly increased in the presence of gypsum, and in the case of 2,4-D the same effect was even more pronounced. In contrast, the activity of metolachlor was reduced in the presence of gypsum. These differential effects on herbicide activity would have important practical consequences for herbicide performance, i.e weed control efficacy, selectivity, and behaviour in soil. In the persistence experiment, the activity of all herbicides decreased with time. However, the presence of gypsum had a significant effect on the rate of dissipation of only atrazine. In the presence of gypsum the rate of loss of atrazine was significantly less compared to its rate of loss in soil that did not contain gypsum. The rate of loss of metolachlor was not significantly affected by the presence of gypsum, and in the case of 2,4-D the trends were not clear at all. A further experiment was conducted to determine the leaching potential of metolachlor and atrazine in soil irrigated with either gypsiferous water or uncontaminated water. In the leaching experiment metolachlor showed a significant growth reduction of 39% in the first 10 cm column zone in soil irrigated with gypsiferous water and no further losses were observed in deeper column segments, and this indicated that there would be no threat of groundwater contamination. However, the results showed that weeds with shallow roots would be effectively controlled in this column. Similar results were observed in soil without gypsiferous water irrigated. The findings of this experiment appear to contradict the findings of Chapter 4 for metolachlor, however it is to be considered that in Chapter 4 the "close system" was used and in the leaching experiment an "open system" was used. In addition, the calcium sulphate concentrations for the two experiments were different. In the atrazine experiment it was found that 0.1 mg kg-1 would pose a serious threat to groundwater contamination and sensitive follow-up crops. There is a need to reduce the atrazine dosage rate to 0.05 mg kg-1 because no threat to groundwater was observed at this rate. However, weed control efficacy at this low rate maybe poor. / Dissertation (MSc (Agric): Weed Science)--University of Pretoria, 2006. / Plant Production and Soil Science / unrestricted

The major aim of this study was to analyse the dynamics of stakeholder participation in the agricultural sector during the first five years of the water reform process in Zimbabwe. Specific reference is made to water allocation, conflict management and the payment of costs related to water use. Stakeholders investigated are those in communal smallholder irrigation schemes, large-scale commercial white and black farms and those resettled under the government's fast track land resettlement programme. The study was undertaken in the Middle Manyame Subcatchment area, which falls under the Manyame Catchment area.

The major aim of this study was to analyse the dynamics of stakeholder participation in the agricultural sector during the first five years of the water reform process in Zimbabwe. Specific reference is made to water allocation, conflict management and the payment of costs related to water use. Stakeholders investigated are those in communal smallholder irrigation schemes, large-scale commercial white and black farms and those resettled under the government's fast track land resettlement programme. The study was undertaken in the Middle Manyame Subcatchment area, which falls under the Manyame Catchment area.

Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: In the study, six irrigation schemes based in the Eastern Cape have been considered and evaluated, according to two levels of supply (LOS) of irrigation water. The two levels of supply are that of a commercial irrigator and that of a smallholder irrigator. The irrigation infrastructure for each of the six schemes was designed, and the associated costs determined, for each level of supply. The primary objective of the study is to determine the impact of infrastructure costs and irrigation areas on the target user, either the commercial or the smallholder irrigator. This is related directly to the assumption that lower water volumes are used by the smallholder irrigator. The study addresses the impact of different designs on the amount of water used, land utilised and resultant costs of the infrastructure. The initial capital costs and the on-going operational and maintenance costs (O&M) for each level of supply for each of the schemes have been calculated. The evaluation of the two LOS has shown that the capital cost for the commercial LOS is approximately 18 % higher than for the smallholder LOS and the O&M costs 6 % to 36 % higher. The schemes that were investigated can be grouped into five general scheme types. The first type is gravity schemes, which need rehabilitation, while the bulk supply is in place with no augmentation or rehabilitation required. The second is pumped scheme which is in need of rehabilitation, while the bulk supply is in place with no augmentation or rehabilitation required. The third type includes run-of-river schemes where water is abstracted and pumped directly to the lands. The fourth type includes run-of-river schemes where water is abstracted and pumped to storage. The fifth type is the gravity scheme where the bulk supply needs to be installed as part of the scheme. These types are then grouped and can be used to give guidance on the anticipated costs dependant on the scheme type and the required level of service. A further objective of the research is to determine the impact on the smallholder irrigators who find themselves on a commercial LOS system. This can be either on a scheme that has already been designed, or on a new system. The evaluation of the commercial under-utilised LOS and the smallholder LOS has shown that the commercial capital cost is 18 % higher and the O&M costs 5 % to 29 % higher. The study further aligns the estimated costs with the farmer typology providing a broader understanding of the design to be adopted for different levels of supply. This provides the linkage between farmer types, the design to be implemented and the anticipated costs thereof. / AFRIKAANSE OPSOMMING: As deel van hierdie narvorsing word ses verskillende besproeiingsskemas in die Oos-Kaap ten opsigte van twee voorsieningsvlakke ondersoek. Die twee voorsieningsvlakke ter sprake is vir ‘n kommersiële en kleinboerdery opset. Die besproeiingsinfrastruktuur is vir elk van die ses besproeiingsskemas ontwerp en ‘n kosteberaming vir elk van voorsieningsvlakke gedoen. Die hoofdoelwit van hierdie verslag is om te bepaal wat die impak van kostes en besproeiingsareas op beide kommersiële- en kleinboerderye is. Dit is direk gebaseer op die aanname dat kleinboerderye minder water gebruik. Die verslag ondersoek die impak van verskillende ontwerpe op waterverbruik, besproeiingsoppervlak benodig en die gevolglike infrastruktuurkostes. Die aanvanklike kapitaalkostes asook bedryfs- en onderhoudsuitgawes (B&O) vir elk van die voorsieningsvlakke, is vir elk van die besproeiingskemas bereken. Die resultaat van die ondersoek van die twee voorsieningsvlakke het aangetoon dat die kapitaalkoste van kommersiële besproeiingskemas 18 % hoër as die van kleinboerderye is, en bedryfs- en onderhoudsuitgawes 6 tot 36 % hoër. Die skemas wat ondersoek is, kan in vyf algemene skema tipes verdeel word. Die eerste is die gravitasieskemas wat rehabilitasie benodig terwyl die hooftoevoer in plek is met geen uitbreidings- of rehabilitasiebehoeftes. Die tweede is pompskemas wat rehabilitasie benodig terwyl die hooftoevoer in plek is met geen uitbreidings- of rehabilitasiebehoeftes. Die derde is rivierskemas waar besproeiingswater direk uit die rivier na die landerye gepomp word. Die vierde is rivierskemas waar besproeiingswater direk uit die rivier na a reservoir gepomp word. Die vyfde skema tipe is die gravitasieskemas waar die hooftoevoer ook gebou moet word as deel van die skema. Die skema tipes kan gebruik word om leiding te verskaf ten opsigte van verwagte skema kostes afhangende van die skema tipe en vereiste voorsieningsvlak. ‘n Verdere doelwit van die studie is om die impak op kleinboere te bepaal wat op ‘n kommeriële voorsieningsvlak boer. So ‘n stelsel kan ‘n gevestigde of nuwe stelsel wees. Die resultaat van die ondersoek van die onderbenutte kommersiële voorsieningsvlak en die kleinboerdery voorsieningsvlak het gewys dat die kapitaalkoste van kommersiële besproeiingskemas 18 % hoër as die van kleinboerderye is, en bedryfs- en onderhoudsuitgawes 5 tot 29 % hoër. Die verslag vereenselwig die verwagte kostes met die tipe boerdery en verskaf ‘n beter begrip van die tipe ontwerp wat elk van die voorsieningsvlakke benodig. Dit verskaf dus die verband tussen die tipe boerdery, die ontwerp benodig en die verwagte projekkostes.

Thesis (MScAgric)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: Poor water management and poor water use efficiency (WUE) have been identified as one of the major problems experienced by vegetable growers in most of the developing countries, including South Africa. This poor management and poor utilization of water have led to a drastic decline in the quality and quantity of available water. In South Africa agriculture uses about 50% of available water. Increasing water demand for domestic, industrial and mining uses, may decrease agriculture's share to less than the current 50%, henceforth, better utilization of this resource is imperative. Selection of a good irrigation system can limit water loss considerably. Some irrigation systems have a potential to save more water than others do. Since irrigation systems affect the WUE of crops, care should be taken when selecting an irrigation system under conditions of limited water quantity. Ebb-and- Flood watering systems have been introduced for effective sub-irrigation and nutrient delivery within closed systems. Such a system was adapted in South Africa, to develop a vegetable production unit for use by families in rural communities, while saving substantial amounts of water. A need to further improve the WUE of this system was subsequently identified. Two studies were conducted at the experimental farm of the University of Stellenbosch (Department of Agronomy). The first trial was conducted under controlled conditions in a glasshouse, and the second under open field conditions. In the first trial, Beta vulgaris (Swiss chard) and Amaranthus spp. ('Imbuya') were grown in two root media; gravel and pumice. In addition, an 'Ebb-and-Flood' and a 'Constant level' system were used with nutrient solutions at two electrical (EC) conductivity levels 1.80 and 3.60 mS cm-I. The results of this (2x2x2x2) factorial experiment indicated that a combination of the 'Ebb-and-Flood' system with gravel as a root medium produced the best results at a low EC, when 'imbuya' was used. A high total WUE was found with 'imbuya', (7.35 g L-I) at EC 1.80 mS cmicompared to a relatively low WUE of 5. 90 g L-I when the 3.60 mS cm-I nutrient solution was used. In the second trial, 'Imbuya's' foliage dry mass, leaf area and WUE was evaluated under field conditions at the Stellenbosch University experimental farm, during the summer of2002. The experimental farm (33°55'S, 18°52'E) is situated in the cooler coastal wine grape-producing region of South Africa with a relatively high annual winter rainfall. This trial was conducted on an alluvial soil, with clay content of 25% and a pH of 5.9 (KC!). A closed 'Ebb-and-Flood' system was compared with two open field irrigation systems ('Drip' and 'Flood') using nutrient solutions at two electrical conductivity levels (1.80 and 3.60 mS cm-i) in all three cases. Foliage dry mass, leaf area as well as WUE was best with 'Drip' irrigation, when a nutrient solution with an electrical conductivity of 3.60 mS cm-i was used. In spite of the fact that additional ground water was available for the soil grown 'Drip' and 'Flood' treatments, the 'Ebb-and-Flood' system outperformed the 'Flood' treatment, especially when the nutrient solution with an EC of 3.6 mS cm-i was used. Insufficient root aeration in the flooded soil could have been a contributing factor. The fact that the 'Ebb-and-Flood' and 'Drip' systems gave the best results when the high EC solution was used to fertigate the plants, may indicate that the plants could have hardened due to the mild EC stress, better preparing them to adapt to the extreme heat that was experienced in the field. / AFRIKAANSE OPSOMMING: Swak: bestuur van water en 'n swak: water-gebruik-doeltreffendheid (WOD) is as een van die belangrikste probleme geïdentifiseer wat deur groente produsente in die meeste ontwikkelende lande, insluitend Suid-Afrika, ervaar word. Hierdie swak bestuur en benutting van water het daartoe bygedra dat 'n drastiese afname in die kwaliteit asook in die kwantiteit van beskikbare water ervaar word. In Suid-Afrika gebruik die landbou-sektor ongeveer 50% van die beskikbare water. Toenemende water behoeftes vir huisgebruik, industrieë en die mynbou mag hierdie 50% aandeel van die landbou sektor laat krimp. Beter benutting van hierdie skaars hulpbron is dus noodsaaklik. Die keuse van goeie besproeiingsisteme mag waterverliese merkbaar beperk aangesien sekere sisteme se water-besparingspotensiaal beter as ander is. Aangesien besproeiingstelsels die WOD van gewasse beïnvloed, is spesiale sorg nodig waar 'n besproeiingstelsel onder hierdie toestande van beperkte waterbronne gekies moet word. 'Ebb-en-Vloed' sisteme kan aangewend word om water en voedingselemente van onder in 'n wortelmedium te laat opstoot en in 'n geslote sisteem te laat terugdreineer. So 'n sisteem is in Suid-Afrika ontwikkel waarmee groente vir families in landelike gebiede geproduseer kan word terwyl water bespaar word. 'n Behoefte om die WOD van hierdie produksiesisteem verder te verbeter is egter geïdentifiseer. Twee ondersoeke is by die Universiteit van Stellenbosch se proefplaas (Departement Agronomie) gedoen. Die eerste proef is onder beheerde omgewingstoestande in 'n glashuis uitgevoer en die tweede onder veld toestande. In die eerste proef is Beta vulgaris (Snybeet) en Amaranthus spp. ('Imbuya') in twee tipes wortelmedia; gruis en puimsteen verbou. 'n 'Ebb-en-Vloed' asoook 'n 'Konstante vlak' besproeiingsisteem is gebruik terwyl voedingsoplossings ook by twee peile van elektriese geleiding (EC) teen 1.80 en 3.60 mS cm-I toegedien is. Die resultate van hierdie (2x2x2x2) fakroriaal eksperiment het aangetoon dat 'n kombinasie van die 'Ebb-en-Vloed' sisteem met gruis as 'n wortelmedium die beste resultate teen 'n lae EC lewer waar 'imbuya' gebruik is. Die WOD met 'imbuya' was hoog (7.35 g L-1) by 'n EC van 1.80 mS cm-I, vergeleke met 'n relatief lae WOD van 5. 90 g L-1 waar die 3.60 mS cm-I voedingsoplossing gebruik is. In die tweede proef is 'Imbuya' se droë blaarmassa, blaar oppervlakte en WOD onder veldtoestande op die Universiteit van Stellenbsoch se proefplaas in die somer van 2002 ge-evalueer. Die proefplaas (33°55'S, 18°52'E) is in die koeler kusstreke van die wyndruif produksiegebied in die winterreëngebied van Suid-Afrika geleë. Hierdie proef is op alluviale grond met 25% klei en 'n pH van 5.9 (KCi) uitgevoer. 'n Geslote 'Ebb-en-Vloed' sisteem is met twee veld-besproeiingsisteme vergelyk ('Drup' en 'Vloed') terwyl voedingsoplossings teen twee peile van elektriese geleiding (1.80 en 3.60 mS cm-I) in al drie gevalle gebruik is. Blaar droëmassa, blaaroppervlakte asook die WGD was die beste met 'Drup' besproeiing waar die EC van die voedingsoplossing 3.60 mS cm-I was. Ten spyte van die feit dat ekstra grondwater vir die 'Drup' and 'Vloed' behandelings beskikbaar was, het die 'Ebben- Vloed' stelsel beter as die 'Vloed' behandeling gedoen veral waar die voedingsoplossing se EC 3.6 mS cm-I was. Swak wortelbelugting was waarskynlik die rede waarom vloedbesproeiing swak produksie gelewer het. Die feit dat die 'Drup' en die 'Ebb-en-Vloed' behandelings in die veldproef die beste gedoen het waar die EC hoog was, mag moontlik met die gehardheid van die plante verband hou wat aan ekstreem warm en dor toestande blootgestel was.

The Central Arizona Project (CAP) is a billion-dollar-plus project to construct an aqueduct to transport water from Lake Havasu on the Colorado River into the Maricopa County-Phoenix area and then through Pinal County to Tucson. Upon completion of CAP in 1986, some of the Colorado River water will be delivered to Pinal County for agricultural use. Water available to Pinal County farmers in the initial years of the project is estimated at 659,000 acre-feet annually. Any new importation of water to an established irrigated agricultural area implies adjustments in the organization of the economy of the area. For irrigated agriculture, adjustments will occur in input mix, output mix, acreage farmed, and in gross and net incomes. A complicating factor associated with importation of Colorado River water is that the imported water will contain different dissolvedsalt concentrations than will the groundwater and surface water currently being used. Dissolved salts in irrigation water (salinity) decrease crop yields, i.e., as the salinity of water applied to a crop increases, yield per acre decreases. The magnitude of yield reduction due to salinity is dependent on the level of salinity of the irrigation water and on the crop's salt sensitivity. In areas of Pinal County where local water supplies have a lower average salinity than CAP water, average crop yields will decrease if CAP water is added to the crop-water mix. On the other hand, in those areas where the salinity of local water is higher than that of CAP water, higher crop yields will be realized by using CAP water in the crop-water mix. Thus, the optimal CAP-local water mix is determined in order to evaluate the economic adjustments of Pinal County farmers to the new water source. Pinal County is divided into seven irrigation districts, each of which has filed a letter of intent to purchase CAP water. Representative farm data for each district are stratified by farm size and pumping depth. Farms are divided into four size classes in order to reflect economies due to farm size. Because the cost of local pumped water varies with the pumping lift, the farms are also stratified by three depth-to-water classes. Thus, a total of 12 representative farms are necessary to describe the agricultural activities in each irrigation district, and 84 representative farms are needed for the county. Mathematical programming models of representative irrigated farms in Final County project adjustments implied under several assumptions as to the availability, cost and salinity of irrigation water from various sources. Results show that (1) most monetary benefits of the project will be captured by the Indian farmers of the county, (2) groundwater conservation will be minimal unless farmers are forced to purchase large quantities of CAP water, (3) provision of CAP water will not affect cotton acreage but will significantly increase the acreage of small grains and alfalfa, (4) the possibility of increased salinity from CAP water should not concern farmers in the county since projected decreases in net income occurring because of increased salinity average only 61 cents per acre per year, and (5) increased income to non-Indian farmers resulting from provision of CAP water at the currently proposed price will not be sufficient to pay the additional fixed costs for distribution systems.

The dynamics of salt accumulation in the soil over time is one of major important information input needed for decision-making in regard to irrigate with saline water. As all waters contain some dissolved salts, during the irrigation these salts tend to concentrate in the soil causing depressed plant growth. Saline irrigation water, low soil permeability, inadequate drainage conditions, low rainfall and poor irrigation management all contribute to the tendency of salt accumulation in the soil. The principal salt accumulation problem of economic importance arises when non-saline soils become saline as result of irrigation. The dynamics of salt accumulation in this study, is based on the model for tracing salt distribution in the soil affected by the quantity and quality of irrigation water, amount of nitrogen and initial soil salinity. To verify the model for tracing salt distribution in the soil and to statistically estimate a crop-production function and soil salinity relation, agronomic data were used from field experiment conducted at the University of Arizona, Maricopa Agricultural Center (MAC), during the 1985 growing season and that utilized cotton variety Delta Pine 61. From the point of view of the response functions and salt accumulation in the soil, many assumptions were made before formulating the models. Results show that (1) no conclusions could be drawn with respect to the model of salt accumulation in the soil, (2) in the case of yield production function and soil salinity relation, the water quantity coeffient had an absolute value greater than one, (3) water quality and nitrogen coefficients had an absolute value less than one, (4) initial soil salinity coefficient had negative value, (5) looking for the best combination amoung the variables inputs, the marginal rate of substitution was greater than the ratio of prices, (6) the time path for soil salinity converge to a steady state conditions, and (7) the profitability of cotton irrigated with drip system is sensitive to yield increases and increases in the price of cotton.

No description available.

M.Sc. / Because of South Africa's high rate of population growth, it becomes more difficult to supply in the basic needs of people, of which water for personal use and food may be the most important. South Africa is a dry country with weak and marginal soils in most parts. This necessitates the effective use of these important natural resources. Recent legislation forces commercial agriculture to use care and sustainable methods in their resource use. Justification must also be made for ratio of resources used compared to the product delivered from that use. Therefore it is necessary to examine this use and the role it plays in the supply of basic human needs as well as economic growth. A study of these agricultural resources cannot be undertaken on a large scale, because every agricultural is unique. The purpose of this study is to generate an idea of the physical and agricultural environment of the Ohrigstad valley. This research is mostly based on the assimilation of previous studies and the comparing of results over time. This information is used to compare results from previous studies and to determine possible trends in factors_such as rainfall. A further study of the natural resources that attribute to effective commercial agriculture are made. From here the emphasis falls on the use and distribution of irrigation water to these activities in the valley. These natural sources of water and their means of distribution are studied and described. Rainfall as a direct source of water is determined by information regarding rainfall and microclimatic circumstances. Surface and subterraneous sources are described by information on the general hydrology and geohydrology of the study area. In such an environment there are many factors affecting the supply of water to agriculture such as: forestry, afforestation of riparian zones, as well as geological occurrences in the streambeds. Possible solutions for problems posed by these factors are discussed in relation to previous studies in similar areas, as well as the economic benefits that may be reaped because of such change. Finally the role that legislation (Water Act 36 of 1998) plays in the use of water by agriculture is discussed in terms of possible impacts that it may have on commercial agriculture in the area. In this study it has become clear that a lot more research must be done in such a project before any trends can be related and proved.

Call number: LD2668 .T4 1958 E29 / Master of Science