Seasonal rainfall is an important source of water for rainfed farming in the semi-arid regions of the world, where rainfall is marginal and variable. However, as rains are unpredictable in terms of onset, amount and distribution, there is a need to understand the variability and other basic rainfall features in order to use the information in agricultural decision making. More specifically, combining the seasonal rainfall prediction with crop water requirement and soil water information is the core component to successful agriculture. The ultimate objective of this study was to characterize and obtain a better understanding of the most important rainfall features that form the basis for classifying the areas into homogenous rainfall zones and then to develop a seasonal rainfall prediction model for the Central Rift Valley (CRV) of Ethiopia. The source data for the analyses was primarily obtained from the National Meteorological Services Agency (NMSA) and partly from Melkassa Agricultural Research Centre (MARC) and the web site of the International Research Institute for Climate and Society (IRI). Rainfall variability and time series analyses were done using INSTAT 2.51 and coded time method, respectively. Rainfall onset and March-April- May (MAM) rainfall totals are the two most variable features both at Miesso and Abomssa. For both stations, rainfall end date displays the least variability. Rainfall onset date at Miesso ranges from the lower quartile (25 percentile) of DOY 61 to the upper quartile (75 percentile) of DOY 179 with a 42% coefficient of variation (cv). At Miesso, the main rainy season terminates during the last days of September (DOY 272 - 274) once in four years and terminates before DOY 293 in three out of four years. At Abomssa, the c.v for the lower quartile (DOY 61) to the upper quartile (DOY 134) was found to be 40.5%. At both locations, planting earlier than 15 March (DOY 75) only proves successful once in every four years. Further, at Miesso this upper quartile statistic can extend up to the DOY 179, whereas at Abomssa planting earlier than 15 April (DOY 134) is possible in three out of four years (75 percentile). At Abomssa, rainfall terminates by DOY 286 and the end of October (DOY 305) for the 25 and 75 percentile points respectively. From the time series analyses, there was no conclusive evidence for the existence of a trend for both Miesso and Abomssa, information which is useful for long-term research and development planning, as well as seasonal rainfall prediction for the study area. The classification study for the spatial rainfall pattern resulted in four homogenous rainfall zones that form distinct development and research units, using the FORTRAN- 90 based NAVORS2 program. The south facing Alem Tena-Langano zone has a better rainfall pattern than drier zones and thus formed zone 1. The southern, southwestern and southeastern area has formed the wet zone (zone 2), the northwestern to northeastern facing part (Debre-Zeit-Nazerth-Dera) that receives a higher rainfall amount than zone 1 has formed zone 3 and finally, the drier northeastern part constituted zone 4. Twenty seven seasonal rainfall prediction models with varied performance skills that can be used for the operational farming were developed for the March-September monthly rainfall using the Climate Predictability Tool (CPT v.4.01) from IRI. It was understood that with increased observing networks and data availability, useful operational climate prediction could be achieved for a smaller spatial unit and with a short lead-time. The tempo-spatial water requirement satisfaction pattern analyses were conducted using AGROMETSHELL v.1.0 of the FAO. Fourteen concurrent sorghum-growing seasons that give a general picture of crop water requirement satisfaction were mapped. The southern, southwestern and southeastern parts (zone 2) of the CRV constitute the most favourable location for growing a range of sorghum maturity groups. The northwestern and central (zone 3) parts constitute the next most suitable zone. The wide northeastern drylands (zone 4) of the study area, except the pocket area of Miesso-Assebot plain, does not warrant economic farming of sorghum under rainfed conditions. From the growth stage-based Water Requirement Satisfaction Index (WRSI) analyses, mid-season / flowering stage of the sorghum cultivars was found to be three times more sensitive to changes in sorghum yields for both cultivars and experimental sites as compared to the WRSI from the rest of growth stages. The results from the water production function analyses (WPF) also indicated the potential of WRSI for prediction of the long-term sorghum yields. The cumulative density function (CDF) and stochastic dominance analyses for the 120-day grain sorghum cultivar grown at Miesso show the June planting to be the most efficient set by first degree stochastic dominance (FSD), while May was found efficient for Melkassa. The CDF for Arsi Negele shows April planting date to be the best set. Therefore, these planting dates are to be preferred by farmers seeking âmoreâ yield at the respective locations, regardless of their attitude towards risk. The sensitivity analyses conducted using different levels of the seasonal rainfall related input variable combinations (sorghum planting date, maturity date, number of rainy days and WRSI) for Miesso, Melkassa and Arsi Negele provide useful information. By keeping input variables other than WRSI at the most preferred level (i.e. early planting date, extended maturity date, and greater number of rainy days) and only changing WRSI from 100% to 75% resulted in a 49.7% yield reduction in case of Miesso, 40.8% in case of Melkassa and 24.3% in case of Arsi Negele. Further, when WRSI was reduced down to 50%, there was a total crop failure in the case of Miesso and Melkassa, while the reduction was 48.6% for the Arsi Negele case. Similar results were found when WRSI was varied across other input level combinations. Visual Basic v.6.0 was used to write the algorithm for the decision support tool (DST) relating sorghum planting dates in CRV, to which the name ABBABOKA 1.0 was given. By using the rainfall prediction information from three different sources (the new prediction model developed in chapter 3, NMSA and ICPAC), ABBABOKA suggests the best possible planting alternatives for a given homogenous rainfall zone and planting season. When decision making under this predictive information alone is not sufficient, soil water parameters need to be consulted for more reliable decision making. This simple and briefly constructed ABBABOKA is expected to provide a suite of guidelines to the users. Certainly, this constitutes a significant departure from the fixed âbest betâ recommendations I learned from research systems in the past. It is recommended that the time-space classification of agricultural areas into homogeneous zones needs to be extended to the rest of the country together with the tailored rainfall prediction information. Research needs to be geared towards crop water requirements, climate risks and simulation modelling aspects. A network of weather stations and soil database needs to be developed in order to promote the soilcrop- climate research in Ethiopian agriculture. More importantly, the use of decision support tools and the well-established models (like APSIM) need to be included in agricultural research and development efforts.

Desertification is one of the most serious environmental and socio-economic problems of our time. Desertification describes circumstances of land degradation in arid, semi-arid and dry sub-humid regions resulting from the climate variation and human activities. The fundamental goal of this thesis was to monitor the extend and severity of the land degradation and examine climate variability and change in the Butana area of northeastern Sudan. To explore the climate variability and climate change in terms of rainfall, temperature and the aridity index for the period from 1941 to 2004, the monthly and annual time series for four weather stations (El Gadaref, Halfa, Wad Medani and Shambat) across the Butana area were analysed. The trend of the rainfall at Wad Medani and Shambat shows significant decline, while that of Halfa and El Gadaref does not show a significant decrease or increase. The Cumulative Rainfall Departure (CRD) was used to detect the periods of abrupt changes in the rainfall series. A significant decrease in the annual rainfall was observed at Shambat (p = 0.00135) and Wad Medani (p = 0.0005) from 1968 to 1987, there after the rainfall amount is close to the long-term mean. In El Gadaref there was a decline in the annual rainfall from 1971 to 1974 (p = 0.35) but it was not significant, with a recovery from 1975 to 1982 to a value higher than the long-term mean, followed by another downward turn from 1983 to 1994. In Halfa there was a significant decrease (p = 0.0304) from 1982 to 1993. The trends of maximum and minimum temperature were examined for the summer (March-May), autumn (June-October) and winter (November-February) seasons for the four weather stations. At Halfa and Shambat the trend of maximum and minimum summer and winter temperature was increasing but not significant, while in Wad Medani there was a significant increase for summer and winter minimum temperatures. El Gadaref station showed a significant increase in maximum and minimum temperature (p = 0.00005, p = 0.00016) respectively. The minimum autumn temperature for Halfa increased significantly, while this was the case for both the minimum and maximum autumn temperature at Shambat and Wad Medani. This significant increase in temperature, associated with autumn, is partly due to dry conditions observed during the late 1960s. The relationship between 8 km2 AVHRR/NDVI and rainfall data (1981-2003) was tested in the Butana area. The relationship was strong between the peak NDVI (end of August through the beginning of September) and cumulative July/August rainfall, but weak relationships resulted when annual rainfall and cumulative NDVI were used. The Departure Average Vegetation method showed that the area had a high percentage of departure, reaching about 40% of the long-term average during the drought years and the NDVI recovered during the following year if the rainfall was above average. There were increased trends in NDVI in the study area during the period from 1992 to 2003, despite some years during this period having higher departure although that departure was less than for the period 1981-1991. To monitor the impact of human activities on land degradation it is essential to remove the effects of rainfall on vegetation cover. Using the Residual Trend Method the differences between the observed peak NDVI and the peak NDVI predicted by the rainfall was calculated for each pixel. This method identified degraded areas that exhibit negative trends in NDVI. The human impact is more clear in the northern part. Satellite imagery provides an opportunity to undertake routine natural resource monitoring for mapping land degradation over a large area such as Butana over a long time period. This facilitates efficient decision making for resource management. Five classes of land use were achieved using unsupervised classification, whereafter an image difference technique was applied for 1987-1996 and 1987-2000. This analysis showed that the bare soil and eroded land increased by 3-7% while the vegetated area decreased by 3-6%. Also when comparing the aerial photographs (1960s and 1980s) for Shareif Baraket, Kamlin and El Maseid with Landsat images (2000) severe degradation of the vegetation cover was visible at all the three sites. The Moving Standard Deviation Index (MSDI) is calculated by performing a 3Ã3 moving standard deviation window across the band 3 Landsat images (1987, 2000). MSDI proved to be a powerful indicator of landscape condition for the study area. The MSDI increased considerably from 1987 to 2000, especially for Sufeiya, Sobagh and Banat areas, which are referred to as severely degraded sites in the literature. The Bare Soil Index (BSI) supports the finding from the MSDI. The BSI for the degraded sites Sufeiya, Sobagh and Banat increased from 0-8 in 1987 to 32-40 in 2000. The image difference of the BSI indicated that the index increased by about 14-43 over the 13 years. A Microsoft Excel macro was used to write the algorithms for a decision support tool relating the factors that trigger and propagate desertification in arid and semi-arid areas. This was named âTashurâ. Rainfall, aridity index and NDVI were used to evaluate the condition of the landscape. If these three parameters alone were not sufficient to make a decision, then soil and human activity parameters need to be consulted for more reliable decision making. This simple and concise decision support tool is expected to provide guidelines to planners and decision makers. Different ecosystems in the Butana area are subjected to various forms of site degradation. The desertification has led to sand encroachment and to accelerated development of dunes and also increased the water erosion in the northern part of the area. The area has also been subjected to a vegetation cover transformation. Pastures have deteriorated seriously in quality and quantity, but in many parts the degradation is still reversible if land use and water point sites are organized.

The sustainability of maize production in western Ethiopia is in question despite of favorable environmental conditions. A major reason for this phenomenon is severe soil degradation in maize fields. This soil degradation manifested often in low soil N fertility which inhibited maize yields. The situation is worsened by the financial inability of most farmers to purchase N fertilizer for supplementation. In these conditions two basic approaches can be followed to improve maize productivity in a sustainable way. Firstly, integrated cropping practices can be developed for maize to make better use of N from organic and inorganic sources. Secondly, maize genotypes can be selected that are superior in the utilization of available N, either due to enhanced uptake efficiency or because of more efficient use of the absorbed N. In this context, experiments were conducted to determine the integrated effects of tillage system, residue management and N fertilization on the productivity of maize, and to evaluate different maize genotypes for N uptake and use efficiency. The experiments on integrated cropping practices were done from 2000 to 2004 at five sites viz. Bako, Shoboka, Tibe, Ijaji and Gudar in western Ethiopia. They were laid out in a randomized complete block design with three replications. Three tillage systems (MTRR = minimum tillage with residue retention, MTRV = minimum tillage with residue removal and CT = conventional tillage) and three N levels (the recommended rate and 25% less and 25% more than this rate) were combined in factorial arrangement. Every year yield response, usage of applied N and changes of some soil properties were measured. In 2004 the same experiments were used to monitor the fate of applied N in the soil-crop system. Labeled urea was applied at the recommended rate to micro plots within the MTRR and CT plots for this purpose. During the initial two years of the experiments, there was no significant difference in grain yield between MTRR and MTRV and both were significantly superior to CT. However, during the final two years of the experiments, there was no significant difference between MTRV and CT and both were significantly inferior to MTRR. On average, the grain yield of MTRR was 400 and 705 kg ha-1 higher than that of MTRV and CT, resulting in consequent increases of 6.6 and 12.2%, respectively. The application of N increased the grain yield regardless of tillage system. An application of 92 kg N ha-1 was significantly superior to 69 kg N ha-1, but on par with the 115 kg N ha-1 application. Hence, the recommended fertilization rate of 92 kg N ha-1 for conventional tilled maize was also found adequate for minimum tilled maize in western Ethiopia. This rate remained economically optimum with a 20% decrease in the maize price and a 20% increase in fertilizer cost. The grain differences resulted from the tillage systems and concomitant residue management were attributed to significant changes in some soil fertility parameters, especially in the 0-7.5 cm layer. After five years both indices of organic matter, viz. the organic C and total N contents were significantly higher in the MTRR soils when the CT soils serve as reference. Similarly, the extractable P and exchangeable K contents of the MTRR soils were also higher than that of the CT soils. The only negative aspect of MTRR in comparison with CT was a decline in soil pH. A significantly higher grain N content was recorded with MTRR than with MTRV and CT. The stover N content was not significantly affected by the three tillage systems. However, grain, stover and total N uptake were consistently superior with MTRR compared to MTRV and CT. The NAE, NRE and NPE of maize for the same tillage system were consistently higher at the lower N level range of 69-92 kg ha-1 than at the higher N level range of 92-115 kg ha-1. At the lower N level range NAE and NRE were larger with CT than with the other two tillage systems. Both indices were higher with MTRR than with the other two tillage systems at the higher N level range. The NPE was not significantly affected by the tillage systems. However, the trend at both N level ranges was higher with MTRR than with MTRV and CT. The labeled urea study showed that the grain, stover and total biomass N derived from fertilizer was consistently higher for CT than MTRR. Conversely, grain, stover and total biomass N derived from soil was consistently higher with MTRR than CT. Therefore, the fertilizer N recorded in the MTRR soils was higher with MTRR than CT and mainly confined to the upper 45 cm. The fate of fertilizer N was in MTRR: 47% recovered by maize, 17% remained in the soil and 36% unaccounted for and in CT: 54% recovered by maize, 12% remained in the soil and 34% unaccounted for. The experiments on genotype comparison for N uptake and use efficiency were also done at Bako, Shoboka, Tibe, Ijaji and Gudar. In 2004 the response of five open-pollinated and five hybrid genotypes were evaluated at six N levels from 0 to 230 kg ha-1 with 46 kg ha-1 intervals. Only two out of the ten genotypes evaluated qualify as N use efficient. They were the openpollinated Ecaval 1 and the hybrid CML373/CML202/CML384. These two CIMMYT genotypes showed consistently higher NAE, NRE and NPE at low and high N applications as required. This was not the case with the two local genotypes that were included, viz. the open-pollinated Kulani and the hybrid BH 540. Based on the results that evolved from this study it is clear that: 1. Farmers should be encouraged to practice MTRR instead of CT since this change in tillage system could improve the productivity of maize on Nitisols in western Ethiopia. 2. On these Nitisols the conversion from CT to MTRR need not coincide with an adaptation in the recommended fertilization rate of 92 kg N ha-1. 3. The planting of N use efficient maize genotypes on Nitisols must be advocated to farmers, especially those who can not afford proper fertilization. Aspects that need to be investigated in future are: 1. Quantification of N mineralization and immobilization in the Nitisols when subject to MTRR and CT for maize production. 2. Losses of fertilizer N through volatilization, leaching and denitrification from the Nitisols when subject to MTRR and CT for maize production. 3. Suitability of other soil types which are used for maize production in western Ethiopia for MTRR instead of CT. 4. Performance of the N use efficient genotypes on other soil types which are used for maize production in western Ethiopia. 5. Crop rotation with N fixing crops.

Various studies have been conducted into redox potential (Eh), redox indicators and the measured soil water contents in soil (Franzmeier et al., 1983; Schwertmann & Fanning, 1976; Veneman et al., 1976). Although a measure of success has come from these studies, there are still vast knowledge gaps within this field. The degree of water saturation where reduction in the soil is initiated cannot be determined from literature, although it was approximated that 70% of water saturation (S0.7) was sufficient to initiate reduction (Van Huyssteen et al., 2005). This value will vary for different soil temperatures, varying bulk densities as well as soils with different organic matter contents. This study aimed to determine if it was possible to identify a degree of water saturation at which reduction is initiated for a soil in a closed system. It also aimed to determine the effect of bulk density on reduction. Reduction was defined by a decrease in pe (Eh) of a soil and an increase in the soluble Fe2+ concentration. There were three key aims to the study: to establish the relationship between the degree of water saturation (s) and the onset of reduction; to establish the relationship between the degree of water saturation (s) and the duration of reduction and to establish the effect of bulk density on the above-mentioned processes. A yellow brown apedal B horizon from an Avalon soil form (profile 234) in the Weatherley catchment was used in this study. A soil core experiment was carried out to determine the effect of degree and duration of water saturation on Eh, pH, Fe2+, Mn2+, Ca2+, Mg2+, K+, and Na+. Soil cores were packed to a bulk density of 1.6 Mg m-3 and individually saturated to S0.6 (60% of the pores saturated with water), S0.7 (70% of the pores saturated with water), S0.8 (80% of the pores saturated with water), and S0.9 (90% of the pores saturated with water). Measurements were done in triplicate. The cores were sealed with a double layer of plastic wrap and stored in a laboratory at 23°C until needed. Analysis started three days after initial water saturation. A set of cores (four degrees of saturation with triplicates of each) was analysed every 3.5 days for the first three months after which a set was analysed once a week for the remaining month of analyses. The experiment was terminated after 121 days. The same soil and experimental setup was used for the bulk density experiment. The experiment consisted of a set of three cores packed to an initial bulk density of 1.4, 1.6 and 1.8 Mg m-3. The cores were all saturated to S0.8, each packed in triplicate. The bulk density experiment was terminated after 23 days. There was a good correlation between an increase in degree of water saturation and pe (R2 = 0.95); Mn2+ (R2 = 0.91) and Fe2+ (R2 = 0.92) concentrations. Eh, pH, Fe2+, Mn2+, Ca2+, Mg2+, K+, and Na+ were significantly affected by duration of water saturation and all except Ca2+ and K+ significantly affected by degree of water saturation. Fe2+ and Mn2+ accumulations and depletions (visible segregations or mottles) occurred within 12 months of water saturation in a separate experiment where cores were packed to a bulk density of 1.6 Mg m-3 in a core saturated to S0.9. It was therefore evident that this soil with 0.22% organic carbon and a bulk density of 1.6 Mg m-3 will produce morphological features due to reduction within a year of water saturation at S0.9. An experiment was set up with cores kept at a constant degree of water saturation (S0.8) with varying bulk densities, namely 1.4, 1.6 and 1.8 Mg m-3. All the factors measured (Eh, pH, Fe2+, Mn2+, Mg2+ and K+) except Ca2+ and Na+ were significantly affected by a variation in bulk density. In another part of the experiment two different water temperatures were used to saturated the cores, namely 23°C and 30°C respectively. It was determined that the temperature difference of 7°C caused the cores to react significantly different to each other.. The higher water temperature caused the Eh to decrease more rapidly and therefore a higher Fe2+ concentration occurred in these cores. It was concluded that for this soil at 23°C, Fe3+ and to a certain extent Mn4+ will start to become reduced at a pe of 6 at S0.78. These findings show that the first approximation of Van Huyssteen et al. (2005) where S0.7 was found to be sufficient for reduction is very similar for this soil.

A Climate Predictability Tool was used to evaluate the relationship between sea-surface temperatures and stream flow at different lead-times in the upper Olifants catchment in Mpumalanga, South Africa. Four stream flow stations were selected from each of the subcatchments of the upper Olifants, namely the Groot Olifants on the eastern side and the Wilger on the western side of the catchment. Canonical correlation analyses were used to make three month stream flow forecasts for October-November-December (OND) and January-February-March (JFM) seasons. Monthly global-scale SSTs were used to evaluate the effect of lead-times on correlations between global Sea-Surface Temperatures (SSTs) and stream flow. Then the lead-times with Pearsonâs correlation values greater than 0.50 were selected to be used for evaluating possible origins of stream flow forecasting skill in the Equatorial Atlantic, Southern Atlantic, Equatorial Indian and Pacific Oceans. Although local climatic and hydrological characteristics were not considered in this study good hit score skill from the Southern Atlantic Ocean was found at a short lead-time of two months for both OND and JFM seasons. The equatorial Atlantic Ocean gave a good hit skill score at longer lead-times of seven and eight months. The equatorial Indian Ocean gave a higher Heidke score at a short lead-time of two months during OND and JFM seasons in the Groot Olifants sub-catchment. The oceanic domains adjacent to the southern African subcontinent gave a good Heidke score at a shorter lead-time as compared to the equatorial Pacific Ocean. These forecasts could be used for planning water storage and releases in dams that are down stream of these stream flow monitoring points.

In this study, attempts were made to investigate the growth and yield performance of a Bangladeshi bread wheat cultivar (Sonalica) under the influence of three different nitrogen fertilizer levels and one concentration level of ComCat ® , a commercial bio-stimulant, applied either as a seed treatment before planting or as a foliar spray on seedlings at the 3- leaf growth stage, under glasshouse conditions. Initially the South African (RSA) standard N-level for winter wheat was taken as the medium N- level together with a down scaled (low) and an up scaled (high) rate during the 2001 season in order to ascertain the optimum level. However, it was observed that the Bangladeshi cultivar could not tolerate the RSA standard (medium rate) for nitrogen application. After germination all plants fertilized with the medium and high nitrogen rates, died off. Subsequently, this N-level was taken as the medium level for the 2002 trial and a new down scaled (low) and up scaled (high) N-level was calculated and applied, together with the two ComCat ® treatments. Overall, even though the nitrogen fertilizer application was scaled down substantially during the 2002 growing season, the response of this bread wheat cultivar, in terms of growth and yield, was more positive at the lowest N-level. Results obtained during 2002 consistently confirmed that the application of ComCat ® , especially as a foliar spray at stage 13 of seedling development, affected the vegetative growth of plants. However, the enhancing effect of the bio-stimulant was more pronounced on yie ld, in terms of both the increase in number of kernels and kernel dry mass per plant. Finally, the results of this study and several previous unpublished reports strongly indicate that application of a bio-stimulant such as ComCat ® , in combination with an optimum nitrogen regime, can result in the improvement of yield under glasshouse conditions. In future research attention should be given to the combined effect of ComCat ® and other macro-nutrients, as well as the potential to decrease fertilizer applications when a bio-stimulant is applied in combination, under field conditions.

Soil properties (biological and chemical) and crop response are dependent on the inherent soil organic matter content. Since South African soils are naturally low in organic matter content commercial humates serve as attractive soil amendments in improving soil quality. This is the result of commercialisation giving the impression that humates have biological and chemical properties similar to those in soil humus. In an attempt to substantiate these claims three separate experiments were conducted at the University of the Free State to examine the effect of K-humate on soil properties and wheat response during the 2006 growing season. The biological (bacterial and fungal count) response was evaluated in growth chambers by applying three different K-humate products at rates of 0, 3 and 5 L ha-1 in a band on a red loamy sand topsoil. Soil cores were sampled on a weekly basis for six weeks and microscopically analysed. Bacterial and fungal count differed significantly as a result of the product by application rate interaction but no consistency was found. Over time both the bacterial and fungal activity increased rapidly for week 2 and 3 but decreased at week 3 for the bacteria. Both the organismsâ reactions stabilised from week 3 to 6. The chemical soil properties were also tested in growth chambers but only K-humate (single product) was applied as a coating on granular 2:3:2 (22) fertiliser at 0 and 3 L ha-1 in a band 50 mm below the soil surface. The chemical soil properties showed no response after 5 months to the application of K-humate. A glasshouse experiment was also conducted to evaluate the growth and yield response of wheat on three textural class topsoilâs (8, 22 and 37% clay) and four K-humate applications (0 L ha-1, 3 L ha-1 single application, and 3 and 6 L ha-1 split application â 50% at planting and 50% at tillering). K-humate as a coating on 2:3:2 (22) granular fertiliser was banded and Greensulph (27) topdressed at the required fertiliser rate for a yield potential of 8 t ha-1. Plant growth parameters were analysed at tillering, stem elongation and maturity, both above- and below-ground. Virtually no significant influences were found with the K-humate application rate and soil texture interaction on the measured parameters. Notwithstanding this, positive effects were noticed and a split application whereof half of the K-humate was applied at planting and the other half at tillering showed the best results. A field experiment was also conducted to examine K-humates influence on wheat growth and yield. Two experiments was conducted, one under full irrigation (700 mm) with a yield potential of 8 t ha-1 and the other supplementary irrigation (350 mm) with a yield potential of 4 t ha-1. K-humate was applied as a coating on granular 2:3:2 (22) fertiliser and bandplaced either as a single application (0, 1.5, 3, 5 and 6 L ha-1) or a split application (5 and 6 L ha-1) 50% at planting and 50% (K-humate as a coating on Greensulph (27)) at tillering. Irrigation was applied using a line source irrigation system. The field experiment confirmed the results obtained in the glasshouse with virtually no significant effects as a result of the applied K-humate on the measured plant parameters.

One of the biggest constraints to the expansion of the walnut industry in South Africa, is the availability of good quality and cost effective plant material. Since walnuts are more difficult to propagate vegetatively than most fruit and nut species, controlled conditions are required to ensure grafting success. Hot callus grafting is a bench grafting procedure subjecting grafted trees to controlled, elevated temperature and humidity, and has been implemented successfully in several countries to increase grafting success of walnut. Until now, hot callus grafting has not been investigated as a possible walnut propagation method in South Africa. The present study assessed method of heat supply and time of grafting, as important factors determining grafting success of two walnut cultivars grafted onto Juglans regia rootstocks under hot callus conditions. Although neither method of heat supply provided definite superior grafting success, localized heating of graft unions in a heated trench, gave more consistent results than heating the entire grafted tree in a heated room. Both methods seemed promising, since acceptable grafting success was obtained in some instances with both the heated trench and room. Post-grafting shoot growth on the other hand, was significantly higher for the heated trench than for the room. Both methods did, however, result in trees of a suitable size for orchard establishment after only one growing season. Results further indicated that exposure to increased temperature for a period of 25 days is more than sufficient for callus development of walnut, and very little is gained by heating grafted trees for longer. Earlier grafting, before the onset of bud break of cultivar and/or rootstock, generally resulted in improved grafting success and drastically increased shoot growth during the first growing season, providing grafted trees of saleable size in a shorter time. There were no clear differences regarding callus formation, grafting success or survival between the two cultivars evaluated, âChandlerâ and âSerrâ. As expected, more vigorous post-grafting growth was observed for âSerrâ, since it is the more vigorous grower of the two. A separate hot callus grafting trial, using Paradox rootstocks, also indicated that the type of rootstock utilized in hot callus grafting may impact grafting success. More consistent results were obtained with all four cultivars grafted onto this hybrid rootstock, than with J. regia rootstocks in the preceding trial. For both J. regia and Paradox rootstocks, survival of trees through the first growing season was still unacceptably low, although results were comparable to that of other studies. Since results were available for a single season only, conclusions should be regarded as preliminary. Nevertheless, findings clearly illustrated the potential value of hot callus grafting as propagation method for walnut in South Africa and lay a foundation for the establishment of propagation guidelines using this approach.

Soi ls vary a t all levels of observation. When describing soil physical or chemi cal propert ies we ini t i a l ly think in terms of homogeneous mat e r ial. However, for character izing the land use abi l i ty i t is necess ary to consider varia b i l ity within and between s o i l map uni ts as soils vary significantly over a land and within a homogeneous soil. The combina tions of knowledge about soi l in t e r r e l at ionships and the represent at i on of the soi l var i abi l i ty will be useful in the process of characterizing the var iabil i t y of soi l properties for dif f e rent land use abili t ies, for example precision agriculture. The obj e c t i ves of this study were therefore to (i) characterize the spat i a l var i a tion of sel e c t ed soil properties in and between map uni ts (i i ) describe the relationship between physica l proper t i es of sel e c ted soi l forms and the root densi ty of mai ze ( i i i ) characteri z e the hydrology of the Tukulu, Sepane and Bloemda l s o i l forms a t Paradys. A field experiment was conduct ed on a 55 ha c u l tiv ated f ield on the experimental farm of the University of the Free State, Paradys (S -32°35â21ââ, E -77°43â6ââ). The experimen t a l site was sub divided in to 75 experimen t a l p l o t s . For object i v e 1 a l l 75 plots were analysed for pH, Ca, K, Mg, Na and 7 texture classes . For object ive 2, 13 plots were sel ected from the 75 experimental plo ts to cover a range of relat i ve dry biomass yield plots. Root samples and soil samples were t aken per mas t e r horizon. They wer e analysed for s i l t + clay content , wat e r s table aggregates, modulus of rupture, bulk density and organic carbon content . For objective 3 , three modal profiles were sel e c ted and the instantaneous prof i le method was used to descr ibe the volumet r ic wetness â time relationship, the hydraul i c head â depth rel a t i onships and the hydraulic conductivit y . I t was clear th a t mos t of the soi l physical and chemical prope r t ies had a s t rong relationship with clay. It was found that there was a higher vari a tion between map uni t s than within map uni t s . Despite any var iat ion Inverse Distance Weigh ting (IDW) fai r ly accurately predicted the varia tion with in map uni ts varying f rom 97% to 99% i r r espect ive of hor i zon or s o i l . I t also accur a tely predi ct ed the var iat ion between map uni t s varying f rom 91% to 94%. I t was found t h a t t h e A and C hor izon has var y ing int er rel at ionship due t o varying s i l t + clay content s. The B hor izon i s the main fact or tha t dist inguishes the three s o i l s . Th e s i l t + c l a y c o n t e n t o f t h e B h o r i z on fo r Tu k ul u v a r i ed b e t w ee n 31% an d 34%, t h e S e p a ne b e t w e e n 4 9 % a n d 5 5 % , an d t h e B lo emd a l b e t w e en 28% an d 3 4 % . The B l o e md a l h a d t h e h ig he s t r o o t l e n g t h i n d e x ( R L I ) fo l l owed by t h e S e p a n e a n d Tu ku l u . I t was clear tha t in the case of the Bloemda l and Tukulu , the C hor izon control s the hydrology, while in t h e case o f the Sepane i t i s the B hor izon . I t may be concluded that the variation in soil prope r t ies is higher between t han with in map uni t s. Soi l physical p roper t i es have a clo se int er rel at ionship and varying e f fe c t s on the RLI. The hydrology of the Bloemda l and Tukul u is influenced by the C horizon, whi le the Sepane i s in f luenced by the B horizon.

Land evaluation is currently important in South Africa. Soilscape surveys can make a contribution in this connection by bridging the gap between land type surveys and detail surveys. Land Type Dc17 (area = 237 651 ha) east of Bloemfontein include the densely populated areas near Botshabelo and Thaba Nchu. The objective of this study was to subdivide Land Type Dc17 into smaller more homogeneous land units, to estimate the area of each unit suitable for maize and sunflower production using the In-field Rainwater Harvesting technique (IRWH), and to estimate attainable yields of these crops on the available areas. The soilscape survey technique was developed to serve this goal. Soilscape is defined for this specific study as a mapping unit consisting of a portion of land mappable at a scale of 1:50 000 in such a way that it facilitates the identification of potentially arable land. Earlier Northcote (1978) described soil landscapes as areas of land that have recognizable and specifiable topographies and soils, that are capable of presentation on maps, and can be described by concise statements The delineation of 66 soilscapes was done on 1:50 000 maps. Detailed pedological investigations were made on selected pedoseque nces of some soilscapes using 1:10 000 maps, soil pits, auger holes and depth probe observations. Nine soilscapes with a total area of 82 222 ha were found non-arable. For the remaining 57 soilscapes, covering an area of 155 429 ha, the improved knowledge gained during the detail studies was extrapolated to estimate the area of each one suitable for IRWH. The result was 56 875 ha, or 24 % of the total area of Dc17. The results of previous field experiments on relevant ecotopes predict the following maize yields in tons/ha/yr: conventional tillage = 82 000; simplest type of IRWH = 127 000. It is therefore estimated that this land type can provide the staple maize diet for about 600 000 people using IRWH. The soilscape survey technique proved successful within this land type, but should be refined for application to other land types and other feasibility studies.