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The California Current is the Eastern Boundary Current associated with the North Pacific Subtropical Gyre, transporting cold, nutrient-rich water equatorward. It is also an area of strong mesoscale eddy variance, as well as subsurface zonal currents known as striations. This work examines the causes and variability of these transports using a set of eddy-resolving ocean model simulations. Large-scale meridional transports are found to be driven interannually by the dominant local pattern of wind stress curl variability. This contrasts with earlier work that suggested that these transports were forced principally by tropically-originating coastal- trapped waves. While mesoscale eddies possess a large fraction of intrinsic variance, there is a deterministic component as well. North of the Southern California Bight this component is driven by the same pattern of wind forcing. To the south, eddies respond nonlinearly to both atmospheric and oceanic forcing. Striations are found to develop in response to irregularities in the California coastline. They spin up along with the large-scale circulation, and their magnitude is constrained by the shelf.

Salinity associated with irrigation is and will remain a major obstacle for farmers in most semi-arid regions throughout the world, like the Orange-Riet and Vaalharts Irrigation Schemes in South Africa. On-farm water and salt management should, therefore, be continually evaluated and/or improved. Especially in water table soils where the saturated zone within or just below the potential root zone is not stagnant and lateral flow occurs to lower lying areas and/or artificial drainage systems, which present unique management complexities. Hence, the aim of this study was to evaluate and/or improve on-farm water and salt management of irrigated field crops grown under these conditions. To accomplish this aim the following best water and salt management practices were formulated from literature, i.e. i) use of efficient irrigation systems, ii) introduce scheduling practices that optimize water and salt applications and reduce drainage losses, iii) utilize shallow water tables as a source of water for crop water requirements and iv) monitor root zone salinity to decide when to apply controlled, irrigation-induced leaching for salt removal. Some of these practices were evaluated on a case study basis on two farms within the Orange-Riet and Vaalharts Irrigation Schemes by comparing them to current water and salt management practices. Some aspects of this comparison are difficult to accomplish under field conditions. Supplementing field measurements with mathematical modeling was, therefore, critical to the successful completion of the study. This, however, presented some difficulties because most models require extensive effort to determine input variables and unambiguous numerical model parameters. From the multitude of available models, the Soil WAter Management Program, SWAMP, was selected. According to the aggregated accuracy, correlation and pattern analysis (ISWAMP) of SWAMP, it was found that water uptake of wheat, peas and maize from non-saline water table soils was simulated well (>70%). Consequently it was shown that the soil water balance under fluctuating water table conditions at field level can be solved successfully by SWAMP with limited easily obtainable input variables. This was accomplished by optimizing simply measured in situ field observations, which is vital towards the successful evaluation of water and salt management by irrigation farmers in the region. However, in order to truly revise on-farm water and salt management practices, mathematical models that can simulate the dynamic response of crops to both water (matric) and salt (osmotic) stress are required. A salinity subroutine for SWAMP was, therefore, developed and validated, i.e. mathematical algorithms that can simulate upward and downward salt movement in water table soils according to the cascading principle, and the effect of osmotic stress on water uptake and yield according to the layer water supply rate approach. It was found that SWAMP was able to simulate the accumulation of salt within the root zone above the water table due to irrigation and capillary rise well, and consequently simulate the effect on crop yield. This was possible because SWAMP was able to successfully (ISWAMP > 70%) simulate a reduction in water uptake during the growing season of field crops due to osmotic stress. Consequently SWAMP was used in the case study to solve the water and salt balances of two irrigated fields over four growing seasons and investigate whether the farmers employed best water and salt management practices, using different scheduling approaches. It was concluded that with both centre pivots, crop water stress was prevented, therefore, apparently detracting from the merits of irrigation scheduling. However, it was possible to conserve 20% of irrigation water using scientific based objective, compared to intuitive subjective scheduling, while at the same time also reducing salt additions considerably. Despite less irrigation due to objective scheduling, almost all of the applied salt was still leached into the water table. This was because the presence of a water table within or just below the potential root zone limits storage for rainfall and/or irrigation above the capillary fringe, hence presenting favorable leaching conditions. Since the water below the water table, at both fields, was not stagnant, lateral flow of water through the saturated zone was responsible for removal of the salts. This continual removal of salt is generally not considered good practice because ideally salt must be allowed to accumulate and only periodically leached during high rainfall events and/or fallow periods. Although both scheduling approaches resulted in similar yields, better on-farm water and salt management was achieved with scientific objective scheduling. In doing so farmers can address the environmental problems associated with irrigation, i.e. degradation of water resources due to uncontrolled leaching while achieving similar yields using less water.

Several environmental factors constantly play a role in crop failures. Of these high temperature and limited water supply are major factors that limit plant productivity and threatens food security. Hence, a search for alternative crops with good tolerance characteristics towards abiotic stress is an ongoing process. Amaranth has been established as an annual vegetable and grain crop and is seen as a prospective alternative crop. Seed germination and seedling development are presumed to be the most critical stages in the life cycle of many seed propagated crops. This served as a rationale for the underlying study on two amaranth species in terms of seed germination, as well as the morphological and physiological response of seedlings to different temperature (25, 30, 35, 40ËC) and water potential (0, -250, -500, -750, -1000, -1250 kPa) regimes. For A. cruentus the optimum temperature was between 25 and 30oC and between 30 and 35oC for A. hybridus in terms of seed germination and early seedling growth. A. hybridus showed a greater level of adaptation to the higher temperature regimes as well as when simultaneously exposed to a rather stringent water potential of -1250 kPa by maintaining root growth better than A. cruentus. Moreover, the imposed temperature/drought stress condition had no significant effect on either of the physiological parameters tested in the former species. These included sugar and total water soluble protein levels as well as photosynthesis and respiratory capacity. Together with the ability of stressed seedlings to maintain growth, the latter strongly suggests that the metabolic events were scarcely affected in A. hybridus, supporting the postulate that it showed a higher degree of tolerance towards abiotic stress conditions. Alternatively, more than half of these events were found to be upgraded in A. cruentus seedlings and interpreted as an attempt by this species to counteract the stress effects, but not successfully, as measured by its inability to maintain seedling growth under these stress conditions.

Although there is an increasing need for spatial soil information, traditional methods of soil survey are too cumbersome and expensive to supply in that need. Digital soil mapping (DSM) methods can fulfil that need. Internationally, DSM is moving from the research to the production phase. As soil-landscape interaction and availability of data varies between locations, local DSM research is needed to make its application practical. This research aims to produce a working DSM protocol which can be used for mapping large areas of land in southern Africa. The protocol must meet soil surveyors where they are at, being easy enough to follow, while also allowing for the creation of products needed by industry. To keep the link with industryâs needs, a case study approach was followed. Four case studies were done in succession, with the protocol being improved with every case study. The case studies cover an array of challenges faced by soil surveyors. In the first case study a baseline protocol was created when two land types near Madadeni were disaggregated in a series of soil maps. With each map, more information was incorporated when creating the map. For Map 1 only the land type inventory and terrain analysis were used. A reconnaissance field visit with the land type surveyor was added for the second map. Field work and a simplified soil association legend proved to improve the map accuracy for Maps 3 and 4, which were created using 30% and 60% of the observations points as training data respectively. The accuracy of the maps increased when more information was utilized. Map 1 reached an accuracy of 35%, while Map 4 achieved a commendable accuracy of 67%. Principles which emerged was that field work is critical to DSM, more data input improves the output and that simplifying the map legend improves the accuracy of the map. An unrealistic demand for a soil survey of 37 000 ha of land in the Tete Province, northern Mozambique, possibly infested with land mines, in 8 working days by two persons, created an opportunity to apply the soil-land inference model (SoLIM) as a digital soil mapping tool. Dividing the area into smaller areas where unique soil distribution rules would apply (homogeneous areas, HAâs) was introduced. A free survey was conducted along the available roads of the area. The final soil map for 15 000 ha had an accuracy of 69%. A principle which emerged was that inaccessible areas can be mapped, provided that they occur within surveyed HAâs. Near Namarroi, Mozambique, the potential of DSM soil survey methods to rapidly produce land suitability maps for a large area with acceptable accuracy was evaluated. Conditioned Latin hypercube sampling (cLHS) was introduced to determine field observation positions. SoLIM was used to run an inference with soil terrain rules derived from conceptual soil distribution patterns. A restriction of the expert knowledge based approach was found in that only six soil map units (SMUâs) could be determined per HA. The map achieved an overall accuracy of 80%. Land suitability maps were created based on the soil class map. In the Kruger National Park a soil map was used to create and extrapolate 2-dimensional conceptual hydrological response models (CHRMâs) to a 3-dimensional landscape. This is a very good example on how value could be added to a soil map. An error matrix convincingly identified problem areas in the map where future work could focus to improve the soil map. The current data indicates that at least 28 soil observations are necessary to create a soil map to an acceptable standard. When minimum observation criteria are met, observation density is irrelevant. The cLHS method to pre-determine observation positions improved the usability of observations. Although more research is needed to accurately determine the minimum observation criteria, an observation strategy is suggested. A 15 step protocol is produced with which it was shown that soil surveyors could produce a variety of maps in diverse situations. The protocol relies on the expert knowledge of the soil surveyor, combined with field observations. It has the advantages that fewer observations are necessary, map accuracy assessment is possible, problem areas are identified and under certain conditions unsurveyed areas can also be mapped. On the down side, there is a limitation of six SMUâs per HA. Further research needs to be done to determine the minimum criteria for soil observations, and soil distribution relationships between soil and remotely sensed covariates.

South Africa mainly produces oil seed sunflowers of which 86% is produced in the Free State and North West provinces which are known for their sandy soils. Temperatures can rise to 42°C in these soils when planting commences during November to January. These conditions, in combination with other factors such as planting date and planting depth, soil type, different cultivars, and seedling vigour, can influence the emergence rate of sunflower seedlings. This will cause uneven stand which could affect the yield negatively. In an attempt to evaluate the influence of soil factors and planting techniques on sunflower emergence, three experiments were conducted in the greenhouse at the Department of Soil, Crop and Climate Sciences of the University of the Free State. These experiments evaluated the effect of seed size, planting techniques, and soil factors, and high soil temperatures on the emergence rate of selected sunflower cultivars. Three seed sizes (seed size one to three) of three cultivars (PAN 7049, PAN 7057, and PAN 7063) were planted at two planting depths (25 and 50 mm respectively) during three planting dates (September 2010, November 2010, and February 2011) to determine the influence on the emergence rate of seedlings. It was found that a smaller seed size, such as seed size three, emerged faster than larger seeds, seed size one. The influence of two planting depths (25 and 50 mm) during the previously mentioned planting dates with two soil types (Bainsvlei and Tukulu) on the emergence of sunflower seedlings was also tested. Cultivar emergence was faster at 25 than at 50 mm. It was also observed that the emergence rate was faster during February 2011 than during September and November 2010. Although the emergence was faster during February 2011, above ground growth (plant height and dry weight) was greater during November 2010 than during September 2010 and February 2011. The influence of four soil temperatures (35, 40, 45, and 50°C respectively) on the emergence of sunflower cultivars was tested. An under floor heating wire (23 kW) was attached to a galvanised metal grid and was used to simulate day and night temperatures in the top soil. The grid and seed were placed at a depth of 25 mm (planting depth). Emergence index declined gradually from 35 to 45°C, but a rapid decline in emergence index was observed from 45 to 50°C. Emergence can be measured or calculated as an emergence index. Emergence is determined as the moment that the seedling is visible above the ground and different formulas exist to determine the emergence. Experiments differ from one another and therefore different emergence index models were developed to accommodate the experiment methods or crop that was used. It can therefore be concluded that differences in emergence exist between cultivars. It is also necessary for producers to acknowledge that soil factors and planting techniques play a vital role during planting until the seedling emerge.

Leaf wetness duration (LWD) is a key component of most disease-warning systems which are designed to help growers to determine when to apply control measures to suppress plant diseases. Since LWD is a complex phenomenon due to its spatial and temporal variability, this can affect the performance of such systems. Despite the importance of LWD, it is not usually measured at most standard weather stations because of lack of standard sensor and protocol. This study was carried out to evaluate and characterize the spatial variability of LWD within a citrus canopy and also to evaluate the performance of two commercially available wetness sensors, namely the Campbell Scientific wetness sensor (Model 237) and the Decagon wetness sensor by comparing them with visual observation of water droplets on the leaves. A total of 6 sensors were installed in the upper and lower canopy levels of the citrus canopy to measure LWD at Welgenvallen Experimental Farm of the University of Stellenbosch from 27 July until 30 November 2012. A total of 62 days were visually observed for LWD. Four of the wetness sensors (2 of each type) were mounted at the upper canopy level (top two-thirds), whilst the other two were placed in the lower one-third of the canopy-one on either side. All the sensors were installed at 45o facing South. Other weather parameters such as air temperature, relative humidity, net radiation above the citrus canopy as well as the leaf temperature were measured by a nearby automatic weather station. Visual observation of LWD showed the mean daily LWD in the upper canopy level was significantly (p<0.05) longer, by about 1.7 h, in the upper canopy level than in the lower canopy level. However, no significant differences were noted between the lower eastern and western canopy levels, with a difference of only 24 minutes. When rain was the source of wetness, there was no significant difference between LWD at any of the canopy positions due to penetration of rainfall through canopy to lowest level. The mean daily LWD in the upper canopy was 15.5 h compared to 14.3 and 14.1 h in the lower eastern and western canopy positions. Based on these facts, it can then be concluded that the spatial variability of LWD has to be considered if measurements of LWD are used as inputs to disease-warning system. The linear regression analysis between measured and visually observed LWD showed that the sensors installed in the upper canopy level provided higher accuracy than the sensors placed in the lower canopy level. Although some researchers recommend painting the Campbell sensors, these results showed that even the unpainted Campbell sensors installed in the upper canopy level of a citrus canopy can be used to measure LWD with acceptable accuracy. During dew days, the sensors at the upper canopy level had a MAE of about 1 h compared to more than 2 h for the sensors placed in the lower canopy. An analysis of leaf and air temperature exhibited that in 96% of the nights when dew was observed, dew deposition in the citrus canopy commenced whenever the leaf temperature fell below the ambient dew point temperature. The first occurrence of dew deposition was mostly observed between 19h45 and 22h00, whilst dew dry-off took place more frequently between 8h45 and 10h30. On average, both the visually observed as well as the sensor predicted âfirst onset of dewâ was more than 30 minutes after the leaf temperature had fallen below the ambient dew point temperature. It then follows that leaf temperature together with the dew point temperature can be used as an indicator for the onset of dew deposition in citrus canopy. A study was also conducted under field conditions to evaluate Newton-Raphson iterative method as an alternative approach in the indirect determination of leaf temperature from meteorological data. Three field experiments were performed at two different sites at Cape Peninsula University of Technology, Bellville Campus near Cape Town, using three different plants. Leaf temperatures predicted from the iteration method were compared with field measurements of leaf temperatures obtained from a Ficus microcarpa (local tree), potted Strelitzia nicolai flowering plant and Agapanthus praecox, another indigenous flowering plant growing at CPUT nursery complex. The strongest relation, characterized by reasonable precision (R2 = 0.89), high accuracy (D = 0.96) and a fairly high value of the confidence index (C = 0.91) was obtained when A. praecox was used, whilst S. nicolai yielded a poorer relationship (R2 = 0.71; D = 0.77; C = 0.64), and F. microcarpa had the worst correlation. Leaf temperature computed by the iteration process showed a tendency of underestimation in all these experiments. LWD can be also predicted from both empirical and physical models. Finally, a study was also undertaken with the objective to compare the performance of a physical model (SWEB) and an empirical model (RH) using the weather data for the 62 d of measurement. Both models exhibited a similar trend to that of the sensors, in that the accuracy was higher in the top of the canopy compared to the bottom of the canopy. The result also confirmed that models are poor estimators of LWD at the lower canopy levels. The RH model, however, performed better than the SWEB model with a higher fraction of correct estimates (Fc), correct success index (CSI) and lower false alarm ratio (FAR) when considering all the hours for both levels during wet and rainy events. An analysis of the distribution of the errors showed that whilst the SWEB showed a tendency to overestimate LWD, the converse was true for the RH model. Based on these results, it is concluded that if locally calibrated, the RH model can estimate LWD with acceptable accuracy. Consequently, citrus growers who cannot afford to install wetness sensors may therefore consider the use of RH model as part of their disease-warning system. Nevertheless a site-specific calibration is required prior to the use of the model.

Agriculture is pivotal to the development of most countries in southern Africa, including Zimbabwe, with the sector contributing significantly to the Gross Domestic Product of these countries. The sector also provides labour to the majority of people and most rural populations in these countries derive their livelihoods from agriculture. The relative contribution of agriculture to national economies and to food security is, however, being reduced by climate variability and change. Smallholder farmers in semi-arid areas of Africa are particularly vulnerable to climate variability and change. The overall objective of this study was to establish the extent to which maize yield in the smallholder farming sector of semi-arid Zimbabwe could be affected by climate change, by 2050. The study also sought to establish trends in extreme temperature and rainfall indices, current farmer cropping practices and their current coping/adaptation strategies to climate variability and to assess the likelihood that farmers would adopt selected strategies of adapting to climate change. The study areas, Lower Gweru and Lupane communal areas are located in agricultural regions with low potential, being in Natural Regions III and IV, and lie in the central and western parts of the Zimbabwe, respectively. Extreme temperature and rainfall indices for Bulawayo Airport meteorological station which is in western Zimbabwe and equidistant from the two study areas, Lower Gweru and Lupane, were computed and their linear trends were calculated for the period 1978-2007 using the Statistical and Regional dynamic Downscaling of Extremes for European regions (STARDEX) software. Significance of the trends was tested using the Kendall-Tau's test. It was found that for the period 1978 to 2007, cold extremes represented by frequency of cold days, coldest day-time and night-time temperatures did not show evidence (p>0.05) of warming or cooling for Bulawayo. Warm extremes, however showed significant warming (p<0.05), particularly during winter and spring as well as for the year. The greatest signal for warming was shown by trends in hottest day-time temperature and frequency of hot days. Trends in mean diurnal temperature range were positive, but only significant (p=0.05) during the winter season, while trends in extreme low (10th percentile) and extreme high (90th percentile) diurnal temperature range were also positive but insignificant (p>0.05) across all seasons. Increasing trends in diurnal temperature are not consistent with climate change, suggesting that warming evidenced by warm extremes are probably not due to climate change per se. Only three indices, two of which are less commonly used indices, namely mean dry spell length during the dry season (April, May and June), the longest dry spell during the first half of the rainfall season and the correlation for spell lengths during the second half of the rainfall season (January, February and March) season, show significant trends (p<0.05). Both quantitative and qualitative methods were used to establish agronomic practices of farmers, constraints they faced and their coping strategies to climate variability. Methods used to collect data included structured interviews with farmers, semi-structured interviews with key informants, focus group discussions and a desktop study. Farmers commonly have coping strategies to address some of the general constraints they encounter in agricultural production as well as strategies to cope and adapt to current climate variability. The study has identified a number of research and extension interventions which may enhance crop productivity in the smallholder farming sector in semi-arid western central Zimbabwe. Effects of climate change on days to physiological maturity, maize yield and soil water balance components were simulated using the Agricultural Production Systems sIMulator (APSIM) model version 7.3, for maize grown in Lower Gweru, on a sandy soil. Simulated yields and water balance components were compared across three climate scenarios, the current climate (representing no change in temperature and rainfall, and a CO2 concentration of 370 ppm); Future climate 1 (representing a temperature increase of 3oC, rainfall decrease of 10% and CO2 concentration of 532 ppm) and Future climate 2 representing a temperature increase of 3oC and a rainfall decrease of 15% and CO2 concentration of 532 ppm. The reference period for future climate is the year 2050 under the A2 Intergovernmental Panel on Climate Change (IPCC) CO2 emission scenario. The climate change scenarios were created by perturbing the observed climate data for Gweru Thornhill meteorological station near Lower Gweru. A sensitivity test was done using a range of temperature changes (+0.5 to 3.5oC) and rainfall changes (+5 to -20%) as well as under a range of CO2 concentration (420 to 700 ppm) and all under nitrogen non-limiting conditions. Results of this test showed that CO2 offsets the negative effects of both high temperature increases and rainfall reductions with temperature increases in the low range of 0.5 to 1.5 oC, increasing maize grain yield at higher CO2 concentrations of 580 and 700 ppm. Thus the greatest yield reductions due to either increased temperature or reduced rainfall amounts occurs at lower rather than higher atmospheric CO2 concentrations. The results of this test also show that maize grain yield increased with increased CO2 concentration and suggest that temperature and rainfall changes contribute relatively equally to the overall effect of climate change on maize yield in central Zimbabwe. Significant differences among treatment (different climate scenarios) means were tested using non-parametric tests, namely the Kruskal-Wallis and Mann-Whitney tests for independent samples, for simulated data that were not normally distributed, while for normally distributed data, t-test for independent samples was used. Climate change significantly (p<0.05) reduced the number of days taken by both early and late maturing maize varieties to reach physiological maturity, with the late and early maturing varieties taking 29 and 23 days less, respectively, to mature under climate change compared to under the current climate. Under climate change days to maturity of the SC709 late maturing maize variety are reduced to a duration similar to that of the current early maturing variety SC403, grown under current climate. Therefore maize yields could be maintained by shifting from early maturing to late maturing varieties, in the face of climate change. Climate change reduced maize yield, with slightly greater reductions obtained under the drier climate change scenario of 15% reduction in rainfall. Grain, biomass and stover yields were reduced by 13% for the early maturing variety SC403 while for the late maturing variety SC709, these yields were reduced by 16, 18 and 20% respectively. However, the only significant (p<0.05) yield reduction was that for stover of the late maturing variety. Climate change reduced the amount of water available at sowing by 8-10%, seasonal soil evaporation by about 10% and transpiration by 5-8%. It also reduced the amount of runoff and drainage by about 26-38%, with greater reductions occurring under the drier future climate. However, the reductions were not significant (p>0.05) for any of the components except for runoff. Significant reductions in seasonal runoff due to climate change results in reduced water availability from surface water resources and this calls for efficient use of water. Lower Gweru farmers' opinions on climate change effects on agricultural productivity and their possibility of adopting selected adaptation strategies against climate change were established during focus group discussions with a total of 36 farmers. Pre-requisite exercises for capturing farmersâ reactions to climate change included presentation of the outcome of a survey on farmer perceptions on climate variability and change that had been conducted during 2008 and presentation of the projected climate for Zimbabwe, by 2050. To facilitate discussions on farmers' likelihood of adopting long season maize varieties, use of mulch and planting basins, in the face of climate change, simulated maize grain yield and soil water balance under different climate and agronomic scenarios were presented to the farmers in simple graphical form. Annual simulated yields and water balance were presented for the latest 10 seasons, 1998/99 to 2007/08 seasons. Farmers provided their responses in three groups that were formed based on wealth ranking. All farmers irrespective of wealth category, envisaged negative impacts of climate change on agricultural productivity. They also expressed concern on the likelihood of reduced water availability; reduced food and nutrition security, increased number of school drop-outs and a decline in their general wellbeing. Farmers did not provide alternative strategies (to deal with climate change effects) to those they use to cope with current climate variability. Also most of their responses were biased towards crops and these ranged from crop choice, reduced input levels and use of water conservation techniques. Farmers also recommended an expansion in irrigation development by the government. The resource rich farmers suggested supplementary pen feeding of livestock as an adaptation strategy against climate change. Smallholder livestock producers can employ other adaptation strategies, which include shifting towards small livestock and browsers rather than the current cattle and grazers. Although use of mulch and planting basins clearly improved soil water balance in terms of reducing the amount of soil evaporation and runoff, this did not translate into an overall increase in maize yield. However, in relatively poor rainfall years both mulch and planting basins gave higher yields than conventional ploughing without mulch. Thus, use of reliable seasonal rainfall forecasts can help farmers to decide on when to use mulch and/or basins. Farmers showed that it was relatively easy to shift from growing early maturing maize varieties to late maturing varieties, but indicated that the cost of hybrid seed and its availability have always been prohibiting factors. They are unlikely to adopt the use of mulch and planting basins due to high labour requirements and limited access to "extra" fertilizer required when mulch is used. Mulch availability is also limited as its main source, stover, has other uses that compete with use as mulch. It appears planting basins are a more important alternative for land preparation and crop establishment for farmers who do not have draft power than for those with draft animals. It can be concluded that warming is taking place for the station (Bulawayo Airport) considered in this study and this is particularly evident from warm extremes. There is, however, limited evidence of changes in rainfall extremes. Similar analyses as those done for Bulawayo Airport station should be done for more stations and for longer periods. Climate change was found to significantly reduce the number of days taken by maize to reach maturity, with the long-season variety taking about the same number of days to mature under climate change as the short season variety, under current climate. Maize yields are also negatively affected by climate change. Results from the study also indicate that there is a significant reduction in runoff due to climate change. These effects have implications on food and water availability, hence the need to put appropriate adaptation strategies and policies in place. It was encouraging to note that, generally, smallholder farmers in the study area had a sound inference of the likely impact of climate change on agriculture and their well-being. They were also able to suggest possible strategies to deal with climate change, given the expected rainfall and temperature projections for Zimbabwe by 2050. Smallholder farmers in the study area use several strategies to cope and / or adapt to the numerous constraints they face in crop production. Strengthening farmers' capacity to employ these strategies will improve crop productivity. Based on the current farmer practices in the study areas, the study has identified both research and extension interventions that could be used to increase productivity in the study area and in similar biophysical and economic environments.

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Crop rotation is one of the pillars of conservation agriculture (CA). It has been adopted moderately in the summer rainfall area of South Africa, but the adoption of conservation tillage has been very slow. It has been observed that research information on crop rotation helped with the adoption of the CA concept in the Western Cape. Limited research has been done on crop rotation in the Eastern Free State. This study used the crop matrix trial design to evaluate the impact of different cropping sequences in a CA system on the growth, development, yield and quality of wheat as target crop. The profitability and production risk of the different crop rotations were also determined. Only preceding summer crop sequences had a significant (Pâ¤0.1) influence on the yield parameters of the final wheat crop. For the final wheat crop three preceding sequences, namely sorghum à soybean, maize à sunflower and soybean à maize, led to a lower (Pâ¤0.1) number of plants and ears, with a lower biomass and residue yield unit area. Although the poorest response was always recorded on the preceding sorghum à soybean sequence plots, it did not differ significantly from those of the other two crop sequences. The final wheat crop also had a significantly higher TKM and harvest index on preceding sorghum à soybean sequence plots. It was concluded that the lower number of plants on these plots could be attributed to lesser in-row competition for water and nutrients, which resulted in bigger and heavier wheat kernels with a higher TKM. The study confirmed previous research, namely that the final wheat crop planted on second season sunflower plots had a significantly (Pâ¤0.1) higher number of ears m-2, with a better N(grain) use efficiency. That resulted in a significantly higher grain protein content. However, the yield of the final wheat crop did not differ between plantings on second season summer crop plots. Rotation with oats is often recommended to reduce Take-all, a soil-borne disease of wheat. It was found that the final wheat crop planted on second season oats plots had a significantly lower seedling number, with fewer ears and a lower grain yield per unit area. The wheat plants also had a lower (Pâ¤0.1) precipitation use efficiency and grain nitrogen use efficiency, which led to a lower accumulation of grain protein. It was concluded that oats has a negative influence on wheat yield in a rotation system and that the crop should only be used as a break crop against Take-all. Thirty two of the 50 crop rotations had a total profit margin above the chosen target income of R1,000 ha-1. The soybean à maize à wheat rotation gave the highest total profit of R7,549.76 ha-1, while the sorghum à dry bean à wheat rotation realised the highest total loss of R1,903.93. Maize had a stable yield over two seasons, while the yield of the other four preceding summer crops posed a higher production risk under rainy conditions (pod shattering in dry bean and soybean crops), or potential bird damage situations (sunflower and sorghum). The crop matrix technique proved to be a reliable method to generate more information on cropping sequence in the same trial over a much shorter period. A multi-disciplinary approach in future cropping sequence research will help to provide producers with reliable information. If crop sequences can be proven to be effective at research level, clear guidelines and recommendations can be developed to help producers in implementing conservation tillage more successfully in the Eastern Free State.