Canola serves as a very favorable crop to produce oil world wide. Canola production in South Africa is mainly restricted to the Western Cape Province under winter rainfall conditions. The Protein Research Foundation propagated the production expansion to the central part of South Africa. The semi arid area (Central part of South Africa) is characterized by variable and unreliable summer rainfall. Irrigation is therefore vital for sustainable production of a winter crop like canola. The aim of this study was to establish the cropâs plasticity ability, water use, water use efficiency and transpiration coefficient under a range of water application and plant density treatments combinations for the central South Africa. An experiment with a line source sprinkler irrigation system was conducted near Bloemfontein in the Free State Province. Water applications, excluding 57 mm rain were: W1 = 118 mm, W2 = 176 mm, W3 = 238 mm, W4 = 274 mm and W5 = 363 mm. These water applications were combined with the following planting densities: PD25 = 25plants m-2, PD50 = 50 plants m-2, PD75 = 75 plants m-2, PD100 = 100 plants m-2, PD125 = 125 plants m-2. Seeds (1564 - 4653 kg ha-1) and biomass (3150 - 6733 kg ha-1) yields induced by the treatments proved that canola has a high plasticity. This is because over the full range of water application treatments optimized yields were realized at only one plant density though different for seed (25 plant m-2) and biomass (75 plants m-2) yields. Compensation of yields at lower plant densities resulted from branches and hence pods per plant. Total evapotranspiration increased linear (r2 = 0.97) from 245 mm with 118 mm water application (W1) to 421 mm with 363 mm water application (W5) but was not influenced by plant density at all. Water use efficiency confirmed the optimum plant density for fodder production is 75 plants m-2 and for seed production is 25 plants m-2. The water use efficiency at these two plant densities were 12.9 kg ha-1 mm-1 and 9.6 kg ha-1 mm-1, respectively. The β coefficient of canola was constant (2.26) for the full to moderate irrigation regimes (W5 - W3), but not for the low irrigation regimes (W2 - W1). The β coefficient of 2.26 was used to separate the evapotranspiration of the W3 - W5 treatments into evaporation (56%) and transpiration (44%). This method was not suitable to establish the influence of plant density on the two components of evapotranspiration. A transpiration coefficient of 0.0045 was calculated for canola when planted for fodder at an optimum plant density of 75 plants m-2 under moderate (W3) to full (W5) irrigation.

Pearl millet (Pennisetum glaucum [L.] R. Br.) is a drought tolerant cereal crop planted mainly in arid and semi-arid regions of the world. Water stress still remains one of the challenges facing agriculture. Crops face water stress at various stages due to low and erratic rainfall in arid and semi-arid regions. The response of two pearl millet lines (GCI 17 and Monyaloti) to water stress during vegetative growth was investigated at University of Free State, Department of Soil, Crop and Climate Sciences experimental farm at Kenilworth during the 2009/2010 growing season. The two pearl millet lines were grown under three irrigation treatment levels, namely full (IR3) moderate stress (IR2) and rainfed (IR1). A line source sprinkler system was used to irrigate the experiment. Stressed plants of GCI 17 were about 30% shorter than irrigated plants. For Monyaloti, the stressed plants were 25% shorter than irrigated plants. The highest leaf area index (LAI) of 7.9 was found in IR2 plants of GCI 17 at 7 weeks after planting while the stressed plants of this line attained a highest LAI of 3.6 at 8 weeks after planting. The highest LAI attained by Monyaloti was 9.5 in IR2 plants at 8 weeks after planting and the stressed plants attained a highest LAI of 4.7 during the 9th week after planting thus showing that mild water stress caused a delay in canopy development and limited the size to about half. However, the number of tillers and leaves on the main shoot were not affected by water deficit conditions. The leaf water potential measured by the pressure chamber showed some difference between irrigated and stressed plants after 3 days of withholding rain of 5.6mm from stressed plots. The differences in water potentials of stressed plants and irrigated plants were increasing simultaneously with water stress progression. The water potential of GCI 17 dropped to as low as -1.83 MPa on water stressed plants after 11 days of withholding rain. The leaf water potential for Monyaloti remained significantly higher in the corresponding irrigation treatments. The diurnal changes of leaf water potential showed well watered GCI 17 plants to have water potential of -1.08 MPa around midday while the stressed plants had lower potential of -1.75 MPa. Well-watered plants of Monyaloti had leaf water potential of -0.76 MPa while their stressed counterparts had -1.05 MPa. The seasonal stomatal conductance did not show differences between the pearl millet lines. Stressed plants had lower stomatal conductance values than the irrigated plants, which was also more pronounced as water stress progressed. The stomata of GCI 17 were partly closed for the whole day as revealed by diurnal stomatal conductance. For Monyaloti even the stressed plants had their stomata wide open in the morning and became partly closed by 1300hrs and during the rest of the afternoon. On day 16 after withholding rain (17th February 2010) from water stressed plots, GCI 17 plants had relative water content (RWC) of 72.7% while the well watered plants had 90.3%. Water stressed Monyaloti plants were at 82.8% RWC while the well-watered plants had a RWC of 92.9%. The RWC of stressed plants was continuously decreasing with progress in water stress. The osmotic potential at full turgor was -1.62 MPa for well-watered plants of GCI 17 while -1.83 MPa was measured in the water stressed plants of this line. For Monyaloti, well-watered plants had osmotic potential of -1.11 MPa compared to -1.47 MPa for water stressed plants. At turgor pressure equal to zero, GCI 17 plants from stressed and well-watered plots did not show any adjustments as they were about similar (-2.22 and -2.27 MPa respectively). For Monyaloti water stressed plants had potential of -1.72 MPa and well-watered plants had -1.61 MPa at turgor pressure equal to zero showing an osmotic adjustment of 0.11 MPa. The density of stomata was found to be lower on water stressed plant leaves than on well-watered plants. The abaxial surfaces of pearl millet leaves were found to have lower densities than the adaxial surfaces. The stomata areas calculated from the length and width of the stomata were larger on the adaxial surfaces of GCI 17 plants than those found on the abaxial surfaces. The opposite of this was observed in Monyaloti. The plant height, LAI and biomass accumulation for the two pearl millet lines were found to be lower in water stressed plants when compared with irrigated plants. Monyaloti plants were taller, had higher LAI and accumulated more biomass than GCI 17 plants at corresponding water treatment levels, showing that Monyaloti was less affected by water stress. It was also observed that water stressed plants have lower leaf water potential when compared to irrigated plants. The leaf water potential was maintained higher in Monyaloti plants compared to GCI 17 plants and the same effect was seen with the stomatal conductance which was also lower in water stressed plants than irrigated plants in the pearl millet lines. The highest growth was observed for IR2 plants. Thus from all of growth and physiological field measurements it can be seen that Monyaloti is better adapted to the water stress conditions. It will continue to grow and produce a crop despite the mild water stress due to maintenance of leaf water potential and through osmotic adjustment. Further investigation of the effects of age on the leaf water potential, stomatal conductance, RWC and stomatal characteristics in relation to photosynthesis was recommended.

The biggest challenge in semi-arid areas is finding ways of reducing the major unproductive water loss: evaporation from the soil surface. A large number of subsistence farmers east of Bloemfontein, in and around ThabaâNchu in the Free State Province of South Africa occupy about 11 000 ha of land. The economic potential of this communal land still needs to be unlocked and the natural resource base is critical for this endeavour. However, the prevalence of clay and duplex soils is a major constrain towards improving food security in this area. Poor soil water regimes resulting from prolific runoff and evaporation losses is one of the reasons especially when conventional tillage is used. It was therefore hypothesized that by quantifying soil surfaces evaporation (Es); characterizing of the soil hydraulic properties and understanding the effect of temperature on mulch type and coverage of the Bonheim (Bo) soil can contribute to the improvement of the infield rainwater harvesting (IRWH) system and fill a gap in knowledge under South African conditions that is in terms of promoting water storage capacity and minimizing Es for better crop yields. The ECH2O-TE probes used in this study were calibrated to measure soil water content () and temperature (T). The evaporative desorption procedure (EDP) of Van der Westhuizen (2009) for coir was modified to calibrate probes in undisturbed soils. The probes were evaluated against measured volumetric soil water content (mm mm-1) on their accuracy, precision and repeatability to measure soil water content in the 26oC treatment (Chapter 2). Most of the laboratory derived equations had RMSE close to zero, on average at 0.003 mm mm-1 and precision (R2) ranged between 93 and 99% and accuracies up to 96%. These probes were found to be sensitive to soil temperature changes in the measurement of water content. Under wet to dry soil conditions about 48, 62 and 34% errors were obtained for the A, B and C-horizons, respectively and therefore temperature compensated equations had to be developed in Chapter 3. Temperature compensated equations predicted soil water content measurements with an accuracy, precision and repeatability at 99, 99 and 95%, respectively. Manufacturerâs generic equation tended to over predict soil water content measurements and lacked accuracy with errors ±40% and repeatability. Chapter 4 investigated how mulch type and percentage cover influenced temperature above and below the soil surface. First: results indicated that mulch did not influence air temperature at an elevation of 160 mm above the soil surface. Secondly: percentage coverage affected soil temperature up to 450 mm, and thirdly: the 100% reed mulch cover treatment was recommended for farmers in order to minimise evaporation especially under semi-arid conditions where normally the evaporative demand exceeds supply. Chapter 5 on the other hand profiled and characterized the hydraulic properties of the Bo soil for the A, B and C-horizons. Soil pores were separated into structural and textural pore classes for each of the horizons that were identified for the three master horizon of the Bonheim soil using a method first used in this study known as the âin situ internal drainageâ (ISID) method. The drained upper limit (DUL) for each horizon was determined using the ISID method and were found to be associated with micro pore class. The structural pores of the three horizons were found to be associated with low suctions and that they allowed water to flow at rates between 1-20 mm hr-1. The transitional pore class (Meso pores) conducted water at rates between 3-12 mm hr-1 and micro pores between 3-10 mm hr-1. Five methods were used to estimate evaporation (Es) during three Es drying cycles (Chapter 6) and these estimations were compared to a weighing lysimeter [Es(lys)] measurements in order to evaluate their accuracy in the measurement of Es, using Willmot test statistics for paired values. The field hydraulic method had a good performance with an average D-index value of 0.60 in all the three drying cycles selected and thus estimated Es closer to Es(lys) hence it was recommended for use in estimating Es for Bo soils.

The risks associated with climate and its variability over the Free State Province is the major determining factor for agricultural productivity, and has a major impact on food security across the province. To improve productivity of agricultural lands, producers and decisions makers have to be provided with relevant agrometeorological information that will enable them to make appropriate decisions. This has lead to the investigation of this agroclimatological risk assessment for maize production in the Free State. The ultimate goal was to characterize the agroclimatological risks impacting negatively on dryland maize production and develop a climate risk tool that will assist the stakeholders in their management of agricultural lands. First, meteorological data needed to perform this study was prepared by looking specifically at filling the missing data gaps and using alternative data in cases where measured data was not available to obtain good spatial distribution of weather stations. Frost was identified as one of the climate hazards affecting the maize plant in the Free State. Three frost severity categories were analysed, namely 2°C, 0°C and -2°C representing light, medium and heavy frost respectively. The onset of frost for all the thresholds was earlier over the northern, eastern and far southeastern parts of the Free State province while places over the western and southwestern parts of the province the first frost dates are later. The northern and eastern parts are also marked by late cessation of frost giving a shorter frost-free period (220-240 days at medium frost severity). The western and southwestern areas mostly have earlier cessation of frost resulting in relatively long frostfree period with ranges from 241 to 300 days at medium frost severity level. Cessation of frost occurring later than normal over the Free State can impact negatively on the maize crop if planted in October and early November, especially over the highlands. Productivity of the crops can also be hampered by earlier than normal onset of frost that affects maize at silking and grain-filling stages. The onsets and cessation of rains together with the duration of the rainy season also play an important role in agricultural planning. Over 300 stations across the Free State were analysed to characterize the rainy season. The onsets of rains were found to be early over the eastern parts of the province with median onsets on or earlier than 10 October. In most areas over the Fezile Dabi and Motheo districts, onsets are between 11 to 30 October while over the Lejweleputswa onsets are mostly between 21 October and 10 November. Most of the western parts of Xhariep experience later than 21 November at 50% risk level. The cessation of rains does not vary much over the Free State with most places having their median last rains between 21 April and 30 April. Rainy season lengths are longer over the Thabo Mofutsanyane district with over 200 days in some places. The ENSO episodes are related to Free State seasonal rainfall variability but only have slight effect on the cessation of rains while onsets of rains showed no differences between El Niño or La Niña phases as compared to all the years. In El Niño years the seasonal rainfall amount is lower than normal, being higher than normal in La Niña years which support findings from other studies. The cessation of rains occurs earlier in El Niño years and later than normal in La Niña years. Agricultural drought is one of the most devastating hazards affecting maize production in most growing periods depending on the location. It is important to plant during periods which minimise drought conditions. In this study a simple water balance model developed by FAO called WRSI was used to quantify drought risk. When using the 120-day maize cultivar as a reference, drought index over most parts of the Lejweleputswa, Xhariep and eastern parts of the Motheo district show high vulnerability (WRSI<40) for October planting dates while other areas have relatively low risk of drought. In December and January planting dates drought index over most parts of the province showed much improvement but places that showed low risk are over the Thabo Mofutsanyane, Fezile Dabi and pockets of northern Lejweleputswa district. Poone AgroClimatic Suitability Index (PACSI) was introduced to integrate all the climate hazards affecting maize production in the Free State. The index in made from the combination of frost probability over the growing period, non-exceedence probability of onset of rains and agricultural drought index. The index was further used to delineate the suitable areas across the Free State for planting maize variety requiring 1420 growing degree days (heat units) to maturity. The findings obtained from the resulting maps show areas of high maize production suitability over the Thabo Mofutsanyane district for mid-October to early November planting dates. Places over Fezile Dabi and northern parts of the Lejweleputswa district also showed high suitability of maize especially for planting from mid-November to end of December. The western and southern Xhariep district area is not suitable for planting maize while other marginal dryland maize production areas include western Motheo, southwestern Lejweleputswa and most parts of the central and eastern Xhariep. To conclude the study, the Free State Maize Agroclimatological Risk Tool (FS-MACRT) was developed to provide agroclimatological risk information important to the production of rainfed maize in the Free State Province. The tool is to be used by the farmers, extension officers, policy-makers and agricultural risk advisors. The tool has two main parts, 1) climatological risk and 2) forecasting. The climatological risk enables the user to obtain drought stress risk for the 100-day, 120-day and 140-day maize cultivars for planting window starting in October to January. The best planting dates based on the risk associated with the climatology onset and cessation of both rains and frost can be determined. Using climate forecasts obtained from the national forecasting centres, drought index can be predicted for different planting dates giving the farmer valuable information when planning for the coming season. The tool also has the functionality of predicting onsets of rains using weather and climate forecasts.

Green pepper (Capsicum annuum L.) is gaining popularity and the production and consumption thereof is increasing worldwide. Semi-arid regions are characterized by variable and unreliable rainfall which necessitates the use of irrigation for sustainable green pepper production. In this study two field trials were conducted. Objectives of the first trial were to quantify the effect of irrigation and plant population on the growth and yield of green pepper and to optimize its plant population for different water regimes. Four water treatments, full irrigation (781 mm), 70% of full irrigation (627 mm), 40% of full irrigation (497 mm) and dryland (303 mm) and five plant populations (17 689, 23 674, 29 526, 34 979 and 41 496 plants ha-1) were used in this trial. A line source sprinkler irrigation system was used for water application. The trial layout was a split plot design with water applications as main treatments and plant populations as sub-treatments. All treatment combinations were replicated four times. The full irrigation and 40% of full irrigation treatment increased marketable yield with 274% and 162%, respectively. The 70% of full irrigation treatment increased marketable yield with 253%. The marketable yield of all irrigation treatments was significantly higher than that of the dryland treatment. The full irrigationâs marketable yield was however also significantly higher than that of 40% of full irrigation treatment. The optimum plant population for all water treatments, excluding 40% of full irrigation was not reached in this trial because the yield of plant populations (17 689 to 41 496 plants ha-1) used did not reach a turning point, but still increased linearly beyond 41 496 plants ha-1. The objective of the second trial was to quantify the effect irrigation and mulching on yield, water use and water use efficiency. Four water treatments, full irrigation (547 mm), 66% of full irrigation (481 mm), 33% of full irrigation (417 mm) and dryland (303 mm) and two mulching (bare and 9 t ha-1 maize straw) treatments were used. A line source sprinkler irrigation system was also used for this experiment. The trial layout was a split plot design with water treatments as main treatments and mulching rates as sub-treatments. All treatment combinations were replicated four times. Results indicated that green pepper responded well to irrigation. Full irrigation, 66% and 33% of full irrigation treatment produced marketable yield of 37.54, 29.74 and 20.52 t ha-1, respectively. The marketable yield of irrigation treatments was significantly different from each other and they were all significantly higher than that of the dryland treatment which produced a marketable yield of 11.92 t ha-1. As irrigation proceeded over time, the relationship between water use and leaf area index strengthened. The fully irrigated treatment produced the highest water use efficiency. Mulching conserves water by reducing evaporation and mitigates negative effects of water stress on plant growth and yield under semi-arid conditions. At the end of the season, cumulative water use efficiency from the mulched treatment was 6 g m-2 mm-1, significantly higher than that of the bare treatment of 5.3 g m-2 mm-1. Green pepper is very susceptible to water stress and produces poorly under dryland conditions and any irrigation is beneficial to its production. However results also indicated that green pepper has the ability to adapt quite well to high plant populations and has demonstrated its ability to compete for production resources at such populations. The crop also conforms well to the favourable plant growth conditions provided by the mulch.

Most scientists globally agree that human activities are causing global climate change resulting in pressures on Africaâs agriculture systems and economies. Knowledge gaps still exist in coping with climate change and adaptation, regardless of the increasing country level research on the agricultural systems. With climatic information dissemination and appropriate policy development as major global themes, literature and knowledge on dissemination of climatic information is still limited in Zambia. This study was undertaken in Mujika area of Monze district, southern province of Zambia from 2007 to 2010. Faced with climate change challenges, the Mujika community opted to investigate the possibility of developing an agrometeorological extension strategy. This strategy was to respond to community needs for routine dissemination of climatic information, serving as a warning as well as guide to improving the local agricultural decision making. This study addressed the following specific objectives: ï¬ To analyze long-term rainfall data for two stations as a basis for developing climate risk approaches for Mujika area; ï¬ To establish the current status of climatic risk information and dissemination practices in Mujika area; ï¬ To document the social/institutional aspects that enable farmers to adopt appropriate alternative interventions; and ï¬ To operationalise the community agrometeorological participatory extension service (CAPES) so as to evaluate its effectiveness. Data collection used both quantitative and qualitative methods. The quantitative approach analyzed long-term rainfall data while the qualitative approach used Participatory Rural Appraisal (PRA). Community members from three villages (Nkabika, Bulimo and Malomo) participated in PRA exercises by presenting spatial data (in community sketch maps, farm sketches and transect walks), time related information (by historical time and trend lines) and social data (from household interviews, daily calendar according to gender and institutional analysis) throughout the study. They organized their problems and opportunities into a priority order at the village level, resulting in the creation of a community information dissemination plan (CIDP). The implementation of the CIDP included weekly local radio broadcasts of specially prepared programmes which were then recorded by local club representatives. The farmers organized themselves into five small radio listening clubs where they listened and discussed the re-recorded programmes. Their learning by doing was around the mother field trial managed by the other PhD student, Prospard Gondwe and baby field trials conducted by 16 local farmer volunteers in their own fields. Monitoring and evaluation was incorporated into the project by these volunteer farmers keeping records of most project activities. A community agrometeorological participatory extension service (CAPES) developed out of these interactions between stakeholders, including community members, agriculture extension officers, an agrometeorologist and agronomist during all these activities. CAPES is an agrometeorogical extension service including monitoring, developed together with a community to give tailor-made climatic information for improved agricultural decision making. Stories of five selected Mujika farmers were used to evaluate the effectiveness of CAPES in disseminating climatic information to smallholder farmers in Mujika. This assisted understanding the influence of CAPES on individuals across a range of different types of farmers that are present in Mujika, according to status, education and influence of authority. The study findings led to the following conclusions: ï¬ Although long-term rainfall data analysis was useful in understanding smallholder farmersâ environment, it was also instrumental in characterising available annual and seasonal rainfall trends. Detailed intraseasonal information (start and end of rain, dry spell length) used together with seasonal forecasts helped improve agricultural decision making. ï¬ Indigenous forecast knowledge plays a major role in smallholder farmersâ agricultural decision making and planning of crop management options for every unfolding season when access to seasonal climate forecast information is limited. ï¬ The fact that the community had a good knowledge of the natural resources enabled them to recognize that the use of climate information was a viable opportunity to improve crop productivity. ï¬ The lack of credibility of researchers and Zambia Meteorological Department (ZMD) within the community to produce and disseminate seasonal climate forecasts had a negative influence on farmersâ acceptance and usage of seasonal climate forecasts. ï¬ A sustainable community agrometeorological participatory extension strategy depends on smallholder farmersâ contributions during planning as users because farmers know what climatic information is required for addressing their problems and the best dissemination modes for effective information utilization. ï¬ It is possible to develop an effective and appropriate community agrometeorological participatory extension service with a community when appropriate participatory approaches to community interactions are used. ï¬ The stories of the identified farmers used in the qualitative approach provided the visible evidence of the influence of the CAPES on the farming systems in Mujika. ï¬ All this information was combined into a practical handbook on CAPES to be used to train agrometeorological intermediaries. Recommendations that follow from this thesis and that may also help as starting points for future research are: ï¬ Participatory dissemination of climatic information should be based on a well researched community baseline so as to address actual community problems. ï¬ The participatory multi-disciplinary climatic information dissemination plan should be develop together with farmers and other stakeholders for an effective information flow in the community. ï¬ In order to improve smallholder farmersâ agricultural decision making and crop management options in rainfed systems, an effective dissemination of seasonal climate forecast and a detailed long-term rainfall analysis for their respective area is required. ï¬ The community agrometeorological extension strategy (CAPES) developed during the dissemination of climatic information to smallholder farmers in Mujika area is a model of success and is recommended for application to other areas. ï¬ Use of stories about selected farmers in evaluating the effectiveness of community interactions is a useful approach and is recommended. ï¬ The CAPES handbook, developed during this project, is a useful guide and is recommended for use by anyone intending to interact with communities for the dissemination of climatic risk information. ï¬ The community agrometeorological participatory extension strategy should be evaluated in future in five or ten years after it establishment.

The main aim of this study was to determine the transpiration efficiency coefficient (TEC) for three C3 crops; canola, wheat and lucerne. TEC relates to the efficiency of water management in crop production. It is defined as the ratio of seed or biomass to the product of transpiration and vapour pressure deficit. Of these variables, transpiration is the most difficult to measure. Two experiments (canola, 2007 and wheat, 2007&2008) were therefore designed with the aim of partitioning evapotranspiration (ET) into its components of evaporation (E) from the soil and transpiration (T) from the plant. These experiments were based on a split plot design, with two soils (Clovelly and Bainsvlei) and two surface treatments which comprised of a bare soil for measuring ET and a 50 mm thick gravel mulch for measuring T using the lysimeter unit of the University of the Free State at Kenilworth near Bloemfontein. These components were measured regularly and E was derived by subtracting T from ET. The results showed that for canola, E was 12% of the total ET (809 mm) and for wheat E was 27% of total ET (639 mm). The percentage contribution of T to ET was high in both crops: 718 mm or 88% of total ET of canola and 489 mm or 63% of total ET of wheat. Conclusive evidence showed that crops should be managed differently with respect to their individual irrigation water demands. The remaining three experiments were dedicated to factors influencing the TEC of crops. Specific objectives were to establish the effect of growth periods during the reproductive stage on the TEC of canola, the effect of weather on the TEC of wheat and effect of cutting periods on the TEC of lucerne. All experiments were conducted in the lysimeter unit and measurements were based on the soil water balance of both soils. TEC was expressed as grain yield (GY) or seed yield (SY), above-ground biomass (AGB) and total biomass (TB). Soils had no significant effect on TEC. However, TEC of canola was significantly affected by growth periods. For growth periods, TECABG varied between 3.82 and 4.95 g kPa mm-1 and TECTB between 3.94 and 5.04 g kPa mm-1. For wheat it was concluded that weather had no influence on the TEC based on AGB, but TEC based on GY was significantly lower in 2008 (TEC = 0.9 g kPa mm-1) compared to 2007 (TEC = 2.3 g kPa mm-1). This was caused by severe frost which occurred in the early reproductive stage. The result revealed a mean TECAGB of 4.75 g kPa mm-1 for the two wheat seasons. The results on lucerne suggested that cutting periods do played a significant role in the TECAGB of the crop. TEC decreased from 3.86 g kPa mm-1 for the first cutting period to 2.22 g kPa mm-1 for the sixth cutting period, with a mean TEC value of 2.84 g kPa mm-1 for all six cutting periods. TEC values for canola, wheat and lucerne in this study are consistent with values reported for other C3 crops in the semiarid environments and are therefore recommended for use in models.

The organic carbon stock in South African soils was estimated using existing data with reference to master horizons, diagnostic horizons, soil forms, and land cover classes. The data used for this study was taken from the land type survey which started in 1970 covering the whole of South Africa. Approximately 2 200 modal profiles representing were analysed for physical and chemical properties including organic carbon. The results showed that the organic carbon content in the master horizons ranged on average from 16% in the O horizon to 0.3% in the C horizons. In the diagnostic horizons, the highest organic carbon was recorded in the topsoils and ranged on average from 21% in the organic O to 1.4% in the orthic A horizons. However, the organic carbon content in the diagnostic subsoil horizons ranged from 1.2% in the podzol B to 0.2% in the dorbank B horizons. The organic carbon content was related to the soil forming factors namely climate (rainfall, evaporation, and aridity index), topography (terrain morphological units, slope percentage, slope type, and slope aspect) and soil texture (clay). Organic carbon related poorly with climate and topography in both the master and diagnostic horizons, with low correlations. Organic carbon content was positively correlated with rainfall and aridity index in the A, E, B, G, C, and R master horizons and inversely correlated with evaporation in those horizons. Climate had an opposite effect on organic carbon in the O master horizons. A positive relationship between organic carbon and rainfall was found in the pedocutanic B, prismacutanic B, soft plinthic B, red apedal B, yellow-brown apedal B, red structured B, G, unspecified material with signs of wetness, E, neocarbonate B, neocutanic B, regic sand, stratified alluvium, lithocutanic B, hard rock, unconsolidated material without signs of wetness, unspecified dry material, and saprolite. The relationship between organic carbon and evaporation was negative in those diagnostic horizons. Rainfall and aridity index related negatively with organic carbon content and positively with evaporation in the following diagnostic horizons: soft carbonate B, podzol B, hard plinthic B, saprolite, and the unconsolidated material with signs of wetness. The relationship between organic carbon and topography was not very clear in both the master and diagnostic horizons. However, topography seemed to influence the formation of some horizons by restricting their formation to certain slope percentages. The influence of topography on organic carbon content depends on the morphology of the master and diagnostic horizon and underlying material. A regression was done to study the correlation of organic carbon and the independent variables namely: rainfall, evaporation, slope aspect, aridity index, and clay per master and diagnostic horizon. Unfortunately most of the correlation coefficients were too low for the equations to be used to estimate organic carbon content in South African soils. Organic carbon in the soil forms behaved as their diagnostic topsoils. The environmental conditions such as water content and temperature that influenced the amount of organic carbon in the topsoils also determined the amount of organic carbon in the diagnostic subsoil horizons of that specific soil form. Organic carbon stocks were then estimated using three soil bulk density values namely: low = 1.30 g cm-3, average = 1.50 g cm-3, and high 1.70 g cm-3. The results revealed that the organic carbon stocks of South African soils increased from the warmer, drier western to the cooler, wetter eastern parts of the country. The average soil organic carbon stocks is 73 726 kg ha-1 when calculated using a soil bulk density of 1.50 g cm-3. Most soils had an organic carbon content between 30 000 kg ha-1 and 50 000 kg ha-1. The total organic carbon of the soils of South Africa is estimated to be 8.99 ± 0.10 Pg calculated to a depth of 0.30 m which is 0.57% of the worldâs carbon stocks. Since the worldâs carbon stocks were calculated to 1 m depth this is not a true representative value for the carbon stocks of South Africa in relation to the worlds. Therefore a lower value will be expected if carbon stocks are estimated to a depth of 1 m in South Africa. The organic carbon stocks in the 27 land cover classes ranged from 9 Mg ha-1 in barren rock to 120.2 Mg ha-1 in forest plantations. The highest accumulation of organic carbon per unit area in South African soils was found in the forests plantations > forests > wetlands. However the biggest contribution to the total organic carbon stocks, was reported in the unimproved grassland> thicket and bushland > shrubland and low Fynbos > forests.

Increasing crop yields for an ever growing world population has currently become a topic of great importance for agronomists and plant physiologists alike. The main objective is to find the cheapest and most effective methods to obtain this goal. In this regard seed treatment is one of the approaches that offer great potential. With this in mind, the underlying study was undertaken in order to test a range of products including prototypes and commercially available products. During the laboratory and glasshouse screening phases optimal concentrations for the plant growth regulators ComCat® (25 mg kg-1 seed) and SS (12.5 mg kg-1 seed) were identified in terms of seedling growth response. Additionally, the two fertilizer products Teprosyn® and Seniphos® initially showed promise in this regard when applied on their own or in combination with the plant growth regulators and the uptake enhancer AnnGro⢠. However, of all the seed treatments and purely based on the eventual marked yield increase obtained, ComCat® (+500 kg ha-1) on its own and Teprosyn® in combination with SS and AnnGro⢠(+800 kg ha-1) proved to be the most promising. Although the metabolic response of maize seedlings to the different seed treatments were followed in terms of selected events, no clear picture emerged in terms of the mechanisms of action underlying the eventual yield increase. It became clear that this aspect needed special attention in a follow-up study over a total growing season. From this study it is recommended that ComCat® on its own as well as the Teprosyn®/SS/AnnGro⢠combination treatment can be considered strongly as seed treatments of maize under rain fed conditions, but this should be followed over more seasons. This recommendation is purely based on the consistent enhancing effect that both treatments revealed in terms of seedling growth and final yield. The potential of these treatments should also be evaluated under irrigation conditions.

Phosphorus input is vital to the maintenance of profitable sugarcane crop production in Mauritius. The intensive use of some 5,000 tonnes of P annually during the past 50 years is believed to have built up the P status of the sugarcane soils, perhaps even to excessive levels. While this accumulation of P is desirable from an agronomic perspective, there is growing concern in Mauritius about its possible effect on surface water quality. In response to that concern, a study was initiated with the following specific objectives: i. To review the usage of P fertilisers in sugarcane production in Mauritius and assess their resulting impact on the P status of the main soil groups under sugarcane. ii. To enlarge the scope of the current method used (0.1M H2SO4 extraction) for agronomic P testing so that it also indicates environmental status of sugarcane soils in Mauritius. iii. To determine the environmental threshold P in soils above which the P will represent a hazard to surface waters. The five yearly averages of fertiliser P usage by the Mauritian sugarcane industry showed that from the 790 tonnes of P2O5 (mainly as rock/guano phosphates) consumed at the beginning of the 20th century, P usage attained a peak of 5,675 tonnes in the 1970s before declining thereafter as a result of a decreasing land area under sugarcane. During the period 2005 to 2008, an average of 3,350 tonnes of P2O5 mainly as ammonium phosphates were applied annually to sugarcane which is cultivated in Mauritius mainly on five soil groups, namely the Low Humic Latosol (Humic Nitosol)*, the Humic Latosol (Humic Nitosol)*, the Humic Ferruginuous Latosol (Humic Acrisol)*, the Latosolic Reddish Prairie (Eutric Cambisol)* and the Latosolic Brown Forest (Dystric Cambisol)*. A method based on 0.1M H2SO4 as extractant is currently used as a routine soil test to assess P available to sugarcane in the soils of Mauritius. On the basis of soil P test values, four soil P fertility classes could be discerned, namely: Examination of the soil test P data obtained in 1997/1998 showed that 48% of the land still required P fertilisation while approximately 40% had an excess of P (P ⥠100 mg kg-1). Less than 10% of the soils had an optimum soil P (80 ⤠P < 100 mg kg-1). Moreover, soils with a highly excessive soil P status (P ⥠150 mg kg-1) rose from 23% in 1997/1998 to 34% in 2005/2006 indicating that with the current P management practice in sugarcane, the P status of soils in Mauritius will shift more and more towards an excess of P. In spite of the extensive information available on the soil P status, its significance from the freshwater protection angle was, prior to this study unknown due mainly to a lack of a suitable environmental soil P test method. From this perspective, as a laboratory extraction of soil with 0.01M CaCl2 gives a very reliable representation of the P in runoff, the P extractable in a 0.01M CaCl2 (0.01M CaCl2-P) solution was determined in 112 soil samples representing the five main soil groups under sugarcane. The soil samples whose characteristics of pH, organic matter content, exchangeable bases and cation exchange capacity were also determined, were selected to cover a range of 10 to 250 mg kg-1 P extractable by the 0.1M H2SO4 used for agronomic soil P testing in Mauritius. As the environmental soil test P must be independent of soil properties and the concept of degree of P saturation (DPS) meets that criteria, the ammonium oxalate DPS (DPSox) was determined in the 112 soil samples to provide a reliable pointer of P susceptibility to loss from soils. Since it is very unlikely that ammonium oxalate extraction would be used as a routine soil test, the relationship between DPSox and 0.1M H2SO4-P was established by conventional statistical regression techniques. The results obtained indicate that no single soil characteristic could be said to have a distinct influence on the amount of P extracted by either the 0.1M H2SO4 or the 0.01M CaCl2 or by the DPSox. Indeed the correlation (r2) between the 0.1M H2SO4-P, 0.01M CaCl2- P, DPSox with the individual measured soil characteristics was low and never exceeded 0.28 in the case of 0.1M H2SO4-P and 0.52 with 0.01M CaCl2-P. The DPSox exhibited the poorest relationship with the soil properties with none of the r2 values being above 0.16. Instead the low r2 values observed indicated as confirmed by multiple regression analysis that the amount of P extracted by each reagent would be the result of the combined effects of certain soil characteristics. The results moreover showed that for soil P not to constitute a hazard to the freshwaters in Mauritius, the DPSox should not exceed 3.10±0.10% and the 0.01M CaCl2-P must lie below 18±1µg L-1. Moreover the linear fit regression equation 0.1M H2SO4-P = 17.3 + 23.2 DPSox with r2 = 0.54 was found to most appropriately describe the relationship between 0.1M H2SO4-P and DPSox. From that equation the threshold DPSox of 3.10±0.10% would correspond to a range of 85 to 95 mg kg-1 of 0.1M H2SO4-P which is henceforth considered as the threshold range of P in sugarcane soils in Mauritius above which the soil P would become a hazard to freshwater sources. Using this environmental threshold range of soil P values as basis, the soils can be divided into the following four environmental classes namely: [table]. Application of the above criteria showed that in 1997/1998, 58% of the soils did not represent any hazard to freshwater quality in Mauritius. As much as 42% of the sugarcane fields in 1997/1998 had from the environmental viewpoint unacceptably high levels of P (P ⥠95 mg kg-1) in the soils. After one crop cycle in 2005/2006, the number of fields with unacceptably high levels of P (P ⥠95 mg kg-1) had risen to 53%. The majority (74%) of the sugarcane fields with an environmentally unacceptable P status were located in the Latosolic Reddish Prairie and Latosolic Brown Forest soils. In extending the scope of the current agronomic soil test P using 0.1M H2SO4 as an extractant into an agro-environmental soil P test, this study demonstrated clearly that the agronomic objectives in P management for sugarcane production in Mauritius are incompatible with the environmental aims of protecting the freshwater resources in Mauritius. With the agronomic threshold range of 80 to 100 mg kg-1 P overlapping the environmental range of 85 to 95 mg kg-1 P, soils in Mauritius that are agronomically suitable for sugarcane cultivation are on contrary unsafe from the environment protection viewpoint and vice versa.