An adequate characterization of soil hydraulic properties is a necessary solution for agriculturally and environmentally oriented problems such as irrigation, drainage, runoff and pollutants movement. The three approaches to determine hydraulic properties of soils are field measurements, laboratory measurements and mathematical models. In situ measurements, though representative, have the inherent limitation of being costly and time consuming. Laboratory and mathematical techniques are more convenient but require extensive comparison to field results as bench mark for evaluation. The objective of this study was to characterize the hydraulic properties of Bainsvlei and Tukulu form soils utilizing the above mentioned three approaches and to compare the results. The laboratory methods selected were hanging water column and pressure plate apparatus. Undisturbed soil samples were used to determine θ-h relationships at 0-100 kPa suctions and disturbed soil samples up to 1500 kPa. The water retention characteristics for both soils were generally well defined with little variability between replicates. The main variations were due to texture differences between the horizons. The θ-h relationships were used to estimate textural and structural domains using empirical pore class limits and derivative curves. The suction value separating the structural domain from the textural domain varies from horizon to horizon. The boundary between soil pore categories cannot be taken as a fixed value for all soils and all types of soil use. The measured water retention data corresponded well with the fitted curve via the van Genuchten (1980) model, indicating that the model can be successfully used to describe θ-h relationships for Bainsvlei and Tukulu soils. Soil water sensors were calibrated using undisturbed soil samples in climate controlled room for five horizons of a Bainsvlei form soil and three horizons of a Tukulu form soil. Soil water sensors and circuitry show extremely low sensitivity to temperature fluctuations. Horizon specific calibration is essential to get accurate water content estimates from the sensors if used in different soil horizons. Our study demonstrate that horizon specific calibrations of the water sensors improves the accuracy of soil water content monitoring compared with the manufacturerâs generic calibration equation for the soils tested in this study. Hydraulic conductivity was obtained by measuring the hydraulic head and water content of the Bainsvlei soil form in situ with tensiometers and horizon specific calibrated ECH2O EC-20 probes, respectively. The profile was characterized with several relations of hydraulic conductivity and varied with depth. The reason for this was attributed to heterogeneous nature of the profiles due to variation in particle size distribution. The van Genuchten (1980) model laboratory method was used to predict K-θ relationships utilizing laboratory determined θ-h relationships. The K-θ relationships predicted from the θ-h relationships of the soil cores corresponded well with those determined by the instantaneous profile field method for water contents which they have in common. Thus it appears that this laboratory method is applicable to the soils studied, but the accuracy of the predicted values is quite sensitive to the matching factors. Thus, accurate measurement of these parameters is necessary for its successful use. The instantaneous profile field method is regarded as a reference method to measure in situ unsaturated hydraulic conductivity for both homogenous and layered soils (Hillel et al., 1972). There are, however, several site or profile characteristics that may limit this method (Bouma, 1983). Our studies show that it is not applicable on duplex soils with slow permeable C-horizons i.e. the Tukulu form profile at Paradys, because of negative hydraulic gradients within the profile due to impaired internal drainage. There is a need to adapt this method to duplex soils. Overall results indicate that from a practical perspective, the prediction of K-θ relationship from laboratory determined water retention data can be a viable alternative for determining the hydraulic properties of diagnostic horizons. The prediction of DUL using θ-h relationship has been found to be satisfactory.

A recently commercialized natural bio-stimulant, ComCat®, that contains three active brassinosteroids (BRs) of which two were identified previously, was scrutinized in this study for its potential to be applied in the agricultural industry. Concerning objective (1), seven biotests were employed to quantify the bio-stimulatory activity of ComCat® under laboratory and glasshouse conditions. The product was tested at different concentration levels and the 0.5 mg â-1 application repeatedly emerged as the optimum concentration in terms of contributing towards increases in all of the parameters measured. Treatment with ComCat® had little or no effect on seed germination, but especially root growth of seedlings from different crops was significantly and consistently induced. Concerning objective (2), two cultivars for each of five test crops were treated with ComCat® over two growing seasons under field conditions in order to ascertain their yield response. Some of the test crops, but not all, showed cultivar sensitivity to treatment with ComCat®. However, overall the significant yield increases measured in one or both cultivars of the five different test crops and in one or both seasons confirmed the potential of ComCat® to be applied in agriculture and to contribute to economic prosperity for a farmer. Concerning objective (3), gas chromatographic analyses of a crude extract of the product as well as semi-purified fractions thereof by, using internal BR standards, were employed to identify an unknown BR contained in ComCat®. This was confirmed to be 24-epi-brassinolide. The latter as well as the previously identified 24- epi-castasterone and 24-epi-secasterone are known to be active BRs of the brassinosteroid group. In conclusion, the bio-stimulatory characteristic of ComCat® was confirmed both in vitro and in vivo under laboratory, glasshouse and field conditions in this study. Significant yield increases in all of the test crops over two seasons in some instances, confirmed the potential of ComCat® to be applied sustainably in the agricultural practice. Based on the results obtained in this study, three possible application methods of ComCat® are suggested. These include 1) seed treatment, 2) foliar application or 3) soil application.

Farmers have largely depended on intensive soil cultivation to reduce nutrient stratification and therefore distribute nutrients homogeneously across the root zone for optimum crop productivity. This attempt however, has led to serious soil organic matter degradation and nutrient outflows. Consequently, food production for the increasingly growing world population was severely threatened. Crop residues as a source of organic matter and nutrients, when properly managed, can restore or improve soil fertility, and hence crop yields. The different residue management practices on some soil fertility indicators have been examined since 1979 in a long-term wheat trial at the ARC-Small Grain Institute near Bethlehem in the Eastern Free State on an Avalon soil. The observations established in 1999 indicated that soil nutrient and organic matter stratification still continues, therefore it was found necessary to further investigate the effects of these residue management practices on some soil fertility indicators, nutrient uptake and wheat grain yield. The applied field treatments include two methods of straw disposal (unburned and burned), three methods of tillage (no-tillage, stubble mulch and ploughing) and two methods of weeding (chemical and mechanical). Soil samples were collected in 2010 at various depths viz. 0-50, 50-100, 100-150, 150-250, 250-350 and 350-450 mm and analyzed for organic C, total N and total S as organic matter indices, pH, some macronutrients (P, K, Ca, Mg and Na) and CEC, as well as some micronutrients (Cu, Fe, Mn and Zn). At mid-shooting stage, plants were sampled in each treatment plot, oven-dried at 68 ºC, weighed, milled and analyzed for N, S, P, K, Ca, Mg, Na, Cu, Fe, Mn, and Zn. The grain yield data of wheat for the 26 years were supplied by the ARC-Small Grain Institute for use as a supplement to the soil data. The methods of straw disposal and tillage had variable influences on soil organic matter indices. Unburned straw increased total N and S, but reduced organic C when compared to the burned straw. No-tillage increased organic C only in the 0-50 mm soil depth when compared to stubble mulch and ploughing. No-tillage and stubble mulch resulted in a higher total N to a soil depth of 450 mm relative to mouldboard ploughing. Ploughing on the other hand, and to some extent stubble mulch, increased total S more than no-tillage in the upper 250 mm soil depth. Mechanical weeding enhanced these indices to 450 mm soil depth as opposed to chemical weeding. No-tillage and to some extent stubble mulch suppressed acidification in the upper 100 mm and lower 350-450 mm soil depths. Mechanical weeding also increased soil pH when compared to chemical weeding. No-tillage combined with either chemical weeding or straw burning suppressed acidification in the surface soil, whereas mechanical weeding combined with either no-tillage or mouldboard ploughing retarded acidification in the subsoil. The concentrations of P, K, Mg, Mn and Zn were higher in the burned treatments than in the unburned plots. The reverse was observed with Ca, Na and Cu. In contrast, mouldboard ploughing, and to some extent stubble mulch, resulted in an accumulation of Cu in the upper 100 mm soil depth when no-tillage served as a reference. Chemical weeding enhanced P, K, Mg, Na and CEC, but resulted in lower Ca, Cu, Fe, Mn and Zn contents when compared to mechanical weeding. The applied management practices were also tested on nutrient uptake and grain yield. Although not always significant, the burned straw increased nutrient uptake, but resulted in a lower wheat grain yield when compared to unburned straw. Despite the beneficial effects of no-tillage and stubble mulch on the fertility status of this Avalon soil, higher nutrient uptake and grain yield were perceived under mouldboard ploughing. Mechanical weeding also enhanced the uptake of most of the studied nutrients relative to chemical weeding. Mouldboard ploughing combined with either unburned straw or chemical weeding increased nutrient uptake and wheat grain yield. However, irrespective of the applied field treatments, nutrient concentrations in oat straw were below optimum levels, and possibly plants were already suffering acute nutrient deficiencies.

The influence of temperature on yield and quality of carrots were examined using two pot trials that were conducted in the glasshouse and growth chambers at the Department of Soil, Crop and Climate Sciences, on the Bloemfontein campus of the University of the Free State in 2009 and 2009/10. In the first trial the influence of four temperatures (10, 18, 26 and 32°C) on the growth, yield and quality of two pre-pack carrot cvâs. Nectar and Star 3002 were studied. Carrot seed were sown in 0.34 m x 0.34 m x 0.35 m pots, filled with topsoil of the sandy loam Bainsvlei form. Pots were kept in the glasshouse at 20°C (±1°C) for four weeks to allow the seedlings to establish and reach the first true leaf stage whereupon they were moved to the controlled environment chambers at different temperatures for 20 weeks. Growth parameters such as leaf number, plant height and leaf growth were significantly influenced by temperature and all these parameters performed the best at 10°C at the end of the growth season irrespective of cultivar. Root fresh and dry mass did not differ significantly between the two cultivars but the affect of temperature was significant. The highest root fresh mass for both cultivars was also obtained at 10°C, with âStar 3002â with the highest mass (39.12 g) followed by âNectarâ (34.26 g). Both cultivars exhibited the highest root dry mass at the lower temperature treatment (10°C) with âStar 3002â having a higher root dry mass (4.15 g) than âNectarâ (3.87 g). External quality parameters such as root length and diameter differed significantly between the temperature treatments and only the length of carrot roots did not differ significantly between the cultivars. Both âNectarâ and âStar 3002â exhibited the longest roots at 10°C and the shortest roots at 18°C. Root diameter for both cultivars was significantly greater at 10°C than at 18°C. The only defects observed were green shoulder and misshapen roots. Although not significant, the percentage green shoulders and misshapen roots were higher at 18°C than at 10°C. Carrots were significantly firmer at the low temperature (10°C) than at 18°C. The total soluble solid content of carrots however, grown at 18°C was significantly higher than those grown at 10°C. In the second pot trial the influence of four dual temperatures (15/5, 24/10, 28/20 and 35/25°C) on the growth, yield and quality of two pre-pack carrot cultivars âNectarâ and âCS 1006â was studied. Based on the results of this study, temperature influenced leaf number and plant height of both cultivars, although not always significantly, during the 32 weeks of growth. Leaf number and plant height of carrot plants were greater at 15/5°C treatment. Yield parameters and the external quality parameters such as root length; diameter and absence of defects were also influenced significantly by temperature. Carrot root length and diameter were significantly influenced positively by lower temperatures (15/5°C) and absence of defects such as green shoulder and hairiness were significantly influenced negatively by higher temperatures (28/20°C). Some of the internal quality parameters such as firmness, total soluble solids, carotene, β-pinene and caryophyllene were also significantly affected by temperature. Firmness, total soluble solids and carotene were significantly influenced by lower temperature (15/5°C) whereas β-pinene and caryophyllene were significantly influenced by higher temperatures (28/20°C). Free choice profiling (FCP) was carried out in order to investigate how semi-naïve panelists described and perceived carrot samples cultivated under different temperature conditions. This method allowed participants to use their own attributes to describe and quantify the food product. The FCP procedure generated six descriptors on the attribute taste and one on aftertaste. The two carrot cultivars grown at the higher temperatures (24/10 and 28/20°C) had descriptors like bitter, sour, bland and chemical, with a definite aftertaste while carrot cultivars grown at lower temperatures (15/5°C) had descriptors such as sweet and carrot taste

In order to meet the food requirements of an ever-growing population, agricultural production needs to increase. This is especially true for maize production in South Africa as it is the staple food for a large portion of the rural indigenous population. Climate variability is one of the major causes of volatility in agricultural production and causes uncertainty for maize production at the subsistence level. Small-scale farmers within the Modder River Catchment have a poor quantative understanding of seasonal rainfall and their relationship to their management strategies. In countries prone to high seasonal climatic variability, crop growth models such as APSIM can be used to assist farmers in making decisions regarding the suitability of different management strategies. This means that climate forecasts could be translated into crop production, while alternative management practices would be associated with different economic outcomes. The opportunity arose to aid these farmers by optimising rainfed maize production. Subsequently, the objective of this study was to produce an advisory for small-scale rainfed maize farmers in the Modder River Catchment. Historical rainfall data (1950-1999) from selected rainfed maize production areas within the Modder River Catchment were used to calculate the seasonal rainfall totals for October to December (OND) and January to March (JFM). During dry seasons, the expected rainfall totals was less than 101.0 and 147.5 mm for OND and JFM, respectively. During wet seasons, the expected rainfall totals was more than 204.0 and 267.5 mm for OND and JFM, respectively. Recommended management practices were employed to validate APSIM using observed environmental and maize yield data for the 1980/81 to 2004/2005 seasons in the vicinity of Bloemfontein. Maize yields were simulated using two medium growth period cultivars (PAN 6479 and Pioneer 3237) under different planting dates, plant population densities, fertiliser applications and weeding frequencies. The model simulated PAN 6479 better than Pioneer 3237. For Pan 6479, the best set of management practices corresponded to a R2 of 0.66, D-index of 0.89, modelling efficiency of 0.59 and RMSEu/RMSE of 0.88. For Pioneer 3237, the modelling efficiency values under different management practices were negative. Stepwise linear regression was used to select those yield predictors that adhered to a partial R2 value greater than 0.0001 at a significance level of 0.15. In general itâs usually better to plant early (November) regardless of the seasonal rainfall scenarios. Advisories were set up to convey information regarding the best, second best and worst set of management practices under each seasonal rainfall scenario. These advisories also include the related field costs along with potential yields and economic benefits at the 25, 50 and 75% probability levels for each set of management practices. For example, during AN-AN rainfall conditions, the best set of management practices involved planting during 16-30 November and 1-15 November, weeding twice, 50 and 75 kg ha-1 N and using 21 000 and 18 000 plants ha-1 for PAN 6479 and Pioneer 3237, respectively. Farmers would spend R1 798 ha-1 on field costs when planting PAN 6479, while obtaining a yield of 2 854 kg ha-1 and making a profit of R1 972 ha-1 at the 50% probability level. For Pioneer 3237 the field costs would amount to R2 338 ha-1, while realising a yield of 4 232 kg ha-1 resulting in a profit of R3 253 ha-1 at the same probability level. The recommended management practices under various seasonal rainfall scenarios could assist small-scale rainfed maize farmers to increase their yields and maximise the associated profit. Unfortunately, site-specific calibration of APSIM is required against observed sets of climate, soil and yield data for which the associated management practices are known before these advisories can be used by extension officers to advise small-scale farmers within the Modder River catchment.

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.