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Journal of Agricultural Science and Technology(B) 2012年第6期2卷 703-712页

作者： Jaco Bezuidenhout leon van rensburg Peet Jansen van rensburg School of Environmental Sciences and Development North-West University Potchefstroom Campus Potchefstroom 2520 SouthAfrica School of Physical and Chemical Sciences North-West University Potchefstroom Campus Potchefstroom 2520 South Africa

Besides control of the fungal plant pathogens, another interesting aspect observed when plants are treated with Trichoderma harzianum include effects such as complete and even stand of plants, improved seed germination, increases in plant height and overall enhanced plant growth. No research has yet been conducted to elucidate the mechanism by which these effects occur. Improved seed germination, in particular, suggest that Trichoderma harzianum produces a metabolite that may mimic the plant growth hormone gibberellic acid. The metabolite gliotoxin, produced by Trichoderma harzianum appear to be structurally most similar to gibberellic acid. In this study, common pharmacophore generation and molecular ligand docking simulations were used to evaluate the molecular similarity between gibberellic acid, specifically GA3, and gliotoxin. For the common pharmacophore evaluation, the structure of various gibberellic acids were used to construct a pharmacophore space to which gliotoxin was aligned, and during the molecular docking simulations the gibberellic acid receptor, GID1, served as ligand target for GA3 and gliotoxin. During the common pharmacophore evaluation, gliotoxin was successfully aligned to the common pharmacophore model constructed from various gibberellic acids. Furthermore, molecular docking simulations of gliotoxin and GA3 into the gibberellic acid receptor （GIDI） yielded docking scores of-10.78 kcal/mol for the GA3 molecule from Corina and a docking score of-10.17 kcal/mol for glioto^in. The docking scores suggest that gliotoxin may be able to competitively occupy the receptor space for gibberellic acid, and as such elicit the similar physiological responses observed in literature.

关键词： Gibberellic acid gliotoxin GID 1 molecular similarity Trichoderma harzianum

In-Situ Evaluation of Evaporation in Layered Soils （Tukulu, Sepane and Swartland）

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Journal of Agricultural Science and Technology(A) 2012年第5期2卷 577-590页

作者： Sabelo Sicelo Wesley Mavimbela leon Daniel van rensburg Department of Soil Crop and Climate Sciences University of the Free State P.O. Box 339 Bloemfontein 9300 South Africa

Knowledge about the influence of soil layers on evaporation is essential for the optimization of infield rainwater harvesting （IRWH） in the semi-arid areas of the Free State province of South Africa. Among the soils earmarked for 1RWH development include the Tukulu, Sepane and Swartland soil types that have contrasting soil layers. These soils have to capture and store rainwater within the soil profile layers away from the evaporation zone. To determine how the three soils release and deliver soil water at the evaporating site, a 21-day evaporation experiment was conducted on pre-drained monoliths. Instantaneous soil water content （SWC） from in-situ and soil water characteristic curve （SWCC） from laboratory was measured. Separate soil samples of 15 mm thickness were also evaporated under the same conditions to establish the extent of drying and hydraulic gradient at the soil surface. The Darcian evaporative flux and unsaturated hydraulic conductivity （K-coefficient） were also determined. At the surface suctions of magnitude greater than 1,500 kPa were observed from all monoliths. Total contributions to evaporation from the Tukulu, Sepane and Swartland were 43, 51 and 70 mm, respectively. The low contributions were explained by the presence of the prismacutanic C-horizon in the Tukulu and Sepane at respective depths of 600 and 700 mm. This layer was associated with the steepest suction gradient that restrained further upward fluxes by subsequent lowering for the K-coefficient with more than two orders of magnitudes within a narrow range of SWC. However, the presence of the pedocutanic B-horizon at depths of 300 mm undermined this restrictive function through the appreciable capillary activity demonstrated by clays at near evaporating surfaces. The shallowness and deficiency in structure of the Swartland was consistent with the high contribution to evaporation that gave this soil a dry soil water regime. It was therefore concluded that the Tukulu offered soil profile

关键词： Soil water soil layers evaporation soil hydraulic characteristics.

Surface Treatments Effect on Rainfall Canopy Interception and Runoff-Rainfall Ratio for in-Field Rainwater Harvesting

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Journal of Agricultural Science and Technology(A) 2013年第6期3卷 423-435页

作者： Weldemichael Abraha Tesfuhuney leon Daniel van rensburg Sue Walker Department of Soil Crop and Climate Sciences University of the Free State BIoemfontein 9300 South Africa

The purpose of this study was to ascertain the effectiveness of surface treatments to quantify the partitioning of rainwater falling on the runoff strips and basins as well as to determine the fraction of rainwater available to intercept by maize canopy and infiltrate into the root zone. The rainfall canopy interception （RCI） was estimated as a function of basin leaf area ratio per rain event. The runoffrainfall （RR） ratio was determined for both a single rainfall event and the whole growing season. Infiltration ratio of basin to runoff area was analysed for every unit millimeter of water that infiltrate in the runoff section, some additional of water will infiltrate in the basin area. The plateau value of RCI-rainfall relationships rendered about double in the wider （1.0-1.1 mm） compared to the narrow runoff strips （0.5-0.6 mm）. Statistically, the combined surface treatments （RSL x ML） affected the RR ratio with higher efficiency in bare 1 m runoff （27%） and the lower efficiency group （〈 10%） is associated with the widest runoff length covered with mulch. Variations in fractions of rainwater that can infiltrate into basins and runoffareas can lead one to select alternative strategies for water harvesting techniques.

关键词： Surface treatments rainfall canopy interception runoff rainfall ratio infiltration ratio.

Effect of Wood Compost on Extreme Soil Characteristics in the Lusatian Lignite Region

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Open Journal of Soil Science 2012年第4期2卷 347-352页

作者： Wael Nada Oswald Blumenstein Sarina Claassens leon van rensburg Institute of Earth and Environmental Sciences Potsdam University Potsdam Germany Unit for Environmental Sciences and Management North-West University Potchefstroom South Africa.

Open-cast lignite mining operations result in a loss of soil quality. Soils associated with coal mining are usually characterised by poor physical and chemical parameters. Low pH and heavy metal toxicity are of the main concerns. The lignite and pyrite content of the dump materials of the Lusatian open-cast mining district in Eastern Germany resulted in high acidification potential and low organic matter content of soils. These extreme conditions require considerable amounts of alkaline materials like compost to enable revegetation. This study was carried out to evaluate the effect of different application rates of wood compost on soil physico-chemical properties in two representative soil substrates (tertiary and quaternary) and on some plant growth parameters. Soil in each site was mixed with wood compost and sown with a grass mixture. The data of both studied soils showed an improvement in physical properties such as water holding capacity and bulk density in soil ameliorated with compost. Most soil chemical properties were increased significantly with the increase of compost application rates, particularly organic matter content, total nitrogen and cation exchange capacity. Compared to the control treatment in each site, the treated soil with compost showed a significant increase in grass biomass (fresh and dry matter yield). The results of these experiments revealed that addition of wood compost had significant positive effects on the soil physical and chemical properties, which affected the response of plant growth and can facilitate the revegetation of substrates contaminated with coal spoil.

关键词： Coal spoil Mining Reclamation Revegetation

Ultra-fast Maize （Zea mays L.） Hybrid Growth Response to Plant Population Density

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Journal of Agricultural Science and Technology(B) 2013年第5期3卷 334-343页

作者： Gobeze Loha Yada Gert Michael Ceronio leon Daniel van rensburg Department of Soil Crop and Climate Sciences P.O. Box 339 University of the Free State Bloemfontein South Africa Awassa Agricultural Research Center P.O. Box 06 Awassa Ethiopia

Current arable land and increasing food demand necessitates the practice of double and multiple cropping systems with inclusion of ultra-fast maize hybrids, which are characterized by smaller size, fewer leaves per plant, lower leaf area and fewer self-shading problems, under irrigation. In this context, a field experiment was conducted for two successive cropping seasons 2008/2009 to 2009/2010 at Kenilworth Experimental Station to evaluate the effect of row spacings and plant density on growth. Three row spacing （0.225, 0.45 and 0.90 m） and five plant densities （5, 7.5, 10, 12.5 and 15 plants m^-2） were used. Treatments were combined in a factorial combination and laid out in a completely randomized design with replications consisting of five single plants randomly selected from each treatment for destructive sampling. Growth factors reacted differently to row spacing by plant density. At crop establishment, growth indicators were not significantly affected by either main effects or a combination thereof. However, at the end of the vegetative phase, almost all growth indicators reached a maximum and were significantly affected by treatment interactions. Growth analysis showed that there was an interaction effect of row spacing by plant density on plant height, dry matter （DM） accumulation, leaf area index （LAI）, crop growth rate （CGR） and net assimilation rate （NAR） of maize. Therefore, the current investigation demonstrated that a row spacing of 0.45 m or 0.90 m with a plant density of 10 plants m^-2 was optimum for the selected ultra-fast maize hybrid under irrigation.

关键词： Maize irrigation plant population yield row spacing

Parameters for Use of BEWAB＋ Programme to Schedule Irrigation of Pea （Pisum sativum L,）

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Journal of Agricultural Science and Technology(A) 2013年第8期3卷 622-632页

作者： leon van rensburg Mamus Strydom Alan Bennie Chris du Preez Department of Soil Crop and Climate Sciences University of the Free State Bloemfontein 9300 Republic of South Africa

A large portion of irrigation farmers make use of subjective （intuition） irrigation scheduling methods as supposed to objective or scientific irrigation scheduling methods, which need to be changed. The BEsproeiingsWAterbestuursprogram （BEWAB＋） irrigation scheduling programme is based on the water balance equation and needs：（1） a crop production function; （2） a relative consumptive water demand curve and （3） an allowable depletion subroutine. The objective of this paper was to describe research aimed at obtaining information on （1） and （2） for pea and also to describe the effect of water application on yield and water use of pea. BEWAB＋ uses this information to estimate the daily irrigation water requirements for a particular soil-crop-atmosphere system under irrigation. A field experiment, based on published line-source irrigation methodology, was conducted on a 3 m deep loamy fine sand Bainsvlei or Ustic Quartzipsamment soil near Bloemfontein （26°08′S; 29°01′E） in South Africa. Results showed that there is a linear relationship of the form Ys = 8.07ET - 249 （r2 = 0.91）, where Ys is the seed yield of pea （kg/ha） and ET is evapotranspiration for the growing season （mm）. The relative consumptive water demand curve is represented by the following third order polynomial function that describes the relationship between time and relative ET for a pea growing season of 120 days： ETrelx = 0.09419646 - 0.01302413x ＋ 0.00059008x2 - 0.00000371x3. ETrelz denotes relative ET and x denotes time in days. A workable balance between practical problem solving and advanced irrigation science has been established with BEWAB＋. Pre-plant irrigation schedules can be made for semi-arid areas with the BEWAB＋ programme using easily obtainable inputs, like target yield, soil depth and soil particle size distribution information.

关键词： Crop water demand evapotranspiration irrigation scheduling line source irrigation system pea.

Characterising Vertical Redistribution on Irrigated Furrows in the Tukulu Soil

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Journal of Agricultural Science and Technology(A) 2013年第7期3卷 542-560页

作者： Sabelo Sicelo Wesley Mavimbela leon Daniel van rensburg Alain Cloot Department of Soil Crop and Climate Sciences University of the Free State Bloemfontein 9300 South Africa Department of Mathematics and Applied Mathematics University of the Free State Bloemfontein 9300 South Africa

Subsurface soil water redistribution on the South African Tukulu, also referred as the Cutanic Luvisols in other countries, was evaluated following single run irrigation （20, 40, 80 and 160 L/min inflow rates） in 90 m furrows. Changes in soil water content （SWC） at three horizons were monitored using neutron water meter. Measurements were made every 10 m starting 5 m from the furrow inlet for 455 h. HYDRUS-2D software was used to estimate soil hydraulic parameters through inverse optimization algorithms for redistribution at the inlet, midpoint and furrow end. Optimized model parameters compared with initial estimates recorded satisfactory agreement between measured and predicted soil water content, despite spatial variability. Effective hydraulic conductivity （Keff） for 0-600 mm and 0-850 mm profile flow domains demonstrated linearity with SWC although inconsistencies under field conditions were inevitable. The underlying layer restricted gravity and augmented redistribution with Keff assuming a steeper gradient than normal. Conversion of KCff and soil water content into a ratio assisted in quantifying rate of redistribution at 0-600 mm and 0-850 mm profile depth. Vertical redistribution was found to be limited within the upper 600 mm depth thus providing the opportunity to develop furrow irrigation with confidence that water productivity is optimized.

关键词： Soil water redistribution inflow rates effective unsaturated hydraulic conductivity infiltrated depth HYDRUS-2D.

Determining the Optimum Inflow Rates for Micro-flood Irrigation on the Tukulu Soil

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Journal of Agricultural Science and Technology(A) 2014年第8期4卷 633-649页

The performance of micro flood irrigation （MFI） under different inflow rates was evaluated on 90 m closed ended furrows in the South African Tukulu soil. A single irrigation was used to characterise the surface and subsurface soil water distribution from the 20, 40, 80 and 160 L/min inflow rates treatments. Neutron access tubes were installed to a depth of 1 m at every 10 m distance interval starting at 5 m from the furrow inlet. Soil water content measurements were taken using the WaterMan neutron water meter. The HYDRUS-2D software was also used to provide insight on irrigated furrows soil water content and subsurface water distribution. The 20 L/min produced a stream flow that could advance up to the 60 m furrow distance. The stream flow from the rest of the inflow rates were able to reach the furrow end with the 180 L/min recording the fastest advance time of 23 min. The 20 L/min and 40 L/min had recession period of less than 7 min while the 80 L/rain and 160 L/min lasted more than an hour. Distribution uniformity （DU） at longer furrow distances was the highest from the 80 L/min and 160 L/min with the 20 L/min and 40 L/min recorded similar performances at shorter distances. The 40 L/rain was one of the smaller inflow rates that recorded the highest DU of 0.96 for the generated average infiltrated depth of the 30 m long furrow and therefore should be adopted for furrow distances of less than 60 m on the Tukulu soil.

关键词： Short furrow irrigation infiltrated depth HYDRUS-2D distribution uniformity.

Estimating Soil Hydraulic Parameters Characterizing Rainwater Infiltration and Runoff Properties of Dryland Floodplains

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Computational Water, Energy, and Environmental Engineering 2019年第1期8卷 11-40页

作者： Sabelo S. W. Mavimbela leon D. van rensburg Department of Soil Crop and Climate Sciences University of the Free State Bloemfontein South Africa

The two-layered (0 - 50 and 50 - 250 mm) surface horizon hydraulic parameters of three dryland floodplain soil-types under aquafer water management in Postmasburg, Northern Cape Province of South Africa were estimated with HYDRUS-1D model. Time dependent water infiltration measurements at 30 and 230 mm depths from simulated rainfalls on undisturbed 1 m2 small plots with intensities of 1.61 (high), 0.52 (medium) and 0.27 (low) mm·min-1, were minimised using a two-step inversion. Firstly, separate optimisation of the van Genuchten-Mualem model parameters for the two surface-horizon layers and secondly, simultaneous optimisation for the joint two-layered horizon with first step optimal parameters entered as initial values. The model reproduced transient water-infiltration data very well with the Nash-Sutcliffe model efficiency coefficient (NSE) of 0.99 and overestimated runoff (NSE;0.27 to 0.98). The upper surface horizon had highly optimised and variable parameters especially θs and Ks. Optimal Ks values from higher soil surface bulk-density (≥1.69 g·cm-3) were lower by at least one order of magnitude to double ring infiltrometers and water infiltration properties were different (P < 0.05) for the high rainstorm due to raindrop impact and surface crusting. Optimal α and n parameter values corresponded well with texture of the Addo (Greysols), Augrabies (Ferralsols) and Brandvlei (Cambisols) soil types. However, θs and Ksshowed greater sensitivity to model output and exerted greater influence on dryland floodplain water-infiltration and runoff characteristics. Increasing rainfall simulation period to attain near-surface saturated conditions and inclusion of surface ponding data in the inverse problem could considerable improve model prediction of hydro-physical parameters controlling surface-subsurface water distribution in fluvial environments.

关键词： Floodplain Soil Types Hydrus-1D Model Inverse Parameter Optimisation Objective Function Parameter Sensitivity Sedimentary Crust Rainfall Simulation