| Wheat yield probabilities on the Glen/Shorrocks ecotope with different soil water contents at planting | Hensley, M. | 1991 |
KeywordsCrop failure, Shorrocks series, soil water, wheat, yield probabilities AbstractTo avoid unnecessary crop failures it would be valuable to have a reliable threshold value of the root zone water content for wheat at planting (θ rp ) below which the risk is too high to plant. An attempt has been made to estimate this value for annual wheat on the Glen/Shorrocks crop ecotope. A simple procedure, based on measured values, was developed for predicting runoff, deep percolation and evaporation (and thus water storage) during the fallow season. This made it possible to estimate θ rp values for each season. A simple stress-index yield prediction model, in which θ rp was one of the inputs, was developed and calibrated against measured yields from this crop ecotope over five years. The calibrated model was then used with actual weather data (1922–1987) to predict yields for 66 seasons. Results showed that for θ rp values of 300 mm or less, 320 mm and 340 mm or more, the chances of attaining a minimum target yield of 1 t ha−1 are <50%, 62% and 74% or greater, respectively. Based on these results, 320 mm is considered to be a suitable threshold value of θ rp for wheat on the Glen/Shorrocks crop ecotope with an effective soil depth of 1 800 mm. This value corresponds with 130 mm of potentially extractable water. AuthorsHensley, M. and Snyman, P. J. Year Published1991 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.1991.10634833 This article contributed by:
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| Wheat cultivar identification by electrophoretic analysis of gliadin proteins | de Villiers, O. T. | 1993 |
KeywordsGliadin extraction, kernel identification, Polyacrylamide gel electrophoresis, wheat AbstractPolyacrylamide gel electrophoresis of gliadin proteins in an acid medium was used to identify different spring wheat cultivars. Gliadins were extracted from single kernels or corresponding flour samples using different solvents. Gliadin electrophoretogram formulae using relative band mobilities and staining intensities were determined for each cultivar. Distinctive band patterns were obtained enabling the cultivars to be identified. Single kernels and flour samples gave identical band patterns differing only in the intensity of the staining of the bands. Authorsde Villiers, O. T. and Bosman, M. Year Published1993 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.1993.10634652 This article contributed by:
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| Wheat (Triticum aestivum L.) growth and yield response to saline irrigation water under controlled conditions | Ceronio, G.M. | 2008 |
KeywordsElectrical conductivity, saline irrigation water, wheat growth AbstractAbstract Serious agronomic problems occur where saline water is used for irrigation. The effect of irrigation water salinity on wheat was investigated using electrical conductivity (ECi, mS m−1) as a salinity indicator. A pot experiment was conducted at the University of the Free State during 2003 and 2004 to determine the effect of the different irrigation water ECi levels on the growth and yield of wheat (cv. SST 806) in a sandy loam soil. The pot experiment was laid out as a complete randomised design with five ECi levels viz. 15(control), 150, 300, 450, 600 mS m−1, replicated three times and conducted over two seasons. The effects were tested at three growth stages viz. tillering, flag leaf and maturity. Various morphological indicators were used to quantify the effect of saline irrigation water on the below ground growth of wheat, viz. root mass and root length. For above ground growth, plant height and leaf area index were recorded. All indicators were expressed on a relative basis and showed a decrease in growth with an increase in the ECi of the irrigation water used. At ECi levels of 300 and 600 mS m−1 seed yield were reduced by 18 and 36%, respectively. AuthorsCeronio, G.M., Rensburg, L.D.
van and Dikgwatlhe, S.B. Year Published2008 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2008.10639913 This article contributed by:
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| Weed survey in cotton (Gossypium hirsutum L.) and sunflower (Helianthus annuus L.) fields in the Pandamatenga plains of northeastern Botswana | Abdullahi, A. E. | 2004 |
KeywordsBotswana, cotton, sunflower, weed survey AbstractSunflower and cotton fields in the Pandamatenga plains of northeastern Botswana were surveyed in 1998 and 1999 for weed infestations. Twenty-seven and 24 species were identified from the fields in 1998 and 1999, respectively. Nineteen and 17 species were found to be annuals in 1998 and 1999, respectively, with Amaranthus hybridus L. as the most abundant species. In 1998, Ipomoea coscinosperma Hochst., Phyllanthus maderaspatensis L., Trichodesma zylanicum (Burm. f.) R. Br. and Acalypha crenata L., all broadleaved species, were the most abundant after A. hybridus in that order; whereas in 1999 the most abundant species after A. hybridus were A. crenata, P. maderaspatensis, Euphorbia hirta L., and T. zylanicum. Setaria verticillata (L.)P. Beauv., which was the most abundant grass weed in 1998, declined in abundance in the following year and in 1999 Brachiaria eruciformis (Sm.) Griseb appeared in larger numbers than S. verticillata. Two grass weeds, Sorghum verticilliflorum (Steud)Stapf and Rottboellia exaitata L., which were present in small numbers in both crops during this survey, can pose a serious challenge to crop production in the area if not adequately controlled. AuthorsAbdullahi, A. E. Year Published2004 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2004.10635017 This article contributed by:
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| Watervlakke in sekere gronde van die Noordwestelike Oranje-Vrystaat | Henning, J.
A.G. | 1988 |
KeywordsCapillary rise, clay, plinthic, restrictive layers, water table AbstractDie akkumulasie van vrywater in sekere gronde in die Noordwestelike Oranje-Vrystaat word geassosieer met verskillende tipes stadig-deurlaatbare lae (keerlae). Voorlopige ondersoeke het aangetoon dat die langtermyn-storing van water verskil tussen twee tipes keerlaag, naamlik 'n kleilaag en 'n harde plintiese laag. Kapillêre styging vanaf vrywatervlakke varieer met die tipe keerlaag en ook die diepte van die watervlak. Hierdie verskynsel kan 'n beduidende invloed op die hoeveelheid water wat vir plante in verskillende lokaliteite beskikbaar is, hê. Die moontlikheid dat bykomende plantvoedingstowwe uit die vrywater béskikbaar gestel kan word is bevestig deur analise van die grondwater vir nitraat. Inligting dui daarop dat die grondwater treaties van aard is. AuthorsHenning, J.
A.G. and Nel, D. J. Year Published1988 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.1988.10634263 This article contributed by:
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| Water-holding capacity of rock fragments in rehabilitated opencast mine soils | Schoeman, J. L. | 1997 |
KeywordsCoarse fragments, mine soils, stones, water-holding capacity. AbstractThe water-holding capacity of rock fragments sampled from spoil materials underlying rehabilitated opencast coal mine soils was determined. Four rock types, ranging from grit and coarse sandstone to carbonaceous shale, and four fractions of different size were investigated by means of ceramic plate extraction. Water retention was determined at each of four matric potentials, viz. −33, −80, −500 and −1500 kPa. Between approximately 2 and 40% (average 13.8%) water, on a volume basis, was released from saturation to −1500 kPa. In respect to smaller sized fragments (2–4 mm), 60% or more of the plant available water, taken as the fraction contained at a potential of greater than −1500 kPa, was released at high potentials (0 to -33 kPa), and in respect to larger fragments (above 4 mm), 10 to 40%. There was no relationship between water content and rock type. Rock fragment size correlated reasonably well with water held between 0 and −1500 kPa (R20.78) as well as water released between 0 and −33 kPa and between −33 and −80 kPa (R2 0.64 and 0.85 respectively). Rock fragment size correlated rather poorly with water released between −80 and −1500 kPa. Application of the results is discussed. AuthorsSchoeman, J. L., Kruger, M. M. and Loock, A. H. Year Published1997 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.1997.10635089 This article contributed by:
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| Water use rate and crop factors of Italian ryegrass (Lolium multiflorum Lam.) under simulated grazing conditions in a small plot experiment | Steynberg, R. E. | 1994 |
KeywordsCrop factor, irrigation, Lolium multiflomm, ryegrass, water use AbstractNo species specific irrigation norms are available for pastures in South Africa. A small plot experiment was conducted to establish irrigation norms for Italian ryegrass. Potential evapotranspiration was calculated by the Penman-Monteith formula. Crop factors were determined as the ratio of evapotranspiration to potential evapotranspiration. It was found that monthly mean evapotranspiration rates were generally lower during winter than had previously been assumed. The evapotranspiration rate also varied considerably during the harvesting cycle. Evapotranspiration rates of less than 15 mm week−1 occurred frequently during the first half of the season. They increased to more than 40 mm week−1 during the second half of the season. The highest values were generally measured during the last week prior to the removal of above-ground biomass. The crop factor was as variable as the evapotranspiration rate. The monthly mean crop factor increased as the season progressed except for a slight decline during midwinter. Weekly determined crop factors were generally low after harvesting. Values of 0.4 or less occurred during the first half of the season. During the latter half of the season they increased to 0.9 in the later stages of the harvesting cycles. A few values of more than 1.0 were also recorded. AuthorsSteynberg, R. E., Nel, P. C. and Rethman, N.
F.G. Year Published1994 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.1994.10634306 This article contributed by:
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| Water use of maize in response to planting density and irrigation | Ogola, J.
B.O. | 2005 |
KeywordsEvapotranspiration, soil evaporation, transpiration efficiency, water use efficiency AbstractThis study aimed to quantify the effect of plant population density and irrigation on the water use efficiency (q) of maize crops, with particular emphasis on the partitioning of water use into transpiration (T) and direct evaporation of water from soil beneath the crop canopy (Esc). A field experiment was undertaken using a split-plot design with watering regimes (rainfed and irrigation) as main plots and plant population density (66,667 and 133,333 plants ha−1) as subplots. Evapotranspiration (ET) was determined by monitoring soil moisture content at 7 d intervals using a neutron probe, Esc was measured daily using microlysimeters, and T was calculated as the difference between ET and Esc. An increase in planting density increased q by 24% under irrigation but reduced q by 17% under rainfed conditions. Esc was 4% less, and T was 9% greater at the highest plant population density owing to a larger crop leaf canopy. Irrigation increased both Esc and T by 41%. Neither Esc nor T were affected by the interaction between population density and water regime. The increase in q at high planting density under irrigated conditions was due to an increase in transpiration efficiency (TE) and a decrease in Esc, while the decrease in q under rainfed conditions was as a result of the predominant decrease in TE. Therefore, the water use efficiency of maize was changed through the manipulation of plant population density. AuthorsOgola, J.
B.O., Wheeler, T. R. and Harris, P. M. Year Published2005 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2005.10634692 This article contributed by:
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| Water temperature effect on hydraulic conductivity and infiltration rate of soils | Levy, G. J. | 1989 |
KeywordsCrust, permeability, viscosity AbstractThe effects of temperature of applied water on the hydraulic conductivity (HC), infiltration rate and crust formation were studied on two soils from the Transvaal. The HC was studied using soil columns whereas infiltration rate and crust formation were investigated by subjecting the soils to simulated rain of two intensities, 25 mm h−1 and 45 mm h−1. Water temperatures for the HC study were held constant at 8°C, 21 °C and 45°C. The results showed that increasing water temperature caused a significant increase in the HC of the soils studied. This increase was attributed to a decrease in water viscosity. In the case of the infiltration rate and crusting 10°C and 45°C temperature treatments were studied. Neither the rate at which the crust was formed nor its final infiltration rate (FIR) were affected by changes in the temperature, and hence the viscosity of the water. Furthermore, the FIR remained unaffected by the water temperature when the rain intensity was changed. It is suggested that the conditions under which the water is applied to the soil determine the sensitivity of soil permeability to changes in the water temperature. When soil is exposed to water with energy (e.g. rain or overhead irrigation) the change in temperature of the water does not affect the susceptibility of the soil to crust formation and hence its permeability. On the other hand when no energy is involved during water application water temperature has a significant effect on the permeability of the soil. AuthorsLevy, G. J., Smith, H.
J.C. and Agassi, M. Year Published1989 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.1989.10634520 This article contributed by:
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| Water storage, soil temperatures and maize (Zea mays L.) growth for various tillage practices | Berry, W.
A.J. | 1987 |
KeywordsMaize, soil temperature, soil water storage, tillage AbstractFour tillage treatments ranging from conventional mouldboard ploughing through to direct-drilling were repeated during the second season of an ongoing experiment. At commencement of the new season, differences in plant- available water (PAW) in the top 600 mm of the soil profile were non-significant. Following primary tillage, a strong trend of lower PAW with increasing degree of tillage was observed until just before anthesis, and again midway through grain-filling. These differences were attributed mainly to reduced evaporation prior to planting under the greater maize residue cover on the less disturbed soil. Residue cover at planting was 83% on the direct-drill, 21% on the chisel, 15% on the chisel & disc, and 4% on the mouldboard ploughed treatments. Maximum soil temperatures at 50 mm depth increased with decreasing residue cover which resulted in quicker seedling emergence, and leaf area development during early vegetative growth. The soil water storage advantage and slower initial growth in the direct-drill treatment was associated with highest yield of 7,6 t ha−1. AuthorsBerry, W.
A.J., Mallett, J. B. and Greenfield, P. L. Year Published1987 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.1987.10634231 This article contributed by:
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