| Screening of some South African maize (Zea mays L.) cultivars for acetochlor tolerance | Allemann, J. | 2010 |
KeywordsAcetochlor, corn, cultivar, phytotoxicity, tolerance AbstractAcetochlor containing a safener is registered for pre-emergence use on maize to control mainly annual grasses. It is applied at rates of between 0.49 and 1.89 kg ai ha-~ on soils with a clay content from <10% to 55%. Some cases of acetochlor injury to maize have occurred in the field despite the correct application rates being used. A randomised complete block design trial was conducted in a glasshouse set at 28/18°C day/night to screen 21 maize cultivars for their tolerance to acetochlor (WENNER 700 S EC®). Maize was planted in pots containing a sandy loam soil (15% clay). Five acetochlor rates (0, 0.74, 1.47, 2.94 and 5.88 kg ai ha ~) were applied the next day and leached into the soil. Characteristic symptoms of acetochlor phytotoxicity occurred, particularly at higher application rates. Most cultivars showed significant decreases in both plant height and dry mass at the recommended application rate. Significant differences were noted between cultivars, with slight variations in results for seedling height and dry mass. cultivars were grouped into tolerant, intermediate and sensitive classes based on their reaction to the herbicide. Most cultivars were rated as intermediate, although both tolerantand sensitive cultivars were found, so proving the existence of cultivar differences with respect to acetochlor tolerance. AuthorsAllemann, J. and Mphundi, P.M. Year Published2010 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2010.10639992 This article contributed by:
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| Soil indicators of hillslope hydrology in the Bedford catchments, South Africa | van Tol, J.J. | 2010 |
KeywordsFowpaths, hillslope hydrology, hydropedology, prediction in ungauged basins, soil properties AbstractWater plays a primary role in soil genesis and soil strongly influences hydrological processes (flowpaths, residence times and storage). Morphological soil properties serve as indicators of hillslope hydrological behaviour and can facilitate hydrological predictions. Three catchments in the Bedford district (B3, B4 and B5) were surveyed for hydropedological purposes and the observed soil indicators and related geological, topographical and vegetation features were interpreted. I n B4 & B5 shallow soils are the dominant factor governing overland flow promoting short residence times. Deeper soils and fractured bedrock in B3 facilitate bedrock flow and recharge of regional and phreatic water tables. The presence of lime and mottles in the subsoils of valley bottom soils confirm flow in the phreatic zone. Authorsvan Tol, J.J., Roux, P.A.L. Le and Hensley, M. Year Published2010 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2010.10639993 This article contributed by:
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| Anew optimum value for zinc in the main maize producing sandy soils of South Africa | Biljon, J.J.
Van | 2010 |
KeywordsThreshold value, critical value, soil extraction, maize, zinc AbstractSouth African farmers commenced applying zinc (Zn) during the 1960s at a rate of approximately 2 kg Zn ha−1. Although good yields were produced and Zn levels increased in South African maize fields, a recent survey revealed that maize meal contained subnormal levels of Zn, and therefore needed to be fortified with Zn for human consumption. An existing, valid, historic dataset was revisited to throw light on this subject that has lately become topical. Those experiments were conducted during 1997–2001 at seven localities in the main maize producing area of South Africa to establish a new optimum value for Zn in maize producing sandy soils. Treatments included a reference when all nutrients were applied and another when zinc was omitted. A Zn optimum value of 3.8 mg Zn kg−1 in the topsoil, extracted with 0.1 M HCI-solution was established as obtained with linear-linear and quadratic regression methods. AuthorsBiljon, J.J.
Van, Wright, C.A., Fouche, D.S. and Botha, A.D.P. Year Published2010 PublicationSouth African Journal of Plant and Soil Locations- Hoopstad, Free State, South Africa (-27.8333, 25.9167)
- Bothaville, Free State, South Africa (-27.3882, 26.6252)
- Makwassie, North West, South Africa (-27.3149, 26.0012)
- Bethlehem, Free State, South Africa (-28.2333, 28.3)
- Frankfort, Free State, South Africa (-27.2833, 28.5167)
- Bronkhorstspruit, Gauteng, South Africa (-25.805, 28.7464)
DOI10.1080/02571862.2010.10639994 This article contributed by:
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| Advances in pedology in South Africa | Hensley, M. | 2010 |
Keywordsferrolysis, melanic, predictive mapping, sepiolite, soil series AbstractThe ability of soil to serve as a unique buffer of water, organic carbon, nutrients, pH, redox and temperature is recognised in environmental research. A detailed study on hardpan carbonate and dorbank horizons in the commonly occurring ‘heuweltjies’ of the arid Namaqualand coastal region revealed a ‘sepiolitic’ hardpan carbonate centre through ‘sepiolitic’ / ‘petrosepiolitic’ (hardened) to the dorbank horizon on the edges. Footprints of ferrolysis manifests in various properties of duplex and plinthic soils of the semi-arid eastern Free State as (1) acidity, (2) colour, (3) Fe-Mn, (4) mottles and concretions, (5) CEC and (6) abrupt textural differentiation. Soils with melanic A horizons cover 2% of South Africa and are confined to regions with annual rainfall between 550 and 800 mm (aridity index of 0.2–0.5). The understanding of soil formation is applied to divide a land type into soilscapes with a more homogeneous soil distribution pattern. The quantification of the water regime of South African soils showed that ‘freely drained’ soils may have significant periods of drainable water. AuthorsHensley, M., Roux, P.A.L.
le, Huyssteen, C.W.
van, Roux, P.A.L. Le and Huyssteen, C.W. van Year Published2010 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2010.10639965 This article contributed by:
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| Advances in soil physics: Application in irrigation and dryland crop production | Rensburg, L.D.
van | 2010 |
KeywordsConservation tillage, dryland, in-field rainwater harvesting, irrigation, soil physics AbstractThis is the third soil physics review to be published in South African Journal of Plant and Soil. In the previous reviews the focus was broad and covered almost every aspect of the subject, providing a comprehensive list of contributions in soil physics. For the 25th year anniversary celebration of South African Journal of Plant and Soil, I have chosen to narrow the scope and focus on advances in soil physics in relation to irrigation and dryland agriculture. From a bio-physical viewpoint, South African researchers have made a major contribution to the body of scientific knowledge about irrigation and its application, expressed mainly in the form of irrigation or crop models such as PUTU, SWB and BEWAB. Attention was also given to modern ways of irrigation scheduling based on continuous soil water monitoring. Several irrigation scheduling service providers have adapted their businesses accordingly, with the result that South Africa is probably the leading country in Africa with respect to soil water monitoring and associated communication technology. In contrast, the review has shown that at farm and irrigation scheme level, salt management requires urgent attention. This is necessary as a precautionary measure to protect our natural resources. In the second part of the review the contribution of soil physics in relation to tillage practices is explored, and in particular how these have modified the field water balance components in order to enhance yield and rain water productivity. Based on the results of field experiments, new relationships were established, viz. rainfall and maize yield; water storage and yield; runoff and surface coverage by crop residue mulches; tillage depth, texture and yield relationships. Lastly, the review also showed how the water balance on clay and duplex soils in semi-arid zones can be modified through in-field rainwater harvesting to increase their rain water productivity. This technology has enhanced the livelihoods of many communal families who have applied the technique in their homesteads. AuthorsRensburg, L.D.
van Year Published2010 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2010.10639966 This article contributed by:
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| Advances in sugarcane soil fertility research in Southern Africa | Meyer, J.H. | 2010 |
KeywordsFertiliser, nutritional requirements, Saccharum hybrid sp, soil management, systems agronomy AbstractThe South African sugar industry is a modern, well organised industry and highly cost-competitive in world terms, producing some 2.3 million tons of sugar annually from 20 million tons of cane. The bulk of the cane is produced by some 1626 large scale growers (80%) and the rest is split between 36 500 small scale growers (11%) and milling companies with sugar estates (9%). As part of the 25th anniversary of SA Journal of Plant and Soil, a three-part review is given of recent soil and crop science based research initiatives conducted by the South African Sugar Industry in studying the impact of: (a) Soil fertility in determining the main nutritional requirements of sugarcane, (b) Soil factors limiting climatic potential including water intake due to surface crusting, soil loss through erosion, low available moisture capacity, soil organic matter loss, acidification and water logging during wet seasons, and (c) Better soil management strategies based on crop residue retention, nutrient recycling, minimum tillage, ridge tillage, cover crops and intercropping, to conserve soil and water more effectively, increase soil organic matter, improve fertiliser use efficiency and reduce physical damage to soils during harvesting. It is imperative that the continued success of the industry be underpinned by high standards in environmental management. AuthorsMeyer, J.H. and Antwerpen, R.
van Year Published2010 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2010.10639967 This article contributed by:
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| Maize fertilizer research over the last 25 years – an overview | Biljon, J.J.
Van | 2010 |
KeywordsFertilizer, maize, overview, research AbstractMaize yield as well as fertilizer practices have changed over the last 25 years. Average maize yield for South Africa increased from approximately 2.3 tons ha−1 in the early 1980s to approximately 3.5 tons ha−1 in recent years. The early 1970s to the middle 1990s can be seen as a “boom period” for maize fertilizer research in South Africa. Up until 1995, fertilizer research was grouped in specific projects with clearly defined goals and a definite direction. Research was to a large extent proactive. This research approach is no longer clearly visible and it has become largely reactive, with emphasis on ad hoc problem solving instead of goal oriented research. Such an ad hoc approach can cost us dearly because there will be no real research progress. This paper also gives an overview of research over the last 25 years on soil acidity, macronutrients (N, P and K), secondary nutrients (S, Ca and Mg), micronutrients (Zn) and other contributions (long-term trials and fertilizer placement). The reduction in maize fertilizer research is of concern when seen against the background of the regional and continental importance of maize. Well planned nutrition research can ensure food security and nutrition security both locally and in other parts of the continent, provided there are clear goals and direction, adequate funding, proper management and coordination. Fragmented, ad hoc trials will not create prosperity for all in the region. AuthorsBiljon, J.J.
Van Year Published2010 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2010.10639968 This article contributed by:
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| Crop physiology: A perspective for southern Africa | Modi, A.T. | 2010 |
KeywordsMineral nutrition, seed physiology, source-sink relationships, stress physiology AbstractCrop physiology is a broad subject and a comprehensive treatise of all its aspects is impossible, even in a whole volume dedicated to the subject. With a few exceptions, plant physiology, rather than crop physiology, is commonly the focus when physiological aspects of plant growth and development are reviewed in biological sciences. Plant and crop physiology are distinguishable by the manner in which one is almost purely basic and the other tends towards application of the science in crop management. Therefore, the objective of this review was to highlight crop production-oriented physiological research that has shaped our current knowledge and research activities in the past few decades, especially the latter part of the past century. Source-sink relationships, stress physiology, mineral nutrition and seed physiology were identified as the key aspects of crop physiology that influence crop production. Each of these aspects is addressed to identify its significance in crop performance and to highlight both the breakthroughs and gaps in our contemporary knowledge of crop physiology. There was no attempt to provide fundamental interpretations. The reader is referred to relevant appraisals of crop and plant physiology, to gain further insight into original data. Since the review is also meant to contribute to further education in crop production, views on the challenge of training future crop scientists are expressed in the final section. AuthorsModi, A.T. and Greenfield, P.L. Year Published2010 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2010.10639969 This article contributed by:
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| Modelling crop growth and crop water relations in South Africa: Past achievements and lessons for the future | Rensburg, L.D.
van | 2010 |
KeywordsCrop model, hydrology, irrigation, management, simulation, water balance AbstractMathematical simulation of crop growth and water relations has become indispensable to agricultural science and practice. A critical assessment of how modelling has contributed to the development of crop science and to the management of crop production and natural resources in South Africa (SA) over the past 25 years could give new perspectives on the benefits derived from modelling, the appropriateness of approaches employed and the best way forward. The initial objectives of the major SA modelling initiatives (ACRU, BEWAB, CANE-GRO, CERES, PUTU, SAPWAT, SWB) dictated the approaches that were followed and determined their impacts. Significant advances were made with regard to improved understanding of crop growth and water use and adapting models for local conditions such as dryland grain crop production under very low rainfall. Modelling provided invaluable support for strategic investigations into the impacts of climate change, land use and water use. Many of the models succeeded in providing much-needed information to improve tactical and operational management of irrigated and dryland agriculture. Some models have been (and are being) used operationally to forecast crop production (maize, wheat and sugar) and to monitor droughts in natural vegetation, adding value to the respective industries. Modelling has formed, in some cases, an integral part of tertiary education in crop science and hydrology. This should be strengthened to build more capacity to address the ever-increasing complexity of challenges in agriculture. The review identified factors that are crucial for modelling to maintain effective impacts on the science and practice of crop production and natural resource use. These were excellent scientific leadership, long term funding, effective collaboration between local and with international groups, expertise on local agronomy and high quality experimental data for model testing and adaptation. Future modelling efforts should explore opportunities to integrate information obtained from technologies such as remote sensing and genomics. AuthorsRensburg, L.D.
van, Singels, A., Annandale, J.G., Jager, J.M. De, Schulze, R.E., Inman-Bamber, N.G., Durand, W., Heerden, P.S.
Van, Crosby, C.T., Green, G.C. and Steyn, J.M. Year Published2010 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2010.10639970 This article contributed by:
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| Herbicide resistance in weeds – a threat to effective chemical weed control in South Africa | Pieterse, P.J. | 2010 |
KeywordsChemical weed control, herbicides, integrated weed management, resistance, weeds AbstractApart from the last 40 to 50 years, weed control in crops has always been a labour-intensive and time-consuming mechanical practice. Relief came in the form of chemical compounds that could control weeds, in particular selective herbicides. The development of highly effective selective herbicides has resulted in farmers becoming increasingly reliant on chemical weed control. Continuous application of herbicides with the same mode of action, however, selected for resistant mutations within weed populations to become dominant, rendering the herbicides less effective. Herbicide resistant weeds currently occur in 187 weed species distributed over 60 countries worldwide. South Africa is no exception and resistance in 15 weed species to herbicides in seven modes of action groups has been verified. This situation is compelling farmers to consider alternative weed control strategies and cropping systems. The most effective strategy to manage resistant weeds would most probably be an integrated weed management program that does not rely on any one type of weed control method alone. Farmers will therefore have to adapt weed management systems and cropping systems to delay the onset of herbicide resistance or, if it is already present, to manage it effectively in order to keep future crop production profitable and sustainable. AuthorsPieterse, P.J. Year Published2010 PublicationSouth African Journal of Plant and Soil LocationsDOI10.1080/02571862.2010.10639971 This article contributed by:
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