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Pretoria, South Africa

Van Jansen Rensburg H.G.,University of Pretoria | Claassens A.S.,University of Pretoria | Beukes D.J.,ARC Institute for Soil
South African Journal of Plant and Soil | Year: 2010

The interrelationships between elemental content of selected soil and leaf nutrients and maize grain yield were evaluated in a liming experiment conducted on a Hutton and Oakleaf soil in a resource-poor farming area in the Mpumalanga Province of South Africa. Improved uptake of Mo by maize with increased soil P status was found on the Hutton soil, while N and P uptake improved, due to lime and fertiliser application, on both soils. Boron uptake by maize was depressed with lime application on the Oakleaf soil. Maize yield on the Hutton soil was adversely affected by Al toxicity, while plant Ca deficiency was the dominant factor that limited maize grain yield, followed by Al level and a depressed B uptake on the Oakleaf soil. Nutrient vector analyses showed a toxic build-up of Fe, followed by Al and to a lesser extent Mn. These toxic elements depressed the uptake of Ca, Mg and B by maize on the Hutton soil. On the Oakleaf soil, Al toxicity, followed by high concentrations of Mn and Fe, markedly reduced the uptake of Ca, Mg and K by maize.

Hensley M.,University of the Free State | Bennie A.T.P.,University of the Free State | van Rensburg L.D.,University of the Free State | Botha J.J.,ARC Institute for Soil
Water SA | Year: 2011

This review provides an overview of Water Research Commission (WRC)-funded research over the past 36 years. A total of 28 WRC reports have been consulted, 13 of these compiled by the University of the Free State, 4 by the University of Fort Hare, and the remainder mainly by the ARC-Institute for Soil Climate and Water. This work has resulted in extensive capacity building in this field - numerous technical assistants and 58 researchers have been involved, of which 23 are still active in research. The focus on the water flow processes in the soil-plant-atmosphere continuum (SPAC), with particular emphasis on processes in the soil, has greatly enhanced understanding of the system, thereby enabling the formulation of a quantitative model relating the water supply from a layered soil profile to water demand; the formulation of logical quantitative definitions for crop-ecotope specific upper and lower limits of available water; the identification of the harmful rootzone development effects of compacted layers in fine sandy soils caused by cultivation, and amelioration procedures to prevent these effects; and management strategies to combat excessive water losses by deep drainage. The explanation of the way in which SPAC is expressed in the landscape in the form of the ecotope has been beneficial with regard to the extrapolation of studies on particular SPACs to the large number of ecotopes where detailed studies have not been possible. Valuable results are reported regarding rainfall and runoff management strategies. Longer fallow periods and deficit irrigation on certain crop ecotopes improved rainfall use efficiency. On semi-arid ecotopes with high-drought-risk clay and duplex soils and high runoff losses, in-field rainwater harvesting (IRWH), designed specifically for subsistence farmers, resulted in maize and sunflower yield increases of between 30% and 50% compared to yields obtained with conventional tillage. An indication of the level of understanding of the relevant processes that has been achieved is demonstrated by their quantitative description in mathematical and empirical models: BEWAB for irrigation, SWAMP mainly for dryland cropping, and CYP-SA for IRWH. Five important related research and development needs are identified. The WRC has played, and continues to play, an important role in commissioning and funding research on water utilisation in agriculture and has clearly made an excellent contribution to the progress made in addressing the needs and requirements of subsistence, emergent and dryland farmers in South Africa.

van Rensburg L.D.,University of the Free State | Botha J.J.,University of the Free State | Botha J.J.,ARC Institute for Soil | Anderson J.J.,University of the Free State | Hensley M.,University of the Free State
Irrigation and Drainage | Year: 2012

Hensley et al. (2000) proposed an in-field rainwater harvesting (IRWH) technique for rural farmers located east of Bloemfontein South Africa, a semi-arid environment. This technique combines the advantages of water harvesting, no-till and basin tillage to stop ex-field runoff on high clay soils. The full agronomic potential of the IRWH technique has not, however, been reached because the main cause of water loss is evaporation. Evaporation dominates the hydrological cycle in semi-arid environments. This paper reviews the nature and design of the IRWH system, specifically the effect of mulch type on evaporation and yield. The effect of mulch type on yield is described by an infiltration ratio of the basin versus the runoff area over a period of three years. The function of the basin and catchment area is also discussed. The function of the basin area was to stop ex-field runoff completely, to maximize infiltration and to store the collected water in the soil layers beneath the evaporation sensitive zone. The catchment area was designed to promote in-field runoff and to act as a storage medium for water. Results from this research provide a new perspective on mulch management within water harvesting systems. © 2012 John Wiley & Sons, Ltd.

Adeleke R.,Rhodes University | Adeleke R.,ARC Institute for Soil | Dames J.F.,Rhodes University
South African Journal of Botany | Year: 2014

Truffles are generally known to form a mycorrhizal relationship with plants. Kalaharituber pfeilii (Hennings) Trappe & Kagan-Zur is a species of desert truffle that is found in the southern part of Africa. The life cycle of this truffle has not been fully investigated as there are many unconfirmed plant species that have been suggested as potential hosts. Many mycorrhizal associations often involve other role players such as associated bacteria that may influence the establishment of the mycorrhizal formation and function. As part of an effort to understand the life cycle of K. pfeilii, laboratory experiments were conducted to investigate the role of ascocarp associated bacteria. Bacterial isolates obtained from the truffle ascocarps were subjected to microbiological and biochemical tests to determine their potentials as mycorrhizal helper bacteria. Tests conducted included stimulation of mycelial growth in vitro, indole acetic acid (IAA) production and phosphate solubilising. A total of 17 bacterial strains belonging to the Proteobacteria, Firmicutes and Actinobacteria were isolated from the truffle ascocarps and identified with sequence homology and phylogenetic methods. Three of these isolates showed potential to be helper bacteria in at least one of the media tested through the stimulation of mycelial growth. Furthermore, four isolates produced IAA and one was able to solubilise CaHPO3 in vitro. One isolate, identified as a relative of Paenibacillus sp. stimulated mycelial growth on all the media tested. Other bacterial isolates that showed potential stimulation of mycelial growth were identified molecularly as a Bacillus sp. and two strains of Rhizobium sp. This study has contributed to the existing knowledge on the biotic interactions with K. pfeilii which may be useful in further symbiont and re-synthesis investigations. © 2013 South African Association of Botanists.

Van Huyssteen C.W.,University of the Free State | Turner D.P.,ARC Institute for Soil | Le Roux P.A.L.,University of the Free State
South African Journal of Plant and Soil | Year: 2013

Humans classify their environment to create order, make it understandable, aid recollection and to communicate. The nature of these classifications is not always understood, because they are learnt from an early age. Building on these principles provides a sound basis for any scientific classification. This paper explores these principles, those of the USDA Soil Taxonomy, the World Reference Base for soil resources, and the South African Soil Taxonomy. Knowledge should be ultimate aim of soil classification. A hierarchical system with four levels is proposed for the South African Soil Taxonomy. This can easily be achieved by adding a higher level, proposed to be called a Soil Group, to the current three levels (form, family, and phase). The South African Soil Taxonomy must guard against too many taxa, because humans have a limited ability to comprehend numerous taxa. The distinguishing criteria between taxa should be more clearly defined, while at the same time guarding against becoming too data hungry. The classification should not shy away from intergrades. The object being classified (soils) is a natural system and intergrades will necessarily occur. It is proposed that these should be classified as intergrades, rather than trying to artificially separate natural soil bodies. Copyright © Combined Congress Continuing Committee.

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