Advances in soil physics: Application in irrigation and dryland crop production

Abstract

This 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.

The Nature and Function of the In‐field Rainwater Harvesting System to Improve Agronomic Sustainability

“…The availability of the water depends on several soil and crop properties such as soil texture, structure, organic matter content, rooting density, rooting depth (Bennie and Hensley, ). Plant‐available water (PAW) is defined as the difference between the drained upper limit (DUL) and the lower limit (LL) (van Rensburg, ). …”

Quantifying and predicting soil water evaporation as influenced by runoff strip lengths and mulch cover

“…Thus a considerable proportion of the rainwater that could be used for growth and development is lost. This unproductive loss of rainwater can be reduced by a variety of management practices of which mulching practices (Hensley et al, 2000;Botha et al, 2003) and optimum runoff to basin area ratio are most feasible to enhance rainwater harvesting into the root zone (van Rensburg, 2010). IRWH uses the soil surface crusting as an advantage to enhance runoff collected from the runoff strip length to be stored in a 1 m wide basin.…”

“…IRWH uses the soil surface crusting as an advantage to enhance runoff collected from the runoff strip length to be stored in a 1 m wide basin. The function of the basin area is to stop ex-field runoff to increase infiltration and to store harvested water while runoff is designed to promote in-field runoff and to act as a storage medium for water (van Rensburg, 2010). Addition of mulch on the runoff area decreases in-field runoff to the basin and presumably increases infiltration across the runoff area.…”

Improving Maize Production of In‐field Rainwater Harvesting Technique at Glen in South Africa by the Addition of Mulching Practices

“…() studied E s under different tillage practices such as conventional tillage, stubble mulch tillage and no‐till practices on a diverse range of ecotopes. Van Rensburg () grouped the relevant results of Bennie et al . () into continuous summer cropping and continuous winter cropping.…”