Soil fertility trends and management in Conservation Agriculture: a South African perspective

Abstract

Conservation Agriculture (CA) is an integrated approach that consists of a package of practices, namely no-tillage, cover crops, and a crop rotation which includes at least three crops. Globally CA is implemented widely in South America (Argentina and Brazil) and North America (USA and Canada), with a smaller proportion in Australia and New Zealand. There is very little implementation of CA in the rest of world, mainly due to natural resource constraints. Benefits of the system include increases in soil organic matter (SOM) and related increases in organic N in the soil. Experimental results show extremely strong stratification of important plant nutrients, like P, K and Ca, at very shallow soil depth (less than 5 cm) under no-till due to their low mobility in soil. Results show that there is poor root development near the soil surface under the extreme conditions in the marginal cropping areas that dominate most of South Africa's crop production areas. Plant nutrient uptake is thus much lower under no-till than under conventional tillage. Likewise very little movement of lime was found under no-till, hampering amelioration of soil acidity. Research confirmed international data that maize requires much higher N application under no-till than under conventional tillage.

Aligning Conservation Agriculture among various disciplines in South Africa

“…The barriers are not necessarily identical for all contexts. More detail on reasons for non-adoption of CA, including natural physico-chemical and biological factors, are discussed by Nortje and Laker (2021). Regardless of the diverse factors contributing to the decisionmaking of farmers, research is necessary to understand why agricultural producers are deterred from adopting CA.…”

“…A different approach to managing soil fertility is needed for CA as opposed to conventional systems, which stress the importance of developing integrated soil fertility management practices (Nortje and Laker 2021). Although no-tillage is associated with many benefits to combat soil degradation, improve soil fertility and control weeds, a pragmatic approach to tillage can be considered to facilitate nutrient distribution across soil depths, particularly that of immobile nutrients like phosphorus (P) and lime, and to break up root growthrestricting layers in soil.…”

“…Although no-tillage is associated with many benefits to combat soil degradation, improve soil fertility and control weeds, a pragmatic approach to tillage can be considered to facilitate nutrient distribution across soil depths, particularly that of immobile nutrients like phosphorus (P) and lime, and to break up root growthrestricting layers in soil. The choice of crop (particularly legumes) and the design of crop sequences in rotation systems are important factors to consider for optimal soil nutrient management (Nortje and Laker 2021;Strauss et al 2021b). There are significant gaps in our understanding of management of the soil biological component to facilitate effective nutrient uptake by plants, and for promoting soil resilience.…”

Factors That Determine the Sorption of Mineral Elements in Soils and Their Impact on Soil and Water Pollution

“…P pollution of soils in cultivated areas, from rain fed croplands to highly intensive vegetable and fruit production, is becoming a widespread serious problem in the form of excessive plant-available soil P levels [10][11][12]. Excessive P levels in soils are seldom referred to as the "pollution" of soil, because it is usually caused by deliberate application of Pcontaining inorganic fertilizers or organic amendments with relatively high P contents, such as dairy or chicken manure or compost containing large proportions of such manure [12]. Plant-available P levels build up in fertilized soils because P is immobile in the vast majority of soils and is retained where it is applied, even in soils with a low capacities to fix P into forms that are not available to plants, as seen in Table 1 [13].…”

“…At a farm in the same area, a reduction of about 50% in wheat yields were found at a Bray-2 P level of 110 mg•kg −1 . Bray-1 P values are about 50% of those of Bray-2, and the authors have found several incidences of yield reductions in various crops at Bray-1 P levels of above 50 mg•kg −1 [10,12]. Very high plant-available P concentrations in soils are not directly toxic to plants.…”