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Impacts of conservation agriculture on soil structure and hydraulic properties of Malawian agricultural systems

Eze, Samuel, Dougill, Andrew J., Banwart, Steven A., Hermans, Thirze D.G., Ligowe, Ivy S., Thierfelder, Christian
Soil & tillage research 2020 v.201 pp. 104639
Cajanus cajan, Mucuna pruriens, Vigna unguiculata, agricultural conservation practice, agricultural extension, available water capacity, climate, climate change, continuous cropping, corn, cowpeas, crop residue management, crop rotation, farming systems, food security, intercropping, pigeon peas, plant available water, porosity, rhizosphere, saturated hydraulic conductivity, soil organic matter, soil structure, water storage, Malawi
Sub-Saharan Africa (SSA) faces climate change and food insecurity challenges, which require action to create resilient farming systems. Conservation agriculture (CA) is widely promoted across SSA but the impacts on key soil physical properties and functions such as soil structure and hydraulic properties that govern water storage and transmission are not well understood. The aim of this study was to assess the impacts of long term (10–12 years) maize-based CA on soil hydraulic conductivity, water retention and pore size distribution. Root zone (0–30 cm depth) soil total porosity, pore size distribution, saturated hydraulic conductivity (Kₛₐₜ) and plant available water capacity (PAWC) of conventional maize monocrop farming systems (CP) are compared with those of adjacent CA trials with either sole maize or maize intercrop/rotation with cowpea (Vigna unguiculata L.), pigeon pea (Cajanus cajan L.) or velvet bean (Mucuna pruriens L) in trial locations across central and southern Malawi. Results show that maize-based CA systems result in significant changes to soil hydraulic properties that correlate with improved soil structure. Results demonstrate increases of 5–15 % in total porosity, 0.06−0.22 cm/min in Kₛₐₜ, 3–7 % in fine pores for water storage and 3–6 % in PAWC. Maize monocrop CA had similar effect on the hydraulic properties as the maize-legume associations. The values of Kₛₐₜ for CA systems were within optimum levels (0.03–0.3 cm/min) whereas PAWC was below optimum (<20 %). There was no significant build-up in soil organic matter (OM) in the CA systems. The results lead to a recommendation that crop residue management should be more pro-actively pursued in CA guidance from agricultural extension staff to increase soil OM levels, increase yields and enhance climate resilience of sub-Saharan African farming systems.