Toward greater sustainability: how investing in soil health may enhance maize productivity in Southern Africa

Christian Thierfelder,Lumbani Mwafulirwa,Tim J Daniell,Elizabeth M Baggs,Eric Paterson,Blessing Mhlanga,Jill E Cairns

doi:10.1017/s1742170521000442

Abstract

AbstractClimate change and soil fertility decline are major threats to smallholder farmers' food and nutrition security in southern Africa, and cropping systems that improve soil health are needed to address these challenges. Cropping systems that invest in soil organic matter, such as no-tillage (NT) with crop residue retention, have been proposed as potential solutions. However, a key challenge for assessing the sustainability of NT systems is that soil carbon (C) stocks develop over long timescales, and there is an urgent need to identify trajectory indicators of sustainability and crop productivity. Here we examined the effects of NT as compared with conventional tillage without residue retention on relationships between soil characteristics and maize (Zea mays L.) productivity in long-term on-farm and on-station trials in Zimbabwe. Our results show that relationships between soil characteristics and maize productivity, and the effects of management on these relationships, varied with soil type. Total soil nitrogen (N) and C were strong predictors of maize grain yield and above-ground biomass (i.e., stover) in the clayey soils, but not in the sandy soils, under both managements. This highlights context-specific benefits of management that fosters the accumulation of soil C and N stocks. Despite a strong effect of NT management on soil C and N in sandy soils, this accrual was not sufficient to support increased crop productivity in these soils. We suggest that sandy soils should be the priority target of NT with organic resource inputs interventions in southern Africa, as mineral fertilizer inputs alone will not halt the soil fertility decline. This will require a holistic management approach and input of C in various forms (e.g., biomass from cover crops and tree components, crop residues, in combination with mineral fertilizers). Clayey soils on the other hand have greater buffering capacity against detrimental effects of soil tillage and low C input.

Highlights

Southern Africa is heavily affected by declining soil fertility concurrent with negative impacts of climate change, posing severe risks to the sustainability of farming and food security (Tittonell and Giller, 2013)
Soil texture differed between sites (Table 2), so we divided the sites into two broad textural groups based on their silt + clay content: ‘sandy’ and ‘clayey’
Since the different variables were recorded at different scales, all data were first standardized by scaling using the principal component analysis (PCA)() function of the ‘FactoMineR’ package in R

Summary

Introduction

Southern Africa is heavily affected by declining soil fertility concurrent with negative impacts of climate change, posing severe risks to the sustainability of farming and food security (Tittonell and Giller, 2013). Efforts are required to identify maize crop management systems that will help ensure long-term sustainable production under these conditions. As a consequence of heterogeneity in SOM distribution, changes in organic matter stocks can take several years to be measurable (Chivenge et al, 2007) and under no-tillage (NT) conditions can lead to stratification with soil depth (Luo et al, 2010). Timescales for measurable changes in SOM content may vary with soil type (as a function of change relative to the size of the existing SOM stock) (Chivenge et al, 2007), so informed selection and management of improved cropping systems requires early and quantifiable indicators of trajectories toward sustainability for Downloaded from https://www.cambridge.org/core. Timescales for measurable changes in SOM content may vary with soil type (as a function of change relative to the size of the existing SOM stock) (Chivenge et al, 2007), so informed selection and management of improved cropping systems requires early and quantifiable indicators of trajectories toward sustainability for Downloaded from https://www.cambridge.org/core. 15 Dec 2021 at 13:38:43, subject to the Cambridge Core terms of use

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