Interactive tillage & crop residue management effects on soil properties, crop nutrient uptake & yield in different weathered soils of West Africa

Abstract

Sustainable crop production intensification in West Africa is hampered by constraints such as soil degradation, mainly due to excessive mining of soil nutrients, topsoil loss by surface runoff, and climatic factors like excessive rainfall, droughts, and high temperature. To counteract this problem, alternative management practices need to be adopted that have the potential to prevent and/or reduce the severity of soil degradation and could be suitable for buffering the future extreme climate effects on crop production in a sustainable manner. Considering this fact, the overarching aim of our study was to identify management options to improve crop productivity and livelihood among the farming population in the Sudan Savanna of West Africa under current and future climate conditions by using monitoring data from long-term field experiments on several sites over 5 years and additional simulation experiments.<br /> Thus, this study was implemented stepwise: first, contour ridge tillage, reduced tillage, and crop residue management were assessed as an effective means to improve soil organic carbon stock, nutrient stocks, crop N uptake and N use efficiency (NUE) by setting up a field experiment on four sites [St1: Ferric Lixisol, footslope in Dano (Burkina-Faso); St2: Eutric Plinthosol, upslope in Dano (Burkina-Faso); St3: Haplic Lixisols, footslope in Dassari (Benin); and St4: Plinthic Lixisol, upslope in Dassari (Benin)] of West Africa from 2012 to 2016. On-farm trials were set up in a strip-split plot layout, where 2 levels of tillage (contour ridge tillage and reduced tillage) were considered as a main-plot factor, and sub-plot factors included 2 levels of crop residue management (with and without), and 2 levels of N fertilizer doses (control and recommended dose). In a second step, we calibrated and evaluated the CERES-Maize model in DSSAT and parameterized the tillage component of DSSAT using the experimental data of 2014 (calibration) and 2016 (validation). Finally, we used the calibrated model to assess the potential of contour ridge tillage and reduced tillage along with crop residue retention in terms of buffering the expected future climate change effects under a 2°C warming scenario on crop yield and to provide a site-specific assessment of best management practices. For this purpose, we used the HAPPI weather dataset consisting of three GCMs (ECHAM6, MIROC5, NorESM1), and two climate scenarios: current baseline (2006–2015), and 2°C warmer than pre-industrial levels.<br /> The field experiment demonstrated that in a gently undulated region (St2 and St4) subject to soil degradation through runoff and erosion, implementation of contour ridge tillage along with crop residue retention in upslope areas maintained soil fertility and sustained crop productivity. On the other hand, in footslope areas with well-drained soils and high water retention capacity (St3), the adoption of reduced tillage with crop residue retention could be more beneficial. Model simulations under future 2°C warming scenarios and cumulative probability distribution confirmed that contour ridge tillage along with crop residue application could lead to positive changes in maize yield at upslope field sites, where soil erosion and loss of water and nutrients through runoff is a serious risk. Simultaneously, reduced tillage with crop residue application could be a valuable alternative to farmers’ practice in fields with deep soils and high water retention capacity at footslope position (St3), as it resulted in a higher increase of maize yield under future 2-degree warming compared to the baseline and could be preferred by risk-averse farmers. Maize production on gravelly soils with low water retention capacity (St1) may suffer from future 2-degree warming regardless of the tillage practice. Hence, the application of site-specific tillage operations and crop residue application has the potential to buffer future warming effects on maize yield as confirmed by DSSAT simulations. We must share this information with the local smallholders, policymakers, and scientific communities to adjust their decisions accordingly, and redirect their steps towards improving crop nitrogen use efficiency and soil fertility which in turn can sustain crop productivity.