Maize nitrogen uptake and productivity under reduced and conventional tillage

Reduced tillage (RT) systems have been promoted for crop production intensification in low potential areas through enhancement of fertiliser response of degraded soils and drought mitigation. A 3 year study was conducted from 2015/2016 to 2017/2018 growing seasons in sub-humid (650–1000 mm rainfall year −1 ) Zimbabwe to determine nitrogen (N) uptake and maize yield response to nitrogen fertilisation rate (0, 30, 60, 90 120 150, 180 k gha −1 ) under RT and conventional tillage (CT). The experimental design was a split plot, with the two tillage systems as main plot and seven N rates as the sub-plot treatments. Four sites were established in smallholder farmer fields with clayey soils (160–400 g clay kg −1 ; Chromic Luvisols and Rhodic Ferralsols) and sandy soils (40–100 g clay kg −1 ; Eutric Regosols). Results show that the study sites had rainfall deficits of 4–47% in the first and third growing seasons. Nitrogen uptake rates of 8–60 kg ha −1 resulted in fertiliser N recovery efficiencies of 5–40% which were two fold higher under RT than under CT system. Maize grain yields (0.3–11 t ha −1 ) were 33% higher under RT than CT and increased 1.88–2.72 fold under N fertilisation compared to the control. The mismatch between top dressed N and peak crop demand require precision fertilisation in the dry seasons. Agroecology based quadratic modelling revealed that maximum maize yields of 2–13 t ha −1 were obtainable at optimum N fertilisation rates that were lower under RT than CT. The study provided a robust starting point in the improvement of nitrogen fertiliser management for maize under reduced tillage and climate variability.