Tree rows and grass-strips increase water availability in fruit tree-crop agroforestry systems on sloping land

Soil water conservation in upland areas characterised by slopes is extremely challenging. Information about soil water availability and variability, which can guide appropriate soil water management, is often lacking, including for agroforestry (AF) which is considered a sustainable farming practice in these regions. This study aims to describe how soil water is distributed and how it impacts crop growth and yield in an agroforestry system. Investigations were carried out in 2022-2023, in year 6 and 7 of an experiment wherein a fruit tree (mango and longan)-maize-grass treatment was compared to sole-maize in four replicates. Nine slope positions in each AF-plot were defined based on their distance from the tree rows, whilst three positions along the slope were selected in the sole-maize. Available soil water content (ASWC) down to 60 cm depth varied between 14 and 141 mm and was up to 28 mm higher in the AF system than the sole-maize following rain events. Generally, the ASWC was lower down-slope than upslope of the tree rows and declined more rapidly after rain events. During the early dry season, ASWC was higher in mango-AF but lower in longan-AF compared to sole-maize, whereas the opposite was true late in the dry season. Maize grain yield was consistently lower in the zone immediately downslope (1.0 ton ha(-1)) than upslope (3.2 ton ha(-1)) of tree rows, but the yield-reducing effect downslope decreased with increasing distance from the tree rows and grass-strips. Water was generally not limiting maize yields. To conclude, ASWC was higher in AF than in sole-maize and increased more upslope than downslope of tree rows and grass strips immediately after rain events. The choice of tree species influenced ASWC in the dry season.