Modeling the role of planting density and fertilizer in reducing the negative effects of rainfall viability on sorghum production in eastern Ethiopia using APSIM

Sorghum and groundnuts are crucial for food security crop in lowlands of Ethiopia, however, their production is constrained by erratic rainfall and declining soil fertility. This study examined performance of intercropping productivity, climate resilience, and resource-use efficiency by integrating field experiment with APSIM-NextGen modeling. A comprehensive analysis of long-term climate data revealed high interannual variability (CV = 28%) and a statistically significant decreasing trend (ZMK = -2.243) with irregular monthly rainfall distributions. Furthermore, correlation analysis showed that the positive effect of a delayed end of rainfall (r = 0.289) and length of the growth period (r = 0.5721) was only significant in the treatments recieved highest nitrogen (N) level. These climatic factors accounted for about a 17–33% loss of sorghum yield in monocropping, but intercropped sorghum increased land-use efficiency by > 20% and system productivity by > 18.75% under higher N doses and planting densities. Similarly, the model validation showed satisfactory performance for the grain yield (nRMSE < 27%), root mean squared error (RMSE < 0.663 t/ha), index of agreement (IA > 0.87), and biomass (nRMSE < 26.93%, RMSE < 1.835 t/ha, IA >0.836), although vegetative traits (height, leaf number) were less accurately predicted. Sensitivity analysis also confirmed that optimized N management and spatial arrangements mitigate rainfall-linked vulnerabilities. Consequently, APSIM-NextGen serves as a robust tool for designing climate-resilient agronomic strategies for Ethiopian smallholders. Thus, the model accuracy in biomass and grain yield provides robust decision support for developing appropriate fertilizer and planting density to stabilize yields and enhance climate resilience for smallholder farmers in semi-arid Ethiopia.