Towards sustainable agricultural land use in Nepal: The role of irrigation and fertilizer application

Rice, wheat, and maize are the most important staple food crops in Nepal. Due to the complex topography and climate of the country, and a lack of agricultural inputs, the productivity of the crops has remained low over the last decades, with only moderate increases in recent years. National production cannot meet the national demand for the three crops, and food imports are necessary to close the gap. Climate and demographic change will most likely exacerbate the problem. It is therefore an objective of the Nepalese government to develop strategies to increase the productivity of the crops permanently and sustainably. A first step in this endeavour is to analyse the existing yield gap and how it may be closed, for which we use the biogeophysical crop model EPIC. We divided Nepal into 3430 homogeneous simulation units (based on climate, altitude, soil, and slope class, overlaid by district boundaries) and simulated current management practices on all units for the years 2000-2014. We then compared the resulting yields to crop production data from the Nepalese Ministry of Agricultural Development and calibrated the model until a good fit was achieved. Subsequently, we estimated maximum potential yields by simulating crop growth without nutrient or water stress, and lastly determined the yield gaps by subtracting the yields under current management practices from the maximum potential yields. We found considerable yield gaps for all three crops 2 t/ha for rice, 4 t/ha for wheat, and 4 t/ha for maize. If we compared the yield gaps between current yields and yields simulated without nutrient stress, but under rainfed conditions, the gaps were smaller, indicating that increasing fertilizer application rates should be the first step in closing the yield gap. However, due to the complicated topography of Nepal, yields and yield gaps of the crops vary considerably between regions, and measures to close the gaps will have to be customized to local conditions. This includes expanding the irrigated area in the lowland Terai regions and valleys in hilly areas where precipitation patterns change and temperature increase under climate change. The findings of this study may support policy-makers in their goal to increase grain production and ensure food security in Nepal.

 

Keywords: yield gap, water management, climate change adaptation