Modeling Maize Response to Mineral Fertilizer on Silty Clay Loam in the Northern Savanna Zone of Ghana Using DSSAT Model

Abstract

Maize has become the most important cereal in northern Ghana serving as cash crop and the main staple for most communities. It is the crop that receives most fertilizer input by farmers in the region, although the recommendations being used are over 20 years old. These recommendations were derived from relationships between crop yields and different applied rates of nutrient obtained from field fertilizer experiments. In most cases the experiments do not take care of the full extent of spatial and temporal variability associated with crop production. In addition the experiments are often very expensive and time consuming as they have to be carried out over many years in varied ecologies to be able to make valid recommendations for a region. Computer simulation model is a useful tool in this regard in reducing cost and time required for such studies, and also taking care of the spatial and temporal variability in the production of the crop. Response of maize to nitrogen in the northern Guinea savanna agro-ecology of Ghana was evaluated using the Seasonal Analysis component of the Decision Support System for Agrotechnoloy Transfer (DSSAT 4.02) – Cropping System Model (CSM). A simulation was performed for crop growth, development and yield of maize run for a site at Nyankpala near the University for Development Studies in the northern savanna agro-ecology. A field trial consisting of five nitrogen rates (0, 30, 60, 90, 120, kg/ha) with 30 kg K₂O and 30 kg P₂O₅/ha was simulated for 24 years using measured daily weather and soil records for the site. The field trial was conducted under rain-fed conditions on a silty clay loam soil (Gleyi-ferric luvisol) in 2006. Quality protein maize (QPM) variety (Obatanpa) was the test crop. The economic analysis of the model took account of weather- and price-related risks, after carrying out a strategic analysis. The results showed that increasing levels of N up to 120 kg/ha increased maize grain yield at a diminishing return. The model accurately simulated maize grain yield up to 90 kg/ha nitrogen application but failed to accurately predict maize grain yield when nitrogen was applied at 120 kg/ha. Excessive water stress induced by high N application negatively affected the growth of maize. Nitrogen was leached most at N application rate of 120 kg/ha. Maize production was not profitable at N application rate ≤ 30 kg/ha on silty clay loam of the Guinea Savannah zone of Ghana. DSSAT-CSM can be used to accurately predict maize growth, development and yield in Ghana if well calibrated.