Effects of Nitrogen and Carbon Application on Maize Output in Ntcheu and Dedza Districts of Central Malawi

摘要

This paper uses a translog stochastic frontier model to estimate the relationship between maize yield and an interplay of soil carbon, soil nitrogen and inorganic nitrogen fertilizer using plot-level data collected from smallholder farmers in Dedza and Ntcheu Districts of Malawi in 2013/2014 growing season. One of the covariates in the model is nitrogen applied to a plot from inorganic fertilizers. Farmer use of nitrogen is influenced through participation in a non-random targeted Farm Inputs Subsidy Program (FISP) of the Malawi Government. A control function approach is therefore applied to correct for possible endogeneity of participation in the FISP.Results show that inorganic nitrogen fertilizer has significant positive effect on maize output whereas an increase in soil carbon is associated with low maize output but interaction between soil carbon and soil nitrogen as well as with inorganic nitrogen significantly increases maize output. These results seem to be linked to Carbon to Nitrogen (C:N) ratio in the soil. The accumulation of C beyond the optimal C:N ratio is known to reduce rate of decomposition, nutrient cycling, shoot: root ratio and biomass in grasses including maize. Under such circumstances, increasing nitrogen brings the C:N ratio to beneficial levels. The results further show that inorganic nitrogen is a substitute to labour, seed and land. The substitution relationship suggests that improvements in inorganic nitrogen require reduction in labour, seed use and land. It has further been shown that only 45.03% of the plots have marginal value cost ratios of greater than one which shows that considerable number of plots are not profitable. For 66.20% of the plots, applied inorganic nitrogen fertilizer exceeds optimal levels signifying suboptimal use of the input. The results suggest that inorganic nitrogen is profitable at low levels of application which is largely due to prevailing high nitrogen-maize price ratio. The prominent issue for policy consideration from these results is that soils in Malawi are depleted of nitrogen leading to unfavorably high C:N ratios which negatively impact maize production. Given that nitrogen-maize price ratio is already high in Malawi, farmers will need programs that enhance their access to nitrogen fertilizers at low prices for nitrogen fertilizer application to be profitable. Such programs need to be implemented simultaneously with a package of intensification practices that fix and retain nitrogen in the soil.