Economically Optimal N Fertilizer Rates for Maize Produced on Vertisol and Inceptisol Soils under No-Till Management: A Case Study in Maphutseng, Lesotho

Aims: To determine differences in maize yields, optimal nitrogen (N) rates, and profitability on contrasting soil types and no-till and till management.

Study Design: Randomized block design field trials involving no-tillage and tillage practices were conducted on contrasting soil types (vertisols and inceptisols) to investigate the effect of N fertilizer rates on maize (Zea mays) grain yield.

Place and Duration of Study: Mohale’s Hoek District, Maphutseng, Lesotho over the 2012/2013 agricultural year.

Methodology: Maize response to N was estimated with a linear response plateau function. Economically optimum N rates were estimated for both soil types and tillage practices assuming typical corn and N fertilizer prices for the 2012/2013 agricultural marketing year.

Results: The economically optimal N rates were estimated at 141 kg of N ha-1 with a predicted maize grain yield of 7.75 tons ha-1 for no-till vertisol maize system, 150 kg of N ha-1 with a predicted maize grain yield of 4.90 tons ha-1 for no-till inceptisol maize system, and 73 kg of N ha-1 with a predicted maize grain yield of 7.37 tons ha-1 for the till vertisol maize system. A Monte Carlo analysis suggests these findings are robust to N cost, maize prices, and sampling uncertainty.

Conclusion: Findings of this study suggest that if other production factors remained constant, farmers in Lesotho - a country where access to commercial fertilizer is limited and average fertilizer N use is less than 25 kg ha-1 - would need to increase significantly their N fertilizer rates to meet their food needs.