Response of maize to ammonium nitrate, urea and cogranulated urea-urea phosphate

Urea fertilizers may lose N by ammonia volatilization when applied in the field. In order to reduce this loss, modified urea compounds are being used. Not all of them reduce ammonia loss and improve crop yields. A field study was conducted to evaluate the comparative advantage of cogranulated urea-urea phosphate (340 g N kg−1, 73 g P kg−1) over urea (460 g N kg−1) and ammonium nitrate (350 g N kg−1) when supplied as nitrogen fertilizers to maize. The fertilizer granules were applied at rates of 67, 134 and 202 kg N ha−1, as surface-broadcast or soil-incorporated treatments. Fertilizer application increased crop yields and nitrogen uptake, but the sources were not significantly different from each other. Increasing nitrogen supply up to 134 kg N ha−1 improved maize yield and nitrogen uptake. Incorporating the fertilizer with the soil was not better than surface application. The data available suggest that maize responded to cogranulated urea-urea phosphate, urea and ammonium nitrate similarly.