Effectiveness of cattle manure and nitrogen fertilizer application on the agronomic and economic performance of maize

The effects of N fertilizer and aerobically composted cattle manure, applied separately or in combination, on maize (Zea mays L.) grain yields and net benefits were determined over three seasons. A field experiment was established on a moderately leached sandy loam soil (Typic Kandiustalf). Manure was a poor source of N. In the first year, increase in grain yield was much higher when manure (12.5 t ha-1 and 37.5 t ha-1) was combined with the 60 kg N ha-1 mineral N rate (40% and 25.1%, respectively), and a relatively smaller further increase of 17.5% was recorded for the 37.5 t ha-1 rate while there was a decrease of 3.7% for the 12.5 t ha-1 rate, when mineral N rate was doubled to 120 kg N ha-1. In the third season increase in grain yield was also much higher when manure (12.5 t ha-1 and 37.5 t ha-1) was combined with the 60 kg N ha-1 mineral N rate (66.2% and 16%, respectively) and relatively smaller further increases were recorded when the mineral N rate was doubled to 120 kg N ha-1 (21.4% and 15.1%, respectively). Net benefit indications are that residual effects of cattle manure last for at least three seasons and thus farmers could apply up to 40 t ha-1 in the first season and benefit from its residual fertility in subsequent seasons. It was concluded that smallholder farmers in Zimbabwe and other countries of Sub-Saharan Africa could positively exploit the combined application of manure and N fertilizer to increase maize yield and net benefits.