Inbred Maize Response to Cover Crops and Nitrogen Fertilization In Puerto Rico.

Maize (Zea mays L.) inbred seed production in the southern semiarid coast of Puerto Rico occurs from October to April and fields are usually fallow the rest of the year. Crop yields and nutrient use efficiencies are traditionally lower for inbreds, yet there is a tendency for producers to over fertilize with N.  Inbred maize response to fertilizer-N was evaluated in a covercrop-maize cropping sequence in 2009 and in a fallow-corn sequence in 2010 in a Fluventic Haplustoll. In 2009, previous covercrop of mucuna or cowpea improved grain yields as compared to fallow treatment.  In general, previous cover-cropping improved some crop agronomic indicators, but the results were not consistent. In 2009, optimum grain yields were obtained with 112 kg N/ha with a mean grain yield of 2,726 kg/ha for fertilizer-N in the range of 112 to 224 kg N/ha.  In 2010, optimum grain yields were obtained with 84 kg N/ha with a mean grain yield of 1,447 kg/ha for fertilizer-N in the range of 84 to 211 kg N/ha in 2010. Harvest index was 0.26 and 0.27 in 2009 and 2010 for all fertilizer-N treatments, and higher than unfertilized maize.  In general, agronomic production indicators were higher as a result of fertilizer-N application without consistent differences among fertilizer-N treatments. Highest N use efficiencies were observed for the 112 kg N/ha and 84 kg N/ha fertilizer levels, for 2009 and 2010, respectively, and decreased with increasing fertilizer-N applied. Fertilizer-N management in similar soils, climatic systems, and maize in-breds as the ones tested should be between 84 and 112 kg N/ha. Higher fertilizer-N rates will result in decreased economic benefit and potential environmental degradation.