Inbred Maize response to cover crops and fertilizer-nitrogen

Abstract

Maize (Zea mays L.) inbred seed production fields on the southern semiarid coast of Puerto Rico are usually fallow each year from May to September. Inbreds have lower seed yields than single-cross hybrids, yet producers tend to apply high fertilizer nitrogen (N) levels In efforts to increase yields. Inbred maize response to fertilizer-N was evaluated on the southern semiarid coast of Puerto Rico In a cover crop-maize cropping sequence in 2009, and in a fallow-maize sequence in 2010 in a Fluventic Haplustoll. In general, maize produced after a legume cover crop of velvetbean (Mucuna prurience) or cowpea (Vigna unguiculata 'Iron Clay') had better yields and agronomic traits than maize after the fallow treatment. In 2009, maximum seed yields of 2,726 kg/ha were obtained with fertilizer-N application in the range of 112 to 224 kg N/ha. In 2010, maximum seed yields of 1,447 kg/ha were obtained with fertilizer-N application in the range of 84 to 211 kg N/ha. Harvest index was 0.26 and 0.27 in 2009 and 2010 for all fertilizer-N treatments; higher than that for unfertilized maize. In general, agronomic traits were superior as a result of fertilizer-N application without consistent differences among fertilizer-N levels applied. The SPAD chlorophyll meter, leaf color index and leaf area index were suitable indicators of N status in the maize plants. 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 rates in soils, climatic systems, and maize inbreds similar to the ones tested should be between 84 and 112 kg N/ha. Greater amounts of fertilizer-N will result in decreased economic benefit and potential environmental contamination.