Nitrogen Fertilization of Corn and Sorghum Grown in Oxisols and Ultisols in Puerto Rico1

Abstract

AbstractThe requirement of fertilizer N for high yields, its generally high price, and the ever‐present possibility of large leaching losses of inorganic N makes it essential that fertilizer N be managed as efficiently as possible in the humid tropics. Three rates and 2 times of application of fertilizer N were applied to 15 corn (Zea mays L.) and 3 sorghum (Sorghum bicolor Moench) crops on 2 Ultisols and 3 Oxisols during 5 successive growing seasons in Puerto Rico to determine the most effective means of applying fertilizer N to these crops. Additional objectives were to determine the apparent recovery of fertilizer N by the crops; the interrelationships between crop yield, N fertilization and soil inorganic N content; and the effectiveness of slow‐release sulfur‐coated urea as a source of fertilizer N for corn and sorghum. All soils had been under cultivation for at least 50 years and received relatively high rates of fertilizer for the last 20 years.The results indicated that: 1) postplant sidedress applications of fertilizer N resulted on the average in higher yields and plant recovery of fertilizer N than preplant applications; 2) when there were no limiting factors of climate or disease, and there was a response to N, the recovery of postplant applied N was comparable to that observed in temperate areas; 3) maximum corn grain yields were approximately 6.3 metric tons/ha; near‐maximum corn grain yields were obtained with 67 kg/ha of postplant‐applied N; 5) preplant‐applied sulfur‐coated urea was no more effective than preplant urea in increasing yields or N recovery; 6) soil inorganic N content was generally not a good index of soil N supplying power in these soils; 7) drought and disease frequently reduced yields; 8) there was very little residual effect of the fertilizer N applied in this experiment; and 9) the clayey Oxisols and Ultisols in Puerto Rico had a relatively high N‐supplying power.