Abstract
Field experiments with a high-yielding white-kernel hybrid corn. Funk's G-795W, were conducted on four typical soils of Puerto Rico: two Oxisols (Bayamón sandy loam at Manatí and Catalina clay at Barranquitas) and two Ultisols (Humatas clay at Corozal and Torres clay at Cidra). The main objectives of this study were to determine the yield potential and the optimum level of N fertilizer for this hybrid in these soils. Auxiliary objectives were to determine the N supplying power of these soils and the apparent recovery of fertilizer N by the crop. High corn yields (8.4 tons/ha) were obtained on the Humatas clay with 60 to 120 kg/ha of N fertilizer. Only 5.4 tons/ha of corn were obtained on Bayamón sandy loam at the same rate of fertilization. Apparent N recoveries were 60 to 72% at these rates. Grain/stover ratios averaged 1.20 on Humatas and only 0.72 on Bayamón. The low grain/stover ratio and the lower grain yields at this site probably could be attributed to late planting and the damage done to the plants by Helminthosporium maydis. There were no yield or N uptake responses to applied N fertilizer on the nonirrigated Catalina and Torres soils. A severe drought reduced stover yields to less than half of those of the irrigated treatments. Maximum nonirrigated grain yields on these soils (4.8 tons/ha) were well below the 8.3 tons/ha obtained on Humatas. The N supplying power of these soils was enough to provide 70 to 90 kg/ha of plant N.