AbstractThe effect of rate and timing of N applications on yield, nutrient uptake, and other characteristics was studied in grain sorghum grown on an Oxisol in northwestern Puerto Rico. Studies of the soil nutrient status revealed a 30% Al saturation and rather low Ca, Mg, and K levels. Leaf N content was significantly lower in plants from unfertilized than from fertilized plots. Significant differences by treatment were also noted for leaf content of P, K, Ca, and Mn, but no consistent pattern could be detected. Flowering was significantly delayed in plants not given N. Threshing percentage was not affected by N treatments. Crude protein levels in the grain were higher with split applications of N than with single applications. The Capó fertilizer-yield equation fit the grain yield data fairly well and could be used to predict yields from the amount of N fertilizer applied. Near maximum yields were obtained with applications of fertilizer N at 56 kg/ha. In some cases, more than 70% of the fertilizer N was recovered.
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