The Response of Cotton to Fertilizers in Puerto Rico

Abstract

The results of the six fertilizer experiments with cotton carried on at Isabela, Aguirre, and Lajas, from 1943 to 1956, indicated that: 1. Cotton growing in Guayabo fine sand responded to phosphate and potash fertilizers. The use of 1,000 pounds of 5-10-10 per acre was recommended for this soil. 2. The use of nitrogen at 82 pounds per acre produced the only significant response to fertilizers for a Coto clay. 3. Cotton growing in Altura loam responded significantly only to applications of 100 pounds of nitrogen per acre. 4. Cotton growing on a Santa Isabel silty clay loam did not respond to nitrogen, phosphates, nor potash fertilizers. 5. The fertilizer demands of cotton growing in Santa Isabel clay appeared to be highest for nitrogen and phosphates, with no response to potash. The intensity of these needs varied somewhat with the cotton variety planted. 6. Leaf-blade rather than the petiole tissue was found to be most reliable for foliar analyses in determining the appropriate levels of nitrogen, phosphorus, and potassium in the plant tissue. 7. Leaf samples taken 45 days after planting revealed the greatest difference in response to fertilizers as compared to 60 and 90 days. 8. For tentative use as leaf standards for Sea Island cotton: It is suggested that leaf blades containing, on a dry weight basis at 45 days after planting, above 5.00 percent of nitrogen should show no response to additional nitrogen; above 0.40 percent of phosphorus, no response to phosphates; and, above 3.20 percent of potassium, no response to potash.