Nitrogen and phosphorus fertilization on the cotton crop

Abstract

A study was carried out on 17 factorial 4 x 4 experiments in order to stablish the optimum levels of P and N for cotton (Gossypium hirsutum L.) variety IAC-13.1. The levels of N and P₂O₅ applied were 0-20-40-60 kg/ha and 0-30-60-90 kg/ha, respectively. The results can be grouped in two types of soils: 1) Soils with less than 5 ppm of P, which respond only to P levels; II) Soils with more than 10 ppm of P, which respond positively to both, N and P levels. The results showed no N x P interaction. The response to the N levels were quadratic in both types of soils, although it showed significance only for soils with more than 10 ppm of P (type-II). The response to the P levels were quadratic for the soil type I, and linear for type II soil, and showed significant for both soils. The results for production were ajusted through a multiple regression equation. The coefficients of determination were 0.76 and 0.81 for soil type I and II, respectively. The response surface was calculated and isoquant maps were drawn. The maximum yields attained were 1,519 and 3,197 kg/ha by adjusting groups I and II, respectively. Based on the price of Cr$ 43.00 per kg of the cotton-in-seed the economic level of fertilizing the soil would be 40 kg/ha of N and 181 kg/ha of P for type II soil. For type I soil, the maximum economic level would be 20 kg/ha of N and 70 kg/ha of P. An economic study is also estimated for these levels of inputs.