Explorando as relações antagônicas entre nitrogênio, potássio e boro na adubação do algodoeiro em solos arenosos e argilosos

Abstract

Balanced fertilization is necessary to improve nutrient use efficiency. However, it is not yet known whether better nutrition with boron can reduce the dose of nitrogen and potassium in cotton and if this is dependent on the production environment, mainly in relation to soil texture. The objective of the study was to evaluate the nutrition, yield and fiber quality of cotton as a function of nitrogen and potassium doses in different boron availability in sandy and clayey soil environments. Boron doses of 1.5 and 3.0 kg ha-1, nitrogen between 0 and 210 kg ha-1 and potassium between 0 and 183 kg ha-1 were applied. Better nutrition with boron reduced the need for nitrogen and potassium by the cotton plant, especially in environments with sandy soils with low boron content (less than 0.3 mg dm-3), in this occasion it was possible to reach yield above 1500 kg ha-1 of fiber with only 70 and 50 kg ha-1 of N and K, respectively. When the boron content in the soil was higher than 0.3 mg dm-3, increasing the B dose was not beneficial (regardless of the soil texture). In clayey soil environments with yields above 2000 kg ha-1 of fiber there was a tendency to increase the N requirement when the K dose was higher than 100 kg ha-1, and the highest yields were with doses of 70 kg ha-1 of N and between 50 and 100 kg ha-1 of K. In the irrigated area with high yield, the N content in the leaves was higher than 49 g kg-1. Boll weight increased due to better potassium nutrition, but increasing the dose of B to 3 kg ha-1 in a rainfed environment with high yield potential, it is possible to obtain a higher average boll weight with lower doses of K (100 kg ha-1), as well as in an environment of lower yield potential and sandy soils, it is possible to obtain a higher number of bolls using intermediate doses of N (140 kg ha-1) when increasing the dose of B. Potassium, nitrogen and boron directly affect the fiber quality of the cotton plant, but it depends on the production environment. The effect of increasing boron fertilization to reduce the need for N and K occurs only in sandy soils with low boron content and when cotton was grown in high fertility soil, high doses of K increase the need for N without benefiting the crop yield and fiber quality.