Dry Matter Production and Nutrient Uptake in Irrigated Cotton (Gossypium hirsutum)1

Abstract Dry‐matter production of cotton (Gossypium hirsutum L.) plants in the irrigated San Joaquin Valley of California was slow for 40 to 80 days following seeding, with only 2 to 4% of the total seasonal aerial dry matter present at time of first square, and 7 to 10% at time of first flower (one‐fourth to one‐tenth of the percentages reported elsewhere for these stages). One‐third of the total seasonal dry matter was produced in a 2‐week period in August. Total dry matter ranged from 6,900 to 8,900 kg/ha, distributed in mature plants as stems, 23.1%; leaves, 17.4%; burs, 16.3%; seed, 25.3%; and lint, 17.9%. The proportion of lint was at least 50% higher than reported from early research in other areas. Amounts of N, P, K, Ca, Mg, and Na accumulated in the aboveground parts at first flower were less than 15% of the final amounts. Of total seasonal uptake, 45% of N and P occurred in July, and 67% of K in the 6 weeks beginning July 1. During these peak absorption periods, daily uptake per hectare was 1.5 to 2.0 kg N, 0.17 to 0.34 kg P, and 2.1 to 3.4 kg K. Mature plants contained 142 kg N, 19 kg P, and 127 kg K per hectare. About 70 kg N, 11 kg P, and 21 kg K per hectare were contained in the seed. The amount of dry matter needed to produce 100 units lint contained 10 units N, 1.5 P, and 9 K. More than half of the N and P was in seed, and more than one‐third of the K was in the bur.