Functions for Cotton (<i>Gossypium hirsutum</i> L.) Production from Irrigation and Nitrogen Fertilization Variables: I. Yield and Evapotranspiration¹

Abstract

Abstract Cotton lint yield, evapotranspiration (ET), and efficiency of water use were characterized with 2nd‐degree polynomials as functions of the quantity of irrigation water and nitrogen applied on two widely different soils. Excessive vegetative plant development at high input levels of irrigation water and nitrogen resulted in production functions for lint yield having negative interaction coefficients. By placing lint yield on a relative basis for the two soils, it was possible to express relative yield as a function of ET with a single quadratic regression equation (R. Y. = −266.4 + 10.72(ET) −0.079(ET) 2 ;R 2 = 0.78). Total seasonal ET increased at a decreasing rate with increased water application up to an addition of 119 cm of water during the entire growing season. Peak daily rates of soil moisture depletion were 1.07 cm, occurring near the time when maximum leaf area was attained. Water use efficiency (kg lint per cm of water used) was improved, in some cases, with the addition of nitrogen.