INFLUENCE OF IRRIGATION ON DRY-MATTER PRODUCTION, LEAF COMPOSITION, AND NUTRIENT REMOVAL BY TURNIP

Irrigation scheduling of leafy greens generally consists of applying 1 9 mm of water every four days, which leads to irrigation depths that e xceed the soil water deficit, and requires fertilizer applications hig her than recommended rates. We determined the influence of irrigation scheduled by class A pan evaporation and a variable crop factor on lea f tissue composition and nutrient removal by turnips using a continuou s moisture gradient and different N fertilizer conditions. Irrigation maintained foliar concentrations of N, P, K, Ca, and Mg in the suffici ency range. During dry periods, increasing irrigation increased P, dec reased Mg, and had little effect on N, Ca, or K foliar concentrations. Micronutrient concentrations in the leaves responded to irrigation ra tes, but within a narrow range. Excessive water applications, due to r ainfall or to irrigation rates higher than the model rate, consistentl y reduced nutrient crop removal. Since a combination of water applicat ions that did not exceed soil water deficit and current fertilizer app lications maintained adequate nutrient status and maximized nutrient c rop removal, apparent need for N fertilization in excess of the recomm ended rate for turnips is due to excessive water applications.