Abstract

Utilization of deep-rooted crops in rotation can improve the overall water and N use efficiencies of cropping systems, and minimize nitrate leaching to groundwater. Safflower (Carthamus tinctorius L.) is the deepest-rooted annual crop grown in California. Response to residual soil N and consumptive water use (0 to 2.7 m) by safflower was evaluated in field plots previously used for cotton trials, and treated with nine fertilizer N rates (0 to 230 kg N/ha) over a nine year period. Pre-plant residual soil NO₃ (0 to 2.7 m) increased with increasing cotton N fertilization rates. Safflower responded favorably to prior cotton N fertilization and available residual N. Seed yield rose from 1,700 kg ha^-1 in the unfertilized control to 2,200 kg ha^-1 but declined to 1,800 kg ha^-1 at the highest residual N level. Oil percent and oil yield were not affected by soil N except at the highest residual N level. Consumptive water use, when adjusted for spatial variability by covariate analysis, increased with increasing residual N levels. Seed yield also increased with water use at a rate of 4.8 kg seed mm^-1 of water used. The use of residual N can result in economic safflower yields and should be considered in growers N management programs, provided that enough water is available to the crop.

Key words: Safflower, residual nitrogen, water use, seed yield, oil yield, oil quality