Red Clover Seed Production: I. Crop Water Requirements and Irrigation Timing

Abstract

Information about water management and crop stress response for red clover (Trifolium pratense L.) seed production is limited. This study determined red clover seed crop water requirements and evaluated crop water stress index (CWSI) and fraction of available soil‐water used for timing supplemental irrigation. Experiments were conducted at Corvallis, OR, on a Woodburn silt loam (fine‐silty, mixed, mesic Aquultic Argixeroll) in 1990 and 1991. Six irrigation treatments were used to assess within‐ and between‐crop season water requirements. As a consequence of root disease in 1991, the fraction of availables oil water used by plants in the different treatments was generally less in 1991 than 1990. Also, seed production water‐use efficiency was lower in 1991 than 1990. Two distinct non‐stressed baselines for canopy‐air temperature differences versus vapor pressure deficit were identified that were related to increasing leaf senescence and crop aging. The CWSI values across all treatments were negatively associated with plant water potentials (r = −0.87). The CWSI values were similar within similar treatments in both years indicating that root rot damage rather than available soil‐water was limiting plant water uptake in 1991. The CWSI generally increased faster than fraction of available soil‐water used. Unlike fraction of available soil‐water used, CWSI integrated the total plant environment, detecting changes due to root disease in 1991. Under the conditions of this experiment, a single irrigation filling the actives oil profile at CWSI ≈0.28 substantially increased seed yield compared with the nonirrigated control. The CWSI was a useful indicator of red clover water stress status and can be used to schedule clover seed irrigations under typical western Oregon climatic conditions.