Red Clover Seed Production: II. Plant Water Status on Yield and Yield Components

Abstract

Limited information on crop water stress response is available for red clover (Trifolium pratense L.) seed production. The purpose of this study was to quantify the effects of plant water status on red clover flower production, seed yield, and seed yield components. Five supplemental irrigation treatments were applied in 1990 and 1991 to first and second year red clover grown on a Woodburn silt loam (fine‐silty, mixed, mesic Aquultic Argixeroll) near Corvallis, OR. A nonirrigated control was also maintained. Increased plant water stress reduced the duration of season‐long bud and flower production, stem length, potential seed yield, and seed yield. Application of water soon after haying increased total above‐ground phytomass but increased seed yield less than watering at peak flowering. Root deterioration from a root and crown rot disease complex reduced second‐year seed yield. Root rot index increased with increased levels of plant water stress, indicating that supplemental water applications reduced root rot severity. The reduction in seed yield resulting from increased plant water stress was primarily caused by a decrease in floral fertility, and less conclusively, by reductions in flower number per unit area. One irrigation filling the active soil profile during peak flowering provided adequate water to maintain seed production and achieve high water‐use efficiency. Contrary to popular belief, it was shown that red clover was not adversely affected by high levels of available soil water in a well drained soil. Also, yield losses to root disease in the second year of seed production can be greatly reduced by supplemental irrigation compared to non‐irrigated clover.