Birdsfoot Trefoil Seed Production: I. Crop‐Water Requirements and Response to Irrigation

Abstract

Forage legume seed crop reproduction can be modified by regulating soil-water availability. However, responses to water stress differ for each spedes, so a single optimal water management strategy is not available for all crops. The objectives of this research were to determine the crop-water requirements and the optimal water management conditions for birdsfoot trefoil (Lotus corniculatus L.) when grown for seed production under humid temperate marine climatic conditions of western Oregon, USA. The experiment was conducted on a Woodburn silt loam soil (fine-silty, mixed, mesic Aquultic Argixeroll) near Corvallis. Four single-application treatments varying in water depletion percentage (30 and 60% of field capacity) and replenishment amount (50 and 100% of amount depleted) were applied in 1994 and 1995. A low-stress treatment (LS) that received two to three applications per week of the amount depleted since the last application and a non-irrigated control were also investigated in 1994, 1995, and 1996. Increasing amounts of applied water resulted in increased seasonal crop evapotranspiration (ET C ) with plants grown under low-stress having the greatest ET C and non-irrigated control plants the least (r = 0.91). The fraction of available soil water used by non-irrigated plants was greatest and the LS treatment the least of all treatments. For non-irrigated conditions, the crop-water requirement ranged from 240 to 255 mm. Soil-water conditions favorable for high vegetative development were opposite of the conditions for optimal seed yield water-use efficiency, Unlike other forage legume seed crops, birdsfoot trefoil grown under these conditions required minimal or no supplemental irrigation to achieve maximal seed yield.