Influence of Irrigation on the Yield and Persistence of Forage Legumes1

Abstract The primary purpose of this study was to investigate the effect of irrigation on the yield and persistence of certain legumes as related to disease incidence. The effect of irrigation on the yield of three alfalfa (Medicago sativa L.) varieties, crownvetch (Coronilla varia L.), and ladino clover (Trifolium repens L.) was studied in the field over a 2‐year period. The nonirrigated plants received natural precipitation, whereas the irrigated legumes were supplied with supplemental water in addition to the rainfall whenever soil moisture was depleted to approximately 50% of the available water‐holding capacity. At the first harvest after irrigation in the 1st year, superior growth of all legumes was obtained by the use of supplemental water. The benefits of irrigation to some species and varieties ended at this point. Yields of alfalfa were sharply reduced in mid‐ and late summer of the 2nd year as a result of irrigation. Irrigation of the three alfalfa varieties resulted in an overall decrease in yield of 76% at the last harvest. The alfalfa varieties responded differentially to irrigation. Most of the stand of crownvetch was lost following the first cut on the irrigated plots. In contrast to other legumes, irrigation increased the yields of ladino clover by approximately 19%. Severe infestation by several diseases was probably a primary factor in the severe stand loss and low yields of alfalfa and crownvetch under irrigation. Excessive soil moisture due to precipitation soon after irrigation also possibly contributed to the loss of alfalfa stands.