Alfalfa forage production under solid-set sprinkler irrigation in a semiarid climate

Abstract

Under sprinkler irrigation, local environmental conditions have an important influence on irrigation water losses, plant physiological changes and uniformity of irrigation, leading to different crop water production functions. We studied during three years the effect of irrigation depth on the plant growth, forage yield and N content, evapotranspiration and water use efficiency of an alfalfa (Medicago sativa L.) crop irrigated with a commercial solid-set sprinkler system in a semiarid Mediterranean climate. Six irrigation treatments were tested: 55%, 75%, 85%, 100%, 115% and 130% of the theoretical crop irrigation requirement (CIRt), calculated without considering water losses or non-uniformity. The seasonal irrigation amount applied at the 100% of CIRt ranged from 598 to 786mm. The intercepted photosynthetically active radiation increased as the irrigation applied increased until the 115% of CIRt. Plant height at harvest linearly increased as the irrigation applied increased until the 130% of CIRt in two years. The maximum alfalfa forage yield was lower the first year (17Mgha−1) than in the two following years (20–22Mgha−1). The alfalfa forage yield increased linearly as the irrigation applied increased the first year of the experiment, but in the following two years this increase occurred until the irrigation applied was 115% of CIRt. The N content of alfalfa linearly decreased as the irrigation applied increased. The relationship between alfalfa forage yield and evapotranspiration was linear until the 115% of CIRt all years. The WUE of alfalfa was lower the first year of the experiment and was not affected by the irrigation applied in the rainiest year, but linearly increased as the irrigation applied increased up to 115% of CIRt in the other two years. Considering yield and quality (N content) of alfalfa forage and WUE, sprinkler irrigation with a solid-set system must be increased by 15% over the CIRt to optimize alfalfa forage production under the climatic conditions of the Ebro valley.