Lucerne irrigation and soil water use during bloom and seed set on a red-brown earth in south-eastern Australia

Abstract

Lucerne (Medicago sativa L.) cv. WL45 1, grown on a shallow red-brown earth, was subjected to different irrigation frequencies during bloom to determine the effect on seed yield. The highest yield of 1105 kg ha-1 was produced when the crop was irrigated at an accumulated Epan of 75 mm between irrigations. Yields declined to 528 kg ha-1 as the interval between irrigations increased and the total amount of water applied during bloom was reduced as a consequence. Seed yield was positively correlated with total top growth, number of stems, number of racemes with pods and number of seeds per pod. Neither individual seed weight nor number of pods per raceme was influenced by the irrigation treatments. Soil water extraction by the crop was confined mainly to the 0-1.2 m depth. However, highest seed yields were produced when soil water extraction was confined to the 0-0.6 m depth by regular irrigation. About 16% of the available water in the 0.6-1.2 m depth and 89% of the available water in the 1.2-1.8 m depth could not be extracted by the crop. Failure to extract water from the lower subsoil was attributed to soil physical restrictions and lack of adequate root density.