Effects of regulated deficit irrigation on water consumption, hay yield and quality of alfalfa under subsurface drip irrigation

Abstract: Subsurface drip irrigation (SDI) and regulated deficit irrigation（RDI）are two of the most water-saving irrigation technologies nowadays. In order to study effects of regulated deficit irrigation on forage water consumption, hay yield and quality of alfalfa under subsurface drip irrigation, a field experiment was carried out in 2012 at Shiyang River Drainage Basin, northwest of China. Alfalfa used for the experiment is the second cutting of the establishment year, and the cutting is separated into 3 periods, including pre-branching period, branching period and squaring period. There are seven irrigation treatments in the experiment design. Four of the seven treatments are regulated in whole growth period, lower irrigation limits respectively 70% FC (field capacity)、60% FC (field capacity)、50% FC (field capacity)、40% FC (field capacity), and three are regulated in different growth periods, lower irrigation limits of pre-branching period, branching period and squaring period of different treatment respectively (50%, 50%, 70%)FC, (60%, 60%, 70%)FC, (70%, 70%, 50%)FC. When the soil water content arrives to the designed lower irrigation limit, each plot starts to irrigate. Irrigation amount is 20mm every time. According to these treatments, the effect on water consumption, hay yield and quality of alfalfa of regulated deficit irrigation (RDI) under subsurface drip irrigation(SDI) are studied. The results show with the deterioration of the water deficit degree, alfalfa yield, water consumption, stem/leaf ratio and yield of crude protein (CP) decrease while WUE (water use efficiency) and content of the crude protein (CP) increase， and 60%FC is a critical value. When the lower irrigation limits are higher than 60%FC, hay yield of alfalfa decrease non-significantly, however, when lower than 60%FC, hay yield decrease significantly. While RDI (regulated deficit irrigation) is taken in the whole growth period, squaring period>branching period>pre-branching period appears in water consumption rate during different periods of alfalfa. And this law is more and more significant with the increasing of the water deficit degree. When RDI (regulated deficit irrigation) is taken in branching period, water consumption rate of alfalfa have apparent compensation effect after sufficient irrigation in squaring period. Compared with regulating deficit in squaring period, taking RDI (regulated deficit irrigation) in pre-branching and branching period is more conducive to improve alfalfa quality by reducing stem/leaf ratio and improving content of crude protein (CP) and yield of crude protein. When lower irrigation limits of pre-branching period, branching period and squaring period are 60%FC, 60%FC and 70%FC respectively, alfalfa has the highest crude protein yield (846.11kg/hm2). This study reveals the effects of RDI on water consumption, yield and quality of alfalfa under SDI and provides an experimental base of high quality, high yield and water saving in alfalfa industry in arid areas.