Alfalfa canopy water interception under low-pressure sprinklers

Canopy water interception is an important factor in water use efficiency analysis and sprinkler-based fertigation technique development. In the present study, alfalfa canopy water interception and its influence factors were assessed under low wind conditions. The canopy interception capacity for three growth stages of alfalfa (S1, early vegetative stage; S2, late vegetative stage; S3, bud stage) were measured under two types of low-pressure spray sprinklers. The dynamics of canopy interception and interception ratio with irrigation depth were also observed. The total irrigation depth for all measurements was around 8 mm. A weight-based canopy interception measurement device was installed outdoors and integrated with a 20-psi sprinkler at 1 m above the canopy. The alfalfa canopy interception first increased rapidly with irrigation depth, but then stabilized and reached canopy interception capacity (Im). The minimum irrigation depths to achieve the Im values were 2 mm, 3 mm, and 4 mm at the S1, S2 and S3 stages, respectively. Im increased significantly across growth stages, and ranged from 0.46 mm to 1.49 mm. Interception ratio decreased gradually as irrigation depth increased. With an approximately 8-mm total irrigation depth, interception ratio ranged from 5.27 % to 17.59 % over all growth stages. Water application rate had no effect on Im, and Im decreased with droplet diameter. Generally, Im was higher and reached more quickly with the R3000 sprinkler compared to the D3000 sprinkler. Fresh weight, plant height, and LAI of alfalfa had significant positive correlations with canopy interception capacity, and a quadratic regression model was developed with using plant height as a factor. This study provides valuable and basic information for irrigation schedules and fertigation in alfalfa cultivation.