Rhodes grass is cultivated extensively in Saudi Arabia under center pivot sprinkler irrigation system. The research work was carried out to optimize irrigation water and fertilizer nitrogen levels for the crop. The objectives of the study were: (1) to delineate the field into management zones, and (2) to study the effects of variable rate application (VRA) of irrigation water and fertilizer nitrogen on the yield of Rhodes grass. A field experiment was carried out from June to November 2012, on a 50 ha farmer's field irrigated by center pivot. The experimental field was divided into two management zones (MZ). Spilt-split plot design was employed with MZ as two main treatments. Sub-treatments were: irrigation at 100, 80, 60 and 40% crop evapotranspiration (ET_c); and sub-sub treatments were nitrogen fertilizer levels of 240, 480, 720, 960 and 1200 kg/ha. The mean productivity across three cuts was higher in MZ 2 (8.16 t/ha/cut) than in MZ 1 (7.26 t/ha/cut). The effects of treatments were significant in the last two harvests but not in the first harvest. Significant differences between the management zones were observed only with respect to nitrogen levels but not with respect to irrigation levels. However, deficit irrigation was found to be beneficial in both zones. Across the zones, irrigation at 80 and 60% ETc resulted in higher hay yields in second and third harvests, respectively. By increasing the nitrogen level from 240 to 480 kg/ha, the hay yield increased from 7.58 to 8.46 t/ha/harvest, only in MZ 2, indicating the possible benefit of variable rate application of fertilizer nitrogen. Based on this study, the following conclusions can be drawn: (i) deficit irrigation can be adopted for Rhodes grass by irrigating the crop at 80% ET_c for the first two harvests and at 60% ET_c for the last/subsequent harvests. 2. Fertilizer nitrogen use can be optimized by adopting VRA technology.

 

 

Keywords: Irrigation, nitrogen, precision agriculture, Rhodes grass, variable rate application.