RESPONSE OF RHODES GRASS TO VARIABLE RATE APPLICATION OF IRRIGATION WATER AND FERTILIZER NITROGEN

A field experiment was conducted to study the effects of variable rate application (VRA) of irrigation water and fertilizer nitrogen on the yield of Rhodes grass (Chloris gayana Kunth) under two different management zones (MZ). On a 50 ha field irrigated by center pivot, spilt-split plot design was employed with the MZ as two main treatments, the four irrigation levels (I1-100%, I2-80%, I3-60% and I4-40% of crop evapotranspiration [ETc]) as sub-treatments and five fertilizer nitrogen levels (F1-240, F2-480, F3-720, F4-960 and F5-1200 kg ha(-1)) as sub-sub treatments. The mean cumulative Rhodes grass hay yield across three harvests (made in July, September and November 2012) was significantly higher in MZ-2 (24.47 t ha(-1) per harvest) than in MZ-1 (21.78 t ha(-1)). Deficit irrigation was found to be a suitable water saving strategy in both the management zones. Across the two zones, irrigation at 80% ETc resulted in the highest mean hay yields in first and second harvests (7.58 and 8.77 t ha(-1), respectively), while irrigation at 60% ETc resulted in highest hay yield in the third harvest (8.59 t ha(-1)). By increasing the nitrogen level from 240 to 480 kg ha(-1), the cumulative hay yield of the three harvests was increased from 21.70 to 22.18 t ha(-1) (i.e. increase of 2.21%) in MZ-1 and from 22.75 to 25.38 t ha(-1) (i.e. increase of 11.56%) in MZ-2, indicating the benefit of VRA of fertilizer nitrogen. Rhodes grass showed differential response to various combinations of irrigation and fertilizer nitrogen levels. A combination of I2-F2 resulted in the highest cumulative Rhodes grass hay yield in both MZ-1 (24.70 t ha(-1)) and MZ-2 (27.78 t ha(-1)). Precision fertigation, involving deficit irrigation at 80% ETc and adopting VRA technology for fertilizer application can be beneficial strategy for enhancing water and fertilizer nitrogen use efficiency for optimal Rhodes grass production.