Soil aeration and relationship to inorganic nitrogen during aerobic cultivation of irrigated rice on a consolidated land parcel
Girsang, Setia S. | Correa, Teodoro Q. | Quilty, James R. | Sanchez, Pearl B. | Buresh, R. J.
Efficient use of irrigation water in Asia can be achieved through production of rice (Oryza sativa L.) on aerobic soil rather than submerged, anaerobic soil. Rice grown on aerobic soil is referred to as aerobic rice. The irrigation of aerobic rice without soil submergence might result in fluctuations and spatial variability in soil aeration, which can affect N transformations. We examined variability in soil aeration and inorganic N during the vegetative and ripening growth phases of aerobic rice grown on one 3.3-ha parcel with frequent irrigation using an overhead sprinkler to maintain soil water potential not less than −10 kPa without soil submergence. Water-filled pore space (WFPS) of soil ranged from 70–96% at 36 locations. The WFPS was inversely related to sand content (r = –0.66, P < 0.001). Soil ammonium-N was unrelated to WFPS, but nitrate-N was inversely related to WFPS (r = –0.84, P < 0.001) and directly related to sand content (r = 0.67, P < 0.001). The WFPS during production of aerobic rice favored nitrate accumulation at only some locations in the 3.3-ha parcel. Rice yield was inversely related to nitrate-N (P < 0.001). Nitrate-N, originating from both soil and fertilizer N, accumulated and exceeded ammonium-N at ≤77 % WFPS. Nitrate-N was small and < ammonium-N at>90 % WFPS, presumably due to N loss by denitrification. Precise irrigation of aerobic rice did not prevent spatial variability in soil aeration and nitrate, which was associated with inherent soil properties such as sand content.
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