Supply and uptake of urea 15N by rice.
1988
Lu W. | Lindau C.W. | Patrick W.H.
Air-dried soil (2.2 kg) ground to pass through or 1-mm mesh sieve was placed in polyvinyl chloride (PVC) pots (20 cm long and 15 cm internal diameter). Deionized H2O containing 0.15 g P/kg soil and 0.20 g K/kg soil was added to establish water depth of 2-4 cm. Three 20-d-old Lemont seedlings previously grown in a sand culture were transplanted into each of 20 pots. Four N treatments were applied using urea 15N (29.991 atom %) at 0.44 g urea N/pot. Urea-15N solutions were injected into the rice root zone. Each N treatment, including control, was replicated four times. At harvest, each pot was destructively sampled and total Kjeldahl N and 15N content determined on soil and plant components (roots, shoots, grain). Plant recovery of applied urea-15N was from 5-8% in the roots, 10-15% in the shoots, and 22-29% in the grain. Total plant 15N recovery was 38-51%; highest recovery was with treatment 3. Control grain yields were significantly different from those of the N treatments. About 60% of the 15N taken up by the rice plant was in the grain. 15N remaining in the soil after harvest ranged from 14 to 24%. About 34% of the 15N applied was unaccounted for. The two sources of N to rice are soil N (% NdfS) and fertilizer N (% NdfS). In treatment 1, plant N was 69% NdsF and 31% NdfF; in treatment 2, 65% NdfS and 35% NdfF; in treatment 3, 67% NdfS and 33% NdfF; and in treatment 4, 64% NdfS and 36% NdfF. Rice uptake of fertilizer N was significantly correlated with grain yield (r = 0.634* ).
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