15N point placement technique: a new technique for investigating uptake, distribution, and losses of nitrogen in irrigated rice
2004
Sheehy, J.E. | Pablico, P.P. | Mnzava, M.N.W. | Robles, R.P.,International Rice Research Inst., Los Banos, 4030 Laguna (Philippines)
The techniques delivers a small amount of urea 15N adjacent to the roots of a rice plant in a few minutes. The amount of 15N delivered is equivalent to 4-8 h of the daily N uptake of a rice plant. 15N was placed in a gelatin capsule attached to a wooden handle and the capsule was inserted into 5 cm soil depth beneath the rice plant. The gelatin capsule dissolved in a few minutes. The plants were harvested at varying intervals until maturity and their 15N content measured. The uptake of 15N followed an exponential pattern and it took 14 d to reach a maximum of about 65 percent of the initial quantity supplied. The time to reach maximum uptake was unexpectedly slow and a simple theory was developed to understand the processes governing the uptake and loss of 15N. There were no differences between application made at the soil surface and those made 5 cm below the surface. The technique worked very well for tracking the fate of N acquired by the plant at different growth stages. For example, 14 d after application at 10 d after transplanting (DAT) 66 percent of the labelled N acquired by the plant was found in the leaves, 20 percent was in the culms and sheaths and 5 percent was in the roots. About 37 percent of the labelled N supplied at 10 DAT was located in the grain at maturity. The findings suggest that the technique can be used to describe the N dynamic of irrigated rice crops.
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