Root growth and nitrogen uptake in rice: concepts for modelling.
1994
ten Berge H.F.M. | Thiyagarajan T.M. | Mishra B. | Rao K.S.
Data from field experiments are used to examine the rate-limiting step in nitrogen (N) uptake by lowland rice. For the vegetative phase over a wide range of fertilizer levels, N uptake per ha (Nc) and uptake rates per ha (dNc/dt) increased with the amount of N applied (A). dNc/dt did not reach an upper limit. Increases in dNc/dt with A were more than in proportion to increases in root mass (Mr). After panicle initiation (PI), there was no consistent relation between A, dNc/dt, and Mr. The root-shoot ratio decreased with development stages and was independent of A at any stage. Up to PI, Mr and the rate of N absorption per unit Mr both increased with A to the extent that fertilizer N recovery increased as A increased. An approximate calculation showed that changes in cumulative recovery with A could be explained by differences in Mr. Two hyphothesis to explain dNc/dt during the pre-PI stage were consistent with the experimental data: 1.) the uptake rate was diffusion-limited and proportional to the concentration of NH4+ in the root zone bulk soil solution [NH4+] and to root length density (RLD), and, 2.) the uptake rate was independent of [NH4+] and governed by the plant internal N content through a mechanism superimposed on the effect of Mr. Total N uptake over the season was a linear function of A. This linearity was the result of a positive feedback between Nc and dNc/dt during vegetative growth, followed by a negative or neutral feedback after PI.
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