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The nitrogen cycle in shallow water sediment systems of rice fields Part III: The influence of N-application on the yield of rice
Authors:H L Golterman  C Bonetto  F Minzoni
Institution:(1) Station Biologique de la Tour du Valat, le Sambuc, 13200 ARLES, Fr.;(2) C.E.C.O.A.L., Casilla de Correo 291, 3400 Corrientes, Argentine;(3) Università di Parma, Istituto di Ecologia, Via P. Groppi 18A, I-42100 Parme, Italie
Abstract:Fertilizer application to rice-fields in the river-deltas in the Mediterranean area is a potential menace for wildlife protection, through eutrophication.Fertilizer use shows a trend of increasing rates of N application. A rate for N of 200 kg ha–1 has become normal and a rate of 400 kg ha–1 has already been recorded.Denitrification causes large losses of N with the result that more fertilizer is applied. This is especially true for the Camargue (S-France), where N is applied long before the rice (Aryza sativa) can take it up.Therefore we have tried to develop techniques which need the application of smaller amounts of N which are used more efficiently. In order to do this we tried to establish a N budget for rice-fields.Experiments were therefore set up in the field (plots of 550 m2) and in pots (2–3 l). Our results suggest that a late application of N (e.g. when the rice shows signs of N-deficiency by becoming yellowish), but at lower concentrations (70 kg ha–1) can produce the same ultimate yield. The introduction of carp without any further input of N produced the same final yield.The N budget shows that 15±1.5 g m–2 of N is needed for a normal crop. N losses due to denitrification may be as high as 12.2–13.6 g m–2 of N. The input by irrigation water may provide up to about 20% of the input; N fixation is negligible. We estimate that 25–50% of the N missing in the budget comes from minderalization of the organic N pool in the soil. Denitrification may render part of this pool bio-available by oxidation. In sum, this work has revealed some surprising effects with potentially important consequences for farming practice and, in consequence, for conservation.
Keywords:rice-yield  N-fertilization  Camargue  N-cycle
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