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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

โœ Scribed by H. L. Golterman; C. Bonetto; F. Minzoni

Publisher
Springer
Year
1988
Tongue
English
Weight
536 KB
Volume
159
Category
Article
ISSN
1573-5141

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โœฆ Synopsis

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-' has become normal and a rate of 400 kg ha-' 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 m 2 ) and in pots (2-3 1). 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 -l ) 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 ยฑ 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%ยฐ7 of the input; N fixation is negligible. We estimate that 25 -50%ยฐ7 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.

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