Nitrogen application technology for tropical rice as determined by field experiments using 15N tracer technique

日本 タイ
Technical bulletin of the Tropical Agriculture Research Center
ISSN 03889394
書誌レコードID(総合目録DB) AA00857848
To improve the growth and yield of rice crop, the behavior of nitrogen element in the soil-plant system should be clarified. Therefore, the tracer technique using 15N was adopted to study the behavior of nitrogen in field experiments by distinguishing the supply of nitrogen from the soil nitrogen from that of fertilizer.
With the standard fertilizer application practice, i.e., 37.5 kg N/ha for basal dressing at the time of planting and 37.5 kg N/ha for top-dressing at the panicle primordia initiation stage, an improved variety P.B. 76-63, absorbed 82 N kg/ha, 36% of which was derived from the fertilizer while the balance, 64% was from the soil nitrogen. It was also made clear that of the total quantity of nitrogen (30 kg N /ha) absorbed by plants from fertilizer N, about 1/3 of it was from the basal dressing and 2/3 from the top-dressing.
As the same amount of nitrogen was applied for both basal- and top-dressing, it can be said that the recovery rate of top-dressing nitrogen is just twice that of the basal dressing. The rate for the former was 54%, and that of the latter was only 27%. Some trials were carried out in order to improve, such a low recovery rate of the basal dressing nitrogen, and it was found that whole layer application method (fertilizer is mixed with top soil to the depth of 10 cm) gave a rate twice of that of top layer application method and the mixture of nitrification inhibitor raised the recovery rate of basal dressing by about 50%.
In the light of the high effectiveness of top-dressing in increasing yields a study have been made on the timing of top-dressing. The top-dressing applied at 25-30 days prior to the flowering was particularly effective for improved photoperiod non-sensitive varieties. The effectiveness was largely influenced by the length of growth duration. Namely, when the growth duration was prolonged by an early planting the earlier application than that indicated above gave the best result, whereas when the growth duration was around 130 days, same as that of improved photoperiod non-sensitive varieties, the proper application time of top-dressing came around 25-30 days prior to flowering just like improved varieties. Therefore, the proper time of top-dressing must be determined by considering the growth duration of plants, but it can be concluded that with improved varieties the proper time is around 25-30 days prior to flowering.
A study was made to know what is the reason for such high effectiveness of top-dressing observed in Bangkhen, and it was found that soil nitrogen was mineralized mainly during the period of early stage of plant growth: the percentage distribution of the mineralized soil nitrogen absorbed by plants was 60% during the period up to the end of tillering, 36% during the panicle formation stage, and 4% during the ripening period.
Compared with the percentage distribution of 45: 27: 28% observed with high-yielding Nagano soils in Japan, it is clear that the release of soil nitrogen during the late period is very low in the Bangkhen soil, and this can be a major reason for the high effectiveness of top dressing of nitrogen on the Bangkhen fields.
The total amount of soil nitrogen mineralized during the growth duration of rice was 131 kg N/ha in the Bangkhen soil as compared to 249 kg N /ha in the Nagano paddy field. It can be said that nitrogenous soil fertility of the Bangkhen soil, which is regarded rather fertile, is not sufficient.
Another important finding obtained by the authors is that an application of fertilizer nitrogen promotes mineralization of soil nitrogen, and as the result uptake of soil nitrogen by plants is increased.
An application of basal dressing of nitrogen caused an increase in absorption of soil nitrogen by 7. 7 kg N/ha and top-dressing resulted in an additional uptake of soil nitrogen of about 7.1 kgN/ha on the Bangkhen paddy soils. The total amount of soil nitrogen, absorbed additionally by plants as the effect of fertilizer application, constituted 18% of the total nitrogen absorbed by plants during a whole growth duration.
Accordingly, it is necessary to enhance nitrogenous soil fertility in order to raise further the yield level at Bangkhen field. The facts that nearly two thirds of the total nitrogen absorbed by plants grown in Bangkhen was derived from soil nitrogen and that the grain yields showed a very high correlation of γ=0.90 to the soil nitrogen absorbed up to the flowering time furnish a good evidence for that concept.
It is also import to know to what extent the soil nitrogen will be consumed by adopting double-cropping of rice in a rainy season. The authors' result indicated the consumption as much as 16%, Although the percentage may be lower than 16% with soils of higher fertility, yet this problem must not be neglected in practicing the double-cropping of rice.
作成者 Takeo Koyama Chittana Chammek Natee Niamsrichand
公開者 Tropical Agriculture Research Center
開始ページ 1
終了ページ 87
言語 eng