The long-term decrease in nitrogen-suppling power from subsoil in two soil types of paddy field in Hokkaido [Japan], low-moor peat and heavy clay, and its effect of nitrogen uptake of rice plant and protein content of milled rice
2002
Fueki, N. (Hokkaido. Central Agricultural Experiment Station, Naganuma (Japan)) | Konno, K.
In order to understand the long-term decrease of soil nitrogen-supplying power with time (from 1967 to 1999), we investigated the changes of soil chemical properties, such as content of total carbon, total nitrogen and available nitrogen in two paddy fields sited on a Low-moor Peat soil (LP) and a Heavy Clayey soil (HC). We also measured nitrogen uptake of rice, yield of rice and nitrogen content of ear. The results are summarized as follows. 1) The remarkable decrease of total carbon and total nitrogen in subsoil (10 to 45cm) of LP from 1967 to 1977 showed rapid decomposition of peat. However much the decomposition rate had dropped off, the decline of available nitrogen at sub-peat layer (25 to 45cm) had continued since 1977. The decline of available nitrogen was observed in subsoil (10 to 22cm) of HC too, although the degree was less than that in subsoil of LP. 2) The nitrogen uptakes in ripening stage decreased gradually as nitrogen-supplying power of subsoil declined with time. This trend was more noticeable in LP than HC. The degrees of decrease in nitrogen uptake in heading stage were less than in ripening stage, because nitrogen uptake from subsoil became vigorous with extension of root after heading stage. 3) Although the yields of rice in +N plots where proper amount of fertilizer was applied remained stable, the yields in -N plots decreased with time. This might result from the gradual decrease of nitrogen uptake before heading stage in -N plot.
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