Investigation on nutrient salt loadings from a paddy field aera, 1: Nutrient salt loadings from a paddy field area during the irrigation period
1997
Sonoda, K. (Shiga-ken. Agricultural Experiment Station, Azuchi (Japan)) | Tokuda, Y. | Okamoto, S. | tanaka, Y. | Kitano, A. | Ohashi, K.
We investigated the outflow loadings of nutrient salts in 3.89 ha of paddy field area, Gray Lowland Soil in Yuge, Ryuou town, Gamo-gun for three years, from 1993 to 1995. The results obtained are as follows: 1) The mean nitrogen balance ((outflow)-(inflow)) over the three years was -0.5 kgN per ha. The mean phosphorus balance was +8.0 kgP per ha. 2) The present results were compared with a similar investigation conducted at the same site in 1982. The present results showed distinctively lower nitrogen balance. This was attributed to improvement in the application of fertilizer, i.e. the shift from basal to additional dressing. 3) Outflow loadings of nitrogen tended to increase both in puddling or rice-planting season, from the last 10 days of April to the first 10 days of May, and during the top dressing season in the middle of June. 4) Outflow loadings of phosphorus tended to increase during the top dressing followed by the drainage season around the middle of June. 5) As a result, it was shown that outflow loadings of nutrient salts were strongly effected by the amount of precipitation, however, it was also considered that such factors as the methods of fertilizer application and irrigation effected on the loadings
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