The runoff of suspended, substances, nitrogen, and phosphorus by enforced draining during the ploughing season Experiments in paddy fields

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  • しろかき期の強制落水による懸濁物，窒素とリンの流出―圃場における流出実験―
  • シロカキ キ ノ キョウセイ ラクスイ ニ ヨル ケンダクブツ チッソ ト リン ノ リュウシュツ ホジョウ ニ オケル リュウシュツ ジッケン
  • ―圃場における流出実験―

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The runoff of suspended substances (SS), nitrogen, and phosphorus by enforced draining during the ploughing season was calculated from experiments in two paddy fields. The area of a paddy field was 3000m2. The total fluxes were 33kg (SS), 85g (total-N), and 46g (total-P) in Field A, with a small decrease in water levels (8mm), 110kg (SS), 589g (total-N), and 146g (total-P) in Field B with a major decrease in water levels (72mm). Furthermore, the nitrogen/phosphorus ratios (mol ratios) of the waste water by the enforced draining were 4.1 (Field A) and 8.8 (Field B). In comparison with N/P of the phytoplankton (16), it was found that the phosphorus flowed out efficiently with the enforced draining. Increasing the supply of the phosphorus to Lake Biwa is not desirable in view of the current problems of eutrophication. The careless water management of paddy fields was a crucial factor in any plan to improve the water quality of Lake Biwa.

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