Nitrogen Uptake by the Rice Plant and Changes in the Soil Chemical Properties in the Paddy Rice Field during Yearly Application of Anaerobically-Digested Manure for Seven Years

This study investigated the changes in the chemical properties of the plow soil during a 7-year period with yearly application of anaerobically-digested manure (ADM), and the effect of the different ADM application methods on nitrogen (N) uptake by rice plants and the apparent N balance (input N minus output N). Among the treatments significant differences were observed in the pH, total N, and available N in the plow soil. The cumulative N uptake by rice plants in the ADM split application plots was significantly higher than that in single application plots. Consequently, the apparent N balance (input N minus output N) in the single ADM application plots was more positive. This result suggests that split application of ADM is more favorable for N uptake by rice plants. Although the apparent N balance was negative in the plots without N fertilizer, with chemical N and with low ADM, there was no observable decline in the total N and available N in the plow soil. This result implies that input and output of N in these plots were well balanced by additional N supply other than fertilization. On the other hand, the apparent N balance during the 7-year study under standard and heavy application of ADM was positive, indicating the preservation of soil fertility.