Effects of the Long-Term Application of Anaerobically-Digested Cattle Manure on Growth, Yield and Nitrogen Uptake of Paddy Rice (Oryza sativa L.), and Soil Fertility in Warmer Region of Japan

The suitability of anaerobically-digested manure (ADM) from a biogas plant, as an alternative to chemical fertilizers for rice cultivation was evaluated by a long-term study. At the standard nitrogen (N) application rate (10 g m(-2)), the aboveground biomass, N uptake, and grain yield in rice plots with ADM application (MF) were not significantly different from those in the plots treated with chemical fertilizer (CF). Split application of ADM improved the apparent N efficiency. The N application rate corresponding to maximum grain yield was approximately 15 g m(-2) by a split application, and more N application by using ADM saturated grain yield due to decrease in ripened grain ratio and individual grain weight. On the whole, the soil total-C, total-N and available N in the ME plot were not significantly different from those in the CF plot. The available phosphate (P) levels was lower in the ME plot than in either the CF plot or plot without N application (NF), mainly due to lower content of P in ADM. However, the P level remained much higher than the fatal threshold level for the growth of paddy rice. These findings suggest that under appropriate fertilization conditions, ADM is a valuable organic resource, and can be used continuously as an alternative to chemical fertilization for rice cultivation, without substantial changes in soil C and N fertility.