Abstract
A field study has been carried out in since 1986 to examine the effects of the long-term application of organic matter on the soil properties of Jahgaru, a calcareous, claley, poorly structured soil with low permeability and high water retention formed on weathered marl. This study reports the results for the period from 2001 to 2010. The sweet corn yield was 11% and 7% higher on soils to which had been added 25 Mg ha^<-1> year^<-1> of sesbania (Sesbania cannabina) as green manure (SC-soil) or 25 Mg ha^<-1> year^<-1> of cattle manure compost (CM-soil), respectively, than on soil treated with only chemical fertilizers (CF-soil), despite the fact that the amount of applied N was 30% lower in the SC- and CM-soils than in the CF-soil. The C and N contents in the soil microbial biomass and the microbial activity were significantly higher in the SC- and CM-soils than in the CF-soil, and there were no significant differences between the SC- and CM-soils. PCR-DGGE analysis revealed that fungal community structure of each soil differed from those of the other soils. Organic C and total N remained at constant levels. In contrast, available N increased each year in all soils and was significantly higher in the SC- and CM-soils than in the CF-soil. Exchangeable Mg and K increased each year, while ex-Ca did not change. Compost application increased the amount of available P, while sesbania application did not. No remarkable differences between treatments were observed in the soil physical properties. We conclude that the increased amounts of available N, microbial biomass, and microbial activity contributed to the higher sweet corn yields on the SC- and CM-soils. There were no remarkable differences between sesbania and compost in the effects of long-term application on soil properties, except in the amount of available P. Sesbania may therefore be an alternative source of organic matter to compost for amelioration of the low fertility of Jahgaru soil.
