Abstract
Effect of long-term application (ca. 30 years) of compost at different levels on humus composi-tion of whole soils and their particle size frac-tions in a field subjected mainly to double cropping (barley and paddy rice) was investi-gated. Soil samples were collected from three plots of different types of management: (a) F plot, only chemical fertilizers containing N, P and K were applied; (b) F+LC plot, both chemi-cal fertilizers and a low level of compost were applied; (c) F+HC plot, both chemical fertilizers and a high level of compost were applied (the amount of compost applied in the F+HC plot was three times larger than that applied in the F+LC plot). Each soil sample was divided into coarse sand- (CSA), medium sand-(MSA) and fine sand-(FSA) sized aggregate, silt-sized ag-gregate (SIA) and clay-sized aggregate (CLA) fractions by wet-sieving and sedimentation. In addition, the CSA and MSA fractions were sub-divided into “mineral particles” (MP) and “de-cayed plants” (DP) by a density fractionation. Humus composition was influenced depending upon the level of compost applied. The applica-tion induced an increase in the amounts of total humus (TH), humic acid (HA) and fulvic acid (FA) in the whole soil and many size fractions, par-ticularly, SIA fraction. The increase was re-markable in the F+HC plot. In the CSA and MSA fractions, the amounts of TH, HA and FA were much larger in the CSA- and MSA-DP fractions than in the CSA- and MSA-MP fractions. The amounts of TH, HA and FA in the SIA fraction were larger than those in the CLA fraction for the F+HC and F+LC plots, and the reverse was true for the F plot. On the other hand, the de-grees of humification of humic acids in whole soils and many size fractions, particularly SIA fraction, decreased by compost application. The decrease was markedly in the F+HC plot. These findings suggest that the SIA fraction play an important role in the quantitative and qualitative changes of humus, including HA and FA, as in-fluenced by a long-term compost application.
Highlights
A variety of organic amendments such as compost, farmyard manure, plant residues, food processing wastes and sewage sludge is applied to various agriculture soils
Three plots (200 m2 each) of the field experiments were selected: (a) F plot, only chemical fertilizers containing N, P, and K were applied; (b) F+LC plot, both chemical fertilizers and a low level of compost were applied; (c) F+HC plot, both chemical fertilizers and a high level of compost were applied
The distribution values increased in the order of clay-sized aggregate (CLA) < FSA < MSA < sized aggregate (SIA) < coarse sand- (CSA) fractions
Summary
A variety of organic amendments such as compost, farmyard manure, plant residues, food processing wastes and sewage sludge is applied to various agriculture soils. Many researchers have reported beneficial effects of these amendments on the physical, chemical and biological properties, and fertility of soils in upland and paddy fields. The role of the amendments in the soils of double cropped fields (upland and paddy crops) has received little attention. The authors began to investigate the effect of continuous compost application on various properties of soils in a field subjected to long-term double cropping (paddy rice and barley). The results obtained are summarized as follows: Compost application increased (1) the activities of organic C, N and P decomposing enzymes, (2) the microbial biomass N content and the hyphal length, (3) the degree of water-stable macroaggregation (>0.25 mm) and (4) the contents of total humus (TH) including humic (HA) and fulvic (FA) acids, organic C, total N, hydrolysable carbohydrates and active Al [1,2,3]. Regarding the effects of organic amendments on humus composition, we can find some papers. Roppongi et al [4] reported that the in-
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