Effects of different organic waste amendments on soil microaggregates stability and molecular sizes of humic substances |
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Authors: | A Piccolo J S C Mbagwu |
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Institution: | (1) Istituto Sperimentale per lo Studio e la Difesa del Suolo, Piazza M. D'Azeglio 30, I-50121 Firenze, Italy;(2) Department of Soil Science, University of Nigeria, Nsukka, Nigeria |
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Abstract: | Three soils which had been amended for several years with pig slurry, cattle slurry, and sewage sludge were dry-sieved to
obtain microaggregates in the size range of 250–125, 125–50, and <50 μm. With amendments, aggregate size distribution of whole
soils was shifted to larger sizes, especially for the most fragile soil, whereas percent content of microaggregates decreased
except for the lower size aggregates of the fragile soil. Particle size distribution of microaggregates revealed an increase
in percent sand and a reduction of percent silt and clay in the <50 μg size fraction for all soils. These results showed the
aggregation effect induced by the organic waste additions. Aggregate stability of microaggregates revealed significant correlation
with humic substances content (humic acids alone and humic plus fulvic acids) and non significant with total organic matter
substantiating the belief that humic substances are the predominant binding agents in this aggregation range. Molecular weight
distribution of humic acids extracted from microaggregates of unamended soils demonstrated that the lower the soil aggregate
size distribution, the larger the contribution of the high molecular weight fraction. All microaggregates from amended soils
showed a progressive increase of the high molecular weight humic acids with decreasing size, reaching a maximum in the <50
μm fraction. In this aggregate size a parallel enhancement of the aggregate stability was also evident. It is concluded that
a close relationship exists between aggregate stability and high molecular weight humic substances. Additions to soils of
organic material containing high molecular weight constituents would represent a useful management practice to improve aggregate
stability. |
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Keywords: | aggregate stability amendments cattle slurry humic substances management practices microaggregates molecular sizes pig slurry sewage sludge soils |
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