The Effect Of Organic Inputs On Strength And Structural Stability

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Abstract. The study aims to understand the impact of organic inputs on strength and structural stability of aggregates in a sandy loam soil. Tensile strength, friability and water stability of aggregates; and the carbon contents in bulk soil and in large macro (>2 mm), small macro (0.25-2 mm), micro (0.053-0.25 mm) and silt+clay size (<0.053) aggregates were evaluated on soils from a long-term experiment with rice-wheat rotation at Modipuram, India with different source and amount of organic C inputs as partial substitution of fertilizer N. Addition of organic substrates significantly improved soil organic C (SOC) contents, but type and source of inputs had different impacts. Tensile strength of aggregates decreased and friability increased through organic inputs, with maximum effect under green gram residue (rice)-farm yard manure (wheat) substitution. Higher macroaggregates in crop residue and FYM treated soils resulted in higher aggregate mean weight diameter, which also had higher SOC contents. The bulk SOC had a strong relation with MWD of aggregates, but SOC content in all aggregate fractions were not necessarily effective for aggregate stability. The SOC content in large macroaggregates (2-8 mm) had significant effect on aggregate stability, although aggregates <0.25 mm had negative impact. Partial substitution of nitrogen by organic substrates improved aggregates properties and SOC content in bulk soil and aggregate fractions, although the relative effect varied with

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