English

Abstract

A good soil structure is indicated by the abundance of soil aggregates which has an important role in sustainable agricultural management and soil productivity. As it affects hydraulic conductivity, gases transport within the soil and seed germination, root respiration and eventually plant growth. The different sized fractions of soil aggregates are influenced significantly by both the amount and the composition of organic matter present in the soil (Piccolo, 1996). The degree of soil aggregation and aggregate stability is the result of the interaction between organic and inorganic soil components. Soil structure degradation occurs mostly due to the decrease in soil organic carbon caused by excessive soil cultivation and soil erosion. Eroded soils have consistently shown lower soil organic carbon and nutrient concentrations in upper profiles than cultivated soils, this is also true for other physical properties such as soil texture and saturated hydraulic conductivity (Heckrath et al., 2005). Soil organic carbon (SOC), includes soil organisms (e.g. microbial biomass), simple organic compounds (e.g. polysaccharides), large and complex humic substances, as well as relatively fresh residue at various stages of decomposition (Weil and Magdoff, 2004). The effect of different composted and un composted products on soil aggregate stability across time scales vary from weeks, months to years after the incorporation (Monnier, 1965). The various components of organic carbon such as microbial biomass carbon, polysaccharides and humic substances play very important role in the aggregate formation mechanism. The polysaccharides are highly complex polymers, consisting of many structural units, and are naturally resistant to decomposition or become resistant through reaction with other soil constituents and serve as binding agents. Microbial biomass carbon is an active form of carbon and it influences aggregate formation and stability. Humic substances account for the largest and most decomposed proportion of soil organic matter (SOM) with chemically complex and ill-defined structure, and act as persistent binding agent for stabilization of aggregates. Stabilization of aggregates by organic matter (Six et al., 2004) and interactions between aggregative factors and aggregate structures is well documented. In most studies, the organic matter additions were characterized by their elemental composition but additional information such as contents of humic and non-humic substances were seldom provided. In this study we hypothesized that addition of organic sources on equivalent carbon level basis affect the soil aggregate formation differently as composition of materials vary. The objectives of the present study were, to examine the quality (fundamental characteristics) of the traditional organic manures and their direct effect upon formation, Pak. J. Agri. Sci., Vol. 53(4), xxx-xxx; 2016 ISSN (Print) 0552-9034, ISSN (Online) 2076-0906 DOI: 10.21162/PAKJAS/16.4205 http://www.pakjas.com.pk