Thursday, November 16, 2006 - 8:40 AM

Aggregate Associated Carbon, Nitrogen and Sulphur and their Ratios in long-term Fertilized Soils.

Bal Singh, Dep.- Plant and Environmental Sci., Norwegian University of Life Science, AAS, N-1432, Netherlands and Zhihui Yang, Dept. of Plant and Environmental Sci. Norwegian University of Life Sciences, P.O.Box 5003, Aas, 1432, Norway.

Farmyard manure (FYM) and fertilizer applications are important management practices to improve nutrient status, crop productivity and organic matter in soils. However, the long-term effects of fertilization on carbon (C), nitrogen (N) and sulphur (S) associated with aggregates, especially on soil S are not fully known. We investigated the effects of more than 80 years of FYM and mineral fertilizer application on the concentrations of C, N, and S, on their ratios and total masses in bulk soil and in dry and water stable aggregates. Farmyard manure application increased the proportion of small dry aggregates (<0.6 mm) and decreased the proportion of large dry aggregates (> 20 mm and 6-20 mm). However, it resulted in increased proportion of large water stable aggregates (>2mm). Water stable macroaggregates (>2 mm and 1-2 mm) and microaggregates <0.106 mm showed higher concentrations of total C, N and S than the other aggregate sizes, but medium size water stable aggregates (0.5-1 mm) showed higher total masses of C, N and S. Mineral fertilizer or FYM application  not only increased the total C, N and S concentrations in bulk soils, but it also increased their concentrations in  dry and water stable aggregates. Farmyard manure application resulted in greater increase in total C, N and S concentrations than mineral fertilizer. High C/N, C/S and N/S ratios were found in large dry aggregates (>20 mm and 6-20 mm) and the smallest aggregates (<0.6 mm). For water stable aggregates, C/N ratio generally increased with decreasing aggregate sizes. However, macroaggregates >2 mm showed higher C/S and N/S ratios. In conclusion, longterm application of fertilizer and FYM resulted in C, N and S accumulation in both dry  and water stable aggregates, but their accumulation was dependent on aggregate size and the element (C, N and S) considered.