Carbon and N mineralization as affected by soil cultivation and crop residue in a calcareous wetland ecosystem in Central Iran

Mineralization of soil organic matter plays a key role in supplying nutrient elements essential to plant growth. Soil cultivation and crop residue affect C mineralization and nutrient availability in wetland ecosystems. This study evaluated the combined impacts of soil cultivation and crop residue on C and N mineralization in a calcareous wetland soil (Luvic Calcisol) in Central Iran. Soil samples were collected from 0 to 15 cm depth in cultivated and uncultivated plots and analyzed for selected soil attributes. Wheat (Triticurn aestivum L.) and alfalfa (Medicago sativa L.) residues were collected and analyzed for the chemical composition. Nitrogen and C mineralization rates were studied using laboratory incubations for 60 days. Results show that in this calcareous wetland soil, cultivation decreased soil total organic carbon and total N contents, while total organic carbon/total N ratio, bulk density, pH, and extractable P and available K levels remain unaffected. Cultivation resulted in a significant increase in soil C and N mineralization. Wheat residue had a significantly lower quality than alfalfa residue, and therefore decomposed more slowly. Results also indicate that plant residue has a significant impact on decomposition rate and nutrient cycling. Soil cultivation and residue quality had a significant influence on C and N cycling and nutrient contents. The combined effects of soil cultivation and crop residue play a significant role in changing the nutrient balance and availability in calcareous wetland soils with conventional agricultural practices. In summary, significant differences occurred in soil attributes and residue decomposition affecting C and nutrient dynamics, and therefore crop productivity. (c) 2005 Elsevier B.V. All rights reserved.