Mineral nitrogen accumulation in soils as affected by water‐soluble organic carbon extracted from composted dairy manure

The soluble organic matter in composted manure contains labile carbon (C) and nitrogen (N) that may stimulate microbial activity. Evaluating the effects of water‐soluble organic carbon (WSOC) on N mineralization will improve our understanding of the short‐term N turnover in soil. Three soils with textures varying from 3 to 54% clay were amended with water extracts from composted dairy manure (0–80 mg C/kg soil) and incubated for 11 weeks at 23°C. Water‐soluble organic C additions enhanced net N mineralization only in the soil containing the largest amount of clay; the increased net N mineralization was similar to the amounts of organic N added in the water extract. The WSOC in the composted manure had little effect on net N mineralization, particularly in coarse textured soils. The short‐term effect of WSOC inputs on the net N mineralization in soils may depend on the mineral N concentration of the water extract.