Soil Total Nitrogen and Natural 15Nitrogen in Response to Long-Term Fertilizer Management of a Maize-Wheat Cropping System in Northern China.

The Fengqiu long-term field experiment was established to examine effects of organic manure and mineral fertilizers on soil total nitrogen (N) and natural 15N abundance. Fertilizer regimes include organic manure (OM), one-half N from organic manure plus one-half N from mineral N fertilizer (1/2OMN), mineral fertilizers [N-phosphorus (P)-potassium (K), NP, NK, PK], and a control. Organic manure (OM and 1/2OMN) significantly increased soil total N and δ15N, which was expected as a great amount of the N applied remained in soils. Mineral NPK fertilizer and mineral NP fertilizer significantly increased total N and slightly increaed δ15N. Phosphorus-deficient fertilization (NK) and N-deficient fertilization (PK) had no effect on soil total N. Significantly greater δ15N was observed in the NK treatment as compared to the control, suggesting that considerable N was lost by ammonia (NH3) voltalization and denitrification in this P-deficiency fertilization regime. [ABSTRACT FROM AUTHOR]