Importance of matching soil N transformations, crop N form preference, and climate to enhance crop yield and reducing N loss.

The preferential uptake of nitrogen (N) by plant species is generally considered to be tightly associated with soil N transformation characteristics and climatic conditions. In the present study, the yield, N recovery, and N balance of wheat (an NO3--preferring crop) and rice (an NH4+-preferring crop) planted in two sites with significantly different soil N transformations and precipitation were compared to test the connections among soil N transformations, species-specific N preferences, crop yield, N use efficiency (NUE), N loss, and climate. Nitrogen recoveries of 15N applied as either an NH4+ or NO3- based fertilizer in crops and soil were determined, and N losses were calculated using the 15N balance. The results indicated that the match (or mismatch) of crop N preference, soil N transformation characteristics, and climate conditions could significantly affect the crop yield, recovery, and loss of applied 15N. A crop preferring NH4+ (e.g., rice) planted in soil with low nitrification and low pH tended to have a higher yield and NUE, and a lower N loss compared with plants growing in soil characterized by a higher nitrification rates. In contrast, NO3--preferring crops (e.g. wheat) planted in soil with higher nitrification rates and lower precipitation achieved a higher yield and lower N loss than those planted in acid soil with a lower nitrification rate and higher precipitation. Replacement of ammonium N fertilizer with nitrate N fertilizer improved the NUE for NO3--preferring crops (wheat) planted in arid and semi-arid regions, but not in humid regions because of the mobility of NO3-. Thus, a good match of crop N preference, soil N transformation characteristics, and climate conditions is critical to enhance crop yield and reduce N loss. This intimate connection needs to be taken into consideration in terms of the choice of crop species and N fertilizer type to optimize N fertilization management.