Contribution of Anaerobically Incubated Nitrogen to the Diagnosis of Nitrogen Status in Spring Wheat

Abstract

Current wheat (Triticum aestivum L.) N fertility diagnosis models do not take into account organic N provided by mineralization. Anaerobically incubated N (Nan) could contribute to assess this N pool for crops. The aim of this research was to assess the Nan contribution to spring wheat yield without added N (GY0N), to grain N export (GNE), and to N fertilization response. A total of 28 N fertilization experiments were conducted in 2006, 2008, 2009, 2010, and 2011 in southeastern Buenos Aires Province (Argentina). At sowing, soil organic matter (SOM) content, Nan, and NO3−–N availability varied between 44 and 68 g SOM kg−1, 34 and 94 mg NH4+–N kg−1, and 39 and 130 kg NO3−–N ha−1, respectively. Average grain yield and protein content without N added were 3450, 4330, 5020, 5288 and 6262 kg ha−1, and 116, 97, 95, 91, and 90 g kg−1, for 2006, 2008, 2009, 2010, and 2011, respectively. Initial NO3−–N availability explained only 24% of GY0N variation, but R2 increased to 66% when Nan was integrated into the model. Soil NO3−–N content and Nan explained 58% of GNE variation, with a higher partial contribution of Nan to GNE than to GY0N (51 and 41%, respectively). A model was developed to predict the response to N (RN = –625.7 + 7.2Pp – 31.6Nan + 0.28GY0NPp, where Pp is total precipitation from July to December; R2 = 0.58). Soil Nan determination and initial NO3−–N content should be taken into account together when assessing spring wheat N needs.