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 (GY 0N ), 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 NO 3 − –N availability varied between 44 and 68 g SOM kg −1 , 34 and 94 mg NH 4 + –N kg −1 , and 39 and 130 kg NO 3 − –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 NO 3 − –N availability explained only 24% of GY 0N variation, but R 2 increased to 66% when Nan was integrated into the model. Soil NO 3 − –N content and Nan explained 58% of GNE variation, with a higher partial contribution of Nan to GNE than to GY 0N (51 and 41%, respectively). A model was developed to predict the response to N (RN = –625.7 + 7.2Pp – 31.6Nan + 0.28GY 0N Pp, where Pp is total precipitation from July to December; R 2 = 0.58). Soil Nan determination and initial NO 3 − –N content should be taken into account together when assessing spring wheat N needs.