Quantify the effect of manure fertilizer addition and optimal nitrogen input on rainfed wheat yield and nitrogen requirement using nitrogen nutrition index.

Combined manure fertilizer addition with optimal nitrogen (N) input reduces nitrogen demands for wheat while maintaining or increasing its yield and nitrogen productivity. However, the effect of manure addition has not been well explored for dryland wheat production on the Loess Plateau, especially in year with less precipitation. Therefore, a 4-year field experiment was performed: manure fertilizer (with and without) and N fertilization levels (0, 60, 120, 180 and 240 kg ha–1) under two precipitation years (normal and dry year). The target was to quantify the effect of manure addition on: i) wheat yield and nitrogen use efficiency (NUE), ii) crop growth and soil properties, and iii) wheat N status [N accumulation, N nutrition index (NNI)]. Compared with chemical N alone, manure addition increased topsoil organic matter, total nitrogen and the stability of macro-aggregate (R 0.25). Manure addition increased grain yield by 12.5% in normal year and by 38.2% in dry year. The improved topsoil quality, root system, biomass (nitrogen) accumulation all occurred in NM120 or NM180 with manure addition, which brought an improvement of wheat yield and NUE with a suitable nitrogen nutrition status. NM180 (i.e., 150 kg N ha–1 +2000 kg ha–1 manure) and NM120 (i.e., 90 kg N ha–1 +2000 kg ha–1 manure) achieved the highest grain yield in normal and dry years, respectively. In summary, the optimal fertilization decision strategy based on precipitation and nitrogen nutrition index can be applied for dryland wheat production. • Manure addition increased yield and NUE by regulating soil quality, root growth and post-anthesis N accumulation. • NM120 or NM180 with manure addition achieved the highest grain yield in dry and normal years, respectively. • Critical nitrogen dilution curves were established for diagnosing dryland wheat N nutrition status. • Combined manure addition with optimal N input reduced yield loss in years with less precipitation. [ABSTRACT FROM AUTHOR]