Matching NPK fertilization to summer rainfall for improved wheat production and reduced environmental cost

Driven by a national commitment to achieve food security in China, policies have unintentionally favored overfertilization, with implications for the environmentally concerning release of reactive nitrogen (Nr) and greenhouse gas (GHG) emissions. We assessed current winter wheat yield, protein concentration, Nr losses, GHG emissions, and net profit in the winter wheat–summer fallow system in the Loess Plateau of China, using a combination of (i) original data from a 14-year field experiment, including five N fertilizer rates from unfertilized control to 320 kg N ha–1, (ii) surveys from 1167 farmers, and (iii) modeling. The study emphasized on N, with a secondary focus on phosphorus (P) and potassium (K). Farmer yields ranged from 1500 to 13,500 kg ha–1, and fertilizer rates ranged from 0 to 465 kg N ha–1, 0–454 kg P2O5 ha–1, and 0–279 kg K2O ha–1. Five yield scenarios were compared: (1) Ymax, defined as the maximum from the yield–N rate curve; (2) Yuptake, defined as the yield when N application rate equaled N uptake; and (3) low, (4) moderate and (5) high yields in farms. The yield–N rate curve accounted for summer rainfall, with Yuptake expected to return smaller environmental impacts than Ymax. Compared with Ymax, targeting Yuptake would reduce N fertilizer rate (40%), Nr losses (25%), and GHG emissions (14%), with modest reductions in yield (7%), protein concentration (6%), and net profit (11%). Compared with current practice, Yuptake would increase net profit (140%) and decrease Nr losses (23%) and GHG emissions (14%). Scaling to the Loess Plateau region (246.3 × 104 ha wheat-growing area), targeting Yuptake would return a production of 1.4 × 107 t yr–1 and increase annual net profit by US$7.3 × 108 with less Nr losses (17,200 Mg) and GHG emissions (1.2 × 106 Mg CO2 eq) in relation to farmer practice. Therefore, targeting Yuptake and matching NPK fertilization to summer rainfall should be adopted to improve wheat yield and net profit and reduce environmental risk in the Loess Plateau and similar regions.