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

Abstract

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 (N r ) and greenhouse gas (GHG) emissions. We assessed current winter wheat yield, protein concentration, N r 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 P 2 O 5 ha –1 , and 0–279 kg K 2 O ha –1 . Five yield scenarios were compared: (1) Y max , defined as the maximum from the yield–N rate curve; (2) Y uptake , 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 Y uptake expected to return smaller environmental impacts than Y max . Compared with Y max , targeting Y uptake would reduce N fertilizer rate (40%), N r losses (25%), and GHG emissions (14%), with modest reductions in yield (7%), protein concentration (6%), and net profit (11%). Compared with current practice, Y uptake would increase net profit (140%) and decrease N r losses (23%) and GHG emissions (14%). Scaling to the Loess Plateau region (246.3 × 10 4 ha wheat-growing area), targeting Y uptake would return a production of 1.4 × 10 7 t yr –1 and increase annual net profit by US$7.3 × 10 8 with less N r losses (17,200 Mg) and GHG emissions (1.2 × 10 6 Mg CO 2 eq) in relation to farmer practice. Therefore, targeting Y uptake 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. • Five yield scenarios were modeled using data from a field experiment and farm survey. • Yield, protein, N r losses, GHG emissions, and net profit were compared between scenarios. • Promoting fertilization accounting for summer rainfall and crop N uptake were recommended. • Targeting Y uptake reduced N r (23%) and GHG (14%) compared to current practice.