Greenhouse gas emissions and nutrient use efficiency assessment of six New York organic dairies

Abstract

Improving nutrient use efficiency and reducing greenhouse gas (GHG) emissions are important environmental priorities for organic-certified dairy operations. The objectives of this research were to quantify annual nutrient use and GHG emissions in 6 organic New York dairy farms. Farm-gate nutrient mass balances (NMB) were estimated with the Cornell NMB calculator. Whole-farm GHG emissions were estimated using Cool Farm Tool (CFT) and COMET. Farm-gate NMBs were low, ranging from -6.5 to 19 kg N ha-1 for N1 (without legume N fixation), 26 to 71 kg N ha-1 for N2 (including N fixation), -2.4 to 8.2 kg P ha-1 for P, and 1.1 to 19.8 kg K ha-1 for K. Additional nutrient imports, coupled with nutrient management planning, adequate legume stands and diet balancing may help improve P balances, and ensure no N deficiencies in the system. Estimates of annual GHG emission intensity ranged from 0.98 to 2.10 kg CO2-eq per kg of fat and protein corrected milk (FPCM) estimated by CFT, and from 0.69 to 2.48 kg CO2-eq kg FPCM-1 estimated by COMET. Enteric fermentation, feed production and fuel and energy use represented the largest sources of GHGs. For farms with liquid manure storages, manure management was also a significant source. Estimates of soil carbon (C) stock changes from CFT were in agreement or smaller than previous studies, and estimates from COMET were in agreement or greater. Variability and uncertainty in the results for soil C stock change indicate more research and new protocols are needed. Impact of individual management changes on GHG emissions intensity were small, ranging from -8 to +7% in CFT, and -8% to +8% in COMET. The management changes that resulted in the largest reductions in GHG emissions intensity included increasing individual cow productivity and milk to total feed ratio, and implementation of manure treatment systems.