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

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.

Carbon and nitrogen dynamics in agricultural soil after application of cattle manure and eastern redcedar wood chips.

Uncontrolled proliferation of eastern redcedar tree (Juniperus virginiana) in the Midwest United States requires new alternatives for utilization of waste wood, such as mulching, that promotes efficient tree management by landowners. Similarly, efficient use of manure from animal feeding operations in cropping systems can reduce negative environmental impacts and increase cropland productivity. The objectives of this study were to quantify the nitrogen (N) and carbon (C) decomposition rates, availability, and effects on soil chemical properties of eastern redcedar wood chips (WC), cattle manure (CM), and the combination of cattle manure and wood chips (MW). A 120-day incubation and a 12-month field experiment were conducted in Nebraska. In the incubation study, CM decomposed the fastest, followed by MW and WC. At the end of the experiment, WC induced N immobilization. In the field experiment, most decomposition for all amendments occurred during the period between May and August (spring/summer). Decomposition was most rapid for CM and WC with 44% and 55% organic-C loss by mass, respectively. Approximately, 40% of the organic N in CM mineralized during the 1-year field study. Wood chips induced N immobilization after 6 months for shallow soil layers compared to control (no amendment) but did not induce N immobilization when combined with manure. Changes in soil organic matter concentration due to amendment application were not observed at any stages of the field experiment, likely due to the length of the experiment. However, consecutive applications of comingled MW may provide benefits of C contribution to the soil without inducing N limitations.

Key nitrogen and phosphorus performance indicators derived from farm-gate mass balances on dairies.

Efficient management of N and P on dairy farms is critical for farm profitability and environmental stewardship. Annual farm-gate nutrient mass balance (NMB) assessments can be used to determine the nutrient-use efficiency of farms, set efficiency targets, and monitor the effect of management changes with minimal inputs required. In New York, feasible N and P balances have been developed as benchmarks for dairy farm NMB, alongside key performance indicators (KPI) that serve as predictors for high NMB. Here, 3 yr of NMB data from 47 farms were used to evaluate the main drivers of N and P balances and identify additional KPI. From the 141 farm records, 26% met both the feasible N balances per hectare and per megagram of milk produced. For P, 53% of the records met both benchmarks. Imports, rather than exports, drove NMB primarily by feed and fertilizer purchases, consistent with earlier findings. Linear regression analysis showed that a selection of KPI currently used, particularly animal density, nutrient-use efficiency, and the amount of home-grown feed, explained a large portion of variation in NMB. Heifer-to-cow ratio and the relative proportion of various forage crops may provide further insight into the drivers of feed and fertilizer imports and ultimately farm-gate NMB. This study provides avenues toward a better assessment of whole-farm nutrient management and means for farms to communicate progress to stakeholders and consumers.