Factors Contributing to Nitrous Oxide Emissions from Soil Planted to Corn in No till Dairy Crop Rotations.

Nitrous oxide (N₂O) is a potent greenhouse gas released from soils as a by-product of the microbial processes of nitrification and denitrification. We investigated how different cropping system practices that include differences in crop residues, nitrogen (N) inputs (dairy manure and inorganic fertilizer), timing of N amendment applications, and environmental conditions influence N₂O emissions from no-till soil.  In 2015 and 2016, N₂O fluxes were measured using closed chambers in the Northeastern Sustainable Agriculture Research and Education (NESARE) Dairy Cropping Systems experiment at the Pennsylvania State University Russell E Larson Agronomy Research Farm PA, USA. Gas samples were collected with vented chambers biweekly prior to and during the period of anticipated N₂O fluxes in five cropping systems, where corn was planted after each of the following crops:  i. alfalfa (Medicago sativa) and orchardgrass (Dactylis glomerata), ii. crimson clover (Trifolium incarnatum) iii.  soybean (Glycine max) with broadcast manure, iv.  soybean (Glycine max) with injected manure, v.  soybean (Glycine max) with inorganic fertilizer. Random Forest method was used to identify and rank the predictor variables for N₂O emissions. In 2015, the most important variables driving N₂O emissions considered with Random Forest were: time after manure application, time after previous crop termination, inorganic N fertilization, soil nitrate and precipitation. Integration of legumes and grasses in the cropping systems helped meet corn yield goals and reduced use of inorganic fertilizer; however, direct N₂O emissions were not reduced. Results suggest that timing N inputs close to crop uptake and avoiding N applications when there is a high chance of precipitation can reduce nitrate accumulation in the soil and potential N losses from denitrification. Data collected in 2016 will also be analyzed and presented.