Impacts of low disturbance liquid dairy manure incorporation on alfalfa yield and fluxes of ammonia, nitrous oxide, and methane

Authors: Sherman, Jessica; Young, Eric; JOKELA, WILLIAM; CAVADINI, JASON - UNIVERSITY OF WISCONSIN

Submitted to: Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/3/2021
Publication Date: 8/6/2021
Citation: Sherman, J.F., Young, E.O., Jokela, W.E., Cavadini, J. 2021. Impacts of low disturbance liquid dairy manure incorporation on alfalfa yield and fluxes of ammonia, nitrous oxide, and methane. Agriculture. https://doi.org/10.3390/agriculture11080750.
DOI: https://doi.org/10.3390/agriculture11080750

Interpretive Summary: Dairy manure is an important nutrient source for crop production and also contributes to maintaining soil health. Applying liquid manure after hay crop forage harvesting can help meet phosphorus, potassium, nitrogen, and micronutrient needs while reducing fertilizer expenses, however the method of application affects the amount of nutrients retained and possible the risk of crop damage. While applying manure to the soil surface (broadcasting) can reduce plant disturbance compared to mechanical incorporation/injection, it also encourages rapid ammonia-nitrogen loss to the atmosphere and leaves phosphorus and ammonium-nitrogen vulnerable to erosion and hydrologic transport from the field. A three-year study conducted by USDA-ARS scientists in Marshfield, Wisconsin compared broadcast manure application to two low disturbance incorporation methods (shallow disk injection and aeration/banding) on alfalfa yield and fluxes of ammonia, nitrous oxide, and methane. Results indicated minor yield differences among the methods suggesting no overall yield risk associated with low disturbance methods compared to broadcast. Shallow disk injection had the greatest reduction in ammonia losses but also generated greater nitrous oxide emissions after manure application. Aerator band application conserved less ammonia but also had lower nitrous oxide losses. Results indicate that shallow disk injection is a viable option for increasing manure nutrient use efficiency without a large yield depression risk.

Technical Abstract: Liquid dairy manure applied to the soil surface (i.e., broadcasting) after alfalfa (Medicago sativa L.) harvest is a common practice in cold climate dairy agroecosystems. Low disturbance manure incorporation (LDMI) may offer multiple benefits including lower ammonia (NH3), greenhouse gas (GHG) and hydrologic nutrient losses compared to broadcast. However, few studies have simultaneously quantified LDMI impacts on alfalfa yield, NH3 and greenhouse gas (GHG) fluxes. We measured NH3, nitrous oxide (N2O), and methane (CH4) fluxes for liquid dairy manure treatments applied to alfalfa plots for broadcast and LDMI over three seasons (2014 to 2016) in central Wisconsin, USA. There were minor differences in alfalfa yield and nitrogen (N) uptake across treatments and years. Shallow disk injection and aerator/band reduced NH3 loss by 95 and 52% of broadcast, respectively, however both substantially increased N2O fluxes (6 and 4.5 kg ha/yr vs. 3.6 kg/ha/yr for broadcast, respectively). The magnitude and timing of N2O fluxes were related to manure application and precipitation events. Average CH4 fluxes were similar among methods and increased with soil moisture after manure application. Results highlight the importance of quantitatively evaluating agri-environmental tradeoffs of LDMI versus broadcast manure application for dairy farms.