Nitrous Oxide Emissions from Injected Vs. Surface Applied Liquid Dairy Manure in Alfalfa and Tall Fescue.

Injecting manure can reduce odors and preserve nitrogen through reducing ammonia volatilization. However, manure injection may mechanically damage the root system of hay crops including tall fescue (Festuca arundinacea L.) and alfalfa (Medicago sativa L.) and possibly result in stand and yield reduction. The objective of this study was to compare injection versus surface application of liquid dairy manure on (i) crop yield, and (ii) nitrous oxide (N₂O) emissions. The experimental design was a randomized complete block design with six replications. Treatments were injection and surface application of manure, injection without manure, and no manure application. Manure application rates were 37 and 74 kL ha^-1 in 2014 and 2015, respectively, based on equipment availability. Manure application in tall fescue occurred in spring (after 1^st cutting) and fall (after 2^nd cutting) while manure was applied to alfalfa only in after 1^st cutting in the spring. Alfalfa was harvested three times in 2014 and four times in 2015. Tall fescue was harvested two times in 2014 and four times in 2015. Emission measurements were done during both growing seasons. Manure application increased N₂O emissions compared with no manure addition. Injecting manure did not impact yield or N₂O emissions in either alfalfa and tall fescue in 2014, suggesting no detrimental effect of the injection itself but also reflecting the low initial yields. In 2015, injecting manure to tall fescue increased N₂O emissions by 48% compared with surface application of manure reflecting greater nitrate availability coupled with higher soil moisture content that year. Injecting manure did not increase N₂O emissions compared with surface application of manure in alfalfa during the 2015 growing season. Yields were higher in 2015 than in 2014, in part reflecting higher manure application rates, and inclusion of yields from the 1^st cut of both crops. Our results indicated that manure injection can be implemented without negatively impacting yield in hay crops. Impact on N₂O emissions is crop specific and weather dependent.