Denitrification from Soils of a Year‐Round Forage Production System Fertilized with Liquid Dairy Manure

Abstract

Abstract Denitrification is an important potential sink for N in liquid manure and the amount of denitrification may affect sustainability of crops grown with liquid manure as a nutrient source. This study examined gaseous N loss by denitrification and the changes in soil N pools after liquid manure application. Liquid dairy manure was applied at four N rates (246, 427, 643, and 802 kg N ha −1 yr −1 ) to four quadrants of a center‐pivot in a year‐round forage production system. Denitrification (using the acetylene block technique on intact cores) and soil N pools were determined before and for 2 yr after beginning liquid manure application. Nitrous oxide evolution from soil cores was compared to denitrification for a third year of the study. Denitrification rates and soil N pools increased after manure application at all rates of application. The two highest rates of manure had highest denitrification rates, although differences in soil moisture due to soil and drainage properties complicated the interpretation of manure rate effects. At the two highest rates of N application and two lowest rates of N application, the quadrant with higher soil moisture had higher denitrification. Nitrous oxide emissions accounted for about 29% of total denitrification. Denitrification ranged from 11 to 37% of total N applied in the manure. Highest rates of denitrification and highest proportions of total N denitrified were found with the second highest manure application rate because these soils were wetter. Annual denitrification totals ranged from 32 to 114% of the excess N (application‐crop uptake) available.