Dell, Curtis (USDA-ARS, University Park, PA.USDA-ARS-PSWMRU, Building 3702, Curtin Road, University Park, PA, 16802; Phone: 814-863-0984; Fax: 814-863-0935; Email: curtis.dell@ars.usda.gov)

Nitrous Oxide Emissions From Soils Receiving Combinations of Dairy Manure and Mineral Nitrogen Fertilizers

C.J. Dell *

The nitrification and denitrification of fertilizer and manure N applied to agricultural soils contributes substantial quantities of the greenhouse gas nitrous oxide to the atmosphere. Since manure application adds organic C as well as N, increased microbial activity in manure-amended soils could increase nitrification and denitrification activity compared to soil receiving only mineral N fertilizer. In a effort to reduce P movement to water supplies, many states now recommend or require producers to limit quantities of manure applied to the amount needed to supply crop P requirements. With lower manure application rates, the addition of inorganic N fertilizer is also needed. However, it is unclear if the use of a combination of manure and inorganic fertilizer presents a greater potential for nitrous oxide production than the use of only inorganic fertilizer. Nitrous oxide emissions were measured in 2003 and 2004 from experimental plots planted to corn. All plots received the recommended additions of N (145 kg N per hectare), but the source of the N was varied among ammonium nitrate, dairy manure, and a combination of the two. Gas samples were collected over a 30 min time span each week using small, vented chambers. Nitrous oxide concentrations were measured of by gas chromatograph equipped with an electron capture detector. Most nitrous oxide emissions occurred within two months of the spring manure or fertilizer application. By late in the growing season, emissions were near or below the minimum detection level. On several sampling dates, emissions from plots receiving some or all N as manure were significantly greater than those receiving only ammonium nitrate. Estimates of N lost as nitrous oxide during the growing seasons ranged from 1 to 6% of applied N. In 2003, total emissions were similar among N source treatments. In 2004, total emissions from plots receiving manure were significantly greater than those receiving only ammonium nitrate. However, emissions were similar between experimental plots receiving all manure compared to those where N application was split between manure and ammonium nitrate. The results suggest that manure application, even at reduced P-requirement based rates, can increase the potential for nitrous oxide production. Reducing nitrous oxide emissions following land application presents a major challenge. Additional research on the impact of manure and fertilizer application timing and techniques is needed in order to develop management practices that lead to reduced emissions.