Net nitrogen mineralization from past year's manure and fertilizer applications.

Authors: Lentz, Rodrick; Lehrsch, Gary

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2011
Publication Date: 6/4/2012
Citation: Lentz, R.D., Lehrsch, G.A. 2012. Net nitrogen mineralization from past year's manure and fertilizer applications. Soil Science Society of America Journal. DOI:10.2136/sssaj2011.0282.

Interpretive Summary: The U.S. dairy herd of 9 million animals produces 22 million tons of manure annually, much of which is applied to cropland. To maximize their use of manure and minimize losses of nitrogen (N) to the environment, growers in the intermountain West need to understand how soil N changes in years following application of manure. This is particularly important for sugarbeet because yield or beet quality is sensitive to both insufficient and excess supply of N. Our experimental treatments included two rates of manure applied from one to five years prior to the year crops were grown. We measured net nitrogen (N) mineralization in surface and subsoils. The fraction of total manure-applied N made available in the soil decreased as a power function of the year applied, which differed depending on the application rate. The subsoil played a greater role in manure mineralization than previously known. These findings will allow growers in semi-arid, irrigated regions to better estimate the quantity of N available to crops grown in fields treated with stock-piled dairy manure. This will improve N utilization.

Technical Abstract: Manure from the semiarid West’s dairy industries is a rich nutrient source, but its use for crops can be problematic because soil N availability from manure may vary substantially depending on the year of application. Experimental plots established in Idaho on a Portneuf silt loam (coarse silty, mixed, superactive, mesic Durinodic Xeric Haplocalcid) included six manure treatments and two non-manure treatments with four replicates. The six manure treatments included combinations of two manure rates, Man-1x (0.31 Mg total N/ha) and Man-3x (0.97 Mg total N/ha) applied in the fall either 1, 2, or 3 years previously. The two non-manure treatments were urea fertilizer applied per soil test (Fert) and a control with no amendment. We measured net N mineralization (0-30 cm) in the plots using buried bags in 2006, 2007, and 2009 for a sprinkler-irrigated barley, sugarbeet, and dry bean crop, respectively. This resulted in i) two years of net N mineralization data for each manure rate applied 1, 2, or 3 years prior to measurement; and ii) one year of data for each manure rate applied 4 or 5 years previous to the measurement year. A 5-year decay series for each of the two manure rates was derived from functions fitted to the net N mineralization data, expressed as a fraction of total manure-N applied. The decay series (y1-y5) for the manure-1x treatment was 0.23, 0.12, 0.10, 0.09, and 0.08 while that for the manure-3x rate was 0.20, 0.08, 0.05, 0.04, and 0.03. Soil at the 30-to-60-cm depth contributed up to 28% of the total N mineralized in the 0-to-60-cm soil layer of manure-amended soils in the 3rd year after application, with lesser amounts contributed in earlier years due to immobilization. The efficacy of N mineralization processes decreased as the manure application increased, thus using a single decay series to predict N availability across a range of manure application rates could lead to substantial estimation errors.