Impact of Repeated Dairy Manure Applications on Nitrogen Mineralization Potential and Soil Physical Properties in Southern Idaho Calcareous Soils.

Dairy manure, a beneficial soil amendment, is commonly applied to crops as a source of plant available nitrogen (N), yet little is known about how N mineralization and soil physical properties in the Southern Idaho calcareous soils get affected with a history of repeated dairy manure applications. This information is important to manage the nutrient source, rates, and frequency of application to maximize crop profitability and improve soil health. The objective of this study was to determine the effect of different rates of repeated dairy manure applications on N mineralization potential (based on laboratory incubation study) and in-situ soil physical properties in a sprinkler irrigated calcareous silt loam soils. The study was a randomized complete block design with the following treatments: a control (no nutrient source applied), fertilizer, and three rates (17.3, 34.8, and 52.0 Mg ha^-1; dry weight basis) of manure that were fall-applied either every year or every other year from 2012 to 2016. Pre-plant soil samples were collected from the treatment plots in the spring of 2012-2016 at the 0-30 cm depth and analyzed for total N, organic matter, organic N, Olsen P, and Olsen K. Subsamples of pre-plant soils from different treatment plots were incubated aerobically at 23⁰C for 100 d at field moisture (~20-22%) in the laboratory to monitor Potentially mineralizable N (PMN). Effects of treatments on PMN and how PMN values are compared to soil test parameters to determine if a general N mineralization potential prediction equation can be developed for Southern Idaho silt loam soils with dairy manure application histories will be discussed. After 4 y history of dairy manure application, treatment plots were sampled in July 2016 to measure bulk density, gravimetric water content, porosity, and organic carbon. Significant decreases in soil bulk density and significant increases in porosity and organic carbon with increasing cumulative manure application rate suggests that manure additions are significantly improving soil structure.