|Van Kessel, Jo Ann|
|Reeves Iii, James|
Submitted to: Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 20, 2002
Publication Date: July 25, 2002
Interpretive Summary: The nutrients in manure can be an important commodity and an essential part of crop production. However, in recent years the importance of nutrient accountability on dairy farms has become increasingly evident. Excess nutrients can have a detrimental environmental impact. Therefore it is essential to be able to accurately estimate the plant availability of nutrients in manure prior to determining land application rates. Currently a single fixed value is used to estimate the availability of organic nitrogen in manure. The objectives of this study were to determine the variability in dairy manure organic N availability, to determine if organic N availability can be predicted by manure composition, and to determine if N availability can be predicted by spectroscopic techniques. Dairy manures were collected from farms in MD, VA, PA, NY, and CT. The concentrations of nutrients (such as N) in these samples were highly variable. This variation strongly supports the necessity for testing individual manure samples rather than using standard book values for manure composition. The availability of organic nitrogen in these manures was also highly variable. As much as 55% of the organic nitrogen was available in some samples and in other samples the addition of manure N had a negative affect on total available nitrogen. The concentrations of nutrients in the manures and spectroscopic methods were not good predictors of nitrogen availability. Based on the results of this experiment, there is a strong need for further research into the development of rapid methods for predicting the potential plant availability of nitrogen in of dairy manures.
Technical Abstract: Currently most nutrient management plans incorporate a fixed percentage when accounting for available organic N. The objectives of this study were to determine the variability in mineralization of dairy manure N, to determine if N mineralization can be predicted by compositional factors, and to determine if N mineralization can be predicted by near- or mid-infrared diffuse reflectance spectroscopy. Dairy manures (n = 107) were collected from farms in MD, VA, PA, NY, and CT. Compositions ranged from 14 to 386 g kg-1 dry matter, 0.9 to 9.5 kg/m3 total N, and 0.3 to 4.7 kg/m3 NH4+-N. Manure-amended soil was aerobically incubated at 25 C and concentrations of NH4+-N and NO3--N were determined at d 2 and d 56. The manures were highly variable in their N mineralization characteristics, ranging from a net mineralization of 54.9% to a net immobilization of 29.2% of the organic N. When compositional parameters were individually regressed against % mineralized organic N, the highest coefficient of determination (R2) was 0.101. A stepwise regression of all 11 variables yielded a maximal R2 of 0.236. These results suggest that the availability of dairy manure organic N is highly variable and that the availability cannot be predicted by simple compositional parameters. No relationship was found between NIR spectral characteristics and N mineralization suggesting that no simple relationship exists between N mineralization and compositional characteristics. While NIR was unsatisfactory, there appears to be some potential for the use of mid-IR for determining the mineralization potential of manures.