|Rouppet, B - COLORADO STATE UNIV|
|Westfall, D.G. - COLORADO STATE UNIV|
|Peterson, G.A. - COLORADO STATE UNIV|
Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 19, 1996
Publication Date: March 19, 1997
Interpretive Summary: Conversion of organic forms of nitrogen (N) to inorganic forms ("mineralizaion" done by microbes) is an important soil process when considering N fertility management of agricultural crops. Accurately measuring this process directly in the field has been dificult and consequentlym not widely done. More common are procedures done in the lab, which measure a "potential" of the soil to mineralize N and thus are indirect results. The difficulty of direct field measurements mostly stems from the high degree of variability that exists from one particular spot to the next in a given area. Large differences can occur within mere inches of each other. This study attempted to quanitify (using statistical methods) the number of soil cores needed in order to detect a given difference in N mineralization in undisturbed (no-till) soil conditions. Soil cores (5 by 15 cm) with resins at the bottom were incubated (3-4 wk) in the field over 3 periods in two locations in eastern Colorado. More N was mineralized midway between old corn rows than in-the-row. This method appears to be a reliable method of measuring N in the field, but many observations are needed in order to detect a treatment difference with an acceptable level of confidence.
Technical Abstract: Direct quantitative measurement of soil net N mineralization in agricultural soils under field conditions has not been widely used. A potential method of in situ net N mineralization was investigated in the fallow phase of 3-yr no-till crop rotation at two sites. Undisturbed soil cores (5 by 15 cm) with anion- and the fallow phase of 3-yr no-till crop rotation at two sites. Undisturbed soil cores (5 by 15 cm) with anion- and cation-exchange resins (Sybron Ionac ASB-1P and C-249) at the bottom were incubated in situ. Nitrate-N plus ammonium-N extracted from soil was added to extracted amounts from resin bags to determine net N mineralized during each of three incubation periods (3-4 wk each). Total net N mineralization was 33.7 and 26.5 kg N ha-1 during 84 and 75 d of incubation at Sterling and Stratton, respectively. Relative amounts of resin did no affect N captured but cores placed midway between old corn (Zea mays L.) rows tended to accumulate more (P>F=0.13) N than cores placed in rows. This in situ method appears to be a reliable method for measuring net N mineralization in the field; however, variation is large and many observations are required to obtain net N mineralization rates within an acceptable confidence interval.