Tuesday, November 6, 2007
205-6

Protocol Comparison for Quantifying in Situ Mineralization.

Brian Wienhold, Gary Varvel, and Wally Wilhelm. East Campus, UNL, USDA-ARS, USDA-ARS, 120 Keim Hall, Lincoln, NE 68583-0934

In situ mineralization methods are intended to quantify mineralization under realistic environmental conditions. This study was conducted to compare soil moisture and temperature in intake soil cores contained in cylinders to that in adjacent bulk soil, compare the effect of two resin bag techniques on drainage from soil within cylinders, and assess the effect of installation time on inorganic N retention by resins. The study was conducted at a dryland conventionally tilled corn site and a no-tillage irrigated corn site in eastern Nebraska. Soil in cylinders was moister (<0.05 g g-1) and warmer (< 1oC) than adjacent soil. Soil water content was <80% water-filled pore space at all sampling times and differed little between resin bag techniques. Greatest differences in water content between soil in cylinders and adjacent bulk soil was for cylinders installed into very moist soil following a precipitation event late in the study. Installation under very moist soil conditions likely resulted in compaction of soil below the cylinder impeding drainage. Greater soil water content and higher temperature conditions observed during most of the study period likely enhanced mineralization within the cylinder compared to mineralization in adjacent bulk soil but the magnitude is less than core-to-core variation normally observed in a field. We attribute these water content and temperature differences to root exclusion eliminating water uptake by the crop from soil within cylinders. Installing cylinders for more than 60 days resulted in loss of inorganic N from resins. The in situ method utilizing intact soil cores and resin bags replaced at 28 to 40 day intervals is a viable method for measuring mineralization. Care is needed during collection of the intact soil core to insure that compaction of soil below the cylinder does not impede drainage after resin bag installation.

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