Container and Installation Time Effects on Soil Moisture and Temperature and Inorganic Nitrogen Retention for an In Situ Mineralization Method

Authors: Wienhold, Brian; Varvel, Gary; Wilhelm, Wallace

Submitted to: Communications in Soil Science and Plant Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/22/2008
Publication Date: 6/29/2009
Citation: Wienhold, B.J., Varvel, G.E., Wilhelm, W.W. 2009. Container and Installation Time Effects on Soil Moisture and Temperature and Inorganic Nitrogen Retention for an In Situ Mineralization Method. Communications in Soil Science and Plant Analysis. 40:2044-2057.

Interpretive Summary: Mineralization of crop residue, added animal waste, and soil organic matter results in release of nitrogen and other nutrients needed by subsequent crops. It is difficult to accurately predict the amount or timing of nitrogen that will be available for a crop. Accurately predicting availability of mineralized nitrogen is a necessary component for calculating optimum fertilizer rates to reduce the potential for environmental degradation and ensure crop productivity. Models that accurately predict nitrogen availability are needed and field-based measurements of nitrogen mineralization are required for development of these models. Methods using cylinders to enclose intact soil cores with resin bags below the core to capture leached nitrogen are available for measuring mineralization under field conditions but information about how these methods modify soil moisture and temperature are needed. Information on how long resin bags can be left in the soil is also needed. We compared soil moisture and temperature of soil in intact cores to that of adjacent field soil in corn fields under irrigated and rainfed conditions. We also compared nitrogen retention by the resin bags for installation times ranging from 28 days to 91 days. Soil contained in mineralization tubes had greater water contents and temperatures than adjacent bulk soils but these differences were small and should not significantly affect mineralization. Nitrogen retention by resin bags was highly variable when bags were installed for longer than 40 days. With proper installation and duration of installation this method accurately measures nitrogen mineralization.

Technical Abstract: Mineralization contributes significantly to agronomic N budgets and is difficult to accurately predict. Models for predicting N mineralization contributions are needed and development of these models will require field-based data. In situ mineralization methods are intended to quantify N mineralization under ambient environmental conditions. This study was conducted to compare soil moisture and temperature in intact soil cores contained in cylinders to that in adjacent bulk soil, compare the effect of two resin bag techniques on water content for soil within cylinders, and assess the effect of installation duration on inorganic N retention by resins. The study was conducted at a dryland conventionally tilled corn (Zea mays L.) site and an irrigated no-tillage corn site in eastern Nebraska. Soil in cylinders was slightly moister (<0.05 g g-1) and warmer (< 1oC) than adjacent soil. Soil water content was <80% water-filled pore space (WFPS) at all sampling times and differed little between the two resin bag techniques. Greater soil water content and temperature conditions (though small) observed during most of the study period likely enhanced N mineralization within the cylinder compared to N mineralization in adjacent bulk soil but the magnitude is likely much less than core-to-core variation normally observed in a field. Installing cylinders for more than 60 days resulted in loss of inorganic N from resins. Care is needed during installation to insure that compaction of soil below the cylinder does not impede water movement through the intact soil core. The in situ method utilizing intact soil cores and resin bags replaced at 28 to 40 day intervals is a viable method for measuring N mineralization.