How Quantitative Are in-Situ Mineralization Columns in Sandy Soils?.

Nitrogen mineralization in sandy soil cropping systems is difficult to quantify. This study used an in-situ soil incubation column technique based on Brye et al. (2002) to determine the effect of an oat cover crop and N fertilizer on in-situ mineralization and seasonal PAN in a sandy soil, under an irrigated sweet corn cropping system. The study was conducted across two growing seasons at the Hancock Agricultural Research Station in the Central Sands of Wisconsin and the experimental design was a randomized complete block, split-plot design with two whole-plot treatments (oat and no cover) and two split plot treatments (no N and 168 kg-N ha-1). Nitrogen mineralization rates were measured using in-situ incubation cores and ion-exchange resin sachets. Cores were constructed of polyvinyl chloride pipes (30.5 cm in depth and 20 cm in diameter) and incubated during three 30-day periods throughout the 90-day sweet corn growing season. In both study years there was no effect of the oat cover crop on N mineralization when N fertilizer was applied. Mineralization column mass balance calculations were completed and discrepancies were determined between total N recovered in the mineralization column versus total N applied. These findings suggest that while the in-situ mineralization column method lacks quantitative precision for N budgeting, it is a useful tool for determining mineralization trends between treatments.