Refinements to an In‐Situ Soil Core Technique for Measuring Net Nitrogen Mineralization in Moist, Fertilized Agricultural Soil

Diffusion of NO − 3 –N ions and nonuniform distribution of surface‐applied N fertilizers contribute to large variations in field measurements of net N mineralization. An in situ soil core–ion exchange resin bag (ISC–IERB) field method has been used reliably to measure net N mineralization in intact soil cores but has not been widely tested in moist, though nonirrigated, N‐fertilized agricultural soils. From 1996 through 2000, net N mineralization was measured in the top 20 cm using a refined version of the ISC/IERB technique for the first 1‐mo period following planting and fertilization of N‐fertilized and N‐unfertilized, no‐tillage and chisel‐plowed corn ( Zea mays L.) agroecosystems on Plano silt loam (fine‐silty, mixed, superactive, mesic, typic argiudoll) in south‐central Wisconsin. Progressive modifications were made to the ISC/IERB technique, which ultimately resulted in reduced sample variability. Following the refinements, a significant N fertilization effect was shown for the most variable period of the growing season where net N mineralization rates for N‐fertilized corn treatments were significantly higher ( p < 0.001) than for N‐unfertilized corn treatments.