Estimating Mineralizable Nitrogen in Indiana Soils.

Previous field research across 20 site-years in Indiana found soil N supply was the most important factor determining fertilizer N rate needed to optimize corn yield. Current soil testing methods did not predict soil N supplying capacity in these experiments. The inability to estimate mineralizable soil N prior to the growing season limits our ability to develop more accurate N rate recommendations for corn production. We assessed N mineralization in major soil types of Indiana that differed substantially in organic matter, texture, and previous crop with a laboratory incubation procedure. Soils were incubated at 25℃ and a water suction of 10 kPa and leached weekly with 100 ml 5mM CaCl₂ solution in 3-50 ml increments for 10 weeks. The leachate was collected and analyzed colorimetrically for inorganic N to determine the mineralization rates. Laboratory mineralization rates were compared to field measurements of N supplying capacity and related to soil properties.