Soil N Mineralization in Burley Tobacco (Nicotiana tabacum L.) Tillage and Rotation Systems.

Soil nitrogen mineralization (SNM), the microbial and biochemical transformation of organic N into inorganic N, is of central importance to nitrogen management and the productivity of agricultural soils. However, the accuracy and reliability of soil N mineralization analysis depends on the methods used. In our study, the long-term in-situ resin-core tube and a laboratory incubation method were both used to predict net soil N mineralization in six burley tobacco tillage and rotation systems. The main effects of different tillage and rotation system treatments, on both  in-situ and laboratory methods, as well as the effect of N fertilizer rates on native soil N mineralization, were determined. The laboratory method results found that mineralized N was significantly higher with no-tillage than with plow tillage, and also when grass sod, rather than corn and soybean, was grown for two years in rotation with tobacco. The in-situ method found no statistical difference in N mineralization due to tillage or the contrast between grass sod and row crops. With field incubation, the N fertilizer rate had no effect on soil N mineralization rates across the six tillage-rotation systems examined. Comparisons between the in-situ and laboratory methods demonstrated that laboratory incubation tended to overestimate SNM with no-tillage, but underestimated SNM in some row crop rotation systems, due to different soil sample pretreatment.