The influence of tillage on net nitrogen mineralization out of sod for two toposequences was estimated by several different methods. A field procedure utilizing small rain shelters to prevent leaching was employed to measure N mineralized in no-tillage (NT) and plowed (CT) treatments for six soils. Potentially mineralizable N and autoclavable N were also determined. An intact soil core procedure was developed to measure N mineralization. With the field procedure, mineralized N was generally greater in the well-drained soils but decreased with decreasing drainage. There was a highly significant interaction between soil type and tillage with greater amounts of N mineralized in the plowed well-drained soils but less in the poorly drained soils when compared to the corresponding no-tillage treatment. The standard laboratory estimates were able to predict differences between soils but did not predict the tillage effect. The development of a laboratory intact core procedure allowed for simulation of tillage effects and was correlated to the field estimates (r = 0.76). More importantly, the tillage ratios for mineralized N (NT:CT), which varied from 1.38 to 0.43, were reasonably correlated (r = 0.73) between the field and intact core procedures. Key words: Mineralized N methods, no-tillage, moldboard plow tillage, intact cores
Effects of in situ freezing on soil net nitrogen mineralization and net nitrification in fertilized grassland of northern China
