Study on Undisturbed Soil Sample Incubation for Estimating Soil Nitrogen Supplying Capacity in Loess Plateau

【Objective】The purpose is to assess the effects of N supplying capacity on Loess Plateau using long-term alternate leaching aerobic incubation with undisturbed soils. 【Method】 Based on the results from pot experiments treated with leaching soil initial NO3--N and non-leaching soil initial NO3--N, long-term alternate leaching aerobic incubation with undisturbed soil samples was conducted to study the soil nitrogen supplying capacity of 11 surface soil with different fertilities on Loess Plateau. 【Result】The results indicated that when initial NO3--N was not leached, soil initial NO3--N and mineral N extracted by CaCl2 before aerobic incubation were closely related with raygrass nitrogen uptake, the correlation coefficients were 0.856 and 0.862, respectively, both reached at 1% significant level. When initial NO3--N was leached,, it was no good relationship between mineralizable N extracted by aerobic incubation, soil initial mineral N and mineralizable N extracted by aerobic incubation, N0 and soil initial mineral N and N0 with raygrass nitrogrn uptake, the correlation coefficients were 0.410, 0.553, 0.492 and 0.419, respectively, indicating that the poor effects of mineralizable N on reflecting soil N capacity were influenced and disturbed by initial nitrate. When initial NO3--N was leached, the correlation coefficients between soil initial NO3--N and mineral N extracted by CaCl2 before aerobic incubation with raygrass nitrogen uptake were decreased to 0.613 and 0.607, respectively, and both reached 5% significantly level. However, the correlation coefficients between mineralizable N extracted by aerobic incubation, soil initial mineral N and mineralizable N extracted by aerobic incubation, N0 and soil initial mineral N and N0 with raygrass nitrogen uptake were raised obviously, and all reached 5% and 1% significant level. 【Conclusion】It is concluded that NO3--N in soil extracted by CaCl2 before aerobic incubation is a good soil N index, reflecting soil N supplying capacity at present, but it is difficult to reflect soil potential N supplying capacity, and the long-term alternate leaching aerobic incubation with undisturbed soils is good laboratory method to estimate soil nitrogen supplying capacity, if compared with plant nitrogen uptake in pot experiment with leaching soil initial NO3--N.