中国亚热带耕作雏形土及强酸土的可蚀性与渗透性关系

To evaluate the validity of different indices in estimating soil readily mineralizable N, soil microbial biomass (Nmic), soil active N (SAN), soluble organic N (SON), net N mineralization rate (NNR) and gross N mineralization rate (GNR) in mineral soils (0-10 cm) from six forest stands located in central Germany were determined and compared with two sampling times: April and November. Additionally, soil density fractionation was conducted for incubated soils (with addition of ¹⁵NH₄-N and glucose, 40 days) to observe the sink of added ¹⁵N in different soil fractions. The study showed that Nmic and NNR in most stands differed significantly (P ≤ 0.05) between the two sampling times, but not GNR, SAN and SON. In November, no close relationships were found between GNR and other N indices, or between Nmic, SON, and SAN and forest type. However, in April, GNR was significantly correlated (P ≤ 0.05) with Nmic, SAN, and NNR along with Nmic under beech being significantly higher (P ≤ 0.05) than under conifers. Furthermore, density fractionation revealed that the light fraction (LF, 0.063-2 mm, > 1.7 g cm^-3) was not correlated with the other N indices. In contrast, results from the incubation study proved that more ¹⁵N was incorporated into the heavy fraction (HF < 0.063 mm, > 1.7 g cm^-3) than into LF, indicaing that more labile N existed in HF than in LF. These findings suggested that attention should be paid to the differences existing in N status between agricultural and forest soils.

Relationships between permeability and erodibility of cultivated acrisols and cambisols in subtropical China

The relationships between soil erodibility factor (K) and soil saturated permeability (K_fs) for cultivated Acrisols derived from Quaternary red clay and Cambisols derived from red sandstone were studied and quantified using a rainfall simulator and Guelph permeameter in a hilly area of subtropical China. A negative correlation existed between K_fs of the topsoil (0–5 cm) and K. The empirical expression K ≈ a × K^−b_fs + c, where a, b and c are the structural coefficients related to soil properties, such as soil type, soil parent material, organic matter, pH and mechanical composition, best described the relationship between soil saturated permeability and soil erodibility.