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Abstract
This study was conducted in an agro-pastoral transitional zone near Inner Mongolia, northern China, to assess the influence of land use conversion from native steppe to intensive agriculture and from intensive agriculture to alfalfa on soil chemical and biological properties. At two separate sites, plots representing intensive agriculture, alfalfa, and the respective native steppe type (i.e., meadow steppe and typical steppe), were established in 1980. Intensive agriculture lands were cultivated and alfalfa was sown in these intensive agriculture soils since 2002. A sensitivity index, calculated for each measured property by dividing values for the native steppes by corresponding values in intensive agriculture lands or alfalfa lands, was also used to evaluate the responses of the soil quality to land use conversion. The amount of root biomass in intensive agriculture soils was 88% at a 0–10 cm depth and 76% at a 10–20 cm depth lower than those in native steppe soils at both sites. Concentrations of soil organic carbon (C), total nitrogen (N), total phosphorus (P), organic P, and activities of urease, dehydrogenase, acid and alkaline phosphatase at 0–10 cm depth in both steppe types all significantly decreased after native steppes were converted to intensive agricultural lands. Planting alfalfa in intensive agriculture soils increased root biomass and reduced soil pH. Alfalfa improved soil organic C and total N at the meadow steppe site, but not at the typical steppe site, indicating that the directions steppe systems might take after the native steppe was cultivated depended on initial soil properties of the steppes rather than on the disturbance itself. Sensitivity analysis indicated that dehydrogenase activity, spore density of arbuscular mycorrhizal fungi, and total N were more sensitive to land use conversions than total organic C and other enzyme activities.
At the time of the research, the first author was a postdoctoral research worker at the Institute of Grassland Science, China Agriculture University, Beijing, PR China.
The authors are grateful to Manager Yue Wei from Guyuan Farm for his support in the field experiment and Liu Mei-Zheng for her careful laboratory analysis. The research was funded by Science and Technology Ministry of China (2006BAD16B01).
Notes
∗For each property in same soil depth, values with the same letters are not significantly different according to Tukey's test (P < 0.05).
1D: soil depth; 2L: land use; 3S: site.
For each property in same soil depth, values with the same letters are not significantly different according to Tukey's test (P < 0.05).
∗TOC: total organic C; TN: total nitrogen; AP: available P; OP: organic P; TP: total P; EC: electrical conductance; ACP: acid phosphatase; ALP: alkaline phosphatase; DHase: dehydrogenase.
†∗ and ∗∗ represent significance at P = 0.05 and P = 0.01, respectively.
NS: no significant.
∗TOC: total organic C; TN: total N; AP: available P; OP: organic P; TP: total P; EC: electrical conductance.
†The sensitivity index for a given property (p) was calculated as: (p i ) n /(p i ) a , where the subscript “i” refers to soil property i, “n” to steppe soil, and “a” refers to cultivated soil (alfalfa soil).
‡For each property, sensitivity index with the same letter are not significantly different (LSD, P < 0.05).
∗ACP: acid phosphatase; ALP: alkaline phosphatase; DHase: dehydrogenase.
†The sensitivity index for a given property (p) was calculated as: (p i ) n /(p i ) a , where the subscript “i” refers to soil property i, “n” to steppe soil, and “a” refers to cultivated soil (alfalfa soil).
‡For each property, sensitivity index with the same letter are not significantly different (LSD, P < 0.05).
∗Assigned rank according to the Friedman two-way analysis of variance; when two properties had the same rank they are assigned the average of the tied ranks.