Assessing the effects of different long-term ecological engineering enclosures on soil quality in an alpine desert grassland area

Abstract

• Effects of engineering enclosures on soil quality in alpine grasslands are evaluated. • PCA combined with minimum data set is used to explore the soil quality change. • Soil quality index are built to assess soil quality with different enclosure years. • Long-term engineering enclosures improve soil quality of alpine grasslands. The soil quality assessment is the basis for evaluating the soil quality restoration status of degraded grassland and improving soil management in the enclosure areas. However, the evaluation of the effects of different long-term ecological engineering enclosures on soil quality in alpine grassland areas is still lacking. This study took soil samples of alpine grassland from the Tibet Plateau to examine the soil quality of alpine grassland and analyze the main influencing factors of soil quality under different enclosure years. Based on the soil samples from different and corresponding control plots for 10, 11, and 12 years, principal component analysis was used to screen the minimum data set (MDS) of the 12 physical and chemical properties of the soil samples. The soil quality index (SQI) was constructed to quantitatively evaluate the soil quality by the MDS with different closure years. Results show: (1) The respective grades of the soil fertility levels of nitrogen in the sample plots fenced for 10, 11, and 12 years were 4, 5, and 5. The soil fertility level of the other indicators was grade 6. (2) The 12 soil indicators had medium and low degrees of variation. Only the available phosphorus was at a strong variation level in the sample plots for 12 years. (3) The soil quality in the different enclosure years compared with the corresponding control plots became better. The different enclosure years indicated SQI (0.59 ± 0.11) of 10 years > SQI (0.50 ± 0.04) of 12 years > SQI (0.44 ± 0.05) of 11 years. (4) The MDS of soil quality assessment was composed of total nitrogen, total potassium, silt and total porosity. Compared with the full data set, the MDS could better replace the full data set for soil quality assessment (P < 0.01). This study found that the long-term ecological engineering enclosures have improved the soil quality of alpine grasslands. Total nitrogen and total potassium, total potassium and silt, and total potassium and silt were the main factor affecting the soil quality in 10, 11 and 12 enclosure years, respectively.