_Applied_  
_sciences_  
_Article_  
**Effects of Mixing Feldspathic Sandstone and Sand on Soil Microbial Biomass and Extracellular Enzyme Activities--A Case Study in Mu Us Sandy Land in China**  
**[PERSON] 1,2,3, [PERSON] 1, [PERSON] 1,2,3,4,*, [PERSON] 3 and [PERSON] 5\({}^{\copyright\)**  
1 Key Laboratory of Degraded and Unused Land Consolidation Engineering, the Ministry of Natural Resources, Xi'an 710075, China; [EMAIL_ADDRESS] (X.F.); [EMAIL_ADDRESS] (L.Z.)  
2 Shaanxi Key Laboratory of Earth Surface System and Environmental Carrying Capacity, Northwest University, Xi'an 710127, China  
3 College of Urban and Environmental Sciences, Northwest University, Xi'an 710127, China; [EMAIL_ADDRESS]  
4 State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Water and Soil Conservation, Chinese Academy of Sciences and Ministry of Water Resources, Yangling 712100, China  
5 Department of Microbiology and Plant Biology, Center for Spatial Analysis, University of Oklahoma, Norman, OK 73019, USA; [EMAIL_ADDRESS]  
* Correspondence: [EMAIL_ADDRESS]  
Received: 4 August 2019; Accepted: 17 September 2019; Published: 20 September 2019  
**Abstract:** Microbial biomass, extracellular enzyme activity, and their stoichiometry in soil play an important role in ecosystem dynamics and functioning. To better understand the improvement of sand soil quality and the limitation of soil nutrients after adding feldspathic sandstone, we investigated changes in soil microbial activity after 10 months of mixing feldspathic sandstone and sand, and compared the dynamics with soil properties. We used fumigation extraction to determine soil microbial biomass carbon (MBC), nitrogen (MBN), phosphorus (MBP), and microplate fluorometric techniques to measure soil \(\beta\)-1,4-glucosidase (BG), \(\beta\)-1,4-xylosidase (BX), \(\beta\)-D-cellobiohydrolase (CBH), N-acetyl-\(\beta\)-glucosamine (NAG), and Alkaline phosphatase (AKP). We also measured soil organic carbon (SOC), pH, electrical conductivity (EC), soil inorganic carbon (SIC), and soil water content (SWC). Our results showed that the soil microbial biomass C, N, P, and individual extracellular enzyme activities significantly increased in mixed soil. Similarly, the soil microbial biomass C:N, C:P, N:P, MBC:SOC, and BG:NAG significantly increased by 54.3%, 106.3%, 33.1%, 23.0%, and 65.4%, respectively. However, BG:AKP and NAG:AKP decreased by 19.0% and 50.3%, respectively. Additionally, redundancy analysis (RDA) and Pearson's correlation analysis showed that SWC, SOC, porosity and field capacity were significantly associated with soil microbial biomass indices (i.e., C, N, P, C:N, C:P in microbial biomass, and MBC:SOC) and extracellular enzyme activity metrics (i.e., individual enzyme activity, ecoenzymatic stoichiometry, and vector characteristics of enzyme activity), while pH, EC, and SIC had no correlation with these indices and metrics. These results indicated that mixing feldspathic sandstone and sand is highly susceptible to changes in soil microbial activity, and the soil N limitation decreased while P became more limited. In summary, our research showed that adding feldspathic sandstone into sand can significantly improve soil quality and provide a theoretical basis for the development of desertified land resources.  
**Keywords:** feldspathic sandstone; sand soil; Mu Us sandy land; soil microbial biomass; extracellular enzyme activity; ecological stoichiometry