A dataset of soil physicochemical characteristics and plant species diversity in alfalfa field of abandoned 1–49 years in Shenmu, Shaanxi Province

The abandonment of alfalfa fields is increasing in a semi–arid region. To determine the changes of soil water content, soil bulk density, soil porosity, soil saturated water conductivity, soil pH, soil NH4-N, NO3-N, soil available phosphorus, soil organic carbon, soil total nitrogen, Margalef index, Pielou index, Simpson index, and Shannon–Wiener index in abandoned alfalfa fields are essential for vegetation restoration. This dataset was collected by the National Field Scientific Observation and Research Station of Shenmu Grassland Agricultural Ecosystem in Shaanxi Province. Alfalfa fields with different abandonment times were investigated in 2003 (1–30 years), 2014 (12–41 years), and 2022 (20–49 years), and obtained the data of soil physicochemical characteristics and plant species diversity. In this dataset, field investigation, laboratory measurement, data calculation, data storage, and quality control were carried out in strict accordance with international observation technical standards. The data has a high quality, which could provide data basis for the study of alfalfa succession process in semi–arid areas.