2.1 Study Region
The two study counties, Wugong (34°12′-34°26′ N, 108°0′-108°26′ E) and
Meixian (33°59′-34°19′ N,107°39′-108°00′ E) in Shaanxi, are located in
the western Guanzhong Basin, the south edge of Loess Plateau in China.
The region is typical of a warm-temperate sub-humid continental monsoon
climate with a mean annual temperature of 13 ℃ and average annual
precipitation of 630 mm, with 60-80% occurring between July and
September.
The study area has a more than 2,000 years-long agricultural history and
is a very intensive agricultural area in China now. The main crops in
Wugong and Meixian counties before 1992 were winter wheat and summer
maize, with two harvests each year (Fig. 1). Kiwifruit production
developed rapidly in Meixian County since 1995. In 2017, the kiwi
orchard area increased to 15688 ha, accounting for 64 % of the total
cropland area. The dominant soil textures include loam, sandy loam, and
loamy sand (Gao et al. , 2021).
Winter wheat and summer maize are still the main crops in Wugong. It
provided an ideal case to study the effects of LUCs on nutrient
surpluses and accumulations in soils at the county scale. The total
arable land of Wugong County is 31369 ha. The topography of Wugong
County consists of three types: the frontal zone of the piedmont
alluvial fan, the loess platform and valley alluvial terraces. There are
six soil types in the county: cinnamon soil, loess soil, flavor-aquic
soil, swamp soil, paddy soil, and silt soil. High-quality soils such as
loess soil, account for 94.3%.