Effects of regulated deficit irrigation on soil phosphorus nutrients in spring wheat field Soil carbon sequestration characteristics of plantations and influencing factors in Loess Hilly Semiarid Region Characteristics of soil phosphorus in different aged stands of Chinese fir plantations in Huitong, Hunan Province Long-term changes in area and soil total nitrogen and total phosphorus storage in croplands of the densely populated village landscapes of China′s Yangtze Plain