Quantification of soil element changes in long-term agriculture: A case study in Northeast China

Anthropogenic measures that are implemented to improve the nutrient status of soil for growing food can lead to soil and environmental contamination. The influence of agricultural measures (cultivation and fertilization) on a cropland soil can be explained and quantified by exploring the variety and distribution of elements (calcium iron, rubidium, titanium, etc) in the soil profile. In this study, a cropland soil subjected to long-term (1948-2019, 72 years) anthropogenic agricultural activity was compared with a natural, undisturbed forest soil. Results showed that the anthropogenic activity affected the correlation of different elements in the cropland soil to different degrees, with the degree of the effects ranked as follows: calcium (Ca) > iron (Fe) = rubidium (Rb) > titanium (Ti) = chromium (Cr) > potassium (K) = zirconium (Zr) = strontium (Sr) > sulfur (S) = nickel (Ni) = scandium (Sc) > manganese (Mn) > vanadium (V) = zinc (Zn) = tungsten (W) > copper (Cu) = lead (Pb) = cobalt (Co). The elements were distributed much more evenly throughout the profile of the natural forest soil than the disturbed cropland soil. Some elements, such as Fe, Ti, V, Pb, Cr, Rb, K, Ca, Mn, Sc, Sr, and Cu, can be absorbed by vegetable growth and participate in the plant physiological cycle, while others, such as K, Rb, Cr, and Ti, may be lost readily as the soil is tilled. Elements such as Pb, Sc, Zn, and Sr, gradually accumulate over time from continuous fertilizer applications. In order to maintain the health of cropland soils, both farmers and policy makers should strive to mitigate elemental pollution by carefully managing applications of micronutrient fertilizers.