Abstract
This objective of this study was to investigate the effect of long-term N fertilizer application on Calcium (Ca) saturation in a calcareous farmland soil located in a semiarid to subhumid region. The soil type was a Lou soil (Eum-Orthic Anthrosol). Results from this study provide important information about the relationship between fertilization and soil fatigue in farmland. The study also provides insight about soil factors that impact crop stress resistance and changes traditional concepts regarding the Ca balance in calcareous soils. The results showed that across the landscape there was moderate variation in the soil organic matter content of the 10 to 20 cm soil layer. The soil organic matter content was highest near to the village, reflecting the traditional use of organic manure on the Guanzhong Plain and confirming the principle of “village at the center”. This result also highlighted uneven soil quality across the landscape due to human activity. The soil organic matter content was less but the soil available N content was greater in the 0 to 10 cm layer than the 10 to 20 cm layer. This observation is probably due to the application of inorganic fertilizer in modern agriculture. Soil Ca saturation declined by 15.38 to 14.46% as the distance from the village increased. This observation is probably due to interaction between ancient and modern fertilization practices as well as recent land policies. The pattern of changes for soil Ca saturation across the landscape was similar to the pattern of changes for soil organic matter content but opposite to the pattern of changes for soil available N. This proved that application of large amounts of inorganic N fertilizer can increase inorganic soil N and decrease Ca saturation. This is one symptom of soil potential degradation or soil fatigue. In summary, the application of inorganic fertilizer resulted in a significant decrease in the percent of soil Ca saturation in this calcareous soil. This indicates that the application of inorganic N fertilizer can cause a considerable decline in soil health and reduce the effectiveness of modern fertilizers.
Key words: Calcareous soil, degree of Ca saturation, fertilization, semiarid inclined to humid area.
