| Compared to the cereal cropland, soil physical, chemical and biological properties, such as organic matter, total N, available nutrient (N,P and K), acidity and alkalinity, salinity and bio-activity, have obviously changed with the prolongation of green-house cropping duration, and this has decreased the soil quality, impacted crop growth and potentially threatened human health. In order to sustain the high yield vegetable production with high quality and high efficiency, it is of great theoretical and practical significance to study the soil fertility and its affecting factors in the green-house cropping system. The work in this paper has analyzed soil samples from green-houses with l-,3-,5-,7- and 9-year long cropping history for the purpose of further understanding the soil fertility and establishing rational and effective management measures. The obtained results showed that:1. The pH of the vegetable land soil was significantly lower than that of the cereal cropland soil, and that of the green-house soil was lower than that of the air-opening land soil. With the prolongation of green-house ages, the soil has showed obvious tendency to acidification.2. The organic matter content of green-house soil was observed remarkably higher than that of cereal cropland soil nearby. In green-house system, the content of soil total N increased with the extension of cropping time, maximized at the fifth year, and then tended to decrease.3. The green-house soil was found usually with higher alkaline N contents compared to the adjacent cereal crop land. However, no certain correlation was showed between the alkaline N contents and ages of green-house. The available P content of green house soil was 4.9 times as high as that in the cereal cropland, and it was observed to increase linearly in the first five years. In contrast, the available K content was lower than the cereal cropping land soil and decreased with the prolongation of ages of green-house.4. The soil in green-house usually found abundant with B and Cu, and the B and Cu concentration was extremely high in the 1 to 7 year old green house. However, the soil Fe concentration was decreased with the increase of green-house age, and the available Zn also tended to decrease after 5 years of green-house cropping. Thereafter, Fe and Zn deficiency may happen in soil with the extension of green-house age.5. In the first 5 years, the bulk density of green-house soil tended to be lowered compared the air-opening vegetable land. The Cation exchange capacity of the green-house soil was found in the sequence as: 1 year > 3 year > 5 year > 9 year > 7 year. This indicated that the soil started to harden and to lose its fertility sustaining capacity.6. The salt content was found to be 0.48 to 1.15 g/kg with the average of 1.06 g/kg in the green-house soil, and it was 253.3% higher than that of the cereal cropland soil, especially the Cl\ NO3". This showed that the green-house soil tended to salinization with the prolongation of green-house age.The green-house soil has showed obvious tendency of acidification and salinization, together with the enrichment of N and P, decrease of available K content, deficiency of Fe and Zn, increase of Cl\ NO3" concentration. This has resulted in nutrient imbalance, soil hardening, and decrease soil fertility sustaining ability. Soil in 7 year old green house has showed obvious constrains of fertility. |
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