红壤丘陵区土地不同利用方式对土壤有机质的影响

Effects of Soil Organic Matter in Hilly Red Soils from Mid-Subtropics Region Under Various Utilization Patterns

采用现场采样及室内分析方法,研究了我国中亚热带南、北两端地区土地(红壤坡地和红壤性水稻土)不同利用方式下的土壤有机质的变化。结果表明,中亚热带南缘地区由红壤林地开垦为农用地的土壤有机质数量4年间平均下降了2.1g·kg-1·a-1,以旱作处理的土壤有机质损失最为严重,平均下降4.6g·kg-1·a-1;中亚热带北缘地区由红壤荒坡地开垦为农用地的土壤有机质数量9年间平均增加了0.4g·kg-1·a-1;长期耕种的红壤性水稻土的有机质数量在不断提高(0.3g·kg-1·a-1),且芳构化程度也在增加,活性有机质所占的比例加大。

With population increasing, available land for agriculture is more and more limited. This controversy forces people to exploit forest land and wasteland to meet the rapidly increasing need of agricultural products. Alternation of using ways directly leads to the change of some soil physico-chemical properties. But few reports have appeared concerning the deteriorated soil and thenewly exploited soil. On the other hand, red soil is the widespread land in South China, estimated to be about 1 170 000 Sq. kilometers and accounts for 12%of Chinese land area. This paper is aiming at the change of organic matter in red soil after exploiting the forest land and the waste land. To discover dynamicsof some characteristics of soil organic matter in red soil with the change of utilizing patterns in South China, three locations were chosen in this paper: dryland colonized from good vegetation forest in the southern mid-subtropics for4 years (Huanjiang Spot), upland from the uncolonized red soil in the northern mid-subtropics for 11 years (Xiangbei Spot) and the long-term paddy soil in the northern mid-subtropics (Taoyuan Spot) for 10 years. The results showed that the contents of soil organic matter decreased by net 2.1 g·kg-1 (for 55 soil samples), with an average decreasing speed of 0.53 g·kg-1·a-1 in dry land which exploited from forest land in mid-south of subtropical zone after 4 years (Huanjiang Spot). The average content of soil organic matter was 27.4 g·kg-1 against 29.5 g·kg-1 at 4 years ago. Of 5 different plantation systems, the content of soil organic matter in the dry farmland soil seriously decreased by 4.6 g·kg-1·a-1. In Xiangbei Spot colonized from wasteland, the soil organic matter contents increased by 0.4 g·kg-1·a-1, from 13～14 g·kg-1 to 15.1～22.5 g·kg-1. The contents of soil organic matter with planting oil tea had the most rapidly increasing speed of 50.3%for 10 years andsecondly 41.1%with a dry farmland, respectively. Other treatments also had the increases of 5.5%to 37.6%, respectively. In the long-term reddish paddy soil in Taoyuan Spot, the content of soil organic matter also had an increase of 0.3 g·kg-1·a-1. The ratio between humic acid and fluvic acid was 1.9～2.3 in 1994, and 1.0～1.5 in 1990, respectively,showing that aromatizationof organic matter was improving. The actively organic matter was not significantly increased with the plantation period but the applying of the organic fertilizer could improve the content of active soil organic matter in the long-term reddish paddy soils.