Degradation And Quality Assessment Of Farmlands In The Delta Areas Of Collapsing Hill In Granite Regions In Tongcheng County

Collaping hill is an erosion type in granite red soil regions, which has massive erosion amount and strong perniciousness. Delta areas are the depositional parts of collapsing hill, and the majority of them have been used as farmlands. Affected by reconstruction technology, cultivation periods and activity of collaping hills, the quality of farmlands here have degradated seriously. With the relationship between people and land increasing nervously and the problems of food shortage and food safety increasing prominently, improvement of farmlands’quality in the delta areas of collapsing hill is in a hurry. Carrying out studies on degradation and the quality evaluation of farmlands in the delta areas of collapsing hill is of great importance to enhance farmlands’quality in collaping hill regions and to formulate prevention and control systems of collapsing hill.This study has chosen Tongcheng county in Hubei provinve, the typical region where collapsing hills occur, as the objective. Based on different influence degrees with collapsing hill bodies, delta areas have been divided into three parts, strong influenced zone, weak influenced zone and none influenced zone. According to field investigation, we have chosen11research areas in Wuli town and Daping village, and influence situations between the areas and surrounding collapsing hills have been analysed. Typical farmlands soil samples have been collected in these areas, including4paddy fields,1regular cultivation and5improved drylands in strong influenced zones,1paddy field and1dryland in weak influenced zones,1paddy field and1dryland in none influenced zones, whose profile characters, basic physical characters, and nutrient characters have been analysed. The quality levels of farmlands have been assessed, with the confirmation of crop yields. The method of changing space to time has been adopted to study the degeneration characteristics of farmlands in the delta areas of collapsing hill. The conclusions are as follows:(1) Farmlands’soil physical properties quality, from low to high, are strong influenced zones, weak influenced zones, and none influenced zones, and the changing trend of furface layers is particularly obvious. The physical properties of sandy layer which covers farmland in serious influenced zone are much worse, and the properties become better after improvement measures have been taken.(2) Farmlands’soil nutrient contents, from low to high, are strong influenced zones, weak influenced zones, and none influenced zones. Nutrient contents of farmlands in strong influenced zone are far below former surface layer in new-cover sandy layer, which still affects soil fertility after the majority of mantle has been artificially removed. Improved farmlands soil fertility increases in strong influenced zones, and the fertility indexes of a farmland in weak influenced zone with not long enough period of cultivation are extremely low. Both proluvium of collapsing hill and cultivation periods act on soil fertility.(3) Grade levels of farmland qulity, from low to high, are strong influenced zones, weak influenced zones, and none influenced zones. Farmlands’quality in weak influenced zones are1level lower than those in none influenced zones, and farmlands’quality in strong influenced zones are2-3levels lower than those in none influenced zones. The levels of improved farmlands in strong influenced zones may increase, and the one of short-period cultivation farmland in weak influenced zone is lower. Both proluvium of collapsing hill and cultivation periods act on farmlands quality.(4) Crop yield levels, from low to high, are strong influenced zones, weak influenced zones, and none influenced zones. Farmlands’crop yields in weak influenced zones are1level lower than those in none influenced zones, and farmlands’crop yields in strong influenced zones are2-3levels lower than those in none influenced zones, which confirm the conclusions of farmland quality assessment.According to investigation and analysis, the results show that particles of farmlands in the delta areas of collapsing hill become coarse, and physical properties become worse, acidity inceases, fertility decreases. Combined with cultivation measures, soil physical properties of farmlands here gradually become better, the fertility gradually increases, and the quality gradually recovers with collapsing hill gradually trending to be stable till disappearing.