Changes In Terrace Structures And Soil Properties In Hani Terraces After Conversion To Upland Terraces

Marginalization of cultivated land is an emerging phenomenon in mountainous areas worldwide since the mid to late of 20^th century when industrialization and urbanization drove increasing labors move out the mountainous areas.Terraced fields are among the most affected systems during farmland marginalization.Marginalization of cultivated land means the process of the continuous decrease of the net income from cultivated land under the current land use pattern.The marginalization of cultivated land would result in the decrease of farmers’investment to cultivated land and the land would shift to more extensive farming pattern.Reduction in maintenances or abandonment of terraced fields induced several negative ecological and social effects,including increasing of soil erosion,degradation of cultural landscape,ect.There have been many studies on the marginalization of dryland terraces,but the process and impacts of marginalization of terraced paddy fields are still under-explored.Hani terraces are among the Global Important Agricultural Cultural Heritage and World Cultural Heritage.The conversion of paddy terraces to upland terraces（dryland farming）has become increasingly prominent in recent years,which has adversely affected the maintenance of the landscape and ecosystem service provision.It will contribute to the recovery of Hani terraces to reveal the changes in structure of terraces and soil properties during the process of conversion from paddy terraces to upland terraced fields.Taking Amengkong Village of Panzhihua Township of Yuanyang County,one village in the core distribution area of Hani terraces,as a study area,I selected a total of 111parcels(including paddy fields as control,and upland fields that converted from paddy fields by 2years,3～4years,5～9 years and 10～14years,respectively as sampling plot through random sampling method.I carried out terrace structure investigation,analysis of physical and chemical properties of top soils,assessed soil productivity,and tested soil water-holding capacity in 0～70 cm soil layer.Based on these observations and experiments,I tried to reveal the changes in terraces structures and soil properties during terraced paddy fields converted to upland fields.The specific research results are as follows.（1）When paddy fields are converted to upland fields,the ridges of the terraced fields generally disappeared,the flat section basically maintained in good condition,especially in the duration of 5～9 years.More than 70%of the terrace riser collapsed to varying degrees,and the upland fields cultivated for 10～14 years had the best situation,followed by those cultivated as upland fields for 5～9 years.Combining the ridges,flat section and the risers,the damage degree of terrace structure in different durations of conversion was as follows:2 years>3～4 years>10～14 years>5～9years.Changes in soil water conditions and farmers’management and abodonment of terraces contributed to such trend.（2）The available potassium content of soil,organic matter content,p H value and soil bulk density in top soils were significantly increased when Hani paddy terraces were converted to upland fields.The soil total phosphorus content of some durations of upland fields was significantly higher than that of paddy fields;the clay content of some durations of dryland farming was significantly lower than that of paddy fields.In upland fields,soil total phosphorus content increased gradually with the increase of dryland farming years,available potassium content and p H value fluctuated greatly in the first 4 years of dryland faming,then tended to be stable with the increase of dryland farming years.Soil clay content,bulk density,available water content and soil productivity index decreased first and then increased with the increase of dryland farming years.Soil productivity index increased in all the different durations of dryland farming compared with paddy fields,and showed a trend of decreasing first and then increasing with the increase of dryland farming years.（3）The maximum soil water holding capacity in 0～70cm soils decreased significantly when Hani paddy terraces were converted to upland fields,and the decreasing range increased with the increase of dryland farming years.The maximum soil water holding capacity decreased by 9.16%～21.70%,and the capillary porosity decreased by 12.09%～24.20%during the 2～14 years of dryland farming.The decreasing in maximum soil water holding capacity and the soil capillary porosity were most obvious in the soil layer of 0～30 cm.（4）When paddy fields are converted to upland fields,the soil productivity did not restrict the agricultural production and the restoration of the terraced fields.The restoration of the terraced fields should focus on the restoration of the terrace structure and the soil water holding capacity.This study reveals the impacts of paddy terraced darnation on terrace structure and soil properties,which is helpful to improve the understanding of the characteristics of soil properties during the marginalization process of rice terraces in mountainous areas,and provides useful information for the restoration and fertilization of rice terraces.