不同时间尺度反坡台阶红壤坡耕地土壤水分动态变化规律

为研究反坡台阶对红壤坡耕地土壤水分不同时间尺度变化以及土壤干湿变化的影响,在2016—2017年对布设反坡台阶坡耕地和原状坡耕地0～100 cm深度土壤水分状况进行了持续监测,计算了土壤相对含水率和增墒率。结果表明,反坡台阶对土壤水分的增加作用在枯水年更为显著(P0.05)。坡耕地旱季各土层土壤含水率变化相对不明显,基本上呈现出随着土层深度逐渐增加的规律;7月、9月和11月则呈现出明显的S状的规律;坡耕地布设反坡台阶后,各个时段各个土层土壤含水率均有了明显的提高,尤其是在5月土壤补水期和11月土壤失水期对土壤水分的增加效果更加明显。坡耕地土壤逐日含水率变异程度随着土层深度增加而逐渐减小;反坡台阶处理坡耕地和原状坡耕地5、20和40cm处土壤逐日含水率与降雨量呈现极显著的相关关系(P0.01),60cm处土壤逐日含水率与降雨量达显著相关(P0.05),而80、100 cm深度土壤逐日含水率与降雨量之间相关关系不显著。反坡台阶对坡耕地5、20、40、60、80、100 cm处土壤平均增墒率分别达到15.22%、15.25%、16.91%、15.60%、16.50%和16.17%,而其对不同深度土壤增墒率在年内均呈现出不同的变化规律。坡耕地布设反坡台阶,显著增加了土壤含水率,增加了土壤湿润期的持续时间,并且能显著提高坡耕地降雨利用率,这对于解决坡耕地的生态水文型干旱问题,提高山区坡耕地农业生产力具有重要意义。

Dynamic variation of soil moisture at different temporal scales in red soil sloping farmland under reverse-slope terrace

Abstract: In order to study the effects of reverse-slope terrace on soil moisture changes at different temporal scales and the changes of dry and wet states in red soil slope farmland, the monitoring of the soil moisture were carried out by time domain reflectometer in 2 sloping farmland in central Yunnan Province. One was the sloping farmland with contour reverse-slope terrace, and the other one was the original sloping farmland. Soil moisture at depths of 40, 60, 80 and 100 cm was measured by buried waveguide, and soil moisture at depths of 5 and 20 cm was measured by straight insert waveguide. The monitoring period in this study was from January 1st, 2016 to December 31st, 2017. During this period, soil moisture was measured every 10 days in the dry season (January to April), every 3 days from the dry season to rainy season (May), every day in the rainy season (June to October), and every 3 days from the rainy season to dry season (November to December). The results showed that after the reverse-slope terrace was used, the soil moisture at different depths was significantly improved at annual scale. Effect of reverse-slope terrace on soil moisture were more obvious in dry years at the annual scale. The variable coefficient of soil moisture was higher at the surface soil, reaching about 50%. At the monthly scale, soil moisture followed an obvious "S" shape characteristic in July, September and November along the soil profile. Specifically, the "S" was more pronounced in July. After reverse-slope terrace was laid in sloping farmland, the soil moisture content of all soil layers had been significantly increased in each period. In particular, the effect on increasing of soil moisture was more obvious in May when soil moisture was replenished and in November when soil moisture was decreased. The variation degree of the daily soil moisture content in sloping farmland was decreased with soil depth increasing. There was a extremely significant correlation between daily soil moisture content and daily rainfall at 5, 20 and 40 cm of sloping farmland (P<0.01). Meanwhile, there was also a significant correlation between daily soil moisture content and daily rainfall at 60 cm (P<0.05). However, significant correlation was not found between daily soil moisture content and rainfall at depths of 80 cm and 100 cm. With the increase of soil depth, the correlation coefficient between soil moisture content and rainfall decreased gradually. The average soil moisture conservation rates of reverse-slope terrace at 5, 20, 40, 60, 80 and 100 cm in sloping farmland were 15.22%, 15.25%, 16.91%, 15.60%, 16.50%, and 16.17%, respectively. The soil moisture conservation rates of reverse-slope terrace were different at different soil layers during monitoring period. Reverse-slope terrace lengthened the wet period of sloping farmland, and significantly increased the soil moisture in wet period and dry period. Soil moisture content of sloping farmland stayed at an ideal level for a long time after reverse-slope terrace was used, which had a significant effect on regulating soil moisture of sloping farmland. It also significantly increased the rainfall utilization rate of sloping farmland, which would be of great significance for solving the eco-hydrological drought problem of sloping farmland and improving the agricultural productivity of sloping farmland in mountainous areas.