黄土塬区土地利用变化对深剖面土壤水分的影响

在长武塬区的6个地点分别采集农地、10年果园和20年果园10 m深剖面的土样,通过测定和分析不同样地的土壤水分,定量揭示其对土地利用变化的响应。结果表明:农地和10年果园土壤水分具有相似的垂向分布,随深度增加土壤水分含量增大,而20年果园随深度增加呈减小趋势,但6 m以下3种样地土壤水分随深度增加基本不发生变化;农地、10年和20年果园在0~6 m、6~10 m和0~10 m土层平均土壤水分含量分别为17.8%、17.5%和15.8%,20.4%、20.6%和14.8%,18.8%、18.7%和15.4%,与农地相比,20年果园0~6m、6~10m和0~10 m土层减少的土壤水分分别占农地的11%、27%和18%;农地6~10 m土壤储水量为1 063 mm,而转化为果园后随果龄增大而减小,其中10年果园无明显差异,但20年果园减少了291 mm,在该土层形成稳定的低湿层。20年果园6 m以下稳定的低湿层可能减少水分的深层渗漏进而降低地下水补给量,伴随着大面积的农地转化为人工林草,可能会对区域水循环造成影响。

The effects of land-use change on soil moisture in deep soil profile at Changwu loess tableland

10 m soil profiles were sampled fromthree representative land-use types (farmland ,apple orchard about 10 years old and 20 years old ) at six sites on the Changwu loess tableland .In this study ,soil water content wasmeasured and a quantified analysiswas conducted to evaluate the effect of farmland that had been converted to apple orchard for 10 years and for 20 years .Results showed that there was an increasing trend in soil water contentwith the increase ofdepth in farmlands and apple orchards about 10 years old ,but the trend was remarkably different inapple orchard about 20 years old .In 6~10 m layer ,soil water contents in three land-use types weresimilarlystable withdepthincrease .The average soil water content in 0~6 m ,6~10 m and 0~10 m layers in three land-use types were 17 .8% ,17 .5% and 15 .8%(farmland ) ,20 .4% ,20 .6% and 14 .8% (10 years old orchard ) ,and 18 .8% ,18 .7% and 15 .4% (20 years old or-chard ) ,respectively .Compared with farmlands ,the average soil water contents at 0~6 m ,6~10 m and 0~0 m layers in apple orchard about 20 years oldwere decreased by 11% ,27% and 18% ,respectively .The average soil water storage at 6~10 m layerin farmlands was 1 063 mm ,but the conversion to apple orchardsfor 20 years reduced soil water storage by 291 mm .Land-use change had a significant impact on deep soil water ,which probably reducedthe deep percola-tionofwater and further affected groundwater recharge .Conversion of farmland to grasslands and forests is one of the main types of land-use changes on the Loess Plateau ,which may further alter regional hydrologic cycle .