Precipitation Redistribution And Evapotranspiration Of Cropland And Orchard On The Loess Plateau

Precipitation and evapotranspiration are the most important pathways for water input and output in the dryland ecosystem.Precipitation is redistributed through the plant canopy as canopy interception,throughfall and stemflow.Throughfall and stemflow into the soil are the main or even the sole source of soil water replenishment.Evapotranspiration is formed by canopy interception,soil evaporation and plant transpiration,which is the primary way of water consumption in the dryland ecosystem.The change in land use type will affect precipitation redistribution and evapotranspiration,as well as the long-term soil water balance between replenishment and consumption.Therefore,the differences analysis of each component of precipitation redistribution and evapotranspiration,and the spatial-temporal changes in soil water caused by land use change are useful in understanding the replenishment and consumption relationship between precipitation,plants and soil.This study provides theoretical support for vegetation construction and water resource management in the dryland ecosystem.The land use types have dramatically changed because of “Grain to Green” project.This study was guided by precipitation input and water consumption from vegetation and soil.Spring maize cropland and an apple orchard were chosen as the research objects in the Changwu Tableland.Through continuous field monitoring and multivariate statistical analysis methods,the differences in precipitation redistribution between cropland and apple orchard in the tableland were studied,and each component of precipitation was quantified.The meteorological factors and plant traits influencing throughfall,stemflow and canopy interception were analyzed,as were the differences in evapotranspiration at multiple time scales between cropland and apple orchard.The long-term spatial-temporal variation characteristics of soil water under the two land use types were also compared.The main conclusions are as follows:(1)The comparison of throughfall and stemflow between cropland and apple orchard showed that the ratio of each component of precipitation has changed as the land uses changed.There were significant differences in the ratio of throughfall and stemflow between cropland and apple orchard(p<0.01).The mean ratio of throughfall and stemflow in each precipitation event was 41.4% and 22.4% in cropland,respectively,while in apple orchard it was 69.3% and 1.0%.The precipitation amount was identified as the variable with the greatest influence on precipitation redistribution among the precipitation factors considered.The ratio of throughfall and stemflow in the apple orchard increased exponentially as precipitation increased,and the asymptotic value was close to 90.0% and1.5%,respectively.The replenishment source of soil water varied with different land uses.The soil water input sources for the cropland were throughfall and stemflow,while the input source for the apple orchard was mainly throughfall.The mean efficiency of the replenishment of soil water by precipitation in the cropland(34.1%)was slightly lower than that in the apple orchard(37.7%).(2)The quantitative analysis of canopy interception and its influencing factors in cropland revealed that the cumulative canopy interception accounted for 39.7% of the contemporaneous total precipitation during the study period.The ratio of canopy interception to precipitation decreased as precipitation amount increased.Precipitation event factors(precipitation amount,precipitation duration,precipitation intensity)made the highest contribution to explaining the amount of canopy interception(56.4%).Using precipitation events with similar dates to the measurement of leaf area index improved the explanation of canopy interception by plant traits when compared to the results of all precipitation events.The total explanation of the influencing factors involved in canopy interception was 75.1%.Precipitation amount and raindrop diameter were the most important factors in explaining the amount of canopy interception and the ratio of canopy interception,respectively.The contribution of each factor to canopy interception consisted primarily from average shared importance.(3)The comparison of evapotranspiration and its components between cropland and apple orchard showed that the mean ratio of soil evaporation to evapotranspiration for cropland and apple orchard was 36.3% and 37.7%,respectively,in the growing season(May-September).The amount of canopy interception in cropland was significantly higher than that in apple orchard in the growing season(p<0.01),but the mean ratio of canopy interception to total evapotranspiration between cropland and apple orchard was similar(23.1% and 22.7%,respectively).The mean ratio of total evaporation to evapotranspiration for cropland and apple orchard was 59.4% and 56.6%,respectively,in the growing season.The mean ratio of transpiration to evapotranspiration for apple orchard was 2.8% higher than that for cropland during the growing season.The total change in soil water storage of0-300 cm between cropland and apple orchard were all positive,indicating that precipitation met the evapotranspiration requirements of cropland and apple orchard during the growing season.The mean ratio of evapotranspiration in the non-growing season(October to April of the following year)to total evapotranspiration in the hydrological year for cropland and apple orchard was 29.4% and 31.8%,respectively.(4)The long-term variation characteristics of soil water between cropland and apple orchard revealed that the soil water content of 0-300 cm in orchard showed a decreasing trend,but the soil water content of 200-300 cm did not decrease continuously with the passing of years.The mean soil water content of 0-300 cm between cropland and apple orchard showed an increasing trend of annual fluctuation.The cropland had a higher 7-year mean soil water storage of 0-300 cm(617.3 mm)than the apple orchard(603.1 mm).The mean soil water storage differed significantly in the 200-300 cm between cropland and apple orchard in four of the seven years(p<0.01),indicating the need to replenish soil water of 200-300 cm during the growth of apple trees.The representative depth of soil water content for cropland and apple orchard was 120-160 cm and 120-140 cm,respectively.In conclusion,the mean ratio of throughfall in the apple orchard on the Loess Plateau’s southern tableland was higher than that of cropland,while the mean ratio of stemflow was lower.The precipitation amount had a significant effect on the components of precipitation.The precipitation in the growth season met the demand for evapotranspiration between cropland and apple orchard,but the soil water consumption of deep layer in apple orchard should be monitored.This study is of great significance for understanding the changes in soil water after land use changes in the dryland ecosystem and also provides a scientific basis for regional water resources management and agricultural sustainable development.