| Soil water repellency could increase the retention time of rainfall runoff and surface runoffand intensify soil erosion and water loss, trigger series of environmental problem including thenon-point source pollution and cause crop failures. Influenced by the soil physical and chemicalproperties, soil water repellency is characterized by strong spatial and temporal variation, whichcould deeply influence its impact on soil erosion and water loss. Taking the typical land usepeach orchard and corn field on brown soil from Yimeng mountainous area as a case study, thechange characteristics of soil water repellency before and after a rainfall event and thereresponse to the soil physicochemical properties were explored. Influencing factors and responsecharacteristics of spatial and temporal variation of soil water repellency to the Nitrogen leachingprocess were acquired. On the basis of the research above, the ameliorative measures wereproposed.1Spatial and temporal variation characteristics of soil water repellencyUnder the condition of Yimeng mountainous area during the rainy season, the brown soil ofthe classical farmland showed strong water repellency with evident spatial and temporalvariation. Results showed: Soil water repellency of corn field presented higher water droppenetration time values both before and after the rainfall, while those of peach orchard decreasedmore greatly. The actual water repellency showed no evident response to water content. Underthe condition of oven, the water repellency presented a trend of increasing firstly and decreasingand then being stable at last. However, the relationship between water repellency and watercontent fitted the exponential model. Both the soil water repellency and its soil properties of thebrown soil of two land patches showed strong spatial variation. Soil water repellency of the threeslope position showed a similar trend, with their peak values an order of upslope<mesoslope <downhill.2The spatial autocorrelation and its influencing factors of the soil water repellencyThe SWR in studied brown soil was strong under the condition of lasting drought anddecreased significantly after rainfall. The SWRs before and after rainfall were both moderate invariability and strong in spatial autocorrelation, showing an exponential pattern in distributionwith significant anisotropy. Under the joint function of structural and random variations,spatially the SWR was distributed in band following the direction of ploughing. Soil texture wasthe main factor influencing spatial variability of SWR. SWR was positively related with silt content, but negatively with sand and clay contents in spatial distribution, showing an order ofsilt> sand> clay in degree of spatial correlation with SWR. SWR was also negatively relatedwith soil moisture in spatial distribution. The negative relationship was quite weak before rainfalland became significant after rainfall.3Comparison of the spatial variation and its influencing factors of the soil water repellencyin two land usesTaking the typical land use peach (Prunus persica) orchard and corn (Zea mays L.) field onbrown soil from Yimeng mountainous area as case study, the change characteristics of soilwater repellency(SWR) before and after a rainfall event and its response to the soilphysicochemical properties were explored. Results showed: The actual SWR of both two landuse types were strong and that of corn field were stronger. After the rainfall, the SWR of peachorchard decreased significantly while that of corn field was still strong water repellent. Therewere obvious differences in spatial distribution characteristics of SWR between the two patches,that is, SWR of peach orchard presented spatial autocorrelation and that of corn field didrandom distribution. The soil moisture presented negative spatial correlation with SWR ofpeach orchard and positive with that of corn field, both of them presented not obvious beforethe rainfall and significant after the rainfall. The soil silt content presented significant positivespatial correlation with SWR of peach orchard both before and after the rainfall, and the soilsand and clay content did negative, showing an order of silt> sand> clay in degree of spatialcorrelation with SWR. The soil silt and clay content presented significant negative spatialcorrelation with SWR of corn field before the rainfall and the soil sand content did negative,with an order of clay> sand> silt in degree of spatial correlation with SWR. All of themshowed opposite correlation after the rainfall, with only the silt content reaching significantcorrelation.4Impact of soil water repellency on Nitrogen leaching processUnder the oven condition, soil water repellency of the brown soil presented bimodal trendwith the decreasing of water content. Soil nitrogen leaching rate showed positive correlation withthe water repellency degree and Nitrate Nitrogen was the main form of the leaching Nitrogen.Under no water repellent condition, leakage volume and concentration of the leaching Nitrogenshowed a steady trend while under slight and strong water repellent condition did an obviousunimodal trend. Under no and strong water repellent condition, the concentration of NitrateNitrogen and total Nitrogen showed the peak value at20min and then became steady whileunder the slight water repellent condition, the moment of peak value showed different degrees oflag. The concentration of Ammonia Nitrogen under no water repellent condition decreased steadily with duration of rainfall and showed peak value at50min; while under slight and strongwater repellent condition, it did a stable trend with peak values at different moment, such as20,30or40min.5Amelioration measures of soil water repellencyThere have been two kinds of amelioration measure of soil water repellency, that is, thedirect and indirect measures. The direct measures could delete the causation of water repellencyand the indirect measures aimed to change the management measures of soil water repellency,including surface agent, clay soil, slow release fertilizer, lime and bactericidal agent includingthe earthworm, improved crop varieties, irrigation, cultivation, soil ventilation and compaction,and so on. The further research should devote to the field trial of long-hour and macroscale sothat we can research and develop the the most cost-effective measure for controlling the soilwater repellency. |
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