Study On Spatial Variability And Temporal Stability Of Soil Properties On Jujube Tree In Hilly And Gully Areas Of The Loess Plateau

In the northern loess plateau of china, the growth of vegetation was seriously affectedbecause of the fragile ecological environment. Study on the temporal and spatialcharacteristics of soil properties in the jujube ecological economic forest will help to improvethe ecological construction and water-soil resources high-efficiency utilization. In this study,the temporal and spatial characteristics of soil total nitrogen, organic carbon, saturatedhydraulic conductivity, bulk density, and soil moisture were analyzed, the effects of mulchingtreatment on soil moisture, temperature and the growth of jujube tree were investigated, andthe distributions of soil properties between jujube tree and other different vegetation typeswere researched. The main conclusions of this study were as follows:(1)The soil total nitrogen, total phosphorus, organic carbon, electrical conductivity,saturated hydraulic conductivity, clay and sand content had moderate variability. The pH, siltcontent, bulk density, total porosity, capillary porosity and saturation moisture content hadlow variability. The effects of slope position on total nitrogen, organic carbon, pH, bulkdensity, total porosity, capillary porosity, saturation moisture content, saturated hydraulicconductivity, clay, silt and sand content were significant (P <0.01). The effects of slopeposition on total phosphorus and electrical conductivity were not significant. Thegeostatistical statistics results showed that the soil properties were defined by the exponentialor spherical models. The nugget to sill ratios indicated that all soil properties had moderatedependences except the saturated hydraulic conductivity and silt content. The results ofcross-validation showed that spatial prediction maps from ordinary kriging method accuratelyreflected the distribution of soil properties in the study slope.(2)The coefficients of variation of soil moisture were almost more than0.1withmoderate variability. As the increasing of soil moisture, coefficients of variation decreasedobviously. The time stability analysis was used to investigate the soil moisture by cumulativeprobability function, mean relative deviation and spearman rank correlation coefficient. Theresults showed that the soil moisture at30cm depth had higher time stability than at10cm.The soil moisture at representative measuring site could estimate the mean soil moisture ofthe region. (3)The straw and grave mulching could conserve soil moisture and regulatetemperature,. The impact of conserving moisture would be better as the increasing of strawmulching quantity. The daily changing rate of soil temperature on straw mulching treatmentwas less than the non-mulching treatmeat. The straw mulching could regulate the soiltemperature and favor the growth of plants. In the process of rainfall, the soil moisture on thegrave mulching treatment increased more rapidly than the straw mulching treatment, whichindicated that grave mulching benefit the rainfall infiltration greater than straw mulchingtreatment. The fruit water content, VCcontent, total sugar and soluble solid content on the strawand grave mulching treatment were significantly higher than the non-mulching treatmeat. Theresults showed that the mulching treatmeat was good for the growth and development ofjujube tree.(4)The soil properties were significantly influenced by vegetation types (P <0.01). Theorder of the soil total nitrogen and organic carbon on different vegetation types was millet>alfalfa> jujube> Caragana Korshinskii Kom. The order of the total phosphorus was alfalfa>millet> jujube> Caragana Korshinskii Kom. As the increasing of the soil depth, the pHshowed the increasing trend, and the soil total nitrogen and total phosphorus showed the downtrend with the surface-aggregated distribution. The soil particle size distribution of vegetationtypes in the study region showed heterogeneous distribution and had multifractal feature. Thegeneralized dimensions spectra q-D(q) were decreasing function with inverted S-lag pattern.The multifractal spectrum functions α-(α) were asymmetrical convex curve. The claycontents, silt contents, sand contents, and dimension of silt domain values were significantlyinfluenced by vegetation types (P <0.01).(5)The soil moisture on different vegetation types showed the obvious seasonalvariation, which was closely related with the precipitation. There was significantly positiverelationship between the average soil moisture and the preceding quantity of precipitation(R2=0.6198,P <0.01). The soil moisture was highest on millet land with the lowestcoefficient of variation, which indicated that there was sufficient and stable moisture on milletland. The soil moisture on different vegetation types increased firstly, and then decreased withthe increasing of the soil depth. The0~40cm layer was weak absorbing layer for the verticalchange of soil moisture, the40~160cm layer was absorbing layer, and the160~200cm layerwas regulating layer.