| The gravel-sand mulched field as a dry farming covering technology has the comprehensive benefits. It can improve the microclimate significantly by adjusting the temperature, retaining water and preserving soil moisture in dry and semiarid region of northwest China. The gravel-sand mulched field watermelon industry has become the pillar industry in Ningxia. As a major crop, the main watermelon producing regions of the gravel-sand mulched field locates in the XiangShan mountain arid zone of central Ningxia. Water is the major restriction factor for the agricultural production in this region. Characteristics of soil hydro-thermal property and its effect on watermelon growth on gravel-sand mulching were studied for the year2010and2011in the main watermelon production region in arid zone of central Ningxia. In addition, soil microflora and enzyme activity were also analyzed.Main results and conclusions for this study are listed as follows:1. Significant correlations were observed between soil infiltration rate and precipitation intensity. Almost all soil moisture contents were higher than the control (GM was27.05%higher than CK). Gravel-sand absorbed rainwater better than CK and kept lower cropland water consumption and significantly reduced soil evaporation by57.69%. Crop water consumption pattern reduced early evaporation and increased late transpiration, which was changed by mulching. The soil water content in GM was52.08%,78.93%,76.96%,72.63%and79.42%of field moisture capacity respectively. That of CK was49.23%、58.06%、69.93%、66.26%and57.47%respectively. The soil water content of GM fell in the range of the watermelon growth requirement, i.e.60-80%, while CK was lower than the growth requirement.2. The thermal conductivity of gravel-sand was λ=0.8435J·m-1·S-1·K-1. The gravel sand was demonstrated to be a good thermal insulation material and its thermal conductivity was affected by porosity and humidity. Because of the suppression from gravel sand, the soil unit weight was increased (CK:1.38g/cm3, GM:1.51g/cm3) and soil porosity decreased (CK:47.6%, GM:39.3%). When the water content in surface soil increased, the volumetric heat capacity and heat conductivity increased. For the decreasing evaporation, the water content in sand soil was higher than bare land, and the heat capacity (CK:0.9492×106J·m-3·K-1,GM:1.1689×106J·m-3·K-1) and heat conductivity (CK:0.8921J·m-1·S-1·K-1, GM:1.3008J·m-1·S-1·K-1) were high. As such, Gravel-sand had significant effect of thermoregulation, improved the temperature in low temperature conditions and dropped the temperature in high temperature conditions. The above effect could not only prevent injuries caused by the high temperature of plant roots, but also alleviated soil temperature change and promoted crop growth and development. The daily temperature range in0-10cm soil layer in the growth period in2010was for14.46℃CK and5.42℃for GM.3. Amounts of soil microorganisms significantly increased on GM, especially within0-20cm soil layer. Evenness index decreased since the number of gaps was too large on several main microbes. Soil enzyme activity could improve significantly influenced by soil moisture and temperature, especially soil moisture.4. Watermelon on the gravel-sand mulched field of the speed of emergence was fast and the rate of emergence was high. Vines grew faster than CK, with promoted crop growth and development, enhanced disease resistance and increased yield. SPAD, Pn, Fv/Fm, Fv/Fo, PI on GM were higher than CK. Fo/Fm was lower than CK. Special characteristics on the gravel-sand mulched field was conducive to positively affected growth, yield and quality of watermelon.In addition, the existing problems in the gravel-sand mulched field were also discussed. Continuous cropping obstacles with prolonged planting affected the quantity and quality of watermelon, which could be removed through reasonable crop rotation and intercropping. |
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