Particle-size effects on soil temperature, evaporation, water use efficiency and watermelon yield in fields mulched with gravel and sand in semi-arid Loess Plateau of northwest China

摘要

Gravel and sand mulch is an effective practice in conserving soil and moisture. However, the proportion of different particle size in this kind of mulch layer is an important factor to be considered in order to obtain optimal results from this practice. From 2005 to 2007, a series of experiments including one with watermelon were conducted in the semi-arid Loess Plateau of northwest China to determine the influence of particle size and its proportion in mulch layer on soil temperature, evapotranspiration, water use efficiency (WUE) and watermelon (Citrullus lanatus L.) yield. The treatments in no-watermelon experiments included particle sizes classified as <0.3, 0.3-1, 1-2, 2-4, 4-6, 6-8 and 8-10cm mesh size or various rates of 2-6cm pebble accounting for 0, 10, 20, 30, 40, 50, 60 and 70% with 30% 1-2cm gravel-sand in mulch layer (as well as correspondingly decreasing sand proportions). The watermelon experiment included three particle sizes, 0.3-1, 1-2 and 2-6cm. Soil temperature at 8:00h was highest for the 1-2cm treatment, and the daily average temperature at 14:00h was highest for the 0.3-1cm treatment. Soil temperature decreased with particle size increasing due to porosity enlarging. The relationship between soil temperature and particle size followed a quadratic or cubic curve. Soil temperature was increased by gravel-sand mulch plus plastic film. The increment of soil temperature was larger especially for 1-4cm particle size. In the gravel-sand mulch layer having different size particles, the greater percentage being of 2-6cm pebbles, increases porosity, and lowers soil temperature, and causes more evaporation. The results of the watermelon experiment showed that soil moisture before seeding would not affect the yield during the years of using gravel mulch. Watermelon yield and WUE were higher for 1-2 and 0.3-1cm treatments than 2-6cm treatments in later experiments during 2006 and 2007. In conclusion, 2-6cm large size particles would not account for much in gravel-sand mulching layer. It would be better if the percentage of 2-6cm particles was less than 30%.