3. Results
3.1. Effect of mulch thickness on soil evaporation
Mulch thickness had a significant impact on soil evaporation, and there was a close power-series relationship between the two factors (Fig. 1). When the mulch thickness was less than 7 cm, the evaporation sharply decreased as mulch thickness increased, and evaporation was greater for coarse than for fine gravel. However, when the mulch thickness was >7 cm, the evaporation decreased slowly with increasing mulch thickness, and there was little difference between coarse gravel and fine gravel.