Effects of film mulching and soil wetted percentage of drip irrigation on soil hydrothermal conditions and sweet potato growth

Sweet potato is widely cultivated in China because of its drought tolerance, low planting cost and richness in various nutrients, such as crude protein, carbohydrates, and cellulose. Field experiments were conducted at the Special Potato Experimental Station, China Agricultural University, Rizhao City, Shandong Province, China, in 2020 and 2021 to investigate the effects of film mulching and soil wetted percentage on soil hydrothermal conditions and sweet potato growth. Three mulching treatments (black plastic mulching, BM; transparent plastic mulching, TM; and no mulching, NM) were applied on the raised bed surfaces after drip tape laying and three soil wetted percentages (0 %, P0; 30 %, P1; and 60 %, P2) were conducted during irrigation. Soil temperature and water content, vine length, and stem thickness were monitored at each growth stage and tuber grade, yield, and quality were measured at harvest. The results indicated that mulching had significant effects on soil temperature, sweet potato growth, grading, water use efficiency, and yield. The BM and TM treatments significantly increased the soil temperature at the 0–5 cm soil depth up to 4.4 and 3.7 °C during the seedling stage, respectively. Three hours after the irrigation, the soil temperature at the 5 cm soil depth decreased by 6.4, 7.3, and 6.7 °C in the NM, TM and BM treatments in 2021, respectively. The BM treatment significantly increased the tuber number and weight of the sweet potato (tuber weight > 200 g) by 63.4 % and 73.7 %, respectively, and the TM treatment by 63.5 % and 70.7 %, respectively. The sweet potato yield with the film mulching treatments was 10.8–20.8 % and 44.4–59 % greater than that without the mulching in 2020 and 2021, respectively. The film mulching significantly increased the water use efficiency and decreased the excess water content during the rainy season. Film mulching was more important for the growth of the sweet potatoes than the irrigation in this study.