Influence of different plastic film mulches and wetted soil percentages on potato grown under drip irrigation

Potato (Solanum tuberosum L.), an important food crop of Northwest China, is commonly grown using transparent plastic film mulch for water conservation since both irrigation water and precipitation are scarce. In order to improve production efficiency, field experiments were conducted at Shiyanghe Experimental Station, China Agricultural University, Wuwei, Gansu Province, China using plastic mulch and drip irrigation to study the influence of two typical plastic mulches (transparent and black) and three wetted soil percentages on potato root distribution, evapotranspiration, tuber yield and quality, and water use efficiency (WUE) in 2014 and 2015. Using a wetted soil percentage of 55%, three soil surface treatments were tested: transparent plastic mulch, black plastic mulch, and a non-mulched check. With the transparent plastic mulch, three wetted soil percentages 35%, 55%, and 75% were evaluated. The soil retained moisture better in the mulched treatments than in the non-mulched treatment. As the plant canopy increased, the differences diminished. Potato grown without plastic mulch developed more roots than potato grown with mulch. The soil water fluctuations in the top of the bed with black plastic mulch were greater than with transparent plastic mulch. Potato grown with either plastic mulch had greater yield and WUE than potato grown without plastic mulch. Potato grown with transparent plastic mulch had 10% and 7% greater WUE in 2014 and 2015, respectively than potato grown with black plastic mulch but the differences were not statistically significant. For different wetted soil percentages, the irrigation frequency was higher with the 35% wetted soil treatment than with 55% or 75%. The irrigation at 35% principally only affected the soil water in the upper soil in contrast to the 55% or 75% treatments. The 35% wetted soil treatment had more root development in 2015. Potato evapotranspiration increased as the wetted soil percentage increased. The 75% wetted soil treatment had significantly more evapotranspiration than the 35% wetted soil treatment in 2015. The 35% wetted soil treatment had the highest WUE, 17% and 25% higher than the 75% wetted soil treatment in 2014 and 2015, respectively. The 35% wetted soil percentage irrigation regime combined with transparent plastic mulch merits wider testing for potato production in arid Northwest China.