Effects of mulching years and irrigation methods on residual plastic film in Hetao Irrigation District

Abstract: In order to study the influence of mulching years and irrigation methods on residual plastic film in Hetao Irrigation District of Inner Mongolia, consultation, questionnaire investigation and field sampling were used in combination for in-depth study. This paper mainly analyzed the present situation of plastic film mulching in Hetao Irrigation District and the typical research area (Dengkou County), and studied the effects of 3 factors including mulching years (2 years, 5 years, 10 years and 20 years), irrigation methods (drip irrigation and surface irrigation under film mulching) and crops (maize and sunflower). And the effect on the film residual rate, film damage rate, distribution of residual film in soil and residual film area in the typical research area were mainly discussed. The results showed that as the drip irrigation technology had made great development in Hetao Irrigation District of Inner Mongolia, the amount and mulching area of plastic film in Hetao Irrigation District increased by 125.81% and 147.62% respectively in recent 10 years. The typical research area even increased by 240% and 265.81%, however, the mulching area per unit area decreased by 8.82% and 7.08%. And this may lead to a further increase in the amount of agricultural film residue. Different mulching years and irrigation methods affected the film residual rate and film damage rate significantly (P<0.05), and the film residual rate and film damage rate under the drip irrigation were significantly higher than those of surface irrigation. The film residual rate of mulching 5 years, 10 years and 20 years increased by 80.14%, 163.70%, 273.64% than mulching 2 years respectively on average, and for film damage rate it increased by 20.97%, 38.14%, 60.20% than mulching 2 years on average. Moreover, the film residual rate and film damage rate under drip irrigation increased by 42.92% and 20.01% on average compared with surface irrigation. There was no significant difference in film residual rate and film damage rate between maize and sunflower under the same film mulching years and irrigation method. The film mulching years greatly affected the distribution of the residual film in soil, and the different irrigation methods had few effects on the distribution of residual plastic film in soil. The residual plastic film mainly concentrated in the soil depth of 0-10 cm, which accounting for 64.89%; and the residual film area between 0-4 cm2 and 4-20 cm2 was 31.06% and 27.81% of the total slices in the farmland. With the increase of mulching years, the total slices of residual film residues in the deeper soil depth gradually increased. For example, the residual film slice in soil depth of 0-10 cm was reduced from 71.47% to 54.61% for the mulching years from 20 to 2, but the residual film in soil depth of 10-20 cm was increased from 23.37% to 32.24%. With the increase of mulching years, the proportion of residual film for different area was more significant, especially for the increase of small area of residual film. The amount of residual film for area below 20 cm2 was 1.43, 1.44, 1.51, 1.59 times than the residual film area more than 20 cm2 (P<0.05) for the mulching years of 20 years, 10 years, 5 years and 2 years, respectively. The percentage of residual film in the residual film area of 0-50 cm2 under drip irrigation was significantly higher by 1.82% 4.15%, 8.08% and 9.14% than under surface irrigation (P<0.05) for the mulching years of 2 years, 5 years, 10 years and 20 years, respectively. The results can provide valuable information for the prevention and control of agricultural plastic film residues.