Characteristics of residual mulching film and residual coefficient of typical crops in North China

Abstract: Plastic films have been used extensively as mulching for crops in modern agriculture, and remarkably improved crop yields in the past decades. However, the vast amount of residual plastic films results in serious pollution in the arable land. In order to expound the status of residual films and the residual coefficient of mulch in typical croplands in North China, the amounts of the residual films were studied by using the methods of farm survey with questionnaires and quadrat sampling in 124 study sites from 2008 to 2011 in Beijing, Tianjin, Hebei, Shandong, Shanxi, Henan, Inner Mongolia. During questionnaire survey, the relevant status of mulching application including soil characteristics, crop type, mulching time and recovery method etc. was investigated. Based upon this, the residual coefficient of typical crops (peanut and cotton) was calculated through the methods of field monitoring from 2011 to 2014, by determining the amount of residual film before and after test. The results showed that the amount of film mulch residue in North China fields ranged from 0.2 to 82.2 kg/hm2, with an average value of 26.8 kg/hm2. Among the surveyed sites, 4.8% of fields presented a greater mulch residual volume than the national film residue standard (65 kg/hm2), and 16.1% of fields showed a residual film amount approaching this threshold. The residual amount was significantly different (P＜0.05) between different crops and provinces. The residual amount of mulch film in peanut and cotton field was highest, reaching 32.0 and 31.8 kg/hm2, respectively. The high residue film in peanut and cotton field was caused by different reasons. For peanut, it was attributed to the small mulching thickness which was mostly less than 0.005 mm, while for cotton the reason was the long mulching time. Meanwhile, Hebei was the one with the most residual mulching film (36.8 kg/hm2), because of the large proportion of peanut and cotton fields. In the year of 2011, the total amount of residual film in North China was 1.5×105 t. Vegetables, cotton and peanut field had great contributions to the total amount of residual film in this region, and the amount of residual film was 5.5×104, 3.9×104 and 3.0×104 t, respectively. Three years of residual coefficient test showed that the residual coefficient of peanut and cotton were 9.7% and 14.3%. If the present mulching pattern was carried on, the quantity of residual film in peanut and cotton fields would reach up to 69.1 and 70.4 kg/hm2 in 2021, becoming polluted areas that exceed the national standard of film residue. Although the pollution of residual film was not serious at present, it will become a significant issue if no measure was taken to solve it. It is in urgent need to elevate mulch film standards, develop biodegradable mulch film and enhance mulch film recycling. This study will eventually contribute to promoting effective control and management of residual mulch pollution in North China.