Effect of residual film on soil infiltration under drip irrigation

Abstract: Large tracts of farmland are polluted by residual film with the mulching film widely applied. The residual film has become a major environmental factor which significantly affects agricultural production. Based on lab experiments of infiltration with different residual film, the influence of residual film on soil infiltration was analyzed. Six treatments were designed including T0, T1, T2, T3, T4, T5, which represented for six levels of residual film 0, 45, 90, 180, 360, 720 kg/hm2 respectively. Experimental apparatus consisted of Marriotte bottle, water tube and soil tank. The water applied in the experiment was 0.65 L/h which equaled 1.95 L/h of the drip irrigation. Total water used in one experiment was 1.90 L. During the experiment the numerical value of Marriotte bottle and wetting area were monitored continuously in 1, 2, 3, 6, 10, 15, 25, 35, 50, 65, 80, 95, 110, 125, 150, 175 minutes. The results indicated that residual film could hinder the movement of wetting front. when residual film levels were between 0 and 360 kg/hm2, residual film had a significantly influence on horizontal distance of wetting front. In 50 minutes when wetting front moved to 0-10 cm soil, T2 treatment showed minimum horizontal distance and three horizontal distances of T2, T3 and T4 were gradually increasing due to the preferential flow with more residual film in 0-10 cm soil. While in 175 minutes when wetting front moved to 10-20 cm soil, treatments with increased residual film gave rise to decreases in horizontal distance. Residual film could also affecte the vertical distance of wetting front heavily, however, the vertical distance had no obvious difference among T1, T2, T3 and T4, T5 treatment while it diminished greatly between T0 and T1 treatment in 175 minutes (F=4.53, P<0.05). The soil wetting rate was amplified due to residual film, which the drip irrigation needs to be applied with more water or short dripper distance to achieve proper drip irrigation uniformity in polluted farmland. While the irrigation was stopped, the steady infiltration rate increased from 12.2 mm/h to 16.9 mm/h with the residual film increased from 0 to 360 kg/hm2. Steady infiltration rate showed significant difference between T0.and T1, T2, T3 T4 treatment. Therefore, it is concluded that residual film can make soil wetting body smaller and maintain more water in the soil wetted volume, and the random distribution of residual film affects water general movement, which crops will be difficult in absorbing soil water. The soil infiltration of residual film could be well described by the Kostiakov Function, which the correlation coefficient was over 0.989. When the residual film attained to 720 kg/hm2, excessive amounts of residual film add soil macropore heavily, which lead to preferential flow in total 0-20 cm soil causing increase of the wetting distance, at the same time that decreased the wetting rate and steady infiltration. This research will provide fundamental theory for the control of residual film polluted farmland in term from soil water movement.