Effect of residual plastic film on growth of tomato at seedling and blooming and fruit-setting stages

Although plastic film mulching is critical for crop production, its widespread use has produced a great deal of residual plastic film and destroyed soil structure, damaged the physical structure of soil and seriously impeded the movement of soil water and solute as well as crop growth. In order to determine the negative effects of residual plastic film on growth of tomato (Lycopersicon esculeutum Miller) at seedling and blooming and fruit-setting stages, plot experiment was conducted with different amounts of residual plastic film in 2015–2016 in a solar greenhouse of the Key Laboratory of Agricultural Soil and Water Engineering in Arid Areas (108°02′E, 34°17′N). Six treatments, including residual plastic film amounts of 0 kg.hm^-2, 80 kg.hm^-2, 160 kg.hm^-2, 320 kg.hm^-2, 640 kg.hm^-2 and 1 280 kg.hm^-2, were set in triplicate plots. The total area of plot filed was 75.6 m2 (6.0 m × 12.6 m) with three replications for each treatment, with each micro-plot size of 1.0 m 4.2 m. The height and stem diameter of the tomato plants were collected during the period from October 2015 to January 2016 and analyzed and then fitted with nonlinear Logistic models to determine the effects of residual plastic film on the biomass accumulation at seedling stage, blooming and fruit-setting stage of tomato. During the experiment, root morphological characteristics, plant height, stem diameter and biomass accumulation of the tomato plants were measured. The results showed that residual plastic film hindered the growth of tomato root at both seedling and blooming and fruit-setting stages. Root volume, root length density and root dry weight density decreased with increasing residual plastic film amount. In addition, as the amount of plastic film residue increased, plant height and stem diameter decreased significantly (P < 0.05). Besides, the rates of increase in plant height and stem diameter decreased with increasing residual plastic film amount. Logistic model accurately simulated the growth process of tomato in fields with residual plastic film less than 1 280 kg.hm^-2 (R^-2 > 0.87). As the amount of residual plastic film increased, beginning period and full period of tomato biomass accumulation was ahead of time. This implied that the suitable time of fertilization of tomato should be brought forward. Overall, biomass accumulation decreased for the whole tomato growth period. Contrary to biomass accumulation of leaf, that of root, stem, flower and young fruit decreased with increasing residual plastic film amount. The hindering effects of residual plastic film on tomato growth and dry matter accumulation at seedling stage were higher than at blooming and fruit-setting stage. The early period and middle period of tomato biomass accumulation all occurred in advanced. In summary, strengthening water and fertilizer management at seedling stage and bringing forward the application of fertilizer and irrigation were recommended as the proper measures to weaken the detrimental effects of residual plastic film on tomato.