Concept and estimation of crop safety period of plastic film mulching

Plastic mulching film plays an important role in development of agriculture. However, a series of problems
such as pollution of plastic film residue left in the field occur. It is required to make a reasonable assessment on film
mulching and rationally utilize it. Based on its application, this study proposed a concept of crop safety period of plastic
film mulching, and its estimation methods. Crop safety period through plastic film mulching means the appropriate
choice of a photo-selective mulch film according to the transplant season, to the pedoclimatic conditions of the area
under cultivation and, finally, to the type of crop. In the days before the transplant, the plastic mulching film should be
basic whole, and it works to decrease soil moisture evaporation, to warm soil and to prevent weeds. Successively, these
functions almost reduce. The selection of crop safety period of plastic film mulching is helpful to manage agricultural
activities efficiently; guiding film makers to produce both meet the demand of production and lower cost of plastic
products; to help farmers due to the types of crop and production conditions choosing appropriate plastic mulch film.
Based on measurement of function of plastic film mulching, and crop canopy density, 2 kinds of method were
established. The first one is to continuously monitor soil moisture，temperature and weed control, to build relationship
between the function of soil temperature, moisture, weed suppression and mulching treatments, with that to seek the
intersection of them. The coincidence point means functions disappear of plastic mulching and the days from starting
mulching to this date is a certain crop safety period in a certain site. The second is crop canopy density to determine crop
safety of plastic film mulching period, which includes 2 steps: to measure the change of crop canopy density, and the
functions (soil temperature and moisture etc.) of mulching under no mulching and mulching at same time, to establish
the curve of crop canopy density and the main function of plastic film in order to cross the best condition between crop
canopy density and the contribute of mulch films aimed to the determination of the ideal crop safeguard period. All in all,
plastic mulching film has been widely used in global, especially in China, in the past 30 years, and its application area
and efficacy works better than any other agronomic practices. Concept of crop safety period of plastic film mulching has
been firstly proposed in this paper, and further research in the connotation and extension of its definition still need to be
developed. Moreover, the mentioned estimation methods around crop safety period of plastic film mulching showed
some usefulness in cotton in Xinjiang, corn in Northeast and tobacco in southwest planting, but more extensive research,
application and improvement were needed by far. The findings from this research provide an important information base
for improving adaptability evaluation system of plastic mulching film, investigating the spatial pattern of plastic
mulching film utilization, and biodegradable plastic film production and application.