## 1 Introduction  
The practice of using mulching film to improve the growth and yield of annual and perennial crops has long been recognized [1]. Mulching film preserves heat and moisture, reduces pressure from weeds and pathogens, and conserves water and fertilizer [2; 3; 4]. In these ways, mulching film contributes to sustainable agricultural production.  
Plastic films (e.g., polyethylene (PE), poly(vinyl chloride), polybutylene, copolymers of ethylene with vinyl acetate) are the most widely used materials because of their excellent mechanical properties and low cost. However, the major problem associated with the use of non-biodegradable plastic films is that they can pollute soil when they are buried in landfills; in addition, the removal and disposal of these plastic residues from the field either before or after harvest is costly and time-consuming [1; 5]. For these reasons, farmers usually incorporate used films into the soil; occasionally, they burn the used plastic films, causing harmful pollution [6]. In order to increase the sustainability of agricultural practices and to overcome the disposal problems associated with conventional plastic films, the development and use of mulching films based on biodegradable materials is highly desirable.  
Until now, various films capable of being degraded by microorganisms in the soil have been developed, including oxo-degradable plastic film [7], paper film [8], and biodegradable film [9; 10; 11]. Oxo-degradable plastic is low-cost and easy to install, but the parts of the film that are buried in the soil do not break down and must be exposed to light and air for degradation [12]. Paper film has been considered as an alternative to plastic film; however, paper film suffers from very rapid degradation and is easily broken down after exposure to soil, rain, and wind [13]. Furthermore, in order to cause no undesirable effects to the performance of agricultural soil, no harmful substances resulting from the degradation of biodegradable materials used as mulching film should accumulate in the soil [14].  
The fibrous materials derived from renewable crops or from their by-products or agro-industrial wastes are good candidates for use in blends and composites [15]. Natural fibers have good mechanical properties and are biodegradable, which makes them highly suitable for use in films in combination with biodegradable polymers. Some natural fibers, such as ramie, flax, hemp, and cotton, are abundant in China and are mainly used for textiles. However, the waste fiber has not been suitably recycled after industrial production. Some biodegradable polymers such as starch, poly(vinyl alcohol) (PVA), poly(butylene adipate-co-terephthalate) (PBAT), poly(butylene succinate-co-adipate) (PBSA), and poly(lactic acid) (PLA) have been used to prepare biodegradable agricultural films [13; 14; 16; 17; 18; 19; 20]. Some films based on natural fibers and polymers were also prepared, such as an orange fiber residue/PVA film [21] and an Osage orange wood/PLA film [10]. These films were prepared using the mixture of grinded fibers and a polymer aqueous solution. The aim of this study was to prepare films based on natural fibers and biodegradable polymers as potential substitutes for plastic films. In this work, three mulching films were severally developed from natural fibers (a blend of waste ramie and cotton fiber) and polymers (PA, ST, and PVA) using the method of air laying in nonwoven fabric. The biodegradability of the films was studied in detail.