A standard greenhouse film incorporating EVA includes UV absorbers, HALS and antifog, and a high thermal film combining 19% EVA with LLDPE, also includes mineral fillers. The coextruded greenhouse films were shown to improve crop yields of tomatoes, eggplant and cucumbers.
Biodegradable plastics are increasingly being used in mulch films. The Telles grade Mirel A5004 can be used in cast and blown mulch films with thickness from 8 to 125 microns. In field trials it improved the yield of red and green fruit compared to PE film and it has been tested at sites worldwide. Camp Tecnico of Japan has produced high performance biodegradable film, by blending higher and lower melting point bioplastics. The resulting film has higher strength than conventional LDPE film. Biodegradation speed can be controlled to fit the crop, e.g. 5 months for a rice paddy dyke and 15 months for Chinese chives.
Clariant produces masterbatch for biodegradable plastics and other agricultural films, including IR absorbers, anti-fog and photoselective. Light stabilizers used for polyesters, such as benzotriazoles, can be used for PLA as well, although PLA often does not require additional light stabilization. Fatty acids, talc and silica can be used as anti-blocking agents for bioplastics, and talc and calcium carbonate can be used as nucleating agents during foaming. Clariant has “OK Compost” certification for its bioplastics masterbatches, some of which were developed with Novamont and are pigmented.
Kuhne has tested and adapted machinery for biodegradable film production. Paul & Co. supplies paper cores for winding agricultural films, and these have been tested for weathering. They are made with 100% recycled paper and glue made from naturally occurring materials, and can be included in paper recycling or composted, according to the manufacturer.
In South Africa, GREENCULT has developed netted mulch for use with cucurbit crops like melons and butternut squash. Wind stress causes a lot of problems with these crops, tearing leaves, exposing fruit to excess sunlight and twisting the stems. Conventional mulch films are too smooth and don’t provide anywhere for the vine tendrils to hold on, so nets over the mulch can provide more stability for the plants and also reduce tearing of the films. The system is patented and was tested on a farm in Worcester, where melon yield was raised around 15-20% by using netted mulch compared to conventional material.
Plastic mulch decreases the amount of water required in irrigation. Different films can also improve crop yield, for example, Naksan has presented data showing that yield of water melon using clear plastic was around 30 tons per hectare, and with silver-black mulch this rose to 90 tons per hectare. The reflected light from the coloured mulch enhanced photosynthesis and deterred pests.
