The use of infra-red transparent (IRT) colors on biologically degradable plastic mulch films
- Vytvořeno pátek, 20.12.2013
Mulch films can be used when cultivating crops in order to achieve earlier and higher yields as well as to enhance the quality of many different types of vegetables, such as tomatoes, eggplants, water melons, peppers and cucumbers.
Listed below are the advantages of using plastic mulch films as described by W.J. Lamont, of the Department of Horticulture at Kansas State University (www.agnet.org).
1) Earlier yields: Raising the temperature of the soil makes it possible to achieve earlier yields. Using a black plastic mulch film can result in a 7 to 14-day earlier yield. Transparent mulch films can reduce time to yield by 21 days.
2) Soil moisture: The use of plastic mulch films considerably decreases the loss of soil moisture through evaporation. This means that the soil remains moist and the cost of irrigation can be reduced. Under these conditions, vegetable yields can be almost doubled in comparison to the yields of crop plantings without plastic mulch.
3) Weeds and unwanted flora: Black and combinations of black / white plastic mulch films prevent unwanted flora from appearing and suppress the growth of weeds.
4) Leaching of agrochemicals and fertilizers
The protection provided by plastic mulch films prevents leaching and run off of valuable agrochemicals and fertilizers.
5) Reduced soil compaction
The protective mulch film keeps the soil below it loose. There is reduced soil compaction because of low moisture loss. Formation and growth of roots is guaranteed by the improved absorption of oxygen and the production of nutritive mediums.
6) Control of roots:
Outside of the areas covered by plastic mulch film, the formation of undesirable weed roots can be kept under control through the use of pesticides and agrochemicals.
7) Cleaner produce
Fruit and vegetables under plastic mulch films can be kept cleaner as they are protected from dirt and soil.
8) Higher growth and yield
Photosynthesis for plant growth requires the absorption of CO2 and its transformation into oxygen. The use of plastic mulch raises the CO2 concentration beneath the film as the gas cannot diffuse out of the film. This allows the green leaves to perform the process of photosynthesis.
9) Retention of gaseous nutrients and fertilizers
Plastic mulch films protect sprayed chemical fertilizers from diffusing out through the film so that they can be better absorbed.
Fields covered with plastic mulch are typically laid out with drains so that excess water can run off in the case of heavy rains. This reduces the danger of flooding and the risk of crops drowning.
Colored plastic mulch and its effects on plant growth by means of photoselectivity are now, and have been for years, the subject of numerous studies.
The theory maintains that colored plastic mulch, when it is transparent, displays advantages over traditional black plastic mulch due to the transmission and absorption of certain wavelengths of light. This can lead to higher temperatures in the earthbanks and under the earth.
There have been many more studies done on this topic in the USA and Israel than here in Europe. The range of commercially available products supplied by film manufacturers and plastic granulate producers is also more extensive in these countries.
Plastika Kritis and Kafrit are two manufacturers of additive and color masterbatches for agrofilms that have supplied similar products in earlier years.
Plastika Kritis offers the products „Brown 70964“ and „Brown 70869“ as masterbatches. Recommended addition is 20% for mulch films with a thickness of 20-30 µm. Both masterbatches suppress weed growth due to the dark color and keep the underlying soil warmer by allowing heat to pass through. „70964“ contains an additional IR absorber (such as chalk / talc) which traps the warmth by preventing heat from escaping at night.
Kafrit in Israel added the product „LDPE MB Brown & PA L -8660“ to its portfolio in 2006. This is also a color masterbatch that is used to produce brown plastic mulch. Kafrit recommends adding 5 to 15% depending on the film thickness of the mulch and on the desired degree of heat permeability.
Research being conducted in the Department of Horticulture at Pennsylvania State University is also worth mentioning. M.D. Orzolek and L.Otjen have been performing extensive research on tomatoes using different colored polyethylene mulches.
Studies performed at the Weihenstephan University of Applied Science (under the direction of Ms. K. Kell) in 2006 examined the effect of different colored plastic mulches on the cultivation of kohlrabi and lettuce and looked at the influence of temperature on growth.
A press release issued in the year 2007 (Plasticker News, 27 August 2007) by FKuR introduced an innovative black plastic mulch made of polylactide. FKuR announced that it had been working together with Oerlemans Plastics and the Fraunhofer UMSICHT since 2004 on the development of this product and was now ready for market launch. The release described the “PLA blends“ as a mixture of PLA (polylactide) and other biodegradable polymers and additives. PLA is obtained from corn starch by means of a fermentative process. Oerlemans Plastics b.V. Genderen, Netherlands, had carried out the industrial production and application testing of the PLA mulch. It was reported that the innovative mulch film had the advantage over other biodegradable films, of decomposing significantly slower and being more resistant to fluctuating climatic conditions. Already in the year 2004, the FKuR Kunststoff GmbH had begun with the first tests for biodegradable mulch films. The degradation behavior of the film under “open-air” conditions was studied in the lab. The industrial application of the film has been carried out together with Oerlemans Plastics b.V. since 2005. The most important factor for Oerlemans Plastics in choosing the FKuR PLA mulch film was, among others, the unproblematic production of the film on conventional extruders, such as those used in the production of LDPE films. Before they went ahead with industrial production, the use of the Bio-Flex® mulch film was successfully tested on a variety of crops by different research institutes and testing stations. Since 2005 Oerlemans Plastics‘ biodegradable PLA mulch films have been tested all over the world on a wide range of crops in various climate zones. The crop yields attained with this biofilm are comparable to conventional PE mulch films. Laying out the PLA mulch films can be done with the usual laying machines and is no more difficult than conventional biofilms. A big advantage over other biofilms, e.g. starch-based films, is its significantly slower decomposition and its resistance to fluctuating climatic conditions. Another advantage of bio mulch films in agriculture, is that the films can simply be ploughed into the soil after harvest, where they continue to degrade. The application of Bio-Flex® mulch films reduces the amount of work required and lowers the costs of film disposal. The granules and the film are completely biodegradable in accordance with EN 13432. In addition, they are certified in accordance with DIN Certco, OK Compost, NFU 52001 und Ecocert.
As mentioned above, the most important reason for the application of mulch film is weed suppression as a function of light absorption in the UV and visible (VIS) ranges. In addition, there is strong heat absorption (from the near infrared range NIR) because of the added carbon black. This means that the mulch film heats itself up and passes the absorbed heat on to its immediate environment.
The second generation of mulch films represents the transition from LDPE-based film to films made of biodegradable plastics. Black carbon is still being used as pigment here. The focus is on sustainability through the guaranteed biodegradability in industrial composting.
Heat absorption out in the open air really puts biodegradable mulch film to a hard test in terms of longevity and functionality. The idea of prolonging longevity by adding additives or aggregates would be in contradiction to the original goal of sustainability.
It was only a matter of time before studies began on colored, infrared transparent (IRT), biodegradable plastic mulch. The idea is to suppress weed growth through the complete absorption of lightwaves from the UV and the visible (VIS) ranges. However, the highest possible amount of energy from the near infrared (NIR) should be allowed to pass through.
It is obvious that this effect cannot be achieved with carbon black and this presents some disadvantages: The percentage of colorants used in thin films must be higher and this automatically increases the costs for raw materials.
The color formulations that have been developed are based on the simple color mixture theory, which says that it is possible to create black (dark) colors by mixing a combination of pigments.
The advantages of using infrared transparent colors in mulch films can be summarized as follows:
- High heat transmission
- This results in a higher soil / earth bank temperature
- Excellent conditions for plants that keep their roots in winter.
- No weeds or unwanted flora
- Reduced attacks from rodents and worms.
- Fruits, such as strawberries, are not damaged at contact points with overheated mulch film.
- No chemicals needed to suppress weeds and other vermin, enabling a change to organic farming.
- Earlier and increased yield.
- Improvement in crop quality – and amount.
Mulch films based on biodegradable plastics with IRT coloring were used in these field tests. LDPE-based standard black mulch films were compared to LDPE-based films with IRT coloring. The goal was to measure the effect of the films‘ biodegradability alone (PLA or cellulose) on the growth behavior of the crops.
There are differences between the growth of the cucumbers and tomatoes. The data for the tomatoes show that in the early weeks all films independent of their composition display similar effects. In the later weeks, the PLA film with IRT coloring performs better than all the others. The differences, however, between the different film types are not significant.
The field tests with the cucumbers, however, show differences from the beginning. The ranking of the yields from highest to lowest reads as follows: PLA + IRT, cellulose + IRT, LDPE + IRT and at the end the standard black mulch film can be found.
Further tests (conducted by the Institute for Materials Research and Testing at the Bauhaus University Weimar MFPA) have confirmed the required minimum 90% biodegradability of the IRT-colored film in accordance with DIN EN ISO14855-1. Ecotoxicity tests in accordance with DIN EN13432 have also been successfully completed.
On the basis of these tests, Bioflex F 1130 produced by FKuR has been selected as the most suitable material with a wide processing window and a high level of flexibility, independent of the machinery used. The combination with IRT color mixtures has resulted in a high-performance product representing the next generation of mulch film on today’s market.