Henry Y. Sintim

Is Biodegradable Plastic Mulch the Solution to Agriculture's Plastic Problem?

T global use of agricultural plastic films, which includes films used for greenhouses, mulching, and silage, is expected to grow 69% from 4.4 million tons in 2012 to 7.4 million tons in 2019. The global market for agricultural plastic films is expected to grow at a compound annual growth rate of 7.6% from 2013 to 2019, reaching a market of 9.66 billion USD, with China and the Middle East driving future demand. In 2012, plastic mulch films accounted for over 40% of the total plastic films used in agriculture. Plastic mulch films provide multiple benefits for crop production. They help to control weeds and insects, increase soil and air temperature, reduce evaporation, minimize soil erosion, and prevent soil splashing on fruits or vegetables (Figure 1). These benefits translate into reduced pesticide use, early planting in spring, water conservation, and increased crop yield and quality. Given the world’s projected population growth and need for more food, the use of plastic mulch film in agriculture has great potential to increase food production and security. Plastic mulch films consist mostly of low-density and linear low-density polyethylene, which do not readily biodegrade. As a result, these polyethylene-based mulches must be retrieved and disposed after usage. Agricultural plastic mulch films are often contaminated with soil, and therefore are not accepted by many recycling facilities. This limits disposal options for polyethylene mulches, which often have to be landfilled. Costs of landfilling are high, causing many producers to amass mulches or even burn them on-farm. The release of plastic fragments from amassed mulches or the incomplete removal of plastic mulches from fields is of major global concern as plastic fragments from all sources ultimately accumulate in the sea. In an effort to mitigate the adverse impacts of polyethylene mulch, biodegradable plastic mulch was introduced in the 1980s, but low biodegradation in soils has hindered widespread use so far. However, new promising formulations of biodegradable polymers have been developed in recent years. The advertised advantage of biodegradable plastic mulch is that it can be tilled into the soil after use and that it would be degraded by the action of soil organisms, thus saving labor and disposal costs. To be a competitive alternative to polyethylene mulch, biodegradable plastic mulch must (a) maintain a conducive microclimate for plant growth, (b) be flexible to allow mechanical installation, (c) remain intact during the majority of the cropping season, (d) undergo complete degradation after soil incorporation or composting, (e) have no adverse impact on the environment, and (f) be economical. Studies have shown that some of the commercially available biodegradable plastic mulches perform similarly to polyethylene mulches in terms of ease of laying, weed prevention, and enhancement of crop yield and quality. However, the potential environmental consequences of using biodegradable plastic mulches have not been thoroughly studied, and the international standards (ISO 17088, ASTM D6400, ISO 17556, ASTM D5988) for validating their safeness are, in our opinion, not rigorous enough. For instance, the standards for degradation in compost (ISO 17088, ASTM D6400) specify that at least 90% of the organic carbon need to be converted to CO2, leaving room for up to 10% of the organic carbon to remain. The breakdown products of biodegradable plastic mulch must not be toxic or persist in the environment, but should be completely assimilated by soil organisms. Extensive reports on the breakdown of biodegradable plastic mulch in the laboratory are available, but little is known about effects of biodegradable mulches on soil quality and their breakdown into microand nanometer-sized fragments. Degraded mulch products can be invisible to the naked eye, but out-of-sight does not mean they are safe. Standards used to assess the degradability of plastics under aerobically composted conditions (ISO 17088, ASTM D6400) and in the soil environment (ISO 17556, ASTM D5988) are based on macroscopic (i.e., visual by eye) disintegration and organic carbon conversion to CO2, but do

Coal-Bed Methane Water: Effects on Soil Properties and Camelina Productivity

Every year, the production of coal-bed natural gas in the Powder River Basin results in the discharge of large amounts of coal-bed methane water (CBMW) in Wyoming; however, no sustainable disposal methods for CBMW are currently available. A greenhouse study was conducted to evaluate the potential to use CBMW as a source of irrigation water for camelina [ (L.) Crantz]. We assessed the effects of three CBMW concentrations (0% [1:0], 50% [1:1], and 100% [0:1] tap water to CBMW) on selected soil properties, growth, seed oil, and fatty acid composition of three camelina cultivars: Blaine Creek, Ligena, and Pronghorn. The 100% CBMW reduced seed and estimated biofuel yields by 24 and 23%, respectively, but increased the oil content by 3%, relative to the control. Additionally, the 100% CBMW visibly affected soil through formation of surface crust due to elevated levels of sodium (653 mg Na kg). The 50% CBMW had no significant effects on the seed yield, estimated biofuel yield, and oil content, but the soil Na levels were still high (464 mg kg), which could pose a long-term impact on soil structure. The CBMW tended to reduce the total saturated fatty acid, but it had no significant effects on the total monounsaturated or polyunsaturated fatty acids of camelina seeds. Overall, CBMW diluted with an equal amount of good-quality water could be used to irrigate camelina in the short term. Afterward, only good-quality water would have to be used until the accumulated dissolved solids are flushed out.

Differing Sucrose Requirements for In-vitro Conservation of Cassava Genotypes

Field conservation of vegetative propagated crops poses a major problem to curators of germplasm, especially in developing countries. An alternative method to ensure security of germplasm is the use of tissue culture techniques in media formulated for slow growth. However, tissues of plant species may require different nutrients for optimum growth. The objectives of this study were to a) assess the effects of sucrose on the performance of different cassava genotypes and b) recommend sucrose levels for in-vitro conservation of the genotypes. Four sucrose levels (0, 10, 20, and 30 g l -1 ) and apical meristems of five cassava genotypes (Bankye Hemaah, Bankye Botan, Tek Bankye, Doku Duade, and Essam Bankye) cultured in-vitro was studied at the Kwame Nkrumah University of Science and Technology’s plant biotechnology laboratory. Growth media were prepared using hormone-free Murashige and Skoog (MS) basal media formulation. Inoculated cultures were exposed to 16 hours of light and 8 hours of darkness with light illuminance of 3500 lux and also maintained at 24±2°C temperature and relative humidity of 70%. All genotypes Original Research Article Sintim and Akromah; IJPSS, 7(1): 45-54, 2015; Article no.IJPSS.2015.130 46 showed a direct regeneration without callus formation. Generally, sucrose enhanced the growth performance of plantlets; however, the genotypes responded differently to sucrose in leaf formation, plant height, and rooting ability with time. For long term conservation, growth medium must sustain the health of plantlets with infrequent need for sub-culturing. As such, sucrose levels of 10 g l for Essam Bankye, 20 g l for Doku Duade and Tek Bankye, and 30 g l for Bankye Hemaa and Bankye Botan were the recommended rates for in-vitro conservation.

Interaction of Lumbricus terrestris with macroscopic polyethylene and biodegradable plastic mulch

Polyethylene mulch films used in agriculture are a major source of plastic pollution in soils. Biodegradable plastics have been introduced as alternative to commonly-used polyethylene. Here we studied the interaction of earthworms (Lumbricus terrestris) with polyethylene and biodegradable plastic mulches. The objective was to assess whether earthworms would select between different types of mulches when foraging for food, and whether they drag macroscopic plastic mulch into the soil. Laboratory experiments were carried out with earthworms in Petri dishes and mesocosms. The treatments were standard polyethylene mulch, four biodegradable plastic mulches (PLA/PHA [polylactic acid/polyhydroxy alkanoate], Organix, BioAgri, Naturecycle), a biodegradable paper mulch (WeedGuardPlus), and poplar litter, which served as control. Four and three replicates for the Petri dish and mesocosm experiments were used, respectively. Macroscopic plastic and paper mulch pieces (1.5 cm × 1.5 cm and 2 cm × 2 cm) were collected from an agricultural field after a growing season, after being buried in the soil for 6 and 12 months, and after being composted for 2 weeks. We found that earthworms did not ingest polyethylene. Field-weathered biodegradable plastic mulches were not ingested either, however, after soil burial and composting, some biodegradable plastics were eaten and could not be recovered from soil any longer. Earthworms, when foraging for food, dragged plastic mulch, including polyethylene and biodegradable plastic, and poplar leaves into their burrows. The burial of macroscopic plastic mulch underground led to a redistribution of plastics in the soil profile, and likely enhances the degradation of biodegradable mulches in soil, but also can lead to leaching of plastic fragments by macropore flow.

Using Surface Response Models to Evaluate the Effects of Kinetin on Dioscorea alata Propagated in Vitro

Kinetin is an important growth hormone used for in vitro propagation, but its dynamic and temporal effects on Dioscorea alata have not been thoroughly evaluated. In this study, surface response models were developed to better elucidate the effects of kinetin on D. alata propagated in vitro. Nodal segments were obtained from Akaaba, an important D. alata cultivar in Ghana, and propagated in vitro under five kinetin rates (0, 2.5, 5, 7.5 and 10 μM). The models were developed using segmented multiple regression with time and kinetin as the predictors. The effects on plant height, the number of leaves, shoots and roots were assessed with three-dimensional figures for better observation of temporal trends. The model fit was very good with normalized root mean squared error (NRMSE) = 0.1, R-squared = 0.83 and adjusted R-squared = 0.82, averaged across the different growth parameters. Different kinetin levels elicited the maximum shoot, leaf and root formation, as well as the growth rates over time. Moderate kinetin levels (2-4 μM) provided better growth at early culturing period. Higher kinetin levels (5-10 μM) suppressed the growth of the plantlets at early stages, but the plantlets recovered from the stress and resumed normal growth thereafter. After 4-5 weeks, the growth rates of the moderate kinetin levels (2-4 μM) declined much faster and were lower compared to the higher kinetin levels, except plant height and the number of roots which were still higher at the moderate kinetin level even after eight weeks of culturing. Thus, kinetin requirements vary depending on the growth parameters of interest.