The use of plastic mulch in agriculture has increased dramatically in the last 10 years throughout the world. This increase is due to benefits such as increase in soil temperature, reduced weed pressure, moisture conservation, reduction of certain insect pests, higher crop yields, and more efficient use of soil nutrients. However, disposing of used plastic films, which cause pollution, has led to development of photodegradable and biodegradable mulches. Here we review the use of plastic mulches in agriculture, with special reference to biodegradable mulches. Major topics discussed are (1) history of plastic mulch and impact on crop yield and pest management, (2) limitations of polyethylene mulches and potential alternatives, (3) biodegradable and photodegradable plastic mulches, (4) field performance of biodegradable mulches, and (5) use of biodegradable plastic mulches in organic production. We found that (1) despite multiple benefits, removal and disposal of conventional polyethylene mulches remains a major agronomic, economic, and environmental constraint; (2) early use of photodegradable plastic mulch during the 1970s and 1980s, wrongly named biodegradable mulch films, discouraged adoption of new biodegradable mulch films because they were too expensive and their breakdown was unpredictable; (3) biodegradable plastic films are converted through microbial activity in the soil to carbon dioxide, water, and natural substances; (4) polymers such as poly(lactic acid), poly(butylene adipate-coterephthalate), poly(ε-caprolactone), and starch-based polymer blends or copolymers can degrade when exposed to bioactive environments such as soil and compost; (5) with truly biodegradable materials obtained from petroleum and natural resources, opportunity for using biodegradable polymers as agricultural mulch films has become more viable; and (6) the source of polymer and additives may limit use of some biodegradable mulches in organic production. More knowledge is needed on the effect of biodegradable mulches on crop growth, microclimate modifications, soil biota, soil fertility, and yields.

There has been little information available on the effect of different degradable and non-degradable plastic mulches on soil temperature and their effect on biomass production, enzyme activities, growth, and yield of winter rapeseed. Hence, field experiments were conducted with different types of mulches mulch viz., black polyethylene, transparent polyethylene, herbicidal polyethylene film (herbicide coated), degradable polypropylene, straw mulch, and non-mulched control. The results indicated that, in general, the soil temperature got decreased with the advancement in each phenophases of rapeseed crop up to flowering stage. Thereafter, a gradual increase in the temperature up to harvest was observed, which was mainly due to the weather prevailed during that period. Among the different mulches evaluated, soil temperature was higher under transparent film mulch, followed by degradable, herbicidal film, and black polyethylene film mulches. Interestingly, the soil temperature under straw mulch was lower than non-mulched control in the early stages of the crop and at pod maturity stages. Irrespective of the types and colors, higher soil temperature under all the plastic mulches had significantly improved the growth including shoot length, root length, and root to shoot ratio and vigor index at 15 DAS. The highest total biomass was also produced with plastic mulches due to increased soil temperatures, which was apparent in the early stages of the crop. Higher soil temperature under plastic mulches markedly shortened the days to 50% flowering and maturity. The superoxide dismutase (SOD) and peroxidase POD activities were increased with enhanced soil temperatures, while malondialdehyde (MDA) was decreased with increasing soil temperature under all the plastic mulches. The increased number of pods per plant, number of seeds per pod, and seed yield observed with plastic mulches due to increased soil temperature indicates that modification of field soil temperature through management practices could improve rapeseed production by achieving an optimal balance between vegetative and reproductive growth.

Field experiments were conducted at Regional Research Station, Tamil Nadu Agricultural University, Vridhachalam, India, during autumn 1999 and winter 2000 using groundnut to examine the effect of different colours of polyethylene film mulch on crop yield and soil properties. The results of the experiment conducted with different colours of polyethylene film mulch (black, transparent white and non-mulched control) and three land configurations (flat bed, ridges and furrows and broad bed and furrows) indicated that irrespective of the colours, polyethylene film mulch significantly increased the soil micro-organisms at all stages of observation during both seasons except for bacterial population, which was significantly higher under non-mulched control during the winter season. The soil physical properties such as rate of water loss/day, soil bulk density, percentage of pore space and hydraulic conductivity were also favourably influenced by the polyethylene film mulch. The data on soil available nitrogen, phosphorus and potassium (NPK), showed that effect of polyethylene film mulch was significant at 30 DAS and not during later stages during both the seasons. Similarly the evolution of carbon dioxide (CO₂) (soil respiration) was also significantly improved by polyethylene film mulch. The effect of land configuration was not significant for most of the parameters observed except for bulk density and pore space during winter seasons. With regard to yield parameters and yield, in both the seasons, white polyethylene film mulch out yielded other treatments in terms of groundnut pod yield. However the performance of white polyethylene film mulch was comparable with black polyethylene film mulch during winter 2001 – 2002 seasons. Among the land configurations, the results of yield components and yield were in favour of flat bed during both the seasons of study.

Experiments were conducted over 2 years during the dry season of 2002 (June–September) and wet season of 2002–2003 (December–March) at Regional Research Station, Tamil Nadu Agricultural University, Vridhachalam, India, to study the influence of two colors of polyethylene film mulch (black and white polyethylene film mulch), herbicides (Fluchloralin at 1.0 kg/ha and no herbicide application), and three plant geometries [30×10 cm, 20×20 cm (two seeds/hill), and 20×15 cm] on soil properties, growth, and yield of groundnut. Results indicated that the soil physical properties such as rate of water loss/day was highest with white polyethylene film mulch, the hydraulic conductivity of the soil was significantly more with black polyethylene film mulch, and soil bulk density and percentage of pore space did not differ between the two colors of polyethylene films. The rate of water loss was highest with plots with no herbicide, whereas the hydraulic conductivity of the soil was more with herbicide‐applied treatments. However, the bulk density and pore space did not differ significantly. The plant geometry did not have any significant influence on any of the soil physical properties. With regard to soil microorganisms, the bacterial and fungal population was significantly higher in black polyethylene film mulch at all the three stages of observation, whereas no significant difference between the colors of polyethylene film mulch was observed for actinomycetes at all the stages of observations. Interestingly, no variation in the population of soil microflora was observed between the herbicide and no‐herbicide treatments. The soil‐available nitrogen, phosphorus, and potassium (NPK), at harvest, was significantly higher with white polyethylene film mulch, whereas crop NPK uptake was higher with black polyethylene film mulch. The soil‐available NPK and crop uptake was higher with herbicide application. The evolution of carbon dioxide (CO₂; soil respiration) was significantly influenced by polyethylene film mulch and herbicides, and the evolution of CO₂ was altered by the plant geometry. The crop dry‐matter production, pegging percentage, pod setting ratio number of matured pods/plant, and pod yield were significantly higher under black polyethylene mulch. Herbicide application significantly improved the majority of the growth and yield attributes and significantly higher pod yield was obtained with herbicide application. However, most of the yield and growth attributes and pod yield were not significantly influenced by the different plant geometries studied.

The shoot fresh mass, root length and root numbers of two potato (Solanum tuberosum L.) cultivars Favorita and Helanwuhua were increased significantly by the application of 0.2 – 2 mg dm⁻³ jasmonic acid (JA) in the Murashige and Skoog medium. However, the growth of potato explants was inhibited by JA at high concentrations (20 – 50 mg dm⁻³). Chlorophyll content in explant leaves decreased with an increase in the concentration of JA. In leaves treated with 0.2 mg dm⁻³ JA acid peroxidase activity increased, while in the leaves treated with more than 2 mg dm⁻³ JA peroxidase activity decreased. Under the dark, the microtuber numbers, fresh mass and percentage of big microtubers of two potato cultivars were not promoted by the application of 0.2 – 50 mg dm⁻³ JA.

Studies conducted during the winters of 1997 - 98 and 1998 - 99 (December - March) at the Regional Research Station, Tamil Nadu Agricultural University, Vridhachalam, India, revealed the usefulness of polyethylene film mulching in arresting weed growth and maximizing pod yield in groundnut. Among the various treatments, two (1) crop grown under polyethylene film mulching and (2) pre-planting incorporation of fluchloralin in the flat-bed system of sowing registered the lowest weed numbers at harvest (106.7 and 113.7/plot of 27 m 2 in 1997 - 98 and 1998 - 99 respectively), the lowest weed dry-matter production (51.2 and 54.5 g/plot of 27 m 2 ), maximum weed control efficiency (62.1 and 57.4%) and weed control index (83.0 and 81.1%), the highest number of matured pods/plant (17.6 and 18.0), 100 kernel weight (48.6 and 48.7 g), percentage shelling (72.6 and 72.8) and a dry pod yield of 2451 and 2468 kg ha -1 when compared with non-mulched plots. The net return and benefit:cost ratio was also highest with the same treatment in both the study periods.