Mathieu Ngouajio

Polyethylene and biodegradable mulches for agricultural applications: a review

The use of plastic mulch in agriculture has increased dramatically in the last 10xa0years 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.

Assessment of aliphatic–aromatic copolyester biodegradable mulch films. Part I: Field study

The objective of this work was to study the use of new biodegradable films in agriculture under open field conditions. Three biodegradable mulch films made from modified biodegradable polyester of different thicknesses and colors (black and white) and a conventional low density polyethylene (LDPE) mulch film were used to cover the beds of tomato plants. Changes in physical appearance of the films were recorded as well as changes in their mechanical, optical, and physical properties. Once tomato harvest was completed, the conventional LDPE mulch film was removed and all the tomato plants were cut using a mower. The biodegradable mulch films were plowed into the soil. The change in the appearance of the film was recorded and samples of each film after plowing were characterized according to the properties mentioned above. After the biodegradable films photodegraded, cross-link formation occurred within the films which promoted brittleness. Titanium dioxide, an additive used to produce white color in the films, catalyzed the photodegradation, while carbon black used for black color stabilized the photodegradation. The white films started to degrade after two weeks while it took about eight weeks for the black films to significantly degrade. The black biodegradable film seems to be a more promising alternative as a mulch film because of the comparable yields and weed suppression ability to conventional mulch film.

Effect of cover crop and management system on weed populations in lettuce

Abstract Changes in cropping systems can significantly impact pest population dynamics and management. Field experiments were conducted from 1998 to 2000 to study the effect of summer cover crop and in-season management system on weed infestations in lettuce ( Lactuca sativa L.). The experiment was a factorial with summer cover crop and management system as the two factors. Cover crops were cowpea [ Vigna unguiculata (L.) Walp.] incorporated into the soil in the fall (CWPI), cowpea used as mulch in the fall (CWPM), sudangrass ( Sorghum vulgare ) incorporated into the soil in the fall (SDNG), and dry fallow (DFLW). Management systems were organic (ORG), integrated crop management (ICM), and conventional (CNV). In general, there was no interaction between cover crop and management system. Weed species richness was greatest early in the growing season and was affected by cover crop. Fewer species emerged in CWPM plots in general but perennial species became important with time. The DFLW showed greater weed populations than all cover crop treatments. Weed populations were similar in all management systems in 1999. However, in 2000, there was better weed suppression in the ORG and ICM systems than in the CNV system. CWPI significantly increased lettuce yield and DFLW yield declined the second year. Yield under the ORG system was low in 1999 and equivalent to that in the CNV and ICM systems in 2000. These results indicate that a prior summer cover crops can improve both conventional and organic vegetable production systems.

Seasonal cycles in germination and seedling emergence of summer and winter populations of catchweed bedstraw (Galium aparine) and wild mustard (Brassica kaber)

Abstract Catchweed bedstraw and wild mustard each produce two populations per year: a winter population (WP) in June, and a summer population (SP) in September. Experiments were conducted to determine whether the WP and SP differ in seed mass and seasonal germination. Seeds of both weeds were buried at 0, 5, 10, and 20 cm in cultivated fields, and retrieved at monthly intervals for 24 mo for germination tests in the laboratory. Additionally, seedling emergence from seeds buried at 0, 5, and 10 cm in the field was evaluated for 1 yr. Seeds from the WP were heavier than those from the SP for both species. Germination of exhumed seeds was affected by burial depth and by seed population. It was highest for seeds that remained on the soil surface and declined with increasing depth of burial. The WP of catchweed bedstraw produced two germination peaks per year, whereas the SP and all populations of wild mustard had only one peak. The WP of both weeds germinated earlier than the SP. Seedling emergence for both species in the field was greater for the WP than for the SP. Increasing soil depth reduced seedling emergence of both the WP and SP of wild mustard and affected only the WP of catchweed bedstraw. We conclude that the WP and SP of catchweed bedstraw and wild mustard seeds used in this study differed in seed mass, seasonal germination, and seedling emergence. The ability of a WP to produce large seeds that germinate early and have two germination peaks per year could make these populations a serious problem in cropping systems. Nomenclature:u2003Catchweed bedstraw, Galium aparine L., GALAP; wild mustard, Brassica kaber (DC.) L.C. Wheeler. SINAR.

Assessment of aliphatic-aromatic copolyester biodegradable mulch films. Part II: Laboratory simulated conditions

In a previous paper, we demonstrated that the main mechanism of degradation of poly(butylene adipate-co-terephthalate) (PBAT) biodegradable mulch films when exposed to field conditions was crosslinking due to the photodegradation from solar radiation. The aim of this work was to determine the effect of crosslinking on the biodegradability of PBAT samples. PBAT films were subjected to UV photodegradation in laboratory simulated conditions to investigate the effects of crosslinking and other major changes in the structure and mechanical properties of the films. Crosslinking caused the films to become more brittle and produced a reduction of the tensile strength and percent elongation. Besides the crosslinking degradation mechanism, chain scission also occurred in the samples. After 45d of biodegradation test, the non-crosslinked PBAT sample reached 60% of mineralization. However, the percent mineralization was reduced when samples were crosslinked. The percent mineralization of samples with 10%, 30%, 50%, and 70% gel content was 36%, 43%, 21%, and 24%, respectively. Our results indicate that crosslinking is a key process underlying the degradation of the PBAT film and did affect the biodegradability of the films, since the samples with greater amount of gel content generally showed less percent mineralization in the biodegradation tests.

Winter Annual Weed Suppression in Rye–Vetch Cover Crop Mixtures

Abstract Winter annual weeds can interfere directly with crops and serve as alternative hosts for important pests, particularly in reduced tillage systems. Field experiments were conducted on loamy sand soils at two sites in Holt, MI, between 2008 and 2011 to evaluate the relative effects of cereal rye, hairy vetch, and rye–vetch mixture cover crops on the biomass and density of winter annual weed communities. All cover crop treatments significantly reduced total weed biomass compared with a no-cover-crop control, with suppression ranging from 71 to 91% for vetch to 95 to 98% for rye. In all trials, the density of nonmustard family broadleaf weeds was either not suppressed or suppressed equally by all cover crop treatments. In contrast, the density of mustard family weed species was suppressed more by rye and rye–vetch mixtures than by vetch. Cover crops were more consistently suppressive of weed dry weight per plant than of weed density, with rye-containing cover crops generally more suppressive than vetch. Overall, rye was most effective at suppressing winter annual weeds; however, rye–vetch mixtures can match the level of control achieved by rye, in addition to providing a potential source of fixed nitrogen for subsequent cash crops. Nomenclature: Cereal rye, Secale cereale L.; hairy vetch, Vicia villosa Roth; mustard family, Brassicaceae Resumen Las malezas anuales de invierno pueden interferir directamente con los cultivos y pueden servir como hospederos alternativos para plagas importantes, particularmente en sistemas con labranza reducida. Se realizaron experimentos de campo en suelos areno limosos en dos sitios en Holt, Michigan entre 2008 y 2011 para evaluar los efectos relativos de los cultivos de cobertura Secale cereale , Vicia villosa y la mezcla S. cereale-V. villosa sobre la biomasa y la densidad de las comunidades de malezas anuales de invierno. Todos los tratamientos de cultivos de cobertura redujeron significativamente la biomasa total de malezas en comparación con el testigo sin cultivo de cobertura, con una supresión que varió de 71 a 91% en el caso de V. villosa y de 95 a 98% en el caso de S. cereale. En todos los experimentos, la densidad de malezas de hoja ancha que no pertenecen a la familia de la mostaza (Brassicaceae) no fue suprimida o fue suprimida de la misma forma por todos los tratamientos de cobertura. En contraste, la densidad de la familia de la mostaza fue suprimida más por los tratamientos con S. cereale que el tratamiento de V. villosa. Los cultivos de cobertura fueron más consistentemente supresores del peso seco por individuo de malezas que de la densidad de malezas, y las coberturas que contenían S. cereale fueron más supresoras que la cobertura de V. villosa.

The Critical Period for Weed Control in Corn in Turkey

Field studies were conducted in 2001 and 2002 in the Black Sea Region of northern Turkey to determine the critical period for weed control (CPWC) in corn and the effects of weed interference on corn height. Treatments of increasing duration of weed interference and weed-free period were imposed at weekly intervals from 0 to 12 wk after crop emergence (WAE). The CPWC was determined with the use of 2.5, 5, and 10% acceptable yield loss levels by fitting logistic and Gompertz equations to relative yield data. With 5% yield loss level, the CPWC was 5 wk, starting at 0.2 WAE and ending at 5.2 WAE, which corresponded to the one- to five-leaf stage of corn. The CPWC increased to 8.9 wk, starting at 0 WAE and ending at 8.9 WAE, at the 2.5% yield loss level. At 10% yield loss level, the CPWC decreased to 1.7 wk, starting at 2.1 WAE and ending at 3.8 WAE. Nomenclature: Corn, Zea mays L. Additional index words: Maize, weed competition, weed interference. Abbreviations: AYL, acceptable yield loss level; CLS, corn leaf stage; CPWC, critical period for weed control; DAE, days after emergence; WAE, weeks after emergence.

Allelopathic Potential of Hairy Vetch (Vicia Villosa) and Cowpea (Vigna Unguiculata) Methanol and Ethyl Acetate Extracts on Weeds and Vegetables

Bioassay experiments were conducted to determine the phytotoxicity of methanol and ethyl acetate extracts of hairy vetch and cowpea residues on the germination and radicle elongation of three vegetable crops and three weed species. The species tested included common chickweed, redroot pigweed, wild carrot, tomato, corn, and cucumber. The extracts of both species were dissolved in methanol to yield seven concentrations ranging from 0 to 8 g/L. Germination was significantly reduced by methanol and ethyl acetate extracts of hairy vetch extracts except for corn and tomato. Common chickweed and wild carrot were the only species that showed consistent reduction in germination with the methanol and ethyl acetate cowpea extracts. The radicle growth of most species, with the exception of corn and cucumber, was reduced by the extracts of both cover crops. Corn and cucumber radicle elongation was stimulated at low concentrations of the extracts; however, these observations were not significantly different among treatments. This study demonstrated that methanol and ethyl acetate extracts of hairy vetch and cowpea contained allelopathic compounds and that their phytotoxicity is likely species specific. Future studies should focus on the identification and isolation of the allelochemical(s) found in the methanol and ethyl acetate extracts of the hairy vetch and cowpea residues. Nomenclature: Hairy vetch, Vicia villosa Roth; cowpea, Vigna unguiculata (L.) Walp; common chickweed, Stellaria media (L.) Vill. STEME; redroot pigweed, Amaranthus retroflexus L. AMARE; wild carrot, Daucus carota L. DAUCA; corn, Zea mays L; cucumber, Cucumis sativus L; tomato, Lycopersicon esculentum Mill.

A Repellent Net as a New Technology to Protect Cabbage Crops

ABSTRACT n Floating row covers or insect-proof nets with fine mesh are effective at protecting vegetable crops against aphids but negatively impact plant health, especially under warm conditions. Furthermore, in control of cabbage insect pests, aphid parasitoids cannot enter the fine-mesh nets, leading to frequent aphid outbreaks. To surmount these difficulties, a 40-mesh-size repellent net treated with alphacypermethrin was studied in laboratory and field tests. Results showed both irritant and repellent effects of the alphacypermethrin-treated net on Myzus persicae (Sulzer) (Hemiptera: Aphididae) and its parasitoid Aphidius colemani (Haliday) (Hymenoptera: Braconidae). Under field conditions, there were no pests on cabbage protected with the repellent net. The repellent net allowed combining a visual and repellent barrier against aphids. Because of this additive effect, repellent nets allowed covering cabbage permanently with adequate protection against all pests.

Summer cover crops for weed management and yield improvement in organic lettuce (Lactuca sativa) production

Over the last two decades, the demand for organic products has grown rapidly in the world due to increased concern about side effects of pesticides on the environment and human health. Studies were conducted in organic lettuce (Lactuca sativa L.) from 2004 to 2005 at the Black Sea Agricultural Research Institute in Samsun, Turkey, to determine the suppressive effects of summer cover crops on weeds. The experiment was arranged in a randomized complete block design with four replications. Treatments consisted of grain sorghum [Sorghum bicolor (L.) Moench.], sudangrass [Sorghum vulgare Pers. var. sudanense (Piper) Hitchc.], hairy vetch (Vicia villosa Roth.), grain amaranth (Amaranthus cruentus L.), pea (Pisum sativum L.) and bare ground with no cover crop. Weed density and total weed dry biomass were assessed before and at 14, 28, and 56xa0days after incorporation (DAI) of the cover crops. The cover crops produced between 1.2 and 3xa0t ha−1 biomass and grain sorghum produced more dry matter than any other species in both years. After incorporation of the cover crops, hairy vetch and sorghum treatments showed fewer weed species, and lower weed density than the other cover crops in both years. Hairy vetch, grain sorghum, and sudangrass were the most effective cover crops and reduced total weed dry biomass by 90.3%, 87.4%, and 86.9% in 2004, and by 88%, 86.3%, and 85.2% in 2005, respectively. Cover crop residue suppressed many broadleaved weed species but failed to control grass weeds. Hairy vetch treatments produced the highest yield, followed by sudangrass and grain sorghum. Yields with grain amaranth and pea were similar to that of the control. These results indicate that hairy vetch, grain sorghum, and sudangrass can be used to suppress weeds in early season of organic lettuce production.