Lluís Martín-Closas

Performance and environmental impact of biodegradable polymers as agricultural mulching films

In the aim of resolving environmental key issues such as irreversible soil pollution by non-biodegradable and non-recoverable polyethylene (PE) fragments, a full-scale field experiment was set up to evaluate the suitability of four biodegradable materials based on poly(butylene adipate-co-terephtalate) (PBAT) to be used as sustainable alternatives to PE for mulching application in vineyard. Initial ultimate tensile properties, functional properties during field ageing (water vapour permeability and radiometric properties), biodegradability and agronomical performance of the mulched vines (wood production and fruiting yield) were studied. In spite of their early loss of physical integrity that occurred only five months after vine planting, the four materials satisfied all the requested functional properties and led to agronomic performance as high as polyethylene. In the light of the obtained results, the mulching material lifespan was questioned in the case of long-term perennial crop such as grapevine. Taking into account their mulching efficiency and biodegradability, the four PBAT-based studied materials are proven to constitute suitable alternatives to the excessively resistant PE material.

Jasmonates promote cabbage (Brassica oleracea L. var Capitata L.) root and shoot development

Jasmonates are a new group of plant hormones; their roles on plant development are still little known. The aim of this work is to determine the action of jasmonates on cabbage, Brassica oleracea L. var Capitata,development both in in vitro cultured explants and in whole plants. Jasmonic acid (JA) enhanced nodal explant development when applied at 2–50 nM and inhibited it when supplied at 1250 and 6000 nM JA. Overall plant development was enhanced most under the 10 nM JA treatment; which significantly increased the explant shoot, leaf, and root dry weight. The root system of the explants cultured under the lower JA concentrations appeared more vigorous. Jasmonic acid also promoted the development of isolated in vitro cultured roots when applied at 2 and 10 nM. Root length and weight significantly increased, while concentrations 250 nM JA and over were detrimental. Isolated roots were progressively thicker as the JA concentration increased. Methyl jasmonate promoted both the below-and above-ground cabbage plant development when applied in a confined atmosphere at a concentration of only 1.225 nl.l−1 MJ: plants were higher and heavier, and showed an improved root system development. On the other hand, the 2.43 n1.1−1 MJ treatment decreased plant growth. The present work reveals a role for jasmonates as enhancers of in vitro and in vivo cabbage plant development. To our knowledge, no corresponding studies on the effects of jasmonates on whole plants have been previously published.

In vitro Tuberization of Potato: Effect of Several Morphogenic Regulators in Light and Darkness

Summary A significant increase in the number of tubers was obtained in the presence of either kinetin (11.6·10 -3 mM), paclobutrazol (8.5·10 -3 mM) or acetate (5.4 mM) for in vitro stolons in darkness, and both single-node sections and intact 3-cm long sprouts were produced after long photoperiod (16 h) subculture. Longitudinal growth decreased whenever tuberization was promoted, especially in the presence of paclobutrazol. Calcium chloride (6 mM) slightly induced tuberization in the dark. Putrescine (0.15 mM) favoured vegetative development in all explants.

In vitro induction of potato tuberization by organic acids

SummaryPotato microtubers are usually induced in media containing growth regulatory, typically cytokinins and growth retardants. However, since these substances may imbalance the physiology of the cultured explants and cause adverse carry-over effects on the subsequent performance of the microtubers, the potential acid-induction of in vitro-mass tuberization was investigated as an alternative. For this purpose, a range of explant types (stolons, single-node or apex-containing multinodal sections), organic acids (acetic, propionic, ascorbic, acetylsalicylic or salicylic acid), and photoperiods (continuous dark, 8 or 16 h photoperiod) were established. Gellified medium or raft membranes on liquid medium were also tested.Although variations due to explant type, photoperiod, organic acid supplemented, and medium type were found, all organic acids tested under the different experiments caused tuberization. Multiple tuber formation or bigger tubers did not develop on multinodal explants. In terms of tuberization rate and mean tuber weight, gellified medium performed better than liquid medium with rafts. The recently established role of the salicylic and acetylsalicylic acids on tuberization is corroborated by our system. The results with the acetic, propionic and ascorbic acids show that in vitro hormone-free tuberization can be easily and rapidly achieved.

Above-soil and in-soil degradation of oxo- and bio-degradable mulches: a qualitative approach

Degradable materials have been suggested to overcome accumulation in the field of persistent plastic residues associated with the increasing use of polyethylene mulches. New degradable materials have been proven successful for increasing crop productivity; however, their degradation in the field has been hardly addressed. A qualitative scale was used in the present study to assess the above-soil and in-soil degradation of degradable mulches during the cropping season. Degradation was determined in three biodegradable plastic mulches (Biofilm, BF; Mater-Bi, MB; Bioflex, BFx), two paper sheet mulches (Saikraft, PSA; MimGreen, PMG) and one oxo-degradable plastic mulch (Enviroplast, EvP). Polyethylene (PE) mulch was used as control. Mulches were tested in five Spanish locations (Castilla-La Mancha, La Rioja, Navarra, Aragon and Catalunya), with three crop seasons of processing tomato. Biodegradable plastic mulches BF and MB degraded more and faster above-soil than paper mulches; among biodegradable mulches BF degraded more than MB, and MB more than BFx. The above-soil degradation of the oxo-degradable mulch EvP was highly dependent on location and crop season, and it degraded more than PE. Main environmental factors triggering above-soil degradation were radiation, rainfall and crop cover. In-soil, paper mulches and BF degraded more and faster than MB, whereas BFx and EvP barely degraded. Environmental factors triggering in-soil degradation during the crop season were rainfall and irrigation water. The effect of soil parameters (organic matter, nutrient availability) on degradation during the cropping season was not evidenced. The qualitative scale used proved convenient for determining mulch field degradation. A visual scale for supporting the qualitative evaluation is provided. In order to standardise parameters and criteria for future studies on field mulching degradation evaluation, a unified degradation qualitative scale is suggested.

Agronomic Effects of Biodegradable Films on Crop and Field Environment

This chapter describes the state of the art of the agronomic effects of degradable bioplastics used as agricultural films. Current use of bioplastics and certified commercial biodegradable materials, both as granulates and as final products, are introduced. Following, agronomic effects on crops are reported and compared to the routinely used oil-based nondegradable plastics, basically the polyethylene films. Biodegradable films for agriculture were initially developed mostly for mulching application, which still remains the most significant one. Since last reviews published in 2011, new progress and perspectives have mainly arisen regarding the agronomic effects of biodegradable mulching on vegetable crops, not only as films but also as nonwoven biobased mulches. The film mechanical laying and the effects on yield, earliness, product quality, weed control efficacy, microclimatic improvement and film soil coverage and degradation are presented in detail for tomato crops and for other crops where mulching is a common technique (pepper, melon and other cucurbits, strawberry, lettuce,…). Some information is provided for crops not so frequently mulched (broccoli, sweet potato, sweet corn). New findings published on the use of biodegradable films for solarisation are also reviewed, while no significant progress on the use of films for low tunnel covers has been made. Recent proposals for vineyards and future potential application of bioplastics for orchard crops are also addressed. Finally, pros and cons for the adoption of biodegradable films for cultivating crops are discussed.

An in vitro tuberization bioassay to assess maturity class of new potato clones.

Summary The maturity of a new potato clone can be determined from physiological measurements in field trials that involve considerable time, space and work. To improve the procedure, an in vitro bioassay based on tuberization behaviour of potato cultivars of different maturity classes was established. Twenty-six sets of temperature, photoperiod and photosynthetic photon flux values were assayed on the eight potato cultivars Jaerla, Zorba, Spunta, Kennebec, Turia, Désirée, Baraka and Fénix. In vitro tuberization was influenced by cultivar, photoperiod and temperature. The environmental condition defined by 12 h photoperiod, 34 μmol m–2 s–1 of photosynthetic photon flux and 25°C temperature produced statistical differences in tuberization among maturity classes. Both the earliness of tuberization and the “degree of tuberization” (based on the type of microtubers developed) permitted assigning a cultivar to a maturity class. Early cultivars showed higher readiness to tuberize and higher values of “degree of tuberization” than late cultivars.

Biodegradable Plastic Mulch Films: Impacts on Soil Microbial Communities and Ecosystem Functions

Agricultural plastic mulch films are widely used in specialty crop production systems because of their agronomic benefits. Biodegradable plastic mulches (BDMs) offer an environmentally sustainable alternative to conventional polyethylene (PE) mulch. Unlike PE films, which need to be removed after use, BDMs are tilled into soil where they are expected to biodegrade. However, there remains considerable uncertainty about long-term impacts of BDM incorporation on soil ecosystems. BDMs potentially influence soil microbial communities in two ways: first, as a surface barrier prior to soil incorporation, indirectly affecting soil microclimate and atmosphere (similar to PE films) and second, after soil incorporation, as a direct input of physical fragments, which add carbon, microorganisms, additives, and adherent chemicals. This review summarizes the current literature on impacts of plastic mulches on soil biological and biogeochemical processes, with a special emphasis on BDMs. The combined findings indicated that when used as a surface barrier, plastic mulches altered soil microbial community composition and functioning via microclimate modification, though the nature of these alterations varied between studies. In addition, BDM incorporation into soil can result in enhanced microbial activity and enrichment of fungal taxa. This suggests that despite the fact that total carbon input from BDMs is minuscule, a stimulatory effect on microbial activity may ultimately affect soil organic matter dynamics. To address the current knowledge gaps, long term studies and a better understanding of impacts of BDMs on nutrient biogeochemistry are needed. These are critical to evaluating BDMs as they relate to soil health and agroecosystem sustainability.