Effects of biodegradable mulch on soil quality

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Apr 1, 2014 - and Mount Vernon but at Knoxville, the WeedGuardPlus SQI was not significantly different ...... In: Bottomley, P.S., Angle, J.S., Weaver, R.W..
Applied Soil Ecology 79 (2014) 59–69

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Applied Soil Ecology journal homepage: www.elsevier.com/locate/apsoil

Effects of biodegradable mulch on soil quality C. Li a , J. Moore-Kucera a,∗ , J. Lee b , A. Corbin c , M. Brodhagen d , C. Miles e , D. Inglis e a

Department of Plant and Soil Science, Texas Tech University, United States Department of Biosystems Engineering & Soil Science, University of Tennessee, United States c Washington State University Extension, Snohomish County Extension, United States d Biology Department, Western Washington University, United States e Department of Horticulture and Plant Pathology, respectively, Washington State University, Northwestern Washington Research & Extension Center, United States b

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Article history: Received 19 November 2013 Received in revised form 16 February 2014 Accepted 17 February 2014 Available online 1 April 2014 Keywords: Biodegradable mulch Soil quality Soil management assessment framework

a b s t r a c t Biodegradable plastic films are desirable alternatives to traditional black polyethylene plastic for use as mulches in agroecosystems. Efforts are ongoing to engineer biodegradable plastic mulches that could be incorporated into the soil at the end of the crop season, and decomposed by microorganisms, ultimately to CO2 , H2 O, and biomass. Whether changes in soil quality occur during or following biodegradation is unknown. An 18-month study evaluated the effects on soil quality following burial of four potentially biodegradable mulches and a no mulch control in high tunnel and open field tomato production systems across three geographically distinct locations (Knoxville, TN; Lubbock, TX; Mount Vernon, WA). The mulch treatments included: two starch-based mulches (BioAgri® Ag-Film and BioTelo Agri); one experimental 100% polylactic acid mulch (Spunbond-PLA-10); one cellulose-based mulch (WeedGuardPlus; positive control); and a negative control (no mulch). The soil management assessment framework (SMAF) was used to calculate a soil quality index (SQI) according to five dynamic soil properties: microbial biomass carbon, ␤-glucosidase, electrical conductivity, total organic carbon (TOC), and pH. Within the 18-month evaluation period, the effects of the biodegradable mulches on the SQI were minor, and dependent upon production system and time of incubation at all locations. In general, the SQI was higher in the high tunnel systems for some of the mulch treatments at Knoxville and Lubbock but the opposite was true at Mount Vernon. By the final sampling at 18 months, the SQI was lowest for WeedGuardPlus at Lubbock and Mount Vernon but at Knoxville, the WeedGuardPlus SQI was not significantly different from the no mulch control. Of the five SMAF indicators evaluated, soil microbial biomass and ␤-glucosidase activity were the most responsive to mulch and production systems, supporting the use of these variables as soil quality indicators for short-term changes due to this agricultural management practice. © 2014 Elsevier B.V. All rights reserved.

1. Introduction From a crop production perspective, plastic mulches can increase yields, extend the growing season, reduce weed pressure, increase fertilizer use efficiency, conserve soil moisture, and increase soil temperature (Lalitha et al., 2010; Lament, 1993; Lamont, 2005; Riggle, 1998). For these reasons, polyethylene mulches have been used in agriculture for over half a century (Lamont, 2005). A major limitation of polyethylene mulch involves disposal of mulch material following use. Current disposal options as reviewed by Hayes et al. (2012) and Ren (2003) include burning, incineration, recycling, composting and using landfills; each

∗ Corresponding author. Tel.: +1 806 834 5485. E-mail address: [email protected] (J. Moore-Kucera). http://dx.doi.org/10.1016/j.apsoil.2014.02.012 0929-1393/© 2014 Elsevier B.V. All rights reserved.

have major economic or environmental disadvantages (Kyrikou and Briassoulis, 2007; Lamont, 2005). Material that is not recycled or properly disposed of can fragment, and cause environmental degradation of land and water resources. For example, crop yields were decreased when residual plastic film left in the soil was 58.5 kg ha−1 (Ma et al., 2008). Further, plastic fragments have been found to adsorb toxins that persist in the environment and disrupt terrestrial and aquatic ecosystems (Derraik, 2002; Shimao, 2001). Research advances continue to improve the degradability of polyethylene materials (Esmaeili et al., 2013; Kasirajan and Ngouajio, 2012), but without modification, the high molecular weight, 3-dimensional structure and hydrophobic properties prevent biodegradation from occurring (Klemchuk, 1990). Moreover, polyethylene plastics are non-renewable petroleum-based products, and are produced at an annual increase of 9% (Hayes et al., 2012), warranting the development of alternative mulch products

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that better align agronomic demand with long-term ecological sustainability. In the U.S.A., approximately 162,000 ha are covered with plastic mulch (Miles et al., 2012) with more than 130,000 metric tons of agricultural plastics used for vegetable production alone (Shogren and Hochmuth, 2004). Recently, biodegradable mulch films have been viewed as a more sustainable ecological alternative to plastic polyethylene mulch (see review by Briassoulis and Dejean, 2010). Biodegradable plastic mulch first was synthesized in the mid-1970s (Albregts and Howard, 1972; Otey et al., 1974). However, early biodegradable mulches broke down only partially (Narayan, 2010). Although some commercially available mulches are compostable, reliable in-soil degradation of plastic mulches has not yet been achieved. Biodegradable mulch films theoretically can save significant labor and disposal costs through incorporation via soil tillage operations rather than disposal in landfills (Kasirajan and Ngouajio, 2012). By definition by the American Society for Testing and Materials (ASTM), biodegradable plastics are broken down by naturally occurring microorganisms (ASTM, 2012a), and ultimately converted to carbon dioxide and water under aerobic conditions (Narayan, 2010). To be part of sustainable farming systems, in situ biodegradation of mulches should occur (i) within a reasonable timeframe (within 2 years as proposed by the new ASTM in-soil plastic biodegradation standard D5988-12 and WK29802) (ASTM, 2012b), and (ii) the soil quality should not be impacted negatively (Corbin et al., 2013a, 2013b; Goldberger et al., 2013; Miles et al., 2009). Currently, use of biodegradable plastic mulch in U.S. certified organic production remains prohibited, however, these materials may be allowable in the near future and the ASTM insoil plastic degradation standards (D5988-12 and WK29802) may be used to assess product suitability for use in certified organic production. Sufficient data will be needed to verify that each different biodegradable mulch product is truly biodegradable in an agricultural system (Corbin et al., 2013b). The majority of studies on the effects of polyethylene and biodegradable films on crop and soil properties have been conducted during the growing season (Briassoulis et al., 2013; Briassoulis and Dejean, 2010; Kasirajan and Ngouajio, 2012). In contrast, few studies have evaluated the impacts on soil biological and chemical properties during decomposition of biodegradable mulches (Bailes et al., 2013; Cowan et al., 2013; Kapanen et al., 2008; Moreno and Moreno, 2008). During in situ decomposition of biodegradable films that are C-rich but nutrient poor, microbial community composition and functionality may be altered. Since the decomposition of C-rich residues is associated with N immobilization, subsequent plant growth may be affected, especially if partially degraded mulch fragments exist and are decomposed at the next cropping cycle. Additionally, a ‘priming effect’ may occur in which native soil organic matter is mineralized at accelerated rates in response to the pulse of added C (Kuzyakov, 2010) or as a result of increased soil temperatures associated with mulches at the surface (Li et al., 2004). Soil microbial biomass, as measured by ATP concentration, C mineralization rates, and the ratio of CO2 production to ATP concentration were lowest following incorporation of polyethylene films compared to biodegradable films or bare soil in a tomato cropping study in Italy (Moreno and Moreno, 2008). The authors attributed these reductions in soil microbial properties to high soil temperatures under the mulches and as a reflection of progressive depletion of soil organic matter and overall microbial activity. Soil quality can vary due to both inherent and dynamic attributes of a soil. Inherent attributes (e.g., texture, climate, slope) are factors that change little, if at all, with land use or management practices, and reflect the basic five soil-forming factors (climate, organisms, relief/topography, parent material, and time) proposed by Jenny (1941). On the other hand, dynamic properties of soil quality (e.g., organic matter, microbial biomass C and bulk density) are

more responsive to changes in land use or management practices but the magnitude and rate of change are constrained by inherent soil properties (Larson and Pierce, 1991). The soil management assessment framework (SMAF) provides a single soil quality index (SQI) value, and takes into account multiple soil physical, chemical, and biological indicators that represent different soil functions (Karlen and Stott, 1994). The SMAF also allows for site-specific interpretation because indicators can be chosen and the model can be modified based on specific sets of parameters and management goals. The scores for each indicator are based on inherent soil properties, climate and crops, which then translate into unitless values that then are combined into an overall value ranging from 1 (lowest) to 100 (highest) (Andrews et al., 2004). Currently, SMAF includes 13 indicators with scoring curves, of which five were used in this study: pH, electrical conductivity, total organic carbon (TOC), microbial biomass C, and ␤-glucosidase activity (Stott et al., 2010). These indicators were chosen because of their functional importance in agricultural production. For example, soil pH influences nutrient availability and microbial activity, and thus affects nutrient cycling. Soil electrical conductivity is an indicator of salinity, which can negatively impact plant growth and is responsive to fertilizer applications. Soil organic matter, (measured as TOC for the SMAF), acts as a reservoir of nutrients and water, reduces bulk density, and provides habitat and nutrients to microorganisms. Because TOC changes relatively slowly, measurements of soil microbial biomass C provide early indications of future changes in TOC, and thus, may facilitate early detection of changes resulting from shifts in field management practices (Powlson et al., 1987). Soil enzymes also are sensitive indicators of management changes and are responsible for plant residue decomposition and nutrient cycling (Dick et al., 1996). Soil ␤-glucosidase catalyzes the final step of cellulose degradation, releasing glucose monomers, which universally fuel cellular metabolism (Deng and Popova, 2011). Soil ␤-glucosidase activity is a measure of metabolic capacity, and has been used as a soil quality indicator for over two decades (AcostaMartinez et al., 2007; Dick et al., 1996). The objectives of this study were to determine: (1) whether SQI, using the SMAF model, was affected by buried mulch treatments over an 18-month in situ incubation, (2) the effect of two tomato (Lycopersicon esculentum) production systems (high tunnel and open field) on SQI, and (3) the relationship between SQI and the extent of mulch degradation as measured previously (Li et al., 2014). In order to maximize potential differences in environmental and soil conditions in this study, the experimental design was established at three contrasting locations (Knoxville, TN, Lubbock, TX, and Mount Vernon, WA).

2. Materials and methods 2.1. Experimental locations and agricultural production systems The locations and agricultural systems used in this study are described in detail in Li et al. (2014) and Miles et al. (2012). Briefly, experimental field plots were established at three geographically distinct locations which differed primarily by climate and soil type: (1) the University of Tennessee, East Tennessee Research & Education Center at Knoxville, which receives an average of 1355 mm precipitation year−1 , and has Dewey silt loams (fine, kaolinitic, thermic Typic Paleudults) (Soil Survey Staff, 2011); (2) the Texas A&M AgriLife Research & Extension Center at Lubbock, which receives 475 mm precipitation year−1 , and has Acuff loams (fine-loamy, mixed, superactive, thermic Aridic Paleustolls) and Olton clay loams (fine, mixed, superactive, thermic Aridic Paleustolls); and (3) the Washington State University Northwestern Washington Research & Extension Center at Mount Vernon,

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which receives 831 mm precipitation year−1 , and has Skagit silt loams (fine-silty, mixed, superactive, nonacid, mesic Fluvaquentic Endoaquepts). For all locations, beginning in 2010, a tomato crop (cv. Celebrity) was grown in four replicates of two main plots (high tunnels and open field production systems) with five mulch treatment subplots (i.e., four mulch products described below plus a no mulch control). All plots were irrigated with a drip irrigation system, and fertilized annually with surface and drip applications of NPK. Knoxville plots received an average of 42 kg N ha−1 , 8.7 kg P ha−1 , and 4.6 kg K ha−1 ; Lubbock plots received an average of 47 kg N ha−1 , 17 kg P ha−1 , and 17 kg K ha−1 ; and, Mount Vernon plots received 95 kg N ha−1 , 19.4 kg P ha−1 , and 16.4 kg K ha−1 . Details regarding fertilizer types and rates each year are provided in Li et al. (2014). The effects of the mulch treatments used in this study on crop yield and quality and weed pressure have been reported elsewhere (Cowan et al., 2014; Miles et al., 2012). Prior to tomato planting and mulch laying, baseline soil samples (0–15 cm) were collected using a 5-cm diameter soil probe at Knoxville or by shovel (15 cm wide) at Lubbock and Mount Vernon. At least three subsamples were collected within each assigned mulch treatment subplot. Subsamples for each subplot were mixed gently by hand to obtain one composite sample, and stored in a cooler until transport to the laboratory for soil quality analyses as described below. Samples were collected on February 24 (high tunnel plots) and March 8 (open field plots) at Knoxville; on April 7 for both production systems at Lubbock; and, on May 17 at Mount Vernon. Tunnel installation at Knoxville was completed approximately two months before baseline sampling. At Lubbock, two of the tunnels were installed in March and the remaining two were completed a few days prior to baseline sampling. At Mount Vernon, tunnels initially were installed in April but a wind storm occurred on May 5 which destroyed the tunnels. Reinstallation of tunnels at Mount Vernon was completed approximately one week after baseline soil samples were collected. The high tunnel models varied to accommodate grower preferences and site specific requirements at each location (Miles et al., 2012). At Knoxville, the Windjammer Series 5000 (Cold Frame; Griffin Greenhouse & Nursery Supplies, Knoxville, TN) was used and each of the four tunnels measured 29.3 m long by 9.2 m wide. At Lubbock, the ClearSpan ‘Colossal’ (ClearSpan, Windsor, CT) model was used, and had the same dimensions as the Windjammer Series. At Mount Vernon each tunnel measured 36.5 m long by 8.4 m wide, and was the Haygrove ‘Solo’ model (Haygrove Ltd., U.K). The high tunnels at Mount Vernon were dismantled each winter due to the 3-season nature of the ‘Solo’ model (Miles et al., 2012). During the 18-month study, soil temperature sensors (Hobo® ; Onset, Pocasset, MA) were installed in one high tunnel and one open field replicate at each location, and temperature was measured every 15 min. Soil temperature sensors were placed at a 7-cm depth in the center of each mulch subplot during the growing season. During the winter fallow period, there was no mulch on the soil surface. During this time at Lubbock and Knoxville, soil temperature data from the sensors were averaged across mulch subplots. At Mount Vernon, where high tunnels were dismantled for the winter, soil temperature data were provided by the WSU AgWeatherNet weather station located approximately 500 m away from the study site. Average daily soil temperature was calculated and averaged over each 6-month period prior to the 6, 12, and 18-month mesh-bag extractions.

2.2. Mesh bag incubation study for the five mulch treatments Five mulches were used in this study, and assigned randomly to each subplot. Treatments included two commercially available films (BioAgri® Ag-Film and BioTelo Agri); one experimental mulch

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(Spunbond-PLA-10); a commercially available paper mulch (WeedGuardPlus); and, a bare ground no mulch control (no mulch). BioAgri® Ag-Film (BioBag, Palm Harbor, FL, USA) and BioTelo Agri (Dubois Agrinovation, Waterford, ON, CA) are two leading starch-based commercial mulches produced from Mater-Bi® , a copolyester and starch blend by Novamont (Novara, Italy) (Hayes et al., 2012). Both are black mulch films, and 0.025 mm thick. Spunbond-PLA-10 is a white experimental nonwoven spunbond mulch, 0.56 mm thick, and made from 100% polylactic acid. The feedstock for Spunbond-PLA-10 was provided by NatureWorks LLC (Blair, NE, USA). WeedGuardPlus (Sunshine Paper Co. LLC; Aurora, CO, USA) is a black paper mulch, 0.18 mm thick, and was included as a cellulose control. An 18-month in situ mesh bag incubation study was initiated to monitor mulch degradation and subsequent effects on soil quality under the various experimental conditions. The bags were 250-␮m mesh and measured 161 cm2 . Each was filled with (i) resident soil collected from each respective mulch subplot at a 0–8 cm depth plus (ii) a mulch subsample (approximately 103 cm2 ) cut from each weathered mulch treatment following final tomato harvest in 2010. Resident soil from each subplot was collected as described above for baseline samples. The weathered mulches originally covered the soil surface of the tomato beds in each subplot (0.6–0.9 m wide by 4.3 m long with 1.8 m spacing between bed centers). Each mesh bag with a mulch sample was buried in September (high tunnel plots) and October 2010 (open field plots) at Knoxville, and in October 2010 at Lubbock and Mount Vernon (both production systems), at a depth of 8–12 cm in the center of each subplot. Sufficient bags were buried at each location to recover one bag per subplot at each planned sampling time. Mesh bags were extracted after approximately 6, 12, and 18 months. Those collected at 6 and 18 months followed a winter fallow period, and were collected in early spring in 2011 and 2012, prior to replanting tomatoes. Bags collected at 12 months followed final tomato harvest in fall 2011. Although corresponding mulch again was laid on the soil surface of subplots at the time of tomato planting in 2011 and 2012, all subsequent mulch was removed after each tomato harvest. At each sampling time, one mesh bag per subplot was removed carefully and delivered, on ice, within 24 h to the Soil Microbiology and Biochemistry Laboratory at Texas Tech University. When subplots were plowed and prepared for either winter fallow or summer tomato cropping, remaining buried mesh bags were removed temporarily from the plots, and stored in a walk-in cooler at 4 ◦ C. Within 72 h of removal, bags were re-buried in their respective subplots. 2.3. Soil management assessment framework (SMAF) indicators Upon laboratory receipt, each mesh bag was cut open on three sides. Mulch pieces were removed by gloved hands with forceps and degradation was assessed as described previously by Li et al. (2014). Soil samples were sieved (550 mm precipitation Humid 1:1

Acuff/Olton Ustoll Loam (Acuff) Clay loam (Olton) 22 (Acuff); 29 (Olton) 0–1 Low (calcareous) Non smectitic/non-glassy >170 degree days 90% of the SpunbondPLA-10 remained after 24 months incubation. The percent of area that remained for BioAgri and BioTelo varied across locations and was lowest (2% on average) at Lubbock compared to Knoxville (mean of 49%) and Mount Vernon (mean of 89%). There was no significant correlation between SQI values and degradation levels of the various mulches at any location (data not shown), suggesting that SQI and the variables used to assess soil quality were not good predictors of mulch degradability, or vice versa. This work supports our finding, described elsewhere, that biogeographical effects strongly outweighed any influence of the buried biodegradable mulch pieces on mulch degradation and microbial community structure (Li et al., 2014). By the final sampling time at Lubbock (18 months), the SQI of the WeedGuardPlus treated soil in both the high tunnel (45) and open field (42) plots was significantly lower than all other mulch treatments, including the no mulch control (58 in both systems). At Mount Vernon, the SQI of the WeedGuardPlus treatment was higher at six months (50 and 60 in high tunnel and open field plots, respectively), but then by 12 months in the high tunnel plots, the SQI of the WeedGuardPlus treatment (55) was lower than all other mulch treatments (64). At 18 months at Mount Vernon, the SQI of the WeedGuardPlus-treated soil in high tunnel (48) and open field (55) plots was lower than all other mulch treatments (mean of 58 and 61 in high tunnel and open field plots, respectively). Based on visual measurements of area remaining over time as reported by Li et al. (2014), WeedGuardPlus had degraded completely within 6 months at Lubbock and Mount Vernon. Therefore, it is possible that the WeedGuardPlus treatment provided a nutrient source that permitted rapid microbial growth and consequent degradation of the cellulosic mulch for the first 6 months. However, due to the lack of new organic inputs into the mesh bags, soil microbes subsequently may have been C-limited, causing populations to decline and the SQI to decrease. Microbial biomass C for the WeedGuardPlus treatments at both sites also increased, and then diminished over time (Table 5), supporting the idea of rapid microbial growth followed by C-limitation. Microbial biomass C at the final sampling time was never as low for any other mulch treatment as it was for WeedGuardPlus at Lubbock and Mount Vernon, suggesting that the slower-degrading mulches (Li et al., 2014) do not cause the same growth patterns in soil microbial populations.

4. Conclusions Previous work (Li et al., 2014) that used the same experimental sites and mulch products revealed that mulch degradation was dependent on mulch type and geographic location. The results reported here, however, suggest that impacts on SQI from weathered buried mulches were minor, and more dependent upon production system and sampling time than on mulch type. The SQI was higher in the high tunnel systems than in open fields for some of the mulch treatments at Knoxville and Lubbock and corresponded to increased soil temperature and C inputs (due to increased plant growth) in the high tunnel systems compared to open fields. At Mount Vernon, the SQI was lower in the high tunnel systems but the dismantling of tunnels during the fallow periods may have reduced the overall influence of soil temperature on soil quality. Reduced SQI, such as those associated with degradation of WeedGuardPlus and MaterBi mulches, showed up late in the study, and underline the need for longer-term investigations of

the impact of biodegradable mulches on soil ecosystems, especially considering that these products are comprised of polymers, additives and/or fillers that are foreign to a soil environment. Acknowledgements We thank Dr. Marko Davinic, Dr. Lisa Fultz, Babette Gundersen, Jeffrey Martin, Jonathan Roozen, Dr. Russell Wallace, and Joel Webb for their technical and field support. We also thank Dr. Veronica Acosta-Martinez’s lab for assistance with the microbial biomass analysis and Dr. Arnold Saxton for assistance with statistical models. This study was funded by the NIFA Specialty Crops Research Initiative, USDA SCRI-SREP Grant Award No. 2009-0284. References Acosta-Martinez, V., Cruz, L., Sotomayor-Ramirez, D., Perez-Alegria, L., 2007. Enzyme activities as affected by soil properties and land use in a tropical watershed. Appl. Soil Ecol. 35, 35–45. Acosta-Martínez, V., Lascano, R., Calderón, F., Booker, J.D., Zobeck, T.M., Upchurch, D.R., 2011. Dryland cropping systems influence the microbial biomass and enzyme activities in a semiarid sandy soil. Biol. Fertil. Soils 47, 655–667. Albregts, E., Howard, C., 1972. Effect of mulches on okra, pepper and strawberries in central Florida. Agricultural Research Center, IFAS, University of Florida. Allison, S.D., 2005. Cheaters, diffusion and nutrients constrain decomposition by microbial enzymes in spatially structured environments. Ecol. Lett. 8, 626–635. Andrews, S.S., Karlen, D.L., Cambardella, C.A., 2004. The soil management assessment framework: a quantitative soil quality evaluation method. Soil Sci. Soc. Am. J. 68, 1945–1962. ASTM, 2012a. D883-12 Standard Terminology Relating to Plastics. ASTM International, West Conshohocken, PA, http://dx.doi.org/10.1520/D0883-12 www.astm.org ASTM, 2012b. Wk29802—New Specification for Aerobically Biodegradable Plastics in Soil Environment. ASTM International, West Conshohocken, PA, http://dx.doi.org/10.1520/D5988-12 www.astm.org Bailes, G., Lind, M., Ely, A., Powell, M., Moore-Kucera, J., Miles, C., Inglis, D., Brodhagen, M., 2013. Isolation of native soil microorganisms with potential for breaking down biodegradable plastic mulch films used in agriculture. J. Vis. Exp., e50373. Briassoulis, D., Babou, E., Hiskakis, M., Scarascia, G., Picuno, P., Guarde, D., Dejean, C., 2013. Review, mapping and analysis of the agricultural plastic waste generation and consolidation in Europe. Waste Manage. Res. 31, 1262–1278. Briassoulis, D., Dejean, C., 2010. Critical review of norms and standards for biodegradable agricultural plastics. Part I. Biodegradation in soil. J. Polym. Environ. 18, 384–400. Brookes, P., Landman, A., Pruden, G., Jenkinson, D., 1985. Chloroform fumigation and the release of soil nitrogen: a rapid direct extraction method to measure microbial biomass nitrogen in soil. Soil Biol. Biochem. 17, 837–842. Corbin, A., Miles, C., Cowan, J., Hayes, D., Dorgan, J., Inglis, D., 2013a. Using biodegradable plastics as agricultural mulches. FS103E. In: Washington State University Extension Fact Sheet., pp. 6, http://cru.cahe.wsu.edu/ CEPublications/FS103E/FS103E.pdf (Verified: 8 February 2014). Corbin, A., Miles, C., Cowan, J., Hayes, D., Moore-Kucera, J., Inglis, D., 2013b. Current and future prospects for biodegradable plastic mulch in certified organic production systems. In: eXtension Foundation, eOrganic Community of Practice, May 2, 2013, http://www.extension.org/pages/67951/ (Verified: 22 August 2013). Cowan, J.S., Inglis, D.A., Miles, C.A., 2013. Deterioration of three potentially biodegradable plastic mulches before and after soil incorporation in a broccoli field production system in Northwestern Washington. HortTech. 23, 849–858. Cowan, J.S., Miles, C.A., Andrews, P.K., Inglis, D.A., 2014. Biodegradable mulch performed comparable to polyethylene in high tunnel tomato (Solanum lycopersicum l.) production. J. Sci. Food Agric., http://dx.doi.org/10.1002/jsfa.6504, in press. Deng, S., Popova, I., 2011. Carbohydrate hydrolases. In: Dick, R.P. (Ed.), Methods of Soil Enzymology. Soil Science Society of America, pp. 185–209. Derraik, J.G., 2002. The pollution of the marine environment by plastic debris: a review. Mar. Pollut. Bull. 44, 842–852. Dick, R.P., Breakwell, D.P., Turco, R.F., 1996. Soil enzyme activities and biodiversity measurements as integrative microbiological indicators. In: Doran, J.W., Jones, A.J. (Eds.), Methods for Assessing Soil Quality. Soil Science Society of America, pp. 247–271. Esmaeili, A., Pourbabaee, A.A., Alikhani, H.A., Shabani, F., Esmaeili, E., 2013. Biodegradation of low-density polyethylene (ldpe) by mixed culture of Lysinibacillus xylanilyticus and Aspergillus niger in soil. PLoS ONE 8, e71720. Goldberger, J.R., Jones, R.E., Miles, C.A., Wallace, R.W., Inglis, D.A., 2013. Barriers and bridges to the adoption of biodegradable plastic mulches for us specialty crop production. Renew. Agric. Food Syst., 1–11. Hayes, D.G., Dharmalingam, S., Wadsworth, L.C., Leonas, K.K., Miles, C., Inglis, D., 2012. Biodegradable agricultural mulches derived from biopolymers. In: Khemani, K.C., Scholz, C. (Eds.), Degradable Polymers and Materials: Principles and Practice, vol. 1114, 2nd edition. American Chemical Society, Washington, DC, pp. 201–223.

C. Li et al. / Applied Soil Ecology 79 (2014) 59–69 Jenny, H., 1941. Factors of Soil Formation. McGraw-Hill Book Company, New York, NY, USA. Kapanen, A., Schettini, E., Vox, G., Itavaara, M., 2008. Performance and environmental impact of biodegradable films in agriculture: a field study on protected cultivation. J. Polym. Environ. 16, 109–122. Karlen, D.L., Stott, D.E., 1994. A framework for evaluating physical and chemical indicators of soil quality. In: Doran, J.W., Coleman, D.C., Bezdicek, D.F., Stewart, B.A. (Eds.), Defining Soil Quality for a Sustainable Environment. Soil Science Society of America and American Society of Agronomy, pp. 53–72. Kasirajan, S., Ngouajio, M., 2012. Polyethylene and biodegradable mulches for agricultural applications: a review. Agron. Sustain. Dev. 32, 501–529. Klemchuk, P.P., 1990. Degradable plastics: a critical review. Polym. Degrad. Stabil. 27, 183–202. Klose, S., Wernecke, K.D., Makeschin, F., 2004. Microbial activities in forest soils exposed to chronic depositions from a lignite power plant. Soil Biol. Biochem. 36, 1913–1923. Koch, O., Tscherko, D., Kandeler, E., 2007. Temperature sensitivity of microbial respiration, nitrogen mineralization, and potential soil enzyme activities in organic alpine soils. Global Biogeochem. Cy., 21. Kuzyakov, Y., 2010. Priming effects: interactions between living and dead organic matter. Soil Biol. Biochem. 42, 1363–1371. Kyrikou, I., Briassoulis, D., 2007. Biodegradation of agricultural plastic films: a critical review. J. Polym. Environ. 15, 125–150. Lalitha, M., Kasthuri Thilagam, V., Balakrishnan, N., Mansour, M., 2010. Effect of plastic mulch on soil properties and crop growth—a review. Agric. Rev. 31, 145–149. Lament, W.J., 1993. Plastic mulches for the production of vegetable crops. HortTech. 3, 35–39. Lamont, W.J., 2005. Plastics: modifying the microclimate for the production of vegetable crops. HortTech. 15, 477–481. Larson, W., Pierce, F., 1991. Conservation and enhancement of soil quality. In: Evaluation for sustainable land management in the developing world: Proceedings of the International Workshop on Evaluation for Sustainable Land Management in the Developing World, Chiang Rai, Thailand, 15–21 September 1991. [Bangkok, Thailand: International Board for Soil Research and Management, 1991]. Li, C., Moore-Kucera, J., Miles, C., Leonas, K., Lee, J., Corbin, A., Inglis, D., 2014. Degradation of potentially biodegradable plastic mulch films at three diverse U.S. locations. Agroecol. Sustain. Food Syst., www.tandfonline.com/ doi/abs/10.1080/21683565.2014.884515#preview, in press. Li, F.-M., Song, Q.-H., Jjemba, P.K., Shi, Y.-C., 2004. Dynamics of soil microbial biomass c and soil fertility in cropland mulched with plastic film in a semiarid agroecosystem. Soil Biol. Biochem. 36, 1893–1902. Loeppert, R.H., Suarez, D.L., 1996. Carbonate and gypsum. In: Sparks, D.L., Page, A.L., Helmke, P.A., Loeppert, R.H. (Eds.), Methods of soil analysis part 3—chemical methods. Soil Science Society of America, American Society of Agronomy, Madison, WI, pp. 437–474.

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Ma, H., Mei, X.-R., Yan, C.-R., He, W.-Q., Li, K., 2008. The residue of mulching plastic film of cotton field in north China. J. Agro-Environ. Sci. 2, 570–573. Miles, C., Beus, C., Corbin, A., Wallace, R., Saez, H., Walters, T., Leonas, K., Brodhagen, M., Hayes, D., Inglis, D., 2009. Research and extension priorities to ensure adaptation of high tunnels and biodegradable plastic mulch in the United States. In: Agricultural Plastics Congress, 13–16 July, College Station, PA. Miles, C., Wallace, R., Wszelaki, A., Martin, J., Cowan, J., Walters, T., Inglis, D., 2012. Deterioration of potentially biodegradable alternatives to black plastic mulch in three tomato production regions. Hortscience 47, 1270–1277. Moreno, M.M., Moreno, A., 2008. Effect of different biodegradable and polyethylene mulches on soil properties and production in a tomato crop. Sci. Hortic. Amsterdam 116, 256–263. Narayan, R., 2010. Misleading claims and misuse proliferate in the nascent. Bioplastics Magazine 5, 38–41, Polymedia Publisher GmbH, http://www. bioplasticsmagazine.com/bioplasticsmagazine-wAssets/docs/article/1001 p38 bioplasticsMAGAZINE.pdf (Verified: 22 August 2013). Otey, F.H., Mark, A.M., Mehltretter, C.L., Russell, C.R., 1974. Starch-based film for degradable agricultural mulch. Ind. Eng. Chem. Prod. R.D 13, 90–92. Powlson, D.S., Brookes, P.C., Christensen, B.T., 1987. Measurement of soil microbial biomass provides an early indication of changes in total soil organic matter due to straw incorporation. Soil Biol. Biochem. 19, 159–164. Ren, X., 2003. Biodegradable plastics: a solution or a challenge? J. Clean. Product. 11, 27–40. Rhoades, J.D., 1996. Salinity: electrical conductivity and total dissolved solids. In: Sparks, D.L., Page, A.L., Helmke, P.A., Loeppert, R.H. (Eds.), Methods of soil analysis part 3—chemical methods. Soil Science Society of America, American Society of Agronomy, pp. 417–435. Riggle, D., 1998. Moving towards consensus on degradable plastics. BioCycle 39, 64–70, http://icpe.in/bio%20degradable%20bags%20technical%20know% 20how.pdf (22.08.13). Shimao, M., 2001. Biodegradation of plastics. Curr. Opin. Biotech. 12, 242–247. Shogren, R.L., Hochmuth, R.C., 2004. Field evaluation of watermelon grown on paperpolymerized vegetable oil mulches. Hortscience 39, 1588–1591. Staff, S.S., 2011. Web Soil Survey. Natural Resources Conservation Service, United States Department of Agriculture http://websoilsurvey.nrcs.usda.gov/ Stott, D.E., Andrews, S.S., Liebig, M.A., Wienhold, B.J., Karlen, D.L., 2010. Evaluation of beta-glucosidase activity as a soil quality indicator for the soil management assessment framework. Soil Sci. Soc. Am. J. 74, 107–119. Tabatabai, M.A., 1994. Soil enzymes. In: Bottomley, P.S., Angle, J.S., Weaver, R.W. (Eds.), Methods of Soil Analysis: Part 2 – Microbiological and Biochemical Properties. Soil Science Society of America, pp. 775–833. Wardle, D.A., 1992. A comparative assessment of factors which influence microbial biomass carbon and nitrogen levels in soil. Biol. Rev. 67, 321–358. Wu, J., Joergensen, R.G., Pommerening, B., Chaussod, R., Brookes, P.C., 1990. Measurement of soil microbial biomass C – an automated procedure. Soil Biol. Biochem. 22, 1167–1169.