Pelletized Soy-based Bioplastic Fertilizers for Container-crop Production

Abstract

<jats:p>Research examining biocontainers for container-crop production has demonstrated that bioplastics made from soybean [<jats:italic>Glycine max</jats:italic> (L.) Merr.] can supply mineral nutrients to plants. Using soybean-based bioplastics and biochar (BC), we created pelletized fertilizer designed to be incorporated into soilless substrate. We evaluated the growth of ‘Honeycomb’ marigold (<jats:italic>Tagetes patula</jats:italic> L.), ‘Montego White’ snapdragon (<jats:italic>Antirrhinum majus</jats:italic> L.), and ‘Laser Synchro Scarlet’ cyclamen (<jats:italic>Cyclamen persicum</jats:italic> Mill.) grown with pelletized soy-based bioplastic fertilizers [soy-bioplastic polymer (SP.A) compounded with poly(lactic) acid (PLA) or polyhydroxyalkanoates (PHA), containing 15% or 25% BC] or a synthetic controlled-release fertilizer (CRF). Our objectives were to evaluate the effectiveness of prototype SP.A-based fertilizers and compare their performance to that of a traditional CRF for growing common greenhouse crops. In our first experiment, treatments of 0, 346, or 691 g nitrogen (N)/m<jats:sup>3</jats:sup> of substrate from different fertilizer types were applied to marigold in containers with 15.2-cm top diameter, and in our second experiment, 0, 211, 423, 819, or 1638 g N/m<jats:sup>3</jats:sup> were applied to marigold, snapdragon, and cyclamen in containers with 11.4-cm top diameter. Marigolds grown in larger containers accumulated more shoot dry mass (SDM) when supplied with 346 or 691 g N/m<jats:sup>3</jats:sup> from each type of the SP.A-based fertilizers than did plants in the nonfertilized control group. Plants supplied with synthetic CRF accumulated similar or greater SDM than plants supplied with the same rate of N from SP.A-based fertilizers. In smaller containers, marigold and cyclamen provided with 211 or 423 g N/m<jats:sup>3</jats:sup> from SP.A-based fertilizers accumulated more SDM than nonfertilized plants. Snapdragon provided with SP.A-based fertilizer grew poorly, and plants of this species died before the end of 5 weeks when provided the high and heavy rates of SP.A-based fertilizers. Plants fertilized with CRF had the largest SDM across the three species at most fertilizer concentrations. Tissue N concentration and N uptake were greater for plants provided with SP.A-based fertilizers at most N rates (211, 423, 819 g N/m<jats:sup>3</jats:sup>) or synthetic CRF (all four rates) than for nonfertilized plants. The effectiveness of prototype SP.A-based fertilizers was better at common application rates (211 and 423 g N/m<jats:sup>3</jats:sup>), but showed a diminishing return at high and heavy rates of application (819 and 1638 g N/m<jats:sup>3</jats:sup>). The SP.A-based fertilizers made with PLA copolymer were more effective than those made with PHA. Our results serve as proof-of-concept that pelletized soy-based bioplastic fertilizers can be effective for meeting the nutrient needs of plants during containerized-crop production, but formulations require further development to improve their properties for use with a broad range of species and application rates.</jats:p>

Effectiveness of Biopolymer Horticultural Products for Production and Postproduction Nutrient Provision of Garden and Bedding Crops and Container Ornamentals

“…One of the factors that must be considered when comparing the effectiveness of biopolymer fertilizers to that of synthetic fertilizers in our study is that fertilizer treatments were set to provide equal amounts of N. By setting the treatments in this way, the experiments arbitrarily caused biopolymer fertilizers to be applied at lower amounts of P and K. This factor may explain some, or perhaps most, of the lower results obtained for plants provided with biopolymer fertilizers compared with those provided with synthetic CRF. Although the biopolymer fertilizer materials used in this study have been improved from their original form by making small changes to the formulations (McCabe et al, 2016a(McCabe et al, , 2016bSchrader et al, 2013), at this time the fertilizers are still considered to be in early stages of product development. It is likely that future research and development will produce formulations that will be equally effective to that of synthetic CRF for growing horticulture crops in containers and in the garden, while still being much more sustainable than synthetic fertilizer (Montalbo-Lomboy et al, 2016).…”

“…The granular DDGS material is a nutrient-containing coproduct of corn ethanol production that blends well with bioplastics. Detailed formulations and descriptions of pilot-scale manufacture of biopolymer containers and pelletized fertilizer are available in McCabe et al (2016aMcCabe et al ( , 2016b, respectively. Biopolymer fertilizer spikes were manufactured by using methods similar to those used for making containers, but were formed with a different injection mold.…”

“…Along with extensive consumption of fossil fuel resources, worldwide ammonia fertilizer production is responsible for %5% of global carbon emissions, releasing 2 t of carbon dioxide (CO 2 ) for every ton of ammonia produced (LeCompte, 2013). The biopolymer fertilizers evaluated in our research are made from nearly 100% biorenewable materials (McCabe et al, 2016b), meaning that almost none of the carbon or hydrogen comes from fossil resources. Likewise, when the carbon is released during use of the biopolymer fertilizer, there is little or no net increase in atmospheric CO 2 because the original source of the carbon was CO 2 harvested from the atmosphere by the corn (Zea mays) and soybean (G. max) plants whose seed is the feedstock for the production of the biopolymer nutrient materials.…”

“…The energy savings realized by using the soy-based N source is substantial. Instead of using fossil fuels and/or electricity to fix atmospheric N (N 2 ) to make ammonia (the Haber-Bosch process), the N 2 fixation for biopolymer fertilizer is performed in the root nodules of soybean plants through a symbiotic relationship with Rhizobia bacteria, and the energy for this natural process is provided by the sun through photosynthesis (Calabria et al, 2012;McCabe et al, 2016b;Sawyer et al, 2010;Schrader et al, 2013).…”

“…1). Like standard CRFs, biopolymer fertilizers release nutrients slowly, and thus reduce nutrient loss in leachate compared with water-soluble fertilizers (Calabria et al, 2012;McCabe et al, 2016aMcCabe et al, , 2016b.…”