Fertilizer Effects of Soy-plastic Containers during Crop Production and Transplant Establishment

摘要

As part of a project to develop and assess bio-based, biodegradable plastics for their potential to replace petroleum-based plastics in specialty-crop containers, we evaluated prototype containers made of protein-based polymers from soybean {Glycine max (L.) Merr.] for their effectiveness during production of plants in greenhouses and subsequent establishment of those plants outdoors. Our objective was to assess the function and biodegradation of soy-based plastic containers with special attention towhether a fertilizer effect results from degrading containers before and after plants are moved outdoors. In our first experiment, plants of tomato (Solatium lycopersicum L.) and pepper (Capsicum annuum L.) were grown in soy-plastic containers and control containers of petroleum-based (polypropylene) plastic under greenhouse conditions for 4 weeks. Each plant then was transplanted and grown in an outdoor garden plot for 5 weeks with the container removed, broken into pieces less than 4 cm in diameter,and installed beneath the roots of the transplant. Three additional experiments were performed: a greenhouse trial to quantify the relative concentration and form of plant-available nitrogen (N) released from soy-plastic containers of three types [soy plastic, soy plastic coated with polylactic acid (PLA), and soy-PLA polymer blended 50:50 by weight] during production; a greenhouse trial to evaluate the same three container types under production conditions with five container-crop species; and a fieldtrial to assess the effects of the 50:50 soy-PLA container on transplant establishment. Plant-available N was released from soy-based plastic containers during greenhouse production, and transplant establishment was enhanced when the soy-based containerwas removed, crushed, and installed in the soil near plant roots. During greenhouse production, containers of high-percentage soy plastic released N at an excessive rate (623 mg-L~(-1) in leachate) and predominantly in the form of NH4+ (99.4% at 3 weeksof culture). Containers made by blending soy plastic with PLA released N at a favorable rate during production. In both field trials, growth and health of plants cultured in soy containers were better than those of controls. Although the design and material formulation of soy-plastic containers need to be improved to optimize container integrity and plant health during production, our results illustrate the potential to use soy-based plastics in biodegradable containers that release N at rates that promote growth and health of plants during greenhouse production and establishment of transplants outdoors.