Use of low MW polylactic acid and lactide to stimulate growth and yield of soybeans

Abstract

Polylactic acid (PLA) is an environmentally friendly, degradable polymer which has been suggested for use as a matrix for controlled release of herbicides. The growth stimulation and yield improvement potential of low molecular weight (MW), poly(DL-lactic acid) and D,L-lactide were evaluated using preplant soil incorporation with soybeans (Glycine max (L.) Merrill). Greenhouse studies confirmed that both lactide and PLA increased soybean leaf area, pod number, bean number and bean and plant dry weight. Soybean seed yield was increased most dramatically (130%; 2.3 fold) by weekly 30 ppm lactide addition and also by single addition of low MW (3500 Daltons) PLA (40.6%; 1.4 fold). Low levels of PLA were stimulatory (U-30 ppm), while higher levels were inhibitory, with some interaction with growth conditions being evident. The stimulatory component was most readily provided by weekly lactide addition, but was also provided by slow-release, hydrolytic breakdown of PLA in the soil, with 3500 Daltons MW being better than higher MW PLA. In field studies at two locations, PLA (16.8 and 45.8 kg ha-') increased soybean plot yield as much as 18%, being reflected in increases in both growth and per plant yield components (plant dry wt, seed number, seed dry wt, and number of branch pods and seeds). The levels used in field studies were selected to be similar to the level of a typical carrier used in slow release of herbicides. This study suggests that use of PLA as an encapsulation matrix for herbicides could provide reduced environmental impact and improved weed control, while at the same time increasing yield of soybeans through release of a plant growth stimulant in the form of oligomeric or monomeric lactic acid.

Soybean Metabolites Regulated in Root Hairs in Response to the Symbiotic BacteriumBradyrhizobium japonicum

“…Lactic acid was previously reported to be 4.8 times more abundant in alfalfa nodules than in roots and accumulated in nodules during salt stress (Swaraj and Bishnoi, 1999;Barsch et al, 2006). Polymers of lactic acid were shown to stimulate plant growth in corn (Zea mays) and soybean (Kinnersley et al, 1990;Chang et al, 1996). However, further studies are required to determine a possible role for lactic acid in root hairs colonized by B. japonicum.…”

Concurrent solvent induced crystallization and hydrolytic degradation of PLA by water-ethanol solutions

“…In the medical field, due to its biocompatibility with the human body, PLA has been used for applications such as sutures, stents and drug delivery systems. [3][4][5][6] In agriculture, PLA has been used as a material for the controlled release of herbicides [7][8][9] or as a plastic to protect soil and plants from erosion, insects and birds [10]. In packaging, PLA has been used as both a film and a rigid thermoform for containers for food and non-food products [1,[11][12][13].…”

“…For example, disinfection of electrospun materials for tissue engineering is commonly carried out by ethanol soaking [17][18][19]. In agriculture, for growth stimulation and the controlled release of pesticides, PLA is in a high relative humidity environment or in direct contact with water [7,20]. In packaging applications, when PLA is used for beverage and fresh food containers, it could be in direct contact with water or ethanol, or be exposed to humid environments.…”

Polymeric Nanocomposite-Based Agriculture Delivery System: Emerging Technology for Agriculture

“…Usually, the controlled release system is mainly divided into two groups; (1) encapsulation of active molecules/agrochemicals/micronutrients by using polymeric matrix and (2) polymeric matrix and active molecules/agrochemicals/micronutrients enclosed and formation of macromolecular backbones. Several polymers (natural, synthetic, and synthetic elastomers) such as carboxymethyl cellulose [52], cellulose acetate phthalate [53], gelatin [54], chitosan [55], gum Arabic [56], polylactic acid (PLA) [57], poly-butadiene, poly-lactic-glycolic acid (PLGA) [58], polyhydroxyalkanoates (PHAs) [59], polyvinyl alcohol (PVA) [60], polyacrylamide [61,62], and polystyrene, etc., [63] are extensively used in various delivery systems. Among all of them, natural polymers are extensively used for controlled release of drugs/agrochemicals because of their low cost and being biodegradable.…”