Use of low MW polylactic acid and lactide to stimulate growth and yield of soybeans
1996
Chang, Y.N. | Mueller, R.E. | Iannotti, E.L.
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(D,L-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 (15-30 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-1) 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 momomeric lactic acid.
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