USE OF LOW MW POLYLACTIC ACID AND LACTIDE TO STIMULATE GROWTH AND YIELD OF SOYBEANS

Polylactic acid (PLA) is an environmentally friendly, degradable polym er 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 w ere 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 stim ulatory component was most readily provided by weekly lactide addition , but was also provided by slow-release, hydrolytic breakdown of PLA i n the soil, with 3500 Daltons MW being better than higher MW PLA. In f ield 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 bo th growth and per plant yield components (plant dry wt, seed number, s eed dry wt, and number of branch pods and seeds). The levels used in f ield studies were selected to be similar to the level of a typical car rier 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 tim e increasing yield of soybeans through release of a plant growth stimu lant in the form of oligomeric or monomeric lactic acid.