Submitted to: Soil Science Society of America Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/5/2009
Publication Date: 11/5/2009
Citation: Williams, C.F., Coffelt, T.A., Watson, J.E. 2009. Increased soil sorption of pendimethalin due to deposition of guayule-derived detritus. Soil Science Society of America Journal. 73(6):1952-1957. Interpretive Summary: Commercialization of guayule as a source of circumallergenic latex for the manufacture of medical and other latex products is becoming a reality. Since guayule is a perennial that usually grows for 4 years or more the resins, waxes and rubbers that accumulate in the soil beneath it could affect the effectiveness of pendimethalin for weed control. Results indicate that the accumulation of organic matter derived from guayule increases sorption of pendimethalin to soil and could reduce its effectiveness in guayule production. However, 1 year following guayule harvest the affect was reduced to the level prior to guayule cultivation.
Technical Abstract: Guayule is a perennial shrub that produces high molecular weight latex that is a potential source of circumallergenic natural latex for the manufacture of medical and other latex products. Guayule residues contain a high proportion of rubber, resin and wax. Typical production cycles result in 4 years worth of plant detritus deposition. Consequently, organic plant residues deposited within the soil may impact required rates of herbicide for adequate weed control. Additionally, locations where guayule is grown corresponds to cotton production areas in the southwestern US. Pendimethalin is the only herbicide registered for weed control in guayule and is commonly used in cotton production. Laboratory sorption experiments were conducted to determine the extent to which soil organic matter derived from guayule residues can affect the sorption of Pendimethalin. Continuous guayule cultivation resulted in a modest increase in soil organic carbon from 0.29% to 0.76% after 38 months of production. Adsorption of pendimethalin to soil using batch equilibrium indicated that soil organic matter derived from guayule has a higher sorption capacity for pendimethalin than non-guayule derived organic matter. Soils where guayule was grown for 38 months had a KOC 23 times greater than the control soil where guayule had not been grown (389,400 vs 16,900 L kg-1). However, one year following harvest where guayule was grown for 36 months the combination of time and cultivation resulted in a reduction of KOC from 389,400 to 21,500 L kg-1. This means that in a cotton rotation the use of pendimethalin would not appear to be affected when guayule was grown prior to cotton as long as a sufficient time had passed and proper cultivation was performed prior to planting cotton. But the use of pendimethalin during re-growth of guayule following the first harvest may require higher application rates to control weeds. This is an important consideration since weed competition with the guayule re-growing from the stump, remaining after the first harvest, has the potential to reduce yield over the next two years.