Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2001
Publication Date: N/A
Interpretive Summary: The continued detection of various herbicides in surface and ground waters is a concern in spite of increased research efforts to minimize these occurrences. Some herbicides are sufficiently persistence or mobile enough to classify them as potential risks to surface or ground waters even though they are effective in controlling target weeds. Research was conducted to determine if adding organic amendments to a sandy soil would decrease herbicide persistence by stimulating microbial population in soil or reduce mobility by increasing the binding of the herbicide to soil. We found that organic amendments modify leaching behavior of herbicides by affecting soil physical properties such as soil porosity, sorption and persistence, however the effect depends on the nature of the organic matter applied. For instance, composted urban waste increased degradation and reduced leaching whereas liquified food waste increased leaching. Research is now needed to determine the effect of these organic amendments on herbicide efficacy in controlling weeds. If the rate of degradation becomes too fast, the herbicides would not be around long enough to control the weeds. These results will be of beneift/interest to agricultural scientists who are developing crop production systems that minimize potential adverse environmental effects of herbicide use.
Technical Abstract: The influence of three organic amendments (OA) consisting of a liquid (LOA) and a solid (SOA) humic amendment and a solid urban waste (SUW) on sorption, persistence, and leaching potential of simazine and 2,4-D in a sandy soil (P2) has been investigated. The OAs were added to soil P2 at 5% w/w rate. Sorption was studied by the batch equilibration technique, degradation by incubations at 20oC and -0.33 kPa moisture content, and leaching in handpacked soil columns. Simazine sorption increased in the order P2 P2+LOA < P2+SUW < P2+SOA. 2,4-D did not sorb on P2 soil, but did in amended soils and sorption increased in the same order as simazine. The lower sorption of both herbicides in P2+LOA as compared to P2+SOA and P2+SUW has been attributed to higher dissolved organic matter (DOM) content of LOA. Simazine half-life was reduced upon amendment. 2,4-D followed a sigmoidal rate of degradation in original and P2+SOA and P2+SUW amended soils, but not in P2+LOA, in which 2,4-D persistence was much higher. The higher stability of 2,4-D in P2+LOA has been attributed to 2,4-D-DOM interactions. Leaching studies indicate that degradation affects movement to a higher extent than sorption, specially in the case of 2,4-D in P2+LOA soil, in which the amounts leached are much higher than the corresponding to the unamended soil. In the case of simazine and P2+SUW soil, greater reduction in large size conducting pores upon amendment, revealed in mercury porosimetry studies, resulted in a greater reduction of leaching than that suggested from the small differences in sorption and degradation between P2 and P2+SUW soil.