Organic Fertilizers, Soil Organic-matter, and Insecticides Soil Biodegradations and Efficiencies

The synthesis is presented here of the results obtained from several experiments carried out in cauliflower field crops in different regions and seasons. Fields were divided into plots. One of the organic fertilizers pig slurry, cow manure, city refuse or mushroom cultivation composts was incorporated into the soil of each plot. After cauliflower planting, one of the insecticides chlorpyriphos, chlorfenvinphos, or carbofuran was applied - for plant protection against the root fly - to each plot, by pouring its water emulsion on the soil around the plant stem. The soil persistences of each of the insecticides during crops were greater (it could be as much as 2.4 times greater when measured by the insecticides soil half-lives) in the organic fertilizers treated plots, than in the organic fertilizers untreated control plots. This occurred during the first three quarters of the crop period; at the end of the crop, the insecticides soil concentrations became similar and very low in all the organic fertilizers treated and untreated plots. To the greater insecticides soil concentrations - due to the organic fertilizers soil treatments - should correspond better insecticide protection efficiencies; the first measurements indeed indicated protection efficiencies at least as good in the organic fertilizers treated plots as in the control plots. Soil organic matter analyses indicated that the increase of the insecticides soil persistences - due to the organic fertilizers soil treatments - corresponded to greater total organic matter, humic acids and humin soil concentrations; to greater weight ratios of humic to fulvic acids; to greater nitrogen contents in the humic acids; and to humic acids containing greater percentages (as shown by C-13 NMR) of chemical functions (carboxylic, quinone...) able to fix the insecticides in soil. These observations suggest that the increases of the insecticides soil persistences due to the organic fertilizers soil treatments correspond to greater absorptions of the insecticides into the soil organic matter, which protect the insecticides against the soil metabolizing microbial activity. These conclusions were also sustained by the observations made in commercial cauliflower and sugar beet crops.