The objective is to ascertain the extent to which the agronomic practice of long term monoculture, extensively applied in many countries of the European Community, and the implied repetitive application of specific herbicides to the soil may alter the status and properties of soil organic matter and whether these modifications may affect the mobility of herbicides through the soil and their downward transport to the groundwater.
A project has been set up to ascertain the extent to which the agronomic practice of long term monoculture, such as vineyards, hops and citrus fruits, and the implied repetitive application of specific herbicides may alter the status and properties of soil organic matter and whether these modifications may affect the mobility of herbicides through the soil and their downward transport to the groundwater. Hop soils are slightly acidic; citrus and vineyard soils are slightly alkaline. This suggests a different behaviour of the soils under different monoculture with respect to performances of applied herbicides. Comparing results of the 3 soil sets, citrus soil humic acids were found to have higher acidic and free radical reactivities and lower microbial activity than hop soil humic acids, and those from vineyards showed intermediate values. Data was obtained showing the interaction of the humic acids with the herbicides glyphosate, simazine, diquat, paraquat, atrazine and 2,4-dichlorophenoxy acetic acid, and the adsorption and desorption isotherms for these chemicals with the 3 types of humic acids. Soil column studies were carried out. The average cumulative breakthrough curves for 2,4-dichlorophenoxy acetic acid obtained from the undistributed soil column studies are similar for the 3 vineyard soils, indicating that the vineyard monoculture practices do not influence the downward transport of 2,4-dichlorophenoxy acetic acid. The half life of 2,4-dichlorophenoxy acetic acid in the control soil is higher than in the 2 cultivated soils, suggesting a lower microbial degradation of 2,4-dichlorophenoxy acetic acid in the latter. The cumulative breakthrough curves for simazine show that this molecule is retarded 3 times more in the soil under the plants (in the rows) than in the other 2 soils. The considerably smaller half life value obtained for simazine in the former soil may be due either to nonreversible binding of simazine to soil components and/or to a different microbiological degradation pathway of the herbicide. The dispersion coefficients of 2,4-dichlorophenoxy acetic acid in these soils are lower than those of simazine, probably because of the much lower solubility of simazine. Differently from the vineyard, 2,4-dichlorophenoxy acetic acid appears much more strongly removed from the soil under hops monoculture (in row), than from the soils between rows and control.
3 field soils under long term monocultures typical of each sampling area are being investigated, one in south Germany (hops), one in central Italy (vineyards), and one in southern Italy (citrus). Adjacent, unexploited soils of the same type are also collected and used as controls. The main aspects of the study are as follows.
Firstly, the physical aspects of herbicide leaching through the soil which will be studied by soil column experiments. For each soil type, the herbicide typically used locally (eg diquat for hops fields) will be applied to the column top at normal field rates. Further, the movement and transport of standard herbicides (ie atrazine and 2,4-dichlorophenoxy acetic acid (2,4-D)) actually used within an EC ring test on adsorption and desorption in soil, will be tested in column studies for the 3 soils examined. These standard herbicides will be replaced by others if their use has in the meantime been prohibited in the Community. Both leachates and soil bound fractions of undegraded residual herbicide and their major degradation products will be analyzed by adequate physico chemical techniques. The nature of breakthrough curves will be analyzed by a curve fitting programme, and partition and dispersion constants will be determined for each herbicide and each soil type.
Secondly, the isolation of humic substances (HS) from soil samples and their chemical, physico chemical and spectroscopic analyses. Molecular and quantitative aspects of the interaction occuring between soil HS and selected herbicides will be studied also by the determination of adsorption isotherms. The combined data obtained by comparative physical, chemical, physico chemical and spectroscopic studies of HS from soils under monoculture and from control soils and of herbicide HS interaction products are expected to furnish exhaustive information on the distribution, breakthrough and transport of herbicides through the soil, the modifications in the organic matter quality and the mechanisms involved in adsorption processes. This, in return, will allow the evaluation of the effects of herbicide treatment on HS and on soils under monoculture.
Funding SchemeCSC - Cost-sharing contracts