Soils are considered important components of many pesticide contamination models and are frequently the direct or indirect targets of pesticides applied during agricultural activities. Soil texture is commonly referenced on pesticide labels as an important factor in the selection and application of pesticides and in identifying target areas that are vulnerable to leaching. In general, no guidelines exist for the common interpretation of generic soil texture terms found on pesticide labels, for example, coarse or coarse‐textured soils. In the present study, a significant logistic regression model (P = 0.017) was developed that is based on the soil particle‐size class composition of sections containing wells sampled for DBCP (1,3‐dibromochloropropane). Particle‐size class is a concept used in Soil Taxonomy to describe soil family texture and is a component of soil family names. The model contains terms for the sandy and fine particle‐size classes. The model was validated using data obtained from sources independent of those used to develop the model. Records in the California Soils Map Unit Inventory database that describes the soil map unit composition of >65 000 sections (1600 m2 or 1 mi2) were used to generate probability scores for >15 000 sections located in the San Joaquin Valley, CA. A geographic information system, an information management technique that is becoming an accepted tool for a wide range of regulatory agencies, was used to generate visual images of the probability scores. A map was developed that depicts four distinct probability classes of the DBCP‐contamination status of section‐sized areas and their distribution within the study area.
Cotton (Gossypium hirsutum L.) Alcala SJ‐2 was grown in an activated carbon‐filtered greenhouse and exposed to biweekly 6‐hour ozone fumigations at a concentration of 490 µg m−3. Two ozone treatments were used, differing in age at initial exposure and total ozone dose. Sacrificial harvests were taken from all treatments at 14‐day intervals to monitor plant response and to provide the basis for growth analysis techniques.Ozone reduced the vegetative growth and boll production in both ozone treatments. The dry weights of all partitioned plant parts were reduced with the largest reductions occurring in roots and bolls. Fumigated plants initially produced fewer leaves with significantly less leaf area. A period of stimulated leaf and branch production followed the initial growth depression. Boll production was depressed 48% in both ozone treatments. Mean relative growth rates of partitioned plant parts were extremely good predictors of absolute responses. Mean net assimilation rates of ozone‐stressed plants were reduced throughout growth. The ozone‐treated plants were characterized by larger mean leaf area ratios, which accounted for elevated plant mean relative growth rates at 64 days of age.
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