Cropped studies

Plants grown for longer periods in solid supports such as sand or soil repre-.sent the next level of complexity and, although other techniques are available, carbon flow is most frequently estimated using C labeling experiments. In the laboratory, COt can be supplied to shoots either as a short pulse or continuously, and the carbon flow can be monitored. In the field, due to technical limitations, only COi pulse labeling procedures are possible. A final approach, termed crop studies, involves the measurement of components of crop growth from which... 

Table 3 Examples of Experiments Employing Crop Study Techniques to Examine the Effect of Treatments Influencing Carbon Flow to Roots or Soil...

Morgan and Lenz (1992) showed that the major water-soluble metabolite in wheat grain was 2-amino-3,3-dime-thyl butanoic acid (Figure 7.19). This material accounted for 11% of the total radioactive residue. Degradation of the heterocyclic ring to form the semicarbazone of pyruvic acid was reported in a potato rotational crop study by Prestel et al (1976). However, Scholz (1982) was unable to repeat this observation. 

Crop Recoveries. Post-Column Derivatization (OPA-MERC). The good to excellent recoveries realized for all crops studied resulted from the efficiencies of both the cation exchange cleanup and anion exchange analytical columns, the care taken in the rotary evaporation of the samples ( 5°C condenser temp., maximum aspiration and 40°C water bath), and the selectivity of the OPA-MERC reagent. As seen in Table I, recoveries at 0.1 ppm for AMPA ranged from 61 to 82% and for GLYPH from 70 to 96%. 

Standard deviations for AMPA recoveries were less than 2%, excellent for replicate recoveries while the percentage remained high (82.4%). While GLYPH recoveries have always been higher than AMPA for all crops studied the variability has also been higher ostensibly due to the incompleteness of the Ca(C10)2 cleavage reaction. Still, a standard deviation of less than 8% appears acceptable. 

The first survey to estimate the effects of photochemical air pollution on vegetation was developed in the mid-1950 s (I) for some areas of California. This survey used estimates derived from visible injury and included several major crop types and a single category of weeds, as they responded to certain pollutants. Although the pollutant list was not inclusive, this survey was fairly comprehensive for the crops studied and the California counties included. This survey did not estimate a monetary loss for the area of California covered. However, economic loss predictions have since been based on this early survey following superficial visual estimates of injury in several agricultural areas. These superficial predictions fixed an annual loss of approximately 8 million dollars on the West Coast and 18 million dollars on the East Coast by the early 1960 s for all types of pollutants (2). These estimates were then made countrywide, and yearly losses of between 200 and 500 million dollars have been suggested (3). 

The relatively short-run orientation of crop studies and farm economics works to exclude even those long-run results of interest to the... 

Division of Agriciflture and Conservation. Prepares and distributes publications on agricultural industries of American republics, crop studies for growers, and technical conservation studies. Publishes quarterly Conservation in the Americas (English and Spanish). 

The above steps in secondary metabolism have been known since the mid-1940 s. It has also been known for a long time that certain fungal secondary metabolites end up in crop residues (e.g. Fusarium mycotoxins) although it has been difficult to correlate data from stirred jar fermentors studies with that from crop studies e.g. corn ears. Recently, however. Hale and Eaton (19) demonstrated that the characteristic cavities of wood soft rot fungi (mostly molds) are explained by the fact that filamentous fungi do not grow in a continuous fashion in solid substrates. 

STUDIES REQUIRED ONLY UNDER CERTAIN CONDITIONS (SUCH AS PHOTOLYSIS IN AIR, VOLATILITY STUDIES, TANK MIX STUDIES AND IRRIGATED CROP STUDIES) ARE NOT INCLUDED IN THIS TABLE. 

Wanker E, Schwab H (1993) The cloned Bacillus subtilis levanase gene as a potent system for the exploitation of inulin in biotechnological processes. In Fuchs A (ed) Inulin and inulin-containing crops, studies in plant ccience, vol 3. Elsevier, Amsterdam, pp 289-296... 

Application of S, either as gypsum or from other S sources, generally decreases the uptake of Mo by crops. Studies of soybeans have shown that decreases in plant Mo are not limited only to Mo-S interactions in the soil, because foliar-applied Mo has also been shown to decrease Mo concentrations in soybean seeds and leaves in the presence of soil-added S. On low-Mo soils this can lead to induced Mo deficiency, which can decrease yields and crop quality. On soils with high amounts of Mo, application of S can prevent the accumulation of high Mo concentrations and decrease the potential for Mo toxicity to livestock. Competition between sulfate and molybdate anions, competition between bicarbonate and molybdate, and root-zone pH changes have been suggested as explanations for the action of S to reduce Mo uptake. 

The kj values obtained in this study are shown in Table IX and are similar to values obtained from studies involving other pesticides applied on different crops. This is even more surprising given the range of chemicals and crops studied and considering that the distribution of doses to the body and presumably the exposure mechanisms might be quite different. 

Dowdy and Larson [343] studied the uptake of trace elements by seven vegetable crops (carrot, lettuce, peas, potatoes, radishes, sweet corn and tomatoes) from sludge-treated soil in field conditions and concluded that, in general, metals accumulate in vegetative tissue. Among the crops studied, lettuce was exceptional in the extent to which uptake was increased on contaminated soil, and about fourfold, sevenfold and tenfold increases in plant cadmium, copper and zinc respectively, were observed on adding 450 tonnes sludge/ha. 

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