Following massive nitrogen (N) fertilization, at rates of 224, 448, and 672 kg N/ha applied in April 1969, nitrate accumulation by species and plant groups on mixed-grass prairie was measured for 3 years. All species and plant groups accumulated Nitrate-N in direct relation to rates of applied N. Two annual forbs accumulated nitrate-N above the 2000 ppm level, which is considered toxic to livestock. In 1970, the first year of residual effect, slimleaf goosefoot contained nitrate-N levels two to three times higher than the potentially toxic level, and in 19 71 greenflower pepperweed contained nitrate-N levels slightly above the potentially toxic level. The use of massive rates of N as a range improvement practice should be used with caution unless potentially toxic species are con trolled.
The xylenol method of determining nitrates in water samples was reported to provide advantages of rapidity, specificity, sensitivity, and reproducibility. Since most methods of determining nitrates in forage samples are difficult and time consuming, our objective was to adapt the xylenol method for determining nitrates in forage and to compare it to the nitrate‐electrode method. The first problem originated from an incorrect procedural suggestion concerning the ratio of sulfuric acid to water in the nitration medium. The original recommendation for six parts of sulfuric acid to four parts of water and two parts of acetic acid was satisfactory. The second problem was one of clarifying plant extracts without adding interfering ions or removing nitrate. A source of bone black adsorbed plant pigments without adsorbing nitrate. The third problem was that of interference from sugar, which required quantitative evaluation. Although the amount of that interference was small, amounting to 5.4 ppm of nitrate N per 1% sugar extracted from plant dry matter, it was important in the comparison of xylenol and nitrate‐electrode methods. A rapid colorimetric method of determining extracted sugar by darkening with sulfuric acid was developed. Among triplicate determinations of 12 forage samples ranging from 87 to 1,469 ppm of nitrate N, the xylenol and nitrate‐electrode methods gave equal values and time requirements, but the standard deviation for repeatability was ± 29 ppm by the xylenol method and ± 63 ppm by the nitrate electrode. Consequently, the xylenol method was considered sufficiently accurate, rapid, and precise for routine determinations of nitrate concentrations in forage samples.
Mortality rates of Geyer larkspur(Delphinium geyeriGreene), a poisonous plant, were determined after spraying with (2,4-dichlorophenoxy)acetic acid at various stages of plant development in 1967 to 1969. Sprays of 2,4-D at 2.2 kg/ha were more effective at early than at late stages of development, but seldom exceeded 40% mortality. Uneven-aged stands and early drying (dormancy) of small non-flowering plants often prevented the exposure of all plants to a single application of spray; treated plants contorted but continued growth for 5 to 8 weeks after spraying; residual seed provided a source of new plants; and previously dormant rootstock buds gave rise to new shoot and root growth the year after spraying. These characteristics and escape mechanisms direct attention to possibilities of improving effectiveness by spraying two or three times in a single season.
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