Herbage sampling

Clancy, M.J. and Wilson, R.K. (1966) Development and application of a new chemical method for predicting the digestibility and intake of herbage samples. Proceedings of the Xth International Grassland Congress, Helsinki, 445-452. 

Herbage. Herbage samples must be milled to pass a 1 mm aperture before analysis. This can be achieved by means of a beater mill with a carbon steel construction (as produced by Christie and Norris Ltd., Broomfield Road, Chelmsford, Essex, U.K.). This device introduces no detectable concentration of foreign metals into the sample. A small hammer mill is also satisfactory, but may contaminate the sample slightly with traces of nickel and chromium. 

G. Nitric acid — perchloric acid attack for herbage samples... 

Despite an approximately tenfold difference in the mean levels of EDTA-extractable copper found in the urban and rural soils corresponding to these herbage samples, there is no significant difference between the mean contents of copper in the herbage. Evidently, if the difference between the soil levels... 

Mean levels of boron, copper, lead and zinc in dry matter of herbage samples taken from areas of permanent grass... 

The total number of samples will be determined (above), but the batch size should be chosen to process the samples ready for analysis. There will boiling units, heating blocks and shakers etc., so mize throughput. If an herbage batch size for a advantageous if he added half of the following batch for analysis to 120. This is because of the... 

If the analysis is to be carried out in a similar way to total N in herbage, by acid-digestion in test tubes in an aluminium block followed by a colorimetric autoanaiysis procedure, then take a 0.5-g sample of air-dry soil. If serious frothing occurs, take 0.2 g soil, and adjust the calculation accordingly. Reducing the amount to 0.1 g may give peaks which are too small to be read with confidence. See Chapter 7 (pp. 138-141) for details of standards, reagents and method. 

If the soil contains significant amounts of nitrate, which should be included with the organic and ammonium-N for total nitrogen, it must be reduced to ammonium-N by the following procedure (Method 5.6a.i). Determination of N on duplicates of the same soil sample with and without a reducing step will enable an estimation of the nitrate-N (plus any nitrite-N) by difference. A more precise colorimetric determination of just the nitrate component uses the method described for herbage, except that 10 ml of fresh or freshly thawed soil is used. 

In the Idaho experiments, 5 mg of stable iodine carrier were added to the 1311 in the preparation of the source. There were no significant differences in vD with source/sample distances up to 300 m. In the Jiilich experiments, sources of 25 g I2 were released, and the deposition was assessed from the increase in stable iodine on the herbage, at ranges of about 20 m, giving values of vD not very different from those obtained in Idaho. This suggests that the predicted rapid photolysis of I2 vapour does not affect its deposition greatly at source/sample distances of a few hundred metres. 

Analysis of herbage (of forage) has sometimes been used to detect and identify radionuclides deposited from the atmosphere (Jackson et al., 1981). However, the problem arises that when the deposition rate is low, large areas of vegetation need to be sampled for detection. In the case of plutonium, an alternative is to collect the faeces of grazing animals such as cows, sheep and rabbits. Plutonium is very poorly absorbed by the mammalian gut and so virtually all that is ingested by an animal will appear in its faeces. Also, if the species selected obtains its food entirely by grazing, then the isotopic ratio Pu will be the same in the faeces as deposited on the... 

Tab. 4.5 Average phosphorus content in herbage dry matter of growing plant species sampled at the same locations on seven different extensive managed meadows situated on peat soils in Biebrza River Valley in east-north Poland, May 1972...

In June 1997, the soil samples were taken from the upper 10 cm at each point using a plastic corer with a diameter of 8 cm. The herbage of 1 m was cut using electric hand shears 2 cm above ground to avoid soil contamination. 

The digestibility of a food is closely related to its chemical composition, and a food such as barley, which varies little in composition from one sample to another, will show little variation in digestibility. Other foods, particularly fresh or conserved herbages, are much less constant in composition and therefore vary more in digestibility. The fibre fraction of a food has the greatest influence on its digestibility, and both the quantity and quality of the fibre are important. 

Soil analysis is beset with the further complication that samples have to be taken from different depths, to reflect movement of nutrients during the seasons. Precision agriculture is focusing renewed attention to the selection of methods of sampling flelds, in order to improve the efficiency of fertilizer use. Here the controversy is whether analysis of plant material is more practicable than soil analysis in provision of the necessary information. Plant material, such as grain or herbage, is more readily applicable than soil analysis, as well as being more amenable to analysis by NIR. It also reflects nutrients that are available to the plant. 

Reference was made in Chapter 2.7 to the marked differences in the available levels of trace elements observed between soils in urban parklands and in rural areas under grass (Table 6). The corresponding levels of boron, copper, zinc and lead found in the herbage in the areas from which the soil samples were taken are given in Table 30. 

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