Nitrogen—Inorganic Forms

Plant analysis (sometimes referred to as leaf analysis) is the determination of the total elemental content of a specified plant part. The emphasis in this chapter will be on the determination of those elements required for plant growth. Interpretation is normally based on the use of a "critical value" or "sufficiency range" (Smith, 1962) comparison between the elemental concentration found and a known norm (Goodall & Gregory, 1947; Chapman, 1966; Reuter & Robinson, 1986; Adriano, 1986; Martin-Prevel et al., 1987). An alternative method of interpretation is Diagnosis and Recommendation Integrated System (ORIS), which interprets the ratios of elements (N/P, K/Ca, and K/Mg) as indicators of elemental status (Beaufils, 1973; Sumner, 1977, 1982). Most growers primarily use a plant analysis for diagnosing suspected elemental insufficiencies, while its most significant, yet little used application, is for evaluating the soil/plant elemental status. This is partially reflected in the relatively few plant tissue samples assayed for growers, about 500 000, in the USA each year (Jones, 1985). Tissue testing, an elemental assay of extracted cell sap by means of quick chemical tests in the field, seems to be gaining an interest at levels equal to that observed several decades ago. A plant analysis is carried out in a series of steps as shown in Fig. 15-1. The results obtained are no better than the care taken in collecting, handling, preparing, and analyzing the collected tissue. An error made in one of these steps can result in an erroneous interpretation leading to recommendations that may be either unnecessary, costly, or even damaging to the crop. Therefore, it is important for those employing either a plant analysis or tissue test to follow the proper sampling, preparation, and analysis procedures. This chapter deals with the procedures required to successfully conduct a plant analysis or tissue test.

Sampling, handling and analyzing plant tissue samples.

The measurement of NH4+‐N in soil, and plant digests is one of the greatest needs in laboratories conducting agricultural and environmental research. Many laboratories do not have access to automated equipment for colorimetric analysis of soil and plant digests. The objective of this research was to modify an automated colorimetric analysis procedure for determining NH4+‐N in soil and plant digests for manual use, and compare the proposed technique with the standard distillation‐titration technique. The modified procedure is based on the color reaction between NH4 +‐ and a weakly alkaline mixture of Na salicylate and a chlorine source in the presence of Na nitroprusside. Wavelength scans indicated a very well defined peak for determinations at 650 nm. Time scans showed that color development in the manual procedure was rapid, 12 to 40 minutes depending on temperature, and that the color development remained stable for at least 120 minutes. Regression analysis of the results from 18 soil and 20 pl...

A manual colorimetric procedure for measuring ammonium nitrogen in soil and plant Kjeldahl digests

LECO FP-228 N-determinator has been tested and nitrogen contents in samples of both animal and plant origin have been measured. The results were compared to nitrogen contents obtained by Kjeldahl determinations (Kjel-foss). Reproducibility and repeatability were excellent in FP-228 (within 2%) except in samples like maize, hay, corn silage and maize silage. Good agreement was found between the two methods when analysing feeding stuff, barley, wheat, oat, soy bean, bonemeal, fishmeal, pea, molasse, chicken and lamb. Analyses of maize, hay, grass, straw, grass silage, maize silage, sugar beet and potato resulted in greater differences (>5%), FP-228 with the highest results. The differences might be explained by nitrate in a few of the samples tested, but in the other samples tested there were no obvious explanations.

Determination of nitrogen as elementary N, an alternative to Kjeldahl.

The main goal of this study was to investigate the potential of hyperspectral imaging in the near-infrared (NIR) range of 900–1700 nm for non-destructive prediction of chemical composition in lamb meat. Hyperspectral images were acquired for lamb samples originated from different breeds and different muscles. The mean spectra of the samples were extracted from the hyperspectral images and multivariate calibration models were built by using partial least squares (PLS) regression for predicting water, fat and protein contents. The models had good prediction abilities for these chemical constituents with determination coefficient (R 2 p ) of 0.88, 0.88 and 0.63 with standard error of prediction (SEP) of 0.51%, 0.40% and 0.34%, respectively. The feature wavelengths were identified using regression coefficients resulting from the PLSR analyses. New PLSR models were again created using the feature wavelengths and finally chemical images were derived by applying the respective regression equations on the spectral image in a pixel-wise manner. The resulting prediction maps provided detailed information on compositional gradient in the tested muscles. The results obtained from this study clearly revealed that NIR hyperspectral imaging in tandem with PLSR modeling can be used for the non-destructive prediction of chemical compositions in lamb meat. Industrial relevance The results obtained from this study clearly revealed that NIR hyperspectral imaging in tandem with PLSR modeling can be used for the non-destructive prediction of chemical compositions in lamb meat for the meat industry.

Non-destructive prediction and visualization of chemical composition in lamb meat using NIR hyperspectral imaging and multivariate regression

The LECO FP-228 "Nitrogen Determinator" was compared with the AOAC copper catalyst Kjeldahl method, 7.033-7.037, for the determination of crude protein in feed materials. The completely microprocessor-controlled instrument determines nitrogen by measuring the nitrogen gas following combustion of the sample; it was easy to operate and broadly applicable. A wide variety of feed materials of various nitrogen levels were analyzed in one mixed sequence. Results were precise, accurate, and rapid. Analysis time for one sample was approximately 3 min. Fourteen samples containing 2.5-15.5% N were selected for study and consisted of meals, grains, forages, and standard organic materials. The overall mean for the 14 samples by the LECO combustion method was 8.61% N compared with an overall mean of 8.58% N for the AOAC Kjeldahl method. Within-sample standard deviations for the LECO combustion method ranged from 0.013 to 0.052% N with a pooled standard deviation (SD) of 0.033% N for the 14 samples. Standard deviations for the AOAC Kjeldahl method ranged from 0.006 to 0.035% N with a pooled SD of 0.022% N. Combined average recovery of nitrogen from tryptophan, lysine-HCl, and EDTA determined by the LECO combustion method was 99.94% compared to 99.88% determined by the AOAC Kjeldahl method.

Comparison of LECO FP-228 "nitrogen determinator" with AOAC copper catalyst Kjeldahl method for crude protein.

http://academic.oup.com/jaoac/article-pdf/58/4/811/32488159/jaoac0811.pdf

Total Protein Nitrogen: Evaluation and Comparison of Four Different Methods

The sulfur-containing amino acids cystine and methionine play important roles in animal, especially avian, nutrition. Because these sulfur-containing amino acids are destroyed to varying extents by 6N HCl hydrolysis, oxidation and hydrolysis of cystine to cysteic acid and methionine to methionine sulfone have been widely used for determination of cystine and methionine. Lysine is considered the next limiting amino acid after the sulfur amino acids in poultry nutrition; therefore, determination of the amino acid content of rations focuses first on these 3 amino acids. The objective of this investigation was to establish whether lysine and other amino acids could be accurately determined in proteinaceous materials which had undergone performic acid oxidation. To perform this evaluation, lysine was determined in a variety of protein-containing materials both with and without performic acid oxidation. Performic acid oxidation followed by 6N HCl hydrolysis at 145 degrees C for 4 h allows accurate measurement of 3 amino acids especially important to poultry nutrition, cystine, methionine, and lysine, in a single preoxidized hydrolysate; this method can be extended to another 9 protein amino acids.

Quantitative analysis of cystine, methionine, lysine, and nine other amino acids by a single oxidation-4 hour hydrolysis method

Pollution from the Kjeldahl method for crude protein has been reduced by substituting a low level of copper (0.04 g CuSO4) for the mercury (0.7 g HgO) specified in the AOAC official method, 2.049. Adjustments were made in the salt-acid ratio so the new system could handle hard-to-digest samples in a reasonable time. The new method was rugged for lysine. HCl. It is designed to be used for crude protein in feeds or similar Kjeldahl work. Precision and accuracy were equal to or better than that for the official method in a study of 17 samples analyzed in duplicate on 3 different days. The following samples were used in the study: lysine. HCl, tryptophan, NBS standards, urea, meals, mixed feeds, grains, and forage. The average per cent nitrogen found was 9.52 by the official method and 9.53 by the copper method. The average standard deviation was 0.038 by the official method and 0.033 by the copper method, giving the corresponding relative standard deviations of 0.40 and 0.35%.

Pollution-reduced Kjeldahl method for crude protein.

http://academic.oup.com/jaoac/article-pdf/50/4/964/32612401/jaoac0964.pdf

Paul R Rexroad

Papers

Comparison of LECO FP-228 "nitrogen determinator" with AOAC copper catalyst Kjeldahl method for crude protein.

Total Protein Nitrogen: Evaluation and Comparison of Four Different Methods

Quantitative analysis of cystine, methionine, lysine, and nine other amino acids by a single oxidation-4 hour hydrolysis method

Pollution-reduced Kjeldahl method for crude protein.

Analysis of Limestone