Fert iIizers Charles W. Gehrke and lames P. Ussary, Department of Agricultural Chemisfry, University of Missouri, Columbia, Mo.
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covers the literature reported from December 1, 1964, to January 1, 1967, and includes procedures recorded in rsadily available journals, in Chemical d4bstracts, and in Analytical Abstracts. Some selectivity has been exercised to include only those procedures especially pertinent to, or which, in the authors’ judFement, could be adapted easily to fertilizer analytical problems. Somc attention has b2en given toward developing methods for analyzing nitrogen, phosphorus, and potassium simultaneously. Kessen (45) and Varley ($0) used the Technicon AutoAnalyzer to simultaneously determine ammonium nitrogen, nitrate nitrogen, and phosphorus colorimetrically; and potassium flame photometrically. Constituents in fertilizers including urea and the phosphates, sulfites, chlorides, and nitrates of potassium, calcium, and ammonium and their solid solutiors have been determined by x-ray diffraction using artificial spinel (hSg0.h1,03) as an internal standard ( 3 ) . Fiesults agreed to within *3y0 relative with those of chemical analyses for fertilizers containing 5 to 2OY0 of to,al nitrogen ammonium nitrogen, totril Pz05, soluble PzOs, total KzO, and chloride. However, results for urea-containing fertilizers were unsatisfactory. I n another study, it was pointed out that because of the uncertainties introduced by line broadening, interferencm, and reactions occurring during physical preparation of the sample, it was difficult t o estimate the accuracy of the x-ray diffraction method of analysis (.;). Even with these uncertainties, this technique yielded useful information on the qualitative composition of minerals in mixed fertilizers. HIS REVIEW
OFFICIAL METHODS
The Association of Official Analytical Chemists (AOAC) in 1965 gave “offic’al” status to a method for total nitrog-.n using chromium powder and HC1 to reduce nitrates (2.049). The method is applicable to all fertilizers except those containing highl> refractory organic matter and those :ontaining both nitrate and organic matter. A single, precise, accurate methoci for total nitrogen in all fertilizers has iiot yet been developed. A flame photometric method for sodium using anion sxchange resins to remove interfering anions was given official status (2.117). A spectrophotometric method for cobalt (2.012) and an atomic absorption method for the de-
termination of copper, iron, magnesium, manganese, and zinc were also adopted (2.086). A method for determining slow-release nitrogen which involves adding boiling water to the sample, stirring for 30 minutes, filtering, and analyzing an aliquot by a Kjeldahl method was adopted. An oven method (2.014) for the determination of free water by heating a t 50” C for 2 hours under a partial vacuum was collaboratively studied by the AOAC and given official status ( 5 , 6 ) . SAMPLING
A bulk fertilizer sampling study was designed and initiated in 1965 under the direction of Dr. Charles W. Gehrke, the Associate Referee of the AOAC on sampling and sample preparation. Others cooperating in the program were the Bulk Fertilizer Committee of the Association of American Fertilizer Control Officials (AAFCO), the National Plant Food Institute (XPFI) Chemical Control Committee Task Force on Sampling Fertilizers, and industry. The report by Gehrke et al. (26) presents detailed results of the study on sampling bulk loads of granular, semi-granular, and blended fertilizers. The experiments were designed to obtain information on the various sampling instruments and sampling methods. Five different sampling tubes were studied. The AOAC slotted single and double tubes, a compartmented 524 grain probe, the modified Archer trier, and a illissouri interrupted-core compartmented double tube. It was shown that an accurate fertilizer sample can be secured by passing a stream sampling cup through the entire flow of material a t equal timed-spaced intervals during the loading of a truck; this “stream” sample was found t o be a more accurate indicator of the actual plant nutrient content than any of the trier samples. The stream sample was used as the “reference point”. It was conclusively found that the AOAC double or single tubes were not suitable for sampling bulk loads of fertilizers. Those tubes mere biased and took of the sample by the top 1/3 of the trier. The Missouri interrupted compartmented tube and the 524 grain probe did a good sampling job on semi-granular and granular fertilizers when used in accordance with the BakerGehrke sampling plan and if vertical cores were taken. The sampling plan (26) using these compartmented triers was adopted as official, first action, a t
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the 80th Meeting of the AOAC, October 1966. Smith, in a supporting study (80), concluded that the most representative trier sample was obtained by inserting the probe in a vertical position instead of at an angle. Possible mechanisms of sampler bias on dry mixed fertilizers were investigated in an effort to develop better official sampling instruments and procedures (7). Three lots of dry mixed fertilizers with known physical and chemical composition were prepared in the laboratory. Twelve vertical and twelve horizontal cores, arranged in a Latin square sampling pattern were secured from each lot with four triers: the AOAC: double tube trier, the double tube compartmented triers (524 grain probe and Missouri trier), and an experimental double half-tube trier, “Missouri D Tube,” wherein the core was encompassed in place rather than being required to flow into a compartment as vith conventional triers. Individual cores were analyzed physically and chemically. Only marginal significant differences were found between cores on the basis of tube opening size. The experimental double half-tube trier was less selective to particle shape or size than either the compartmented or AOAC triers. All triers produced more representative samples from vertical cores than from horizontal cores. Also, cores drawn a t an angle of 60-75” from horizontal were not consistently different from vertical cores. Analytical data confirmed the sieve analysis results quite closely. Horizontal cores secured with the “Missouri D Tube” confirmed that the bias observed in horizontal cores was due to a downward drifting of small particles when the core area is disturbed by the insertion of the sampler. Cores secured with the samplerretaining face upward contained an excess of fines, whereas cores secured with the sampler-retaining face to the side or downward more nearly resembled vertical cores in composition. The “Missouri D Tube” secured the most accurate sample and was the easiest sampler to use. WATER
Studies were conducted on the moisture content of peat samples by a federal method using a 5- to 10-gram sample with drying a t 70°C to a constant weight, and a proposed method using a 50-gram sample with drying at 105°C overnight (84). The Federal method VOL. 39, NO. 5, APRIL 1967
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gave significantly lower results in all cases, but both methods gave equal precision indicating that larger sample weights do not greatly improve the precision. Johnston and Smith (40) proposed using the Karl Fischer reagent to determine moisture in granular fertilizers because of the risk of losing bound water with the usual vacuum desiccation or oven-drying techniques. The samples were ground under chloroform, extracted with solvent mixtures such as dry CH30H-CHC13; then aliquots were titrated with the Karl Fischer reagent. Proper selection of the extractant made i t possible to reproduce the results of the various standard oven drying techniques. A relative precision of + 1.570was obtained when the Karl Fischer method was applied to K-P and N-P-Kfertilizers using dry methanol as an extractant (56). After extraction with a mixture of polar and nonpolar solvents, water was determined by measuring the capacitance of the solution with a high frequency titrator (65). The po1ar:nonpolar solvent ratio must be determined for each fertilizer, and it varies with the type of fertilizer analyzed. X single water determination was reported requiring less than 7 minutes with a relative error of
