GIFT OF Digitized by tine Internet Arciiive in 2007 witii funding from IVIicrosoft Corporation littp://www.arcliive.org/details/alunitekelpaspotOOskinricli MA^lo Issued April 10, 19ia. United States Department of Agriculture, BUREAU OF SOILS— CIRCULAR No. 76. Milton Whitney, Chief of Bureau. U. S. Department op Agricxtlture, Washington, D, C, January 25, 191S. Sm: I have the honor to transmit herewith the manuscript of a report covering investigations of alunite and kelp as potash fertilizers, by J. J. Skinner and A. M. Jackson, of this bureau, and to recommend that this article be published as Circular No. 76 of the Bureau of Soils. Respectfully, Milton Whitney, Chief of Bureau. Hon. James Wilson, Secretary of Agriculture, ALUNITE AND KELP AS POTASH FERTILIZERS. By J. J. Skinner and A. M. Jackson, Scientists in Soil Fertility Investigations. The investigations by this bureau of the fertilizer resources of the United States has led to suggestions from time to time of the use of certain miaerals and of kelp as potash fertilizers. The use of these substances as sources of potash salts is described in other publica- tions. In this paper are given the results of several experiments showing the effect of the mineral alunite and of kelp on soils. Alunite has been described in a circular by Waggaman ^ as a double sulphate of potassium and aluminum which, on heating, first gives off water and sulphur trioxide, leaving a residue consisting largely of potash alum, and on further heating at a higher temperature decom- poses with an evolution of the oxides of sulphur, leaving the final residue composed chiefly of potassium sulphate and alumina. Wag- gaman suggested that it might be more practicable from an economic standpoint to use ignited alunite directly as a fertilizer than to leach the potassium sulphate from the residue. He found that a large amount of water is required to free entirely the ignited residue from soluble salts and that the subsequent evaporation is tedious and expensive. ' Alunite as a source of potash. Cir. No. 70, Bureau of Soils, U. 8. Dept. Agr. (1912). 77329°— Clr. 76-13 2 ALUNITE AND KELP AS POTASH FEETILIZEKS. In the experiments made to test the effect of this mineral on the soil both the raw and the ignited alunite were used. The sample of raw aluHrite, containing 10 per cent of potash (KjO), was finely ground. The ignited alunite was also thoroughly pulverized. It con- tained 14.7 per cent KjO. These minerals were applied to soil in such quantities as to add 25, 50, 100, 200, and 500 pounds of potash (KjO) per acre. Equivalent amounts of potash as potassium sul- phate and potassium chloride, the soluble potash salts, were included in the experment in order to compare the efficiency of the potash- carrying mineral, alunite, with the pure soluble potash salts. Cameron and his associates are making a thorough investigation of the kelps of the Pacific coast and conclude that they are at present the most promising source of potash in the United States.^ That kelps have value as a fertilizer has long been known. Seaweed has been used locally as a fertilizer on the Pacific coast, in New England, and in European countries. It is stated that the giant kelps of the Pacific coast, namely, Nereocystis luetlceana and Macrocysiis pyrifera, are essentially different from the Atlantic kelps and those of Japan in that the potash content is higher and the iodine content lower. The dry kelps from the Pacific coast contain 30 per cent or more potassium chloride as an average of a large number of samples. The effect of the kelp on soil was tested. The kelp used was dry and powdered. It contained 19.8 per cent of potash (KjO). It was applied to soil in amounts sufficient to add 25, 50, 100, 200, and 500 pounds of potash (KjO) per acre. This experiment was carried on at the same time as the experiments with alunite, and the fertilizing action of the two substances was compared with potassium sulphate and potassium chloride. CULTURAL METHOD. The effect of these potash fertilizers in soils was tested by growing wheat plants in the treated soil in paraffined wire pots. The wire- pot method for testing the efficiency of fertilizers and the fertilizer requirement of so'ls is described fully in Circular No. 18 of th's bureau. The soil was we'ghed into pans, 3 pounds to each pan. The soil in one pan received no fertilizer and was used as a control. To each of the other pans the fertilizer to be tested was added. To the different pans of soil we<»3 added raw alunite, ignited alunite, kelp, potassium sulphate, and potassium chloride, each in quantities of 25, 50, 100, 200, and 500 pounds of KjO per acre, based on an acre half-foot of soil weighing 2,000,000 pounds. « Cameron, Frank K., and others: Fertilizer Resources of the United States, S. Doc No. 190, 62d Cong., 2d sess., 1912. Further investigations are now in progress. ICir. 761 ALXJNITE AND KELP AS .POTASH FEKTILIZERS. The soil used in the first experiment was the Carrington loam — a soil which is known to respond well to potash fertilizers in field prao tice. The soil was treated with the various fertilizers in pans on October 22, was well mixed by sifting, and was potted October 28. Three pots, each holding about a pound of soil, were used for each treatment. Six wheat plants were planted in each pot. The planta grew until November 29. At the end of the experiment the planta were cut and the green weights recorded. The results of the test are given in Table I. The last column gives the relative growth of the different treatments. The growth of the check or control is taken as 100. The third column gives the green weights of the three cultures in each treatment. Table I. — Effect of alunite and help on qrowth as compared with potassium sulphate and potassium chloride. Treatment. Quantity ol K2O added per acre Oreen weight. Relative growth. Soil untreated . Pounds. Soil + raw alunite. Soil + ignited alunite . Soil + kelp. Soil + KsSO^. Soil + KCl. 25 50 100 200 500 25 50 100 200 500 25 50 100 200 500 25 50 100 200 500 25 50 100 200 500 Orams. 3.35 3.70 4.00 4.02 3.77 3.72 4.58 4.77 4.80 4.80 4.53 3:93 4.67 4.80 4.40 4.30 4.27 4.33 6.12 4.52 4.90 4.40 4.U 4.50 4.37 4.40 Per cent. 100 1101 119 I20I114 112 lllj i3ri 14 il40 14 I35J 117) 130 143 U3I 131 128j 1271 129 152 U3a 135 I4J 1311 129 134 USL 130 131 By examination of the table it is seen that each of the potash fer- tilizers produced an increased growth over the untreated soU. The raw alunite used in amounts of 25 to 500 pounds of KjO per acre increased growth from 10 to 20 per cent. The best results were secured with 50 to 100 pounds of potash (KjO) per acre. The aver- age increase over the untreated soil of the five amounts was 14 per cent. When the growth is compared with that produced by the ignited alunite it is seen. that this caused larger growth with each amount used than did the raw alunite. The increase in growth with ICir. 76J 4 ALUNITE AND KELP AS POTASH FEETILIZERS. ignited alunite over the untreated soil varied from 35 to 43 per cent, the average increase being 40 per cent. The growth with the raw alunite was not as good as with similar amounts of potash as potas- sium sulphate and potassium chloride. The average increase with potassium sulphate was 38 per cent and with potassium chloride was 31 per cent. The effect of ingited alunite was about the same as that of potassium sulphate, and greater than that of the potassium chloride. Kelp produced a considerable increase in growth over the untreated ^oil. The increase varied with the different amounts, from 17 to 43 per cent. The average increase over the untreated soil was 31 per cent. The increased growth was about the same as that produced by potassium chloride, and was slightly less than that resulting from the use of potassium sulphate. It should be here noted that the potash in the kelp is in the form of the chloride. Another experiment was made to test the effect of these potash compounds, using this time a different soil. Otherwise the details of the experiment were the same as in the first test. The soil used in this test was the Volusia silt loam. The plants grew from Novem- ber 19 to December 21. Three pots were used for each treatment. The results are given in Table II. Table II. — Effect of alunite and kelp on growth, as compared with potassium sulphaU and potassium chloride. Treatment. 49oil untreated. 43oU + raw alunite. €k>il + ignited alunite. .-Son + kelp. Sou + KjSOi. 800 + KCI. Quantity of KjO added p3r acre. Pounds. 25 50 100 200 500 25 SO 100 200 500 25 50 100 200 500 25 50 100 200 500 25 50 100 200 500 Green weight. Relative growth. Grams. 2.84 3.35 3.40 3.36 3.36 3.02 3.54 3.70 3.70 3.90 3.94 3.24 3.54 3.69 3.60 3.45 3.08 3.62 3.87 3.68 3.54 3.04 3.50 3.50 3.74 3.60 123 [Cir. 76| ALUNTTE AND KELP AS POTASH FERTILIZEBS. 5 Each of these potash fertilizers had a beneficial effect on Volusia eilt loam. The raw alunite again produced less increased growth than the ignited alunite. This was true with each amount of the substances used. The raw alunite was not as effective as potassium sulphate and potassium chloride. However, the ignited alunite was more effective. The average increase for the raw alunite was 16 percent, for the ignited alunite 31 per cent, for potassium sulphate 25 per cent, and for potassium chloride 22 per cent. As in the first experiment kelp again produced considerable increase in growth. The effectiveness in producing plant growth was practically the same as that of potassium sulphate and potassium chloride. Kelp gave as an average 23 per cent increase in growth, potassium sulphate 25 per cent, and potassium chloride 22 per cent increase. In addition to the amount of potash added to the soil by the kelp, it contains a small amount of nitrogen and phosphorus, which should be effective in the soil. From these two experiments it seems that the dried kelp and ignited alunite are about as effective potash fertilizers as the salts, potassium sulphate and potassium chloride. Approved: James Wilson, Secretary of Agriculture. Washington, D. C, January SO, 191S, {Ox, 761 ADDITIONAL COPIES of this publication ■Lx. may be procured from the Sxtpebintend- ENT OF Documents, Government Printing OfBce, Washington, D. 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