Polysulfides As Soil Conditioners

Polysulfides as Soil Conditioners

Item Type text; Book

Authors McGeorge, W. T.; Breazeale, E. L.; Abbott, J. L.

Publisher College of Agriculture, University of Arizona (Tucson, AZ)

Download date 28/09/2021 11:31:45

Link to Item http://hdl.handle.net/10150/602182

POLYSULFIDES AS SOIL CONDITIONERS

. W. T. McGeorge, E. L. Breazeale and ' J. L. Abbott INTRODUCTION The soil performs three itiajor functions in crop productions: it must have the pore space to supply the air needed for root respiration; ft must have the capacity to meet the water reqiairement of the crop; and finally it must serve as the main source-to.f nutrients. More than any other single factor, soil structure determines the ability of the soil tó fully meet these requirements. In other words, soil particle aggregation, water movement, and plant food avail- ability are integrated characteristics all closely related to the productive capacity of the soil. Tillage, crop sequence, salinity and alkalinity, and the quality of irrigation water Are prominent among the factors which contribute to changes in the physical condition of the soil in the Southwest. Tillage. Baver (I) gives four essential forms of consistency for soils as influenced by moisture content and in decreasing order wet to dry: I. sticky; 2. plastiças manifested b'y the property of toughness; 3. soft as characterized by friability; 4. hard. Research (4) has 'shown that the most severe structural loss occurs when the soil is tilled or si)therwise disturbed at a moisture content represented by the moisture equivalent - plastic consistency. Friability represents the physical condition for tillage which is optimum. Tillage is a very important operation here in the Southwest because in an arid climate the surface soil dries so much more rapidly than the subsurface. This means that often when the surface soil is at optimum moisture content for tillage the subsoil may be wet enough to pack and puddle from the weight and vibra- tion of heavy tillage equipmeht. Over cultivation is also not advisable if the soil is dry, because the soil takes water more slowly if the lumps are reduced to a dust. Salinity and Alkalinity. The'minerais 'which compose the clay fraction of the soil are quite active chemically, particularly in the adsorption and exchahge of bases. When sodium is the dominant base in the irrigation water or the soil solution, it usually becomes the dominant base in the clay mineral. When an excess of adsorbed sodium is present in the clay mineral, the soil becomes highly dispersed and water penetration and soil breathing are seriously restricted. Hard waters are best for irrigation and the word hard, as used in irrigation terminology, refers to the ratio between the sodium and calcium content of the water. Crop Sequence. Plant roots, particularly fibrous roots, will help to improve and maintain aggregation of soil particles if the crop sequence best suited to TECHNICALT BUL LErlN NO.

the land is used as a rotation. The protective covering provided by the crop also influences particle aggregation y protecting th e surface from the pu d dling effect of rain drops. Organic Matter and Calcium. The essential role of organic matter and cal - cium salts in promoting and maintaining good soil structure has been recog ' nized for many years. Practically all the materials which possess soil conditioning properties for alkaline -calcareous soils are direct or indirect sources of organic matter or soluble calium. The fundamental reactions between the clay minerals, calcium salts, and the oxidation products of elemental sulfur are well known. In recent years an increasing number of new materials have been proposed as soil conditioners. Among these are the polysulfides. POLYStILFIDES When aqueous solutions of the hydroxides or sulfides of calcium, ammonium, potassium, and sodium are heated with sulfur, the so called polysulfides are formed. The chemical composition of-polysulfides is quite complex and precise information on their composition and properties is lacking. In addition-to sulfide salts the polysulfide solutions. contain sulfates, thiosulfates, and molecular sulfur. All the commercial polysulfides which have been or are being sold in Arizona are strongly alkaline and have ph values of 10.0 or higher. There is a serious misunderstanding and confusion among farmers con- cerning the value of the various forms of combined sulfur and elemental sulfur as soil conditioners. Sulfuric acid and, calcium sulfate react quickly with the clay minerals to produce the type of reaction which is conducive of aggregation in alkali- soils. Elemental sulfur and polysulfides can function only during and after oxidation to'active forms and not necessarily because of the sulfate which they -form but because of the calcium and hydrogen with which the sulfate is linked. An important property of sulfur is a neutraliza- tion of hydroxyl ions and carbonates in the soil during oxidation. The four polysulfides mentioned contain salts of the respective bases which may enter into base exchange reactions and elemental sulfur which is only active during and after oxidation. The alkalinity of the ppolysulfide solutions is a property which must be reckoned with in a consideration of these materials as soil conditioning agents. s:. OBJECTIVES AND MODE Or ATTACK Soil micro- organisms are instrumental in the oxidation of sulfur and sulfide compounds in the soil and therefore incubation procedures are essential for a study of the effect of polysulfides on soil properties. The oxidation of the pentasulfide has been represented as follows (5) for soils containing . alkaline -earth carbonates. CaS5 + 8 02 ± 4 H2O _ CaSO4 ± 4 H2SO4 H ,SO4 + CaCO3 = CaSO, f CO2 + H2O caching studies are also essential in a study of the effect of polysulfides on soil properties because in alkali' soil reclamation the sodium replaced from the clay minerals, during and after oxidation, must be removed in order to get full benefit from the conditioner. POLYSULFIDES AS SOIL CONDITIONERS One objective of this investigation was to determine whether the polysulfides will oxidize readily in alkaline -calcareous soils and to learn if gypsum is one of the products of oxidation. Where oxidation only was studied, the incubations were . conducted with 100 gram portions of soil. Where both oxidation and the effect of soil properties were to be studied, the incubations were made with 500 gram portions of soil in order to have sufficient soil for tests which might measure the conditioning value of the Another objective was to determine the effect of the products of the oxidation on the soil, particularly the soil properties which conditioning agents are

supposed to alleviate or correct. Five hundred gram portions of soil . were used in these studies. Capillary rise and percolation tests were selected for measuring the effect on the soil because the-'irrigation_ farmer has a major interest in the way his soil "takes water. -.Experiment I The fir experiment compared calcium polysulfide, gypsum, and sulfur. The elemental sulfur was mixed with the soil and subjected to a period of incubation before examining the effect on - soil properties. Calcium poly - sulfide contains soluble calcium and combined and molecular sulfur which functions as a conditioner -during and after, oxidation. In view of the claim that calcium polysulfide,, applied in the irrigation water produces an immediate increase in water penetration, this material was not subjected to a pro- longed period of incubation before examining the effect on the soil. In other words the calcium ,polysulfide was used in a way that would simulate its present use in the field, namely, .a direct effect and an indirect effect of the limited oxidation -obtained during the lea." period. Gypsum is imme- diately effective and therefore there was no period of incubation for this treatment.: This incubation and Ieaching experiment was conducted in one- liter - capacity glazed clay pots using 500 grams of air -dry soil. The soil was protected from evaporation Ioss during the incubation of the sulfur treated soil and the incubation was conducted at laboratory temperature. ,For the leaching operation, one acre- foot -equivalent per 500 grams of soil was calculated and all water applications were made on an acre -foot basis. Laboratory tap water was used This water contains 400 p.p.rn.soluble salts of which 47 p.p.m. is sodium and 56 p.p.m. is calcium-. 'This- is a favorable Na to Ca ratio for an irrigation water. One of the soils used in this experiment was a Cajon- silt loam from an experimental area near Gilbert and the other a silt blanket which represents the surface soil at the Safford Experimental Farm. A partial analysis of each of these soils is given in Table 1. The difference in texture is evident in the exchange capacity. Other important differences are in sodium percentage and organic matter content. Sulfur. The soils to which sulfur were added were incubated for 21 days at a moisture content represented by 60 percent of the water holding capacity. The sulfur was mixed well with the soil at the rates of 0.5, 1, 2, and 4 tons per acre -foot of soil. The sulfur used was 100 mesh fineness. Gypsum. The gypsum was mixed with the soil at the rates of 1 and 5 tons per acre -foot for the Gilbert soil and 5 and 10 tons for the Safford soil. TA.B tial analysis of soils used in peximent GiIhert pI-1, paste 7.7 8..0 pH 1:10 - . 8.8 9.0 Exchange capacity, m.e./100 gms. " 18.4 37.1 Exchange Na, m.e./100 gms. 2.3- 8.5 Exchange K, m.e./100 gms. 5.6 2.2 ' Exchange Mg, rn.e./100 gms. 3.3 6.4 Cond. Sat. Ext., m.rnhos./cm. 16.0 4.8 Perceñt organic carbon 0.2 1.0 Gypsum requirement, torts per acre foot 3 10 Sodium percentage 12.5 22.9

The gypsum was mixed with the soil just preceding the application o leaching water. Calcium polyir/I fide, The calcium polysulfide was applied in the water used to leach the soil. The concentrations used were 1, 5, and 10 ml, each, diluted to 340 ml. with tap water. Three hundred and forty milliliters per 500 grams of soil closely approximates the equivalent of one acre -foot of water per acre -foot of soil. in gallonage the applications are equivalent to 950, 4750, and 9500 gallons per acre -foot or 4 million pounds soil. The. field recommendations for application of calcium polysulfide vary. between 20 and 50 gallons per acre. The commercial grades of calcium polysulfide on sale in the State weigh about 10 pounds per gallon and contain 23 .percent total sulfur and 6 percent calcium_ A 50- gallon application is equivalent to an application of 115 :pounds sulfur and 30 pounds-- calcium per, acre. When .caIciurn pbIysulfide -of the foregoing analysis is applied in a 4- acre -inch application_ of water at the rate of 20 gallons per acre this is equivalent to a dilution of 0.184 ml. per liter and 0.460 ml. per liter is equivalent to an application of 50 gallons per acre. It -is very evident that the applications of polysulfide employed in this experiment 1; are more nearly . e equivalent of the quantity of gypsum required to supply the gypsum requirement of these soils rather than the recommended field applications of 20 to 50 gallons per acre. Elemental sulfur in calcium polysutfrde is held in solution by the alkalinity of the polysulfide solution and it remains in solution only as long as the solution is strongly alkaline' -pH -10.3 for the polysulfide used in this experiment. When added to irrigatìón water the alkalinity is reduced and

the -sulfur separates in a colloidal form. The . calcium salts function in the replacement of sodium if the soil condition is favorable. Following is a list of the soil treatments used in this experiment: 1. Control, no treatment 2. Sulfur 0.5 t.p.a., incubated 3 weeks 3. Sulfur 1 t.p.a., incubated 3 weeks 4. Sulfur 2 t.p.a., incubated 3 weeks 5. Sulfur 4 t.p.a., incubated 3 weeks 6.. Gypsum, I t.p.a. 7. Gypsum, 5 t.p.a. 8. Gypsum. 10 t.p.a. 9. Calcium polysulfide. 940 gals. per acr 1 ml. 500 t0. Calcium polysulfide, 4.750 gals. per acre ml. 500 grams soil) 1. Calcium polysulfide, 9500 gals. per acre 0 ml. 500 grans soll) boue rates are can floe basis of one acre -foot of soil. The soils pots, treated as above, were leached with the equivalent of 4 acre- feet water in one -foot increment. For treatments 9, 10, and 11 the calcium ropy- sulfide was applied only in the first acre -foot of water. No quantitative record was kept of the rapidity with which the water passed through the soils, but the total period of leaching extended over 21 days. Ih the case of the soils treated with calcium polysulfide, .absorption and precipitation of sulfur ú'ere complete, in the Safford soil, from the application of 950 and 4750 gallon applications; but a part: of the 9500 gallon application passed through the soil and there was a subséquent precipitation of sulfur in the leachate. For the Gilbert soil, which has a lower clay percentage, absorption and precipitation were complete for the 950 .gallon application and there was precipitation of sulfur in thco leachates from the two-larger applïcatïoris.. The passage of calcium polysulfide through the soil is of interest because it shows, at least for heavy applications, that this material can penetrate rather deeply into the soil ancl tarry oxidizable sulfur with it When dry sulfur is applied to the sod it'does not move to lower depths until it has oxidized to sulfate. The capacity of these two soils to absorb polysulfide is apparently related to thé clay percentage añd. the gypsum absorbing capacity of the soil, The Safford soil has a higher clay percentage and a higher gypsum absorbing capacity and therefore'retained more of the polysulfide. The drainage from each pot was tested qualitatively for calcium sulfate to determine the extent of the oxidation and reaction between the conditioning agents and the soil. This test was made by mixing 25 ml. of drainage water with 25 ml. of .acetone. If any calcium sulfate is present, it will be precipitated in the 50 percent acetone solution.. Positive tests for calcium sulfate were obtained in the drain from_ ti 10 -ton application of gypsum to the Safford soil and the 5- ton- per -acre app cation to the Gilbert soil. The tests on the other gypsum applications were negative showing complete absorption. For the sulfur treatments, the tests for calcium sulfate were negative in the drainage from the Gilbert soil in all the leachates; but both the 2- and 4 -ton applications to the Safford soil gave positive tests in the leachate. This showed a more active oxidation of sulfur in the Safford soil under the conditions of the experiment - The Safford soils treated with 4750 and 9500 gallons polysulfide per acre gave positive tests for calcium sulfate in the drainage from the application of the second acre -foot -equivalent of water. For the Gilbert soil a positive test for calcium sulfate was not obtained until the fourth-acre-foot-equivalent of water was applied. This is evidence that oxidation of polysulfide took place during the leaching period of this experiment but like sulfur the oxidation was slower in this soil" than in the Safford soil. The drainage from the first 2 acre -feet of water, and the third and 'fourth, were analyzed for sodium and calcium. These data did not show any significant replacement of sodium except for the heavy applications. After Ieaching the soils with the equivalent of 4 acre -feet er they were dried, ground, and analyzed for replaceable sodium to de pine the effect of these conditioning agents on sodium replacement. Thes data are NICA `IN NO. 131

TABLE 2. Water soluble and replaceable Na in soils after leaching, i-n.e. per 100 grams SAFFflRi] SUIL cum soli. nt. peer rirre 1Vnte i Na Re Water soluble Na Replaceable ntrol 2.7 1.3 Sulfur. 0.5 tons 2.8 8.9 3. Stllfur, 1 ton 3.3 8.5 1.4 4. Sulfur, 2 tons 3.1 7.3 1.4

Sulfur. 4 tons 3.3 5.6 ' 1.2 R. Gypsum, 1 ton 2.8 1.1 2.0 ' 7. Gypsum, 5 tons 2.4 7.5 1.2 1.7 R. Gynsum, 10 tons 2.3 4.7 9. Calcium polysultiae,. 1,000 gals. 7.1 .3 1.6 Calcium polyulflde, 5,000 gals. . 5.0 4.3 1.2 1..8 11. Calcium polysulfide,,` 10,000 gals. ' 5.7 4.2 1.3 'given in Table 2. The data show that all three of these conditioning agents were effective in sodium replacement when applied in quantities equivalent to the gypsum requirement of the soil. The calcium and sulfur _equivalents of the three conditioning agents, on the basis of the quantities added to the soils and on the basis of their chemical analyses, are shown. -in Table 3. For this experiment it seemed advisable to select arbitrary quantities of calcium polysulfide, somewhat e uivalent to . the gypsum requirements of :the soils, rather than the small applications of 50 gallons oe less per acre which are being recommended by sales agents,. The sulfur, calcium, and calcium' sulfate equivalents are given in Table 3. On the -basis of the -sulfur and, calcium added, the application of 950 gallons per acre-foot of soil is closely equivalent to one ton of sulfur and 5 tons of gypsum. Referring to Table 2, it will be seen that the:'replacTeable sodium remaining in the soil. after leaching with 4 acre-feet of water is about the same for the soils treated by all three conditioning agents when compared on an equivalent basis. TABLE 3. Equivalent calcium, sulfur, and calcium sulfate values for three conditioning agents based on their calcium and sulfur percentage Grams added pe ) grams of sol Treat nt, s' sulfur Grams calcium Grams calcium tcium ficr a added sulfate added u CALCIUM P©LYSULFIDE 950 gals. ' .273 1.47 .071 .31 4,750 gals. 1.365 7.39 .355 9,500 gals. 2:73 14.78 .710 3.06 SULFUR 1,000 lbs. .12 .67 ' .15 .67 2,000 Ibs. .25 1.34 .31 1.34 4,000 lbs. .50 2.69 .62 2.69 8,000 lbs. 1.00 5.38 1.25 5.38 ;XPSUM 2,000 lbs. .04 .25 .06 .25 10,000 lbs. .23 1.25 .29 1.25 20,000 lbs. .46 2.50 .58 2.50 *Calculated on the basis of 4 pounds soil per acr at. 6 POLYSULFIDES AS SOIL CONDITIONERS 9

SAFFORD GILBERT SOIL SOIL

(J) CC 20 C)

cJ 10011111 ()

o in

o GONTR LFLJR SULFUR GYPSUM CAL.POLY. CONTROL SULFUR S FUR GYPSUM Y A 8 A FIGURE L Capillary rise, cm./24 hours. Values on bars are in tons per acre for sulfur and gypsum; in gallons per acre for calcium polysullide. "B" same "A" soil but desalinized before incubation. Experiment

Capillary Rise. The capillary: movement of water in soils under field conditions, whether-it lie vertical or lateral', is important in irrigation because this property is directly .as-sociated with the efficiency of water use by the crop and the intake and storage of water in the soil. The rate of capillary wetting by capillary movement of water is related to soil texture and struc ture and the factors which contribute to good and poor structure markedly influence capillary rise values. This soil property can be determined in the laboratory by measuring the rate at which water rises in a column of soil when the lower end of the column is standing in water (2). Plastic tubes 1.5 cm. in diameter and 50 cm. length are used for housing the soil column. The soils were ground to pass a 2 m.m. sieve, added to the tubes, and uni- formly compäcted. by tapping on,the table.,Tap,water was used for the tests presented here, in preference to distilled water, for reasons that are obvious. Tests were made in duplicate and average values are given. .The capillary rise data, fo. r the soils from this leaching ex ment are shown in Figure 1. These data are for the soils after they had n treated as shown in the outline of the experiment and then leached with the equivalent of 4 acre-feet 'of water. Comparing the equivalent of 950 gallons of poiysulfide, 1 ton sulfur, and 5 tons gypsurn; the capillary rise was highest for the polysulfide in the Gilbert soil. The gypsum absorbing capacity of this soil is 3 tons per acre-foot so- for an application of polysulfide slightly in excess of the gypsum requirement of this soil the polysulfide p-roduced a higher capillary rise than gypsum. Vor the Safford soil there was very little difference between the three conditioning agents at the equivalent of 10 tons 10 TE N L BULLE NO.

1200 SÁFF©RD SOII..

200

CONTROL SULFUR SULFUR GYPSUM CAL. OLY ONT 4ULFUR SULFUR GYP POLY. .A 0 A a

FIGURE 2. Percolation rate, ml. /24 hours. Values on bars . are In tons per acre for sulfur and -gypsum; in gallons per acre for calcium polysulfide. "B satine sail as "A" but desalinized before incubation. Experiment 1 gypsum per acre -foot of soil. The gypsum absorbing_capacity of this soil is lo tons per acre. The application of .a great excess of calcium polysulfide, 9500 gallons per acre- foot of.soil, gave the greatest increase in capillary rise. Percolation. Percolation rate was determined on columns of soils 5.5 cm. in length, 5.2 cm. in diameter, and under head of 7:5 cm. of tap water using a Mariotte bottle to maintain a constant head of water. The volume of the drainage was measured for a period of 24 hours. The soils were wet by capillarity before starting the test. The percolation rates for the respective oil treatments are given in Figure 2 as ml. drainage water for a 24 hour period. For the Gilbert soil there was not a great deal of improvement in percolation rate as measured by the technique employed here. Comparing the sulfur, polysulfide, and gypsum, for the applications equivalent to 5 tons gypsum per acre, which is slightly in excess of the gypsum requirement of this soil, the percolation rate was least for the polysulfide. For the Safford soil the gypsum treatment produced the greatest_ improvement in percolation rate for the equivalent applications of IO tons gypsum which represents the gypsum requirement of this soil. For both percolation and capillary rise an excessive quantity of polysulfide was required to increase the rates of water movement above that obtained from applications of gypsum and sulfur. Attention is called to an interesting character of the Gilbert soil shown by a comparison between capillary rise and percolation rate as compared to the Safford soil given in Figures 1 and 2. Apparently there is a relation between the .clay percentage or organic carbon and improvement in infiltration rate from conditioning agents. POLYSULFIDES AS SC7II. CONDITIO ERS Experiment 2 Cor Experiment 2 the procedure was somewhat modified with respect to the amount of polysulfide added to the soil, allowance for longer incubation period, comitant application of gypsum, and analysis of the drainage 'water. The calcium polysulfide was added to the soils at the rates of 50, 250, 1000, and 2500 galions per acre -foot of soil. On the basis of the calcium and sulfur percentages in calcium polysulfide, the applications, were equivalent to the following rates of .gypsum and sulfur --- that is stoichiometrically. No assump- tior is made that there was 100 percent oxidation of sulfur or sulfide. Gai. Calcium Equiv. to lbs. Equiv.. to ibs. polysuliide per Equiv. to Ibs. " gYpsunn per acre gypsum to acre acre sulfur Or acre sulfur basis calcium basis 50 . 115 615 130 250 575,' 3085 645 1000 2300 12340 ' 2580 2500 5750 30875 6465 In order to conveniently measure these quantities of calcium polysulfide for 500 grams of sot a dilute solution was prepared containing 5.2 mI. in one liter of tap water. Ten milliliters of this solution added to 500 grams of soil is closely equivalent to 50 gallons per acre -foot of 'soil. There wad; of course, sonic separation of elemental sulfur in colloidal form at this dilution. Ten pots of soil from Field J, Safford Experimental Farm, and ten pots of soil from the Gilbert : experimental area, 500 grams per pot, were irrigated with 340 mi. of water containing calcium polysulfide, gypsum, and combina- tions of the two at the rates given in the following outline. The Safford soil used here is from a different' field than that used in Experiment 1, but the Gilbert soil is the same.. Both .these soils are alkaline carcareous types. I. Irrigated with tap water. A control test. 2. Tap water containing .052 ml. calcium polysulfide ( 50 gals. per acre) 3. Tap water containing - .260 nil. calcium polysulfide ( 250 gals. per acre) 4. Tap water containing 1.04 mL calcium polysultide (1000 gals. per acre) 5. Tap water containing 2.6 mL calcium polysulfide (2500 gals. per acre) 6. Tap water saturated with gypsum (2500 mgm CaS 0.2ìi20 /liter) 7. Same as 2 except in tap water saturated with gypsum 8. Same as 3 except in tap water saturated with gypsum 3. Saline as 4 except In tap water saturated with gypsum 10. Same as 5 except in tap water saturated with gypsum The soils in the pots were irrigated with 6 successive acre -feet equivalent applications of water or above solutions and after each application the soils were allowede to dry slowly in the pots in order to simulate the type of incubation that the soil would get under field conditions. The drainage from . each acre -foot application of water was collected and analyzed for displaced sodium and potassium. Samples of `soil were removed from each pot after irrigation with the second acre -foot and after the sixth' acre -foot of water. The analyses of the drainage waters are given in Table 4 and the soils in Table 5. The gypsum saturated tap water contained 2600 mgms.' CaSO42H2O per liter or 603 mgms. Ca per liter. The calcium polysulfide solutions to which .052, .26, 1.04, and 2.6 ml. were added, solutions number 2, 3, 4, and 5,' contained 11, 54, 218, and 545. mgms. Ca per liter. In other words, the

. 12 TECHNICAL B tl'LLETrN NO. 131

TAFßL, 4. Analyses nage waters frvm Expe Conductivity 1ac, rni. ge mgms. Kf100 mI. drainage u ,n.inhos /cm. A* n. C. A I3 C A II C SAFFORD SOIL I 3.1 1.4 1.3 59 26 26 3.6 1..3 0.9 2 3.1 1.4 1.3 G3 27 26 3.8 1.1 1.3 .3 3.2 1.8 2.2 70 3G 41 3.6 1.5 0.8 4 3.2 2.5 3.0 66 42 ' 51 3.0 2.1 2.5 5 3.3 2.7 3.5 69 49 58 3.3 3.4 2.8 6 5.5 4.3 4.0. 95 63 54. 3.4 2.7 3.2 7 5.5 4.3 4.0 101 64 50 3.6 3.2 3.3 8 5.5 4.2 4.4 103 64 57 . 3.0 2.8 3.6 9 5.5 4.3 4.2 108 66 - 54 .3.4 3.3 .3,8 10 5.5 . 4.3 4.4 99 40 60 3.5 .4.2 4:3, G1I,13FRT SOIL. 1 10.0 1.2 2.7 ;175 22 17 24.2 4.7 4.3 2 10.1 1.4,-_ 0.9 175 26 15 26.8 6.3 4,3 3 10.2 1.7 ' 1.0 178 32 17 27.7 6.7 4.7 4 11.0 2.1 1.4 184 37 20 26.8 7.2 6.7 10.4 2.0 1.6 176 28 21 27.2 9.1 7.7 G 11.8 3.8 3.3 196- 27 - 15 32.4 16.7 15.4 7 11.0 3.8 3.1 201 43 - 16 33.3 18.6 15.1 8 11.0 3.8 3.0, 193 41 17 33.3 19.0 15.1 9 12.0 4.1 3.2 224 44 16 36.6 ' 19.9 17.0 1_0 11.8 4.3 3.3 195 45 15 32.8 19.8 18.6 A, first and second foot..drainage; B, third and fourth foot drainage; C, fifth and sixth loot drainage. `saturated gypsum solution used in this experiment had a higher concentra- tion than any of the polysulfide solutions: Sodium in Drainage. For the Safford` soil the sodium was highest in the first two acre -feet drainage:, but it continued relatively high for the third to sixth acre -foot of water. For the calcium polysulfide treatments, the amount of sodium in the drainage increased with an increase in the amount of polysulfide- applied. Calcium in the polysulfide did, therefore, replace sodium from the soil; but the saturated gypsum solution was definitely more effective in replacement of sodium than the polysulfide solution. When gypsum and . polysulfide were applied together, the Iatter enhanced the replacement of sodium by the former. For the Gilbert soil, which has a high salinity, there is some evidence that calcium polysulfide increased sodium in the drainage over that of the control soil throughout the six acre -feet ápplicatioris of water. Here again the release of sodium from the soil to the drainage was greater for the saturated gypsum solution than for the polysulfide, and the most effective sodium displacement was for calcium polysulfide mixed with saturated gypsum solution. Potassium in Drainage. For the Safford soil there is no positive evidence that the potassium in the drainage was increased by either the gypsum or polysulfide, singly or in combination, for the first 2 acre-feet of water applied. For the third through the sixth acre -foot of water, there was a definite increase in potassium in the drainage above the control. This is true for both the polysulfide and the gypsum, and the displacement was greatest for the gypsum- polysulfide combination. For the Gilbert soil, in which the replaceable potassium' is very high, the soluble potassium in the drainage water is also high particularly in the drainage from the first two acre -feet applied. There was a greater increase POLYSULPIDES AS SOIL CONDITIONERS

TABLE 5. Replaceable Na, K , and Mg in soils from peri- ment 2 Replaceable Nt Replaceable K cable Treatment m.e. /1OO gms. m.e./IO0 grns. 100 gm C e C SAFFORD SOIL (Rep. Cap. 4 ms.) x 5.4 5.3 3.0 7.9 2 55 5.1 3.0 7.9 3 5.5 4.5 3.1 7.5 4 5.1 2.9 2.9 7.7 5 5.0 2.8 7.6 6 3.8 1.7 2.9 6.4 7 3.7 1.7 2.8 7.2 8 3.7 l..f 2.7 7.2 9 3.0 -1.5 2.4 7.0 10 3.6 1.2 2.4 7.0 GILI3EiZT SOIL cR+ep. Ca 00 gms.) j 1 2.2 - 1.3 5.2 2 2.1 1.6 5.4 3.4 3 2.0 ' 1.7 5.8 4.6 4 2.5 1.2 5.6 4.7 2.3 . 1.1 5.7 ' 4.6 1.1 0.7 5.2 4.0 1.5 0.7 4.2 " 3.0 1.2 0.5 4.2 3.1 9 1.1 0.5 4.2 3.2 10 1.6 ..r` 0.5 4.1 3.3 A Soll a irrigation with 2 vaster. C Soll a Irrigation with 6 ater. ci potassium in *the drainage from the gypsum treated soil than from the

soil treated with . polysulfide. There was no increase in potassium in the drainage from the gypsum- polysulfide combination above that of either singly. Replaceable Sodium, Potassium, and Magnesium in Sails. These data are given in Table 5. For the Safford soil the replaceable sodium was not reduced by the polysulfide' during irrigation with the first 2 acre-feet of water but was definitely reduced during irrigation with the next 4 acre-feet.-There was a reduction in replaceable sodium from the gypsum application after both the second and sixth acre -foot of water, and this reduction was -somewhat enhanced by the gypsum- polysulfide combination. None of the treatments gave any significant : reduction in replaceable potassium except the gypsum- polysulfide combination. Replaceable magnesium was definitely reduced by the saturated gypsum solution, and'rstill further reduced by the gypsum- polysulfide combination. For the Gilbert soil, which contained 2 m.e./100 gm. replaceable sodium (Table 1), there was little or no evidence of a reduction from the polysulfide applications after either the second or sixth acre -foot; but there was a definite reduction from irrigation with the-gypsum-polysulfide combination. Replaceable potassium and magnesium were reduced slightly by the saturated gypsum solution and still further reduced when the polysulfide was applied with the gypsum. Turbidity of Drainage Water. There was a notable difference in the turbidity of the drainage water from the differently treated soils. This difference

was measured quantitatively for the - drainage from the second acre -foot of water from the Safford soil using a Beckman Model B spectrophotometer to .t4 I4 TECHNICAL BUL LETIN NO. TAB E 6. Relative light transmittance for leachates fra soil treatments in Experiment 2 rela ent Tap water control 2. 50 gals. calcium polysulfide 43.5 3. 250 gals. calcium polysulfide 52 4. 1000 gals. calcium polysulfide 88 5. 2500 gals. calcium polysulfide 98 6. Sat.' gyp. sol. 94 7. Sat.` gyp. sol., 50 gals. calcium polysulfide 100 8. Sat_ gyp. sol., 250 gals. calcium polysulfide 100 9 Sat. gyp. soI., 1000 gals, calcium polysulfide 100 10. Sat. gyp. sol., 2500 gals. calcium polysulfide 100 measure the light transmittance and using a 525 miilimincron wave length with a .075 slit, The drainage water from treatments 7 to -10 was clear and these readings were taken as 100. The readings obtained are given in Table 6' in which the leachate numbers correspond with the treatment numbers. These readings illustrate an important property of a soil conditioner, namely, a clarification of the soil solution. The data show that the combina-

tion : of gypsum and calcium polysulfide gave the clearest Ieachates. Trans- mittance for the leachates from the gypsum treatment was approximately the same as for the two heaviest applications of calcium polysulfide. It is of interest that there was a progressive clarification in drainage water with

30 SAFFORD GILBERT : SOIL. SOIL

w so

1° IGURE 3. Capillary rise, cm 24 hour. ` *A" field soil samples: "B" same as "A" but desalinized. 1, Control: 2, 3, 4, arid 5, calcium polysulfide at rates of 50, 250, 1000, and 2500 gals.- per acre; 8, gypsum saturated tap water; 7, 8, 9, and 10, gypsum saturated tap water plus calcium polysulfide at rates of 50, 250, 1000, and 2000 gals.. per acre, Experiment .2 POLYSULFIDES AS SOIL CONDITIONERS 15

increase in the quantity of calcium polysulfide applied to the soil. Capillary Rue. A capillary rise test was made on all the differently treated soils from this experiment and the results are given in Figure 3 as cm. rise for a 24 hour period. Two untreated soils are included for comparison, and these are designated by the letters "A" and **B." "A" represents the soil as it came from the field and "B" represents the soil after it had been desalinized. The difference between these two controls reflects the effect of desalinization on water movement. The numbers in the figure correspond with the numbers designating the treatments given in the outline of the experiment. For the Safford soil there is a stepwise increase in capillary rise for the effect of polysulfide treatments, but the maximum is less than the increase for the gypsum treated soil. The capillary rise wait.. further increased, above that of either. conditioning agent singly, for the soils treated with the gypsum-polysulfide combination. For the Gilbert soil the- ;polysulfide had little or no effect on capillary rise and did not further increase the capillary rise for the gypsum treatment when the two were applied together. There is an increase in capillary rise for the gypsum treated soil. There is a good correlation between reduction in sodium percentage and increase in capillary rise. Experiment 3 In order to compare gypsum and calcium polysulfide on soils with a high salinity and high sodium percentage, two soils were selected from the Roll Valley. A partial, analysis of these is as follows Soil Cond. Sat Ext Rep]. Cap. Repi. 1"ia Repi. Nu Repi. 1r No. m.mhos /em rn.e. /100 gins rn.e. /1OO gins percent m.e./100 gins 1 - 85 17,6 7.4 42.0 1.3 2 130 15.2 11.9 78.3 0.9

These soils were laced in gglazed clayYP pots, 500 ggrams Pper l?pot, as in the previous experiments, and leached with water in acre -foot equivalent irrigations as follows: 1. Colorado River water 2. Colorado River water saturated with gypsum (2700 rngms CaSOa211:0 per liter) 3. Colorado River water plus 1 ml. calcium polysulfide per 500 grams soil 4. Colorado River water plus 5 ml. ct lciuzn polysulfide per 500 grams soil 5. Tap water 6. Tap water saturated with gypsum (2600 mgas. CaSO 42R :0 per liter)

For . all the pots the first 2 acre -foot applications of water and solutions drained rapidly through the soils despite the high sodium percentage. This was undoubtedly due to the high salinity and its effect on the hydrolysis of the sodium clay. The percolation rate slowed considerably after the application of the third acre -foot of water for treatments 1, 3, and 5 and finally "froze up." Drainage continued rapid for treatments 2, 4, and 6. In other words, this experiment showed that gypsum saturated water and the heavier application of calcium polysulfide prevented the ,'freezing up" that usually occurs when the excess of salt has been washed out of a soil that has a high sodium percentage in the base exchange complex. The palysulfide application that prevented "freezing up" in these two soils was equivalent to an 16 TECHNICAL BULLETIN NO.

TABLE . Analysis of Roll Valley soils afte eatching, Experi ment 3 ester sol. Na Repl. Na Na percentage nt m.e. /100 gma. m.e./100 gms, SOIL. NUMBER 3. Original s 9.2 7.4 42.0 1. Colorado River water 0.4 3.9 22.2 2. Colorado River water plus gypsum* 2.5 3.1 17.6 3. Colorado River water plus cal. poly.fi 5.2 4.5 25.6 4. Colorado River water plus cal. poly.# 3.6 3.2 18.2 5. Tap water 7.1 4.2 23.9 6. Tap water plus gypsum 3.0 . 0.3 1.7 , SOIL' 211MBER 2

Original soll 5.9 _ .11.9- ' 78.3 1. Colorado River water ': 1.0 3.0 19.7 2. Colorado River water- plus gypsum* 1.6 1.9 12.5 3. Colorado River wateplusr cal. poly.i' 1.1 2.3 15.1 4. Colorado River water plus cal. poly.; 3.4" 2.1 13.8 5. Tap water 1.1 ..1.4 9.2 6. Tap water plus gypsum* . 1.1 1.3 8.6 Saturated'soiution. #1 ml. caicium potysulfide .per 500 grns.. soil. 15 ml. caipium polysulfide per 500 gm s: soll.

application of about 47gb gallons per acre -foot of soils The Iighter application which gave no response, was equivalent to an application of 950 gallons per acre -foot of soil. After the leaching part of this -ex periìnept was completed the soils were dried and analyzed- for water soluble and replaceable sodium (Table 7) . Both the Colorado River water and the tap water have a favorable Na to Ca ratio. The principal difference between the two is that the former contains 800 p.p.m. total salts and the latter contains 400 p.p.m. total salts. All the soils ------those leached with water and those leached with gypsum or polysulfide solutions were reduced in sodium percentage; but water alone and the smaller Application of polysulfide did not prevent the "freezing up" of the soil. The gypsum- treated soils drained most rapidly and this -probably accounts for the better sodium replacement as it was possible to drain more water through the gypsum- treated soils: A test for gypsum in the saturation extract of these two soils gave a positive test for gypsum as a natural ingredient. This undoubtedly contributed to the reduction in replaceable sodium in the soils leached with water and the rapidity with which the water passed - through the soils before they "froze up." This experiment shows that these two soils can probably be reclaimed by leaching with water; but gypsum will definitely speed up reclamation by carrying the soil safely through the "freezing up point. Gypsum was more effective in replacement of sodium and it also gave a more rapid rate of drainage than the polysulfide. POLYSULFIDES AS SO L COND1`T.IGUT+rERS 17 Experiment 4

In the fourth experiment the polysulfides of calcium, ammonium, potassium, and sodium were studied. Up to this point the polysulfide study was confined to calcium polysulfide because this is sold in greatest volume in the State. Following are the chemical analyses of the four commercial polysulfides which were taken from stocks on sale in the State. Sulfur Sodiuni Calcium Ammoni t Potts:siuxzt percent S percent Na percent Ca percent N 4 percent 8 pH Calcium polysultide 25.1 7.2 10.7 Ammonium polysulüde 40.0 29.0 10.2 Potassium polysullide 19.3 19.2 10:2-' Sodium polysuliide ' 19.2 7.2 9.9- On the basis of the above analyses, b lutions were prepared containing equal quantities of sulfur. These dilute solutions were- added to 500 gram portions of Safford Farm soil in_,glazed clay pots at the- rates of 40, 100, 1000, and 2000 pounds sulfur per acre -foot of soil. The 100-pound rate closely approximates a 40- gallon -per -acre application of calcium polysulfide. The soils were incubated at a mosture content represented by 60 percent of the water holding capacity of the soil for. six weeks and at room temperature. The soils were protected from evaporation during this period. At the end of six weeks the soils were dried slowly' in the pots, ground to reduce lumps, and returned to the pots for a second six weeks incubation period at the same moisture content. The soils were then dried and ground to pass a 2 mm. sieve and tested for capillary rise, exteñt of sulfide oxidation, and replaceable sodium and potassium. Capillary Rise. The cpilIary rise data are given in Figure 4. All the polysulfides showed a stepwise 'increase in capillary rise with increase in the quantity applied to the. soil but the maximum rise should be compared with the control, untreated soil, for interpretation. For the calcium and ammonium polysulfides the soils that were incubated with these materials, and gave a test for gypsum at the end of the incubation period, gave an increase in capillary rise over the control. The soils which gave the positive tests for gypsum received polysulfide applications equivalent to 1000 and 2000 pounds sulfur per acre -foot of soil. The greatest increase in capillary rise was for the soil treated with calcium polysulfide Ammonium hydroxide in the ammonium polysulfide solution would precipitate calcium from the soil solution and on this basis alone capillary rise should be less than for calcium polysullide. None of the sodium polysulfide applications gave any increase in capillary rise over the control and only the largest application of potassium polysulfide, gave a response. Test for Gypsum. A test for soluble calcium sulfate in these soils after incubation was made by mixing 25 ml. of a saturation extract of the soil with 25 ml, of acetone. These tests are shown in Table 8, first column, as positive or negative. The test for gypsum in the control soil was negative. All the extracts of soil treated with the equivalent of 1000 and 2000 pounds sulfur per acre -foot of soil gave positive tests and the tests on the extracts of the soils treated with the equivalents of. 40 and 100 pounds sulfur were negative. This showed a complete absorption of calcium' sulfate at these 1",E+CIINI L B LIL ETI NO. 131

1. 40 LBS. SULFUR /ACRE 2. 100 LOS. SULFUR /ACRE 3. 1000 LEIS. SU LFU R /ACRE 4. 2000 LBS. SULFUR /ACRE

41 10

4NP 50 o NTROI,. CA L A POLY. POLY, Y.

FIGURE 4 (Left) Capillary rise, cm. /24 hours. Comparing control soil and calcium, ammonium/sodium, and potassium polysulfides when added on basis of equivalent- amounts of sulfur. Experiment 4 (Right) Percolation rate, rnl. /24 hours. 1, contr ; 2. 100 gaII calcium polysulfide per acre: 4, one ton sulfur per acre; 5, one ton gypsum per acre; 6, 5 tons gypsum per acre; .7 and 8, 110 and 220 gallons sulfuric acid per acre. Soil samples- from field experiment. rates of application. It is of interest that even tthough calcium sulfate was present in the soils- to which sodium and potassium polysulfides were applied there was no corresponding increase in capillary rise of water as was true for the soils treated with calcium and ammonium polysulfide.

Oxidation of Polysrrlfide. - The extent of polysulfide oxidation to sulfate was determined by placing 20 grams of soil on a folded filter paper and washing with 200 ml: of 0.5 percent ammonium Chloride. Sulfate was determined in the filtrate (Table 8). w i The determination of sulfate formed during incubation showed a measur- able oxidation for the 100-, 1000 -, and 2000- pound -sulfur -equivalent applications but not for the 40 -pound application. Since these four polysulfides were applied to the soil on the basis of equivalent amounts of sulfur it is of interest to note that the oxidation obtained for all under the conditions of this experiment were in close agreement. Since the oxidation of the four polysulfides was remarkably uniform, for each of the four levels of sulfur applied, the difference in capillary rise is not therefore due to a difference in calcium sulfate formed during oxidation, but rather to the inherent properties of the four materials. Replaceable Sodium and Potassium. Replaceable sodium and potassium were determined in the soils and these data are given in Table S. The data in the fourth and fifth columns represent determinations made directly on POLYSULFIDES AS SO IL CONDITIONERS 19 TABLE 8. Analysis of soils after incubation with the poly sulfides of Na, NH,, Na, and K. Total exchange capacity of this soil was 45.4 m.e. /100 gms.

Test for SO4 Repl. Na Repl. K 'Repl. Na Repl. K nt* gypsum ms. m.e./10 gms. sollt rn.e./.100 Rms. sollt

, CONTROLS ---- 20 7.2 1.9 5.8 2.1 0 20 7.2 2.1 5.9 2.0 0.. __. 20 7.2 2.2 6.0 1.9 0 20 7.2 2.0 6.2 1.6 IUM POLYSULFIDE 1 --- 20 7.4 '., 2.0 6.0 1:2 2 _.. 28 ' 7.2 1.8 5.8 1.5' . 3 -t- 98 7.1 - 1.9 5.2 1.9 4 -}- 144 7.1 2.1 5.1 1.6 AMMONIUM POLY.SU 1 20 7.5 . 1.4 6.2 1.6 2 __ 28 7.5 1.4 6.0 1.5 3 + 104 7.4 1.9 5.4 1.7 4 -t 160 7.4 2.0 5.0 1.4 SDDIUNI POLYSULFIDE

1 --- 20 - 7.2 1.8 5.8 1.8 2 --- 20 7.6 1.9 6.2 1.6 3 88 7.6 1.6 6.0 1.4 4 160 7.8 1.9 5.4 1.7 POTASSIUM POLYSULF 1 20 7.2 2.0 6.1 1.6 2 `-- `32 8.0 0.9 6.4 1.3 . 3 -¢- 76 7:9 1.9 5.9 1.9 4 160 8.1 1.8 4.9 2.1 ' Co!. 1. Pounds per ac re. sulfur equivalent: 1, 40 lbs.. 2, 1Oti lbs., 3, 7äiß0 lbs., 4, 2000 lbs. tools. 4 and 5 soils not leached after incubation. _ #Cols. 6 and 7 soils leached after incubation. the incubated soils. The data in the sixth and seventh columns represent the soils after they had been leached with 25 ppercent ethanol to remove the products of the reaction between the polysulficde oxidation products and the soil. This determination was made by weighing 10 grams of soil into a folded filter, washing with ethanol, and then extracting the soil on the paper with normal ammonium acetate. The data in columns' four and five do not show any significant difference between the replaceable sodium and potassium in the controls and the soils. This determination was made by weighing 10 grams of soil into a folded filter, washing with ethanol, and then extracting the soil on the paper with normal ammonium acetate. The data in columns four and five do not show any significant difference etween the replaceable sodium and potassium in the controls and the soils eated with polysulfides. The data in column 6 show that the products of the reaction between the conditioner and the soil must be leached out of the soil in order to obtain a reduction in replaceable sodium. This experiment showed that calcium, ammonium, potassium, and sodium polysulfides will all oxidize readily when incubated with soils. 20 TECHNICAL BULLETIN NO. 131 Experiment 5 When sulfur -bearing compounds are added to soils they are subjected to various transformations depending on whether an aerobic or anaerobic environment exists. In most part these changes are brought about by soil micro -organisms. For soils, we are interested primarily in an aerobic environment particularly if the problem is one of soil structure. Biological oxidation of sulfur in soils is largely by the Thiobacillris group although there are. several other groups of bacteria in soils capable of oxidizing sulfur. Atmos pheric carbon dioxide and bicarbonate salts serve as sources of carbon for these organisms. As a further study of the oxidation of polysulfides in -the soil incubation, experiments were conducted in which the evolution of carbon dioxide was determined. The technique was essentially that of Fleck (3) using 100 grams of soil and measuring the evolution of carbon dioxide by absorption. The soils were incubated for a period of three weeks at a moisture content represented by 60 l7éi c?Cnt= of the water -holding capacity. The evolution of carbon dioxide during this incubation is shown in Table 9 as mgms. CO per 100 grams soil. Three soils were used namely, the'Gilbert and Safford soils, used in the previous experiments, and another soil from Greene Cattle Company which is a black alkali soil with an exchange capacity of 16.0 and 50.6 sodium percentage. The data in Table 8 show that an ample supply of carbon dioxide was available in,these soils for polysulfide oxidation. The data for the control soils show that evolution of carbon dioxide was greatest in the Safford soil followed closely. by the black alkali soil, The Gilbert soil, which was the lowest in organic matter content, gave the least evolution of carbon' dioxide. The evolution of carbon dioxide from the soils TABLE 9. Carbon -dioxide evolution and sulfate formation in soils incubated with ammonium, potassium, sodium, and calcium polysulfides Treatment Mgms. S added Mgms. CO: evolved Mg s. SO4 formed As poiysulfidr 100 finis. soil 100 gms. soil Saftord Gilbert Greene Snfrnrrl Gilbert Ammonium polysulfide 5 240 142 . 258 1.8 98 125 _305 -238 263 238 272 assium polysulfide 5 278 189_ 277 46 106 125 262 206 308 256 272 polysulfide 5 242 175 ; 291 42 116 SodiumM N 125 244 214 308 . 198 220 Calcium polysulficie 5 276 185 310 46 102 125 271 213 300 192 204 Control 0 263 135 246 12 96 AFTER CORRE Cr 1NG FOR CONTROi Ammonium polysulfide 5 -23 7 12 6 2 ~ ~ 125 42 103 17 226 176 Potassium polysulfide 5 15 54 31 34 10 M 125 -1 71 62 244 176 Sodium' polysulfide 5 -21 40 45 _30 20 125 -19 ..79 62 186 124 Calcium polysulfide 5 13 . 50 64 34 6 125., 8 78 54 180 108 POLYSULFIDES AS SOIL CONDITIONERS 21

which the polysulfidcs were added was greater for the Greene and Gilbert` soils than the Safford soil. Sulfate formed during the incubation of these soils was determined for the Safford and Gilbert soils. Comparing these two soils there was better oxidation in the former. This is shown in the lower half of the table where the sulfate data have been corrected for the SO4 present in the control soils. Experiment 6 The preceding experiments show that the polysulfides will oxidize readily in calcareous soils; and when applied at rates equivalent to the gypsum requirement of the soil, and time allbwed for oxidation, will improve soil structure as measured by the movement of water in the soil - provided other factors are not present in the soil to interfere with the gypsum effect. There remains the questio'n' about the direct response to the small applications which are being recommended by the trade.' There is some difference of opinion among observers in the field about the immediate or direct value of small applications; that is, will the addition ,of polysulfidcs in small amounts to the irrigation water increase the rate at which irrigation water enters the soil ? This is i1nportant because when applied at the rate of 20 to 50 gallons per acre, the cost, per acre, is reasonable while if applied at rates equivalent to the gypsum requirement of the soil the per acre cost is exces- sively high. In order to study this question, on a laboratory scale, experiments were conducted using capillary rise and percolation rate tests. or these experiments the polysulfide solutions were made up in concentrations of 20, 40, and 100 gallons per acre -four- irC}ies of water. All four of the polysulfides were used in most of these :tests, namely, sodium, potassium, calcium, and ammonium. In each test these polysulfide solutions were compared with tap water which had been saturated with gypsum and also with a tap water control. Several soils were selected for the comparative tests and they covered a wide range of soil types. Partial analyses of these are given in Table 10. The methods used to determine capillary rise and percolation rate have been previously described. 1. Soil from B field, -Safford Experiment Farm. It 'Is typical heavy soil with poor water penetration :and a high sodiuin percentage. TABLE 10. Analyses of soils used to study the direct effect of polysulfides on capillary rise and percolation rate Cond. Na Etichg. K Repi. Cap. Clay Sat. EYt. pli Moisture r.Q m.e./100 gms. cF. m.mhos/cm. 1:10 equivalent 1. Safford Exper. Far 26.1 8.1 27.0 40 4.0 9.0 31 2. Yuma Exper. Farm 9.3 5.0 14.0 23 7.6 8.6 20 3: Avondale 68.0 12.0 15.0 16 36.0 9.9 15 4. Roll Valley 42.4 7.4 17.6 22 85.(} 8.7 20 5. Tucson Exper. Farm 9.2 9.5 27.2 34 3.9 8.8 29 6. Mesa Exper. Farm 5.3 9.2 13.1 20 0.8 8.9 17 22 TECHNICAL BULLETIN NO. 131

2. This soil is from the old University Farm in the Yuma Valley. There is a penetration problem here but it is largely due to a high water table. 3. A saline- alkali type from the Avondale district in the Salt River Valley and obviously the high salinity and sodium percentage classify it as a problem soil. 4. A saline -alkali soil from the Roll Valley. 5. A heavy soil from the University Farm near Tucson. It has a low

sodium - percentage and the penetration problem is therefore düe to other factors which are not evident in the analysis except possibly the high clay percentage. 6. This soil is from the Mesa Experiment Farm: and is by far the best of the group. The capillary rise and percolation rate data are given in Table 11. The former as cm. per 24 hours and the Fatter as ml. per 24 hours.

Sa' f ord Soil. This ` soil gave the best improvement from gypsum for both capillary rise and percolation rate. This soil has a high clay percentage, a high sodium percentage, and a low conductivity for the saturation extract. There was no improvement in water movement, in this. from the polysulfide solutions excéf f for the 100 ga. /acrè application of potassium poly sulfide. TABLE 11. Direçt effect of polysulfides and gypsum solutions on capillary :rise and percolation rate Treatment Cals. per acre - Safford Yuma, Mondale Roll Tucson Mesa Solution 4 -in. water Soil Soil. Soil Soll Soil Soil CAPILLARY RISE. CM. /24 HOURS Acorn.- polysuIfde 20 11 30 18 17 32 51 .. .. 40 11 30 18 12 35 44 " " 100 11 29 15 - 13 38 98 Cal. po2ysulfide 20 11 26 19 13 36 96 40 11 27 18 13 36 47 100 10 26 16 12 31 46 polysulyde ' 20 11 27 17 16 M 40 10 28 19 10 x ^' 100 27 16 14 Sodium polysulfide 20 11 25 19 11 40 11 , 26 18 13. 1d0 11. 26 16 11 Tap water, control ' 11'x 27, ' 20 :` 12 35 51 Gyp. sat. tap water ' 41 27 21 23 41 52 VOL PERCOLATE ML. /24 IIOURS Amm. polysulßde 20 24 110 22 53 °. 40 26 120 16 54 w 100 24 125 20 55 Cal ptilysulfide- 20 19 -130 20 40 ., ^' - 40 17 127' 25 52 ^' 100 17 154 29 39 Potas. Polysulfide 20 24 127 18 43 N M 40 21 151 16 68 M N 100 55 180 ` 14 60 Sodium pclysulfide 20 22 130 20 58 x 40 22 144 25 62 y N 100 22 118 21 68 Tap water, control _19 154 22 36 Gyp. sat. tap water 1200 178 63 110 POLYSULFIDES AS SOIL CONDITIONERS 23

PLATE I. Experiznefital design of plots used in Gilbert field experiment which compared effects of conditioning agents. materials were broadcast and disced into the soil. Several other miscellaneous materials were aiso used- in this experiment, but we are not concerned with any of these in this report. In preparing the land for the experiment, soil was moved from east to west------the A replicates being at the cast end of the field and the D replicates at the west end. This leveling operation, together with considerable N'aria- tion in salinity and replaceable. sodium in the soil, may be the answer to the wide variation between replicates. In view of this variation the data arc presented for each set of replicates separately. The variation in the area is dif- ficult to describe but is illustrated by plant growth in Plate 2 which represents a field of oats adjoining the experimental plots on the south. baler Penetration.. For each of three irrigations, following the application of the materials, the quantity of Nv ater standing on each plot was measured 21 hours after the irrigation water had been applied. These data are given in Table 12 as inches of standing water per plot. As expected there was a wide variation in the four replicates. with water penetration being less proceeding from A to D replicates which is the direction in which the soil was moved in leveling. In other words a large part of the surface soil from A and B was moved to c and D and the poor physical condition is mostly in the surface soil. The measurement of standing water was made on May 16 June 29, and July 13. The data in Table 12 arc depth of standing water iO inches per plot for each treatment in each replicate. The response, in improved infiltration, is very definite for sulfur, gypsum, and sulfuric acid. The 40-gallons- POLYSULFIDES AS SOIL CONDITIONERS - 25

PLATE 2. The variability in the Gilbert soli is illustrated by the irregular growth of oats in the ab'Ove field which adjoins the experimental area.

per-acre application ..of calcium polysulfide ,Shows evidence of improved. infiltration, ,but this evidence is discounted by the slow infiltration of water in the plots to which- lob gallons per acre-wa.s applied and the poor penetra. tion in the D replicate as compared to the other treatments in D plots. Seedling' Emergence. One:of the major problem characters of this soil is a crusting and cracking of the surface. When irrigated the soil disperses badly ("melts") and as the water penetrates the soil this suspended clay and silt is deposited on the surface. This crust not only interferes with penetration of water but also with seedling emergence (Plate 3). . In 1954 sorghum was planted in this experiment and seedling emergence counts were made. These counts are given in Table 13. They show the greatest emergence in the plots treate4 with sulfuric acid and gypsum. TABLE 12. Depth of water, in inches, standing on plots 24 hours after irrigation. Average for all irrigations made. in May, June, and July. Treatment, per acre REPLICATES A Sulfur 0.0 0.0 0.4 0.5 Calcium polysulfide, 40 gals. 0.0 .0.0 0.1 1.3 Calcium polysulficle, 100 gals. 0.0 0.3 0.4 1.0 Gypsum, 1 ton 0.0 0.0 0.0 0.7 Gypsum, 5 tons 0.0 0.0 0.0 0.6 Sulfuric acid, 110 gals. 0.0 0.0 -0.2 0.7 Sulfuric acid, 220 gals. 0.0 0.0 0.2 0.3 Control, no treatment 0.1 0.1 0.8 1.0 26 TECJINIC4L BULLETIN NO. 131

- ,

:4-rs. ),:::. t- 44 1!. '..;"" ,,,

4 -'41 -o 4"'",,, o ,..- "'..4 .. .. 4,.''''' .- iN''....4"k4o.." I"' Ili, 1, ,. ..0 ,...*`'''. ' '''"C" , -' ... r,-.7, ,.. , -- 1 , ... e:-,....- . . .:. ,. Ts. . .."

. " PLATE 3., Illustrating the _surface crusting and cracking in the Gilbert soil after irrigation. Check plot is in the foreground.

There is a good corielation between the average infiltration rate of water and the average seedling .emergence for the four replicated treatments with gypsum and sulfuricacid-(Tables 12, 13). After the sorgliuM crop was harvested in 1954, composite soil samples were-ta.ken from each plot representing the surface-two-inches of soil. This represents the crusted depth which is the principal cause of the structural problem in this soil. These samples were tested for percolation rate in the laboratory using the method already described. The data -obtained from

these tests are given in Figure 5 as ml. drainage/24 hours. , The soils from each replicate were teste&separately but only the average for the four replicates is given in Figure 5, The percolation rates- for all TABLE 13. Plant counts, seedling emergence, on experimental plots Treatment, per acre nEPLICATES A B C D Sulfur 209 297 74 136 Calcium polysulfide, 40 gals. 94 304 179 81 Calcium polysulfide, 100 gals. 407 136 110 118 Gypsum, 1 ton 242 300 350 102 Gypsum, 5 tons 284 269 - 435 110 Sulfuric acid, 110 gals. 242 594 167 210 Sulfuric acid, 220 gals. 330 569 94 180 Control, no treatment 125 210 132 98 POLYSULFIDES AS SOIL CONDITIONERS 27

soil samples were higher in the A and B replicates than in the C and D replicates and thus is in agreement with the field tests. The application of 220 gallons sulfuric acid per acre showed the best improvement in percolation rate except in replicate C where 5 tons gypsum per acre showed best improvement. Considering the variability in the soil between ,plots in the separate replicates the agreement between the field infiltration rate and laboratory percolation tests is good. DISCUSSION Recognizing the importance of soil structure in attaining a maximum approach to the productive capacity of the soil; .western farmers are showing increasing awareness of soil structure problems. Soil - structure has been variously defined but in simple terms it refers- to the arrangement of soil particles within the soil mass. That is, are the soil particles packed tightly together in a mass that Interferes with water movement and root growth or is the soil a mass Of _.loosely packed particles wherein roots can forage at will and air and water enjoy a minimum of restricted movement. The factors that contribute to soil structure are both physical and chemical: physical in that cultural practice is important and chemical because there are important chemical reactions between the minerals which compose the soil particles and the salts in fertilizers and irrigation waters. In like manner cultural practices employed in maintaining good structure or reclaiming poor soil structure may be either physical, chemical, or a combination of the two., For alkalin- calcareous soils the oldest chemical practice involves the application of gypsum to the soil. The use of gypsum on western soils dates back to about 1890.. Some years later sulfur and sulfuric acid proved their value as soil conditioning agents. In recent years a large number of other materials, both organic and inorganic, have been proposed and: the present list of soil conditioning agents offered to the farmer is truly confusing. The sulfur- bearing materials are especially confusing. The fact that gypsum and sulfuric acid are sulfur compounds only serves to cloud the situation. The policy of subsidizing farmers for using gypsum on their land and basing their allowance on the sulfur percentage in the gypsum has further added, to the confusin. Gypsum and sulfuric acid possess soil conditioning value because of the calcium and hydrogen and not necessarily because of the sulfate wit h which they are linked. For example, calcium chloride or nitric acid could be used as soil conditioners if they were available at reasonable cost. The mineral sulfur has soil conditioning value only because when added to calcareous soils it is oxidized to sulfuric acid and -forms calcium sulfate. The same is true for other súlfur bearing materials. That is, unless the sulfur is an ingredient in a salt or mineral which has a cation that is useful as a soil conditioning agent or is present in a form that will oxidize rapidly to a salt of conditioning value, it will have no value when applied to the soil for the purpose of improving the structure or replacing adsorbed sodium. The study presented here involved the use of polysulfides, sometimes referred to as soluble sulfur, as. soil conditioning agents. Four polysulfides 28 TECHNICAL BULLEI'IN NO.

have been offered for sale in Arizona, namely calcium, ammonium, sodium, and potassium polysulfides. The ammonium and potassium polysulfides have some value as fertilizer in soils that are deficient in these two nutrient elements. This is in addition to any conditioning value that they might possess. The sodium polysulfide, because of the high pH and presence of sodium hydroxide in the material, could easily be harmful as sodium hydroxide is ,a form of black alkali. In the case of calcium polysulfide, even though it has 'a high pH and therefore contains some calcium hydroxide, this should change to bicarbonate and carbonate and therefore have no harmful residual effect on the soil. The calcium polysulfide is presently being sold in con - siderable`volume in the State, the ammonium polysulfide in relatively small volume. and the sale of sodiùm and pófassium polysulfides has been dis continued. The incubation experiments'. conducted with these materials in the laboratory showed that -all four of these polysulfides will oxidize quite readily to sulfate in calcareous soils and that calcium sulfate is a product of this oxidation: The effect of the oxidation products on the soil was examined by measuring the rate of water movement, capillary rise and percolation rate, in the soils after the polysulfides had been incorporated with the soil and then subjected to a period of incubation. These experiments showed that if the polysulfides arc added to calcareous soils in amounts equivalent to the quantity of gypsum needed to satisfy the gypsum requirement of the soil, and time allowed for their oxidation, there will be an improvement in physical c6nditiön.

The chemical- ° reaction between the . soil and the oxidation products of polysulfides was examined by analyzing drainage water from the .rested soils for displaced sodium and the soils for reduction in replaceable sodium. In general calcium polysulfide reduced adsorbed sodium, but it was not as effective as equivalent quantities of gypsum in this respect. There is some controversy, or difference of opinion, regarding the direct effect of polysulfide applications on the movement of water in the soil. This was examined by testing the rate of capillary rise and infiltration of dilute solutions of polysulfide. These' tests showed little or no difference between water and polysulfide dilutions ,equivalent to 20, 40, and 100 gallons per acre 4 inches of water. However, satu-rated gypsum solution showed an improvement for all the soils in the group in which there was a need for structural improvement. Several field tests have been conducted with polysulfides but only one on a quantitative scale. In this experiment there was a comparison between gypsum, sulfuric acid, sulfur, and calcium polysulfide. In this field test there was an improvement in infiltration rate for sulfuric acid, gypsum, and sulfur, but little or none from calcium polysulfide at the rates applied. Seedling emergence in this experiment was greatest for the sulfuric acid and gypsum treatments. POLYSULFIDES S 5'O XL C4ND I7`IONL7ZS 29 SUMMARY Studies on the value of polysulfide solutions for soil conditioning purposes were conducted employing laboratory and field experiments. Incubation tests conducted in the Iaboratory showed that calcium, ammonium, potassium, and sodium polysulfides oxidize readily in the soil and 'gypsum is a product of this oxidation. 3. When calcium,polysulfide is added to a soil in an amount equivalent to the gypsum requirement of the soil there is a favorable effect on movement of water in the soil. 4. When calcium polysulfide it rates of-100 gallons per acre or less are applied to the soil it has-little or no value as a soil conditioner. 5. A field experiment was conducted in which calcium polysulfide, at the. rate of 100 gallons per acre, was compared with gypsum, sulfur, and sulfuric acid, at rates equivalent to the gypsum requirement of the soil. There was an increase in water penetration and seedling emergence for the sulfur, gypsum, and sulfuric acid treatments but no increase for the polysulfide application.

REFERENCES 1. Bayer, L. D. 1956. Soil Physics (Third Edition), John Wiley & Sons 2. Gardner, R..1945. Some soil properties related to the sodium salt problem in irrigated soils, LT.S:D.A. Tech. Bui. 902 3. Heck, A. F. 1929. A method for the determination of total carbon and also the estimation- of carbon dioxide evolved 'by the soil, Soil Sci. 28 :225 -255 4. McGeorge, W. T. 1937. Studies on soil structure: Some physical characteristics of puddled soils, Tech. Bul. 67 Ariz. Agric. Exper. Sta 5. Diagnosis and improvement of saline and alkaline,soils, U.S.D.A. Hand- book No. 60