Effects of a Conditioner on Soil Physical PropertiesBryan C. Fitch, S. K. Chong,* J. Arosemena, and G. W. Theseira

ABSTRACTAgri-SC, a soil conditioner manufactured by Four Star Agricul-

tural Services, Inc., Bluffton, IN, was applied to a fallow Stoy siltloam (fine-silty, mixed, mesic Aquic Hapludalf) at rates of 0, 0.15,0.30, and 0.60 L/ha for two successive years. After application, thefollowing soil parameters were measured: organic matter content,mean aggregate diameter, porosity, 48-h aeration porosity, sorptiv-ity, saturated hydraulic conductivity, liquid limit, plastic limit, insitu infiltration and drainage rates, and soil water retention (up to240 cm of suction). None of the soil properties differed significantlyamong treatments, but all decreased significantly the second year,except liquid limit. The detrimental effects to soil physical, hydrol-ogical, and Theological properties could be caused by the decreasesin organic matter.

MATERIALS used as soil conditioners are either in-organic salts or high-molecular-weight organic

chemicals such as polyacrilamide polymer (Schamp etal., 1975). Soil conditioners are commercially avail-able in solid form as powders, and in liquid formeither as solutions or emulsions. The chemicals man-ufactured range from synthetic polymers to complexmixtures of poorly denned and/or understood prod-ucts. The purposes of applying conditioners are to im-prove soil productivity and address environmentalproblems.

Over the past 30 yr, many researchers have evalu-ated the effects of conditioners on soil physical andhydrological properties. Research showed that soilconditioners can improve and stabilize soil aggrega-tion, and increase both water infiltration and hy-draulic conductivity (Martin, 1953; Allison andMoore, 1956;Kijne, 1967; Ahuja and Swartzendruber,1972; Robbins et al., 1972; Pla, 1975; Carr and Green-land, 1975). Soil conditioners, such as polyvinyl al-cohol, polyvinyl acetate, and polyacrylamide, havealso been tested for water or wind erosion controls(Chepil, 1955; Armbrust and Dickerson, 1971; Roose,1975). The results showed that application of thesechemicals improved the stability of sands and reducedsoil loss due to water erosion. Today, soil conditionersare utilized in many areas ranging from pollution con-trol and agricultural production to the managementof water movement and storage in the soil profile.Dep. of Plant and Soil Science, Southern Illinois Univ. at Carbon-dale, Carbondale, IL 62901. Contribution of Dep. of Plant and SoilScience, Southern Illinois Univ. at Carbondale. Received 23 Mar.1988. "Corresponding author.Published in Soil Sci. Soc. Am. J. 53:1536-1539 (1989).

Some soil conditioners are indeed effective in im-proving soil physical and hydrological properties, andthe principles of conditioning are sound. Lately, quitea few new products have been introduced to the mar-ket. Many farmers, agronomists, and soil scientistshave a renewed interest in these products because ofthe costs relative to the benefits.

Agri-SC1 is a relatively inexpensive soil conditioner(about $10/ha when applied as recommended) thathas recently been introduced in the Midwest. Thisconditioner has an active ingredient of ammoniumlaureth, a slightly anionic surfactant. This study ped-ologically evaluates Agri-SC soil conditioner to deter-mine if application can be effective in improvementof soil physical properties.

MATERIALS AND METHODSThe soil used in this study was Stoy silt loam. The ex-

perimental site was in the Agronomy Research Center,Southern Illinois University at Carbondale, IL.

The experimental plot was 35 by 35 m in size and wasdivided into 16 subplots. A randomized complete block de-sign was used with four blocks and four treatments. The fourtreatments, which consisted of a control and three applica-tion rates of 0.15, 0.30, and 0.6 L/ha, (the recommendedrate was 0.3 L/ha), were randomly applied within each blockfor two successive years. The soil conditioner was appliedin May 1986 and April 1987. Corn residue, present from theprevious crop, was incorporated prior to the establishmentof the experimental plot in the spring of 1986. For bothyears, the field was disked to 10 cm deep and harrowedtwice, then Agric-SC was applied with a hand-held CO2-pow-ered sprayer. In addition, 7 L/ha of atrazine (2-chloro-4-ethylamino-6-isopropylamino-l,3,5-triazine) and 3.6 L/haof metolachlor [2-chloro-A^-(2-ethyl-6-methylphenyl)-Ar-(2-methoxy-l-methylethyl)acetamide] were also applied tokeep the plots weed free throughout the experiment.

Infiltration and drainage experiments were conducted us-ing a 30-cm-diam. single ring infiltrometer. The infiltrationwas measured using a constant-head method. The drainageexperiment (Chong et al., 1981) was conducted after com-pletion of the infiltration experiment. The changes in watercontent during the redistribution process were measuredgravimetrically in the surface soil (0-15 cm). Informationobtained from the drainage experiment was used in calcu-lating the drainage rate (1 d after the soil was satiated) and48-h aeration porosity (or macroporosity). The 48-h aerationporosity was obtained from the difference between the initialwater contents and that after 48 h of drainage (after profile

1 Product and name are included here for the convenience of thereader and do not constitute an endorsement or discrimination ofsuch product or name by either the authors or their respective em-ployers.

FITCH ET AL.: EFFECTS OF A CONDITIONER ON SOIL PHYSICAL PROPERTIES 1537

Table 1. Measured organic matter content and soil physical properties of Stoy silt loam (fine-silty, mixed, mesic Aquic Hapludalf) treatedwith different rates of Agri-SC soil conditioner.

Treatment(L/ha)

Organic matter Mean aggregrate diameter Porosity 48-h aeration porosity

1986 1987 1986 1987 1986 1987 1986 1987

Control0.150.300.60Average

.sot

.55

.56

.56

.54

0.961.081.120.981.04

0.25(5.4):):0.24(12.8)0.28(16.2)0.26(10.8)0.26

0.08(15.8)0.16(55.0)0.11(36.4)0.07(20.0)0.11

50.62(3.6)51.08(4.2)51.41(4.6)49.27(4.3)50.62

48.21(1.4)47.35(3.5)48.36(4.4)47.97(2.6)47.97

20.09(19.9)17.28 (9.4)21.66(19.0)18.48(15.9)19.38

8.61(46.7)8.41(53.6)7.26(91.5)6.31(39.4)7.65

t Organic matter contents were measured from a composite sample of the same treatment. Values of other parameters were a mean of four measurements.$ Values in parentheses are coefficients of variation.

was satiated). Using the satiated water content instead oftotal porosity in the calculation was intended to eliminatethose pores occupied by entrapped air.

Intact core samples were also obtained from the field usinga portable soil sampler (Chong et al., 1982). Sorptivity ofthe cores was measured using an unsaturated sorptivity de-vice (Clothier and White, 1981; Chong and Green, 1983).Following sorptivity measurements, cores were saturated for24 h to measure the saturated hydraulic conductivity usinga unit gradient configuration. After the hydraulic conductiv-ity experiment was completed, the core samples were placedon a tension table for measuring the soil water characteristiccurve up to 240 cm of water suction.

Additionally, composite soil samples were collected to 15cm before and after treatment application. These compositesamples were air dried and used for the aggregate, organicmatter and Theological properties analysis. The aggregateanalysis was performed using a wet-sieving method as de-scribed by Kemper and Chepil (1965).

Organic matter was determined by the Walkley-Blackmethod (Nelson and Sommers, 1982). The liquid limit (LL)and plastic limit (PL) were determined using the Atterbergmethod as described by Hough (1975).

RESULTS AND DISCUSSIONThe monthly rainfall at the experimental site during

the entire trial is depicted in Fig. 1. During the ex-perimental period, the plot received 1368 mm of rain-fall. The rainfall amount received between treatmentand sampling time for 1986 was 403 mm, which was71 mm more than that for 1987.

Analysis of variance (ANOVA) showed the meas-.ured soil parameters were not significantly different (a= 0.05) between treatments, but were significantly (a= 0.01) between the two study years. Therefore, thediscussion will focus on change of soil properties be-tween years rather than among treatments. The valuesdiscussed are the means of four samples from eachgiven treatment, except organic matter content. Meanvalues were used for comparison because of the dif-ficulty involved with comparing individual samplevalues. It is interesting to note that, in general, thevalues collected in 1986 are more concentratedaround the mean compared with 1987 values, asshown by the coefficients of variation in Table 1, 2,and 3.

Measured organic matter (OM) contents and phys-ical properties of soil treated with different rates ofAgri-SC soil conditioner are shown in Table 1. TheOM contents in 1986 for all treatments were similar,averaging 1.54%. However, since there was no addi-

Table 2. Measured soil hydrolpgical properties of Stoy silt loam(fine-silty, mixed, mesic Aquic Hapludalf) treated with differentrates of Agri-SC soil conditioner._________________

Saturated hydraulic

(L/ha)Control0.150.300.60Average

19861.72t (28.9)}:1.46 (31.7)1.99 (26.6)1.85 (28.9)1.76

19871.31 (31.2)1.17(31.0)1.30 (31.2)1.37 (29.9)1.29

19861.06 (19.4)§1.11 (7.6)1.41 (66.4)1.14(76.1)1.17

19870.31 (8.88)0.27 (24.3)0.51 (9.2)0.27 (39.3)0.33

t Values of sorptivity and hydraulic conductivity are a geometeric mean offour measurements,

t Values in parentheses for sorptivity are antecedent water contents in percentby volume.

§ Values in parentheses for saturated hydraulic conductivity are coefficientsof variation.

l60r*First Trial*

140

120EE. 100

80

60

40

20

0

_ Second.Trial

hiM J S* 1986

1M M

1987MONTH

Fig. 1. Monthly rainfall received at the experimental site during theentire trial.

tional incorporated OM, all treatment values declinedto an average of 1.05% in 1987. The reduction of OMcontent probably affected all soil parameters discussedin this study, especially soil aggregation since OM isan important cementing agent of the soil.

Fallowing subjected the plot to year-round inter-mittent rainfall, which may have caused the slakingof soil aggregates. The mean soil aggregate diameterfor 1986 was 0.26 mm, which declined to 0.11 mmfor 1987. Even though the mean aggregate diameterswere reduced by more than 57%, the reduction hadlittle effect on the total porosity of the soil for all treat-

1538 SOIL SCI. SOC. AM. J., VOL. 53, SEPTEMBER-OCTOBER 1989

Table 3. Measured rheological properties of Stoy silt loam (fine-silty, mixed, mesic Aquic Hapludalf) treated with different rates of Agri-SCsoil conditioner.

Treatment(L/ha)

Liquid

1986

limit Plastic limit

1987 1986CO. V. _•_!_..

Control0.150.300.60Average

26.9t26.926.226.626.7

(0.9)^ 29.1(2.0) 30.3(1.6) 30.5(1.5) 30.8

30.2

(3.4)(1.1)(3.1)(0.6)

22.4 (2.3)22.6 (6.6)23.2 (3.2)22.8 (4.2)22.8

1987.

22.322.722.522.522.5

(3.1)(2.8)(1.4)(3.1)

Plastic index

1986

—— %, by

4.54.33.03.83.9

1987.

6.87.68.08.37.7

t Values shown in the table are a mean of four measurements.$ Values in the parentheses are the coefficients of variation.

z- 100o

90

UJuiIXoUJa

80

—•— Control—•- O.lSL/ha—— 0.30L/ha—o— 0.60 L/ha

I10' 10° 10"

SOIL WATER SUCTION, mm of water.Fig. 2. Soil water retention curves for Stoy silt loam (fine-silty,

mixed, mesic Aquic Hapludalf) treated with different rates of Agri-SC soil conditioner.

merits; however, it tremendously affected the amountof large-size pores. In Table 1, the 48-h aeration po-rosity is a representation of the large-size pores. Theaverage 48-h aeration porosity (or macroporosity) in1986 was greater than 19%, but averaged less than 8%in 1987. The reduction in macroporosity had a sub-stantial influence on the hydrological properties of thesoil.

Generally, it is not easy to compare hydrologicalproperties between treatments, since some of theproperties vary depending on the initial and surfaceconditions of the soil. In addition, some of the param-eters, such as infiltration and drainage rates, are func-tions of time. Therefore, in order to make a mean-ingful comparison, a consistent condition should beestablished. For example, in comparing drainage, adrainage rate at 1 d after satiation of the soil was used.For infiltration, the steady infiltration rate was usedfor assessing the effects of treatments. In this report,only data of sorptivity, S0, and saturated hydraulicconductivity, Ks, are shown (Table 2), since these pa-rameters are related. However, the ANOVA showedthat the effects of Agri-SC on S0, KB, and infiltrationand drainage rates were not significantly different (a.= 0.05) between treatments, but were significant be-tween years (a = 0.01). Sorptivity values decreasedapproximately 27% from 1986 to 1987, and A; de-creased more than 70% on an average basis. Decreas-ing KS was attributed mainly to the decrease in large-size pores.

In comparison of water retention, the mean soilwater characteristic curve for each treatment in 1987(Fig. 2) was plotted on semilog paper. The degree ofsaturation was used instead of water content to plot

against soil water suction. Figure 2 shows only a slightdifference in water retention among the various treat-ments. However, the treated soils did retain slightlymore water at a given suction than the control soildid, but the difference became less as suction reachedclose to 240 cm of suction.

In evaluation of the effects of Agri-SC on soil rheo-logical properties, the mean values of LL, PL, andplastic index (LL—PL) are shown in Table 3. Liquidlimit increased aboiit 13% over the study, but PL re-mained unchanged. The reasons for the higher LL val-ues for 1987 are not known; however, it is suspectedthat degradation of soil structure and reduction of OMcontent influenced the results.

Combining the edaphological and pedological ap-proach might be a more effective way to evaluate theeffects of Agri-SC. Growing crops will intercept rain-fall, which would reduce slaking of soil aggregates.Also crop residue could be annually incorporated tomaintain more constant amounts of OM from oneyear to the next. Comparing crop yields might be amore practical approach in evaluating conditionerperformance. Comparing soil physical properties of aconditioner-treated soil vs. a control soil when cropsare being grown, can be a problem in that it might bedifficult to distinguish between soil-conditioner effectsand the effects of plant and root growth.

CONCLUSIONSBased on the results obtained in this study, we con-

cluded:1. Fallowing the experiment plot caused a decrease

in OM content during the 2-yr study. Fallowingsubjected the plot to year-round intermittentrainfall that may have caused the slaking of soilaggregates. Slaking action and the decrease inOM combined to reduce aggregate size and sig-nificantly decrease macroporosity. Reduction inKs, S0, and drainage rate was probably the resultof the decrease in macroporosity.

2. Agri-SC did not improve soil hydrological, phys-ical, and rheological properties, nor promote oreven maintain water-stable aggregates. No sig-nificant differences were obtained among thefour application rates of the conditioner.

ACKNOWLEDGMENTS

The authors would like to thank Dr. E.G. Varsa for hisgracious assistance in conducting this research and Mr. J.S.Steiner for his valuable discussion on this work.

LARNEY & KLADIVKO: SOIL STRENGTH PROPERTIES UNDER FOUR TILLAGE SYSTEMS 1539