Non-Traditional Soil Additives:Can They Improve Crop Production?

Mark L. McFarland, Charles Stichler and Robert G. Lemon*

Agricultural producers are con-stantly seeking the most efficientand economical production sys-tems.The use of soil additives suchas soil conditioners, soil activators,wetting agents, soil inoculants,microbial enhancers, soil stimu-lants, etc., has been promotedsince at least the late 1800s.Increasing production costs, espe-cially for fertilizers, have renewedproducers’ interest in these materi-als. However, many of these prod-ucts have not been investigatedscientifically and their benefits areunproven.

Soil and plant additives may beclassified in a number of differentways based on criteria such asintended use or function, applica-tion method, quantity to beapplied, or origin of the material.For consistency, most soil scien-tists and agronomists classify theseproducts under three main cate-gories: 1) soil conditioners; 2) soilactivators and biological inocu-lants; and 3) wetting agents.

In general, soil additives can bedistinguished from fertilizers inthat they usually have little or nonutrient content. Unlike fertilizers,additives are commonly not mar-keted with, nor are they requiredto provide, a guaranteed analysis(e.g., 10-34-0 or 32-0-0). Instead,manufacturers often suggest thatadding these materials to the soil

will enhance crop production byimproving water and/or nutrientavailability and uptake by plants.These enhancements are generallysaid to occur when standard fertil-izer applications are made to thecrop at recommended or near rec-ommended levels, although someadditives claim to replace or signif-icantly reduce the need for fertiliz-ers.

Most traditional soil amend-ments and commercial fertilizershave been tested extensivelythrough research trials to docu-ment both their benefits and limi-tations. Unfortunately, adequateresearch funds often are not avail-able to investigate the many newproducts being marketed, includ-ing non-traditional additives.Nevertheless, consumers should beaware of the types of productsavailable and have some knowl-edge of their potential to benefitcrop production.

Soil ConditionersSoil conditioners usually are

defined as materials that improve asoil’s physical condition or struc-ture and, in turn, the soil’s aerationand water relationships. Certainly,maintaining and/or improving soilstructure is highly desirable incrop production. Adding organicmatter to the soil is the most com-mon method for improving soilstructure. Traditional additivesinclude crop residues, livestockmanures and sewage sludge. Non-traditional soil conditioners

include both organic and inorganicproducts such as:

1) Composted organic materialswhich also may be supple-mented with inorganic mate-rials such as unprocessedrock phosphate or groundlimestone. The compositionof these materials is quitevariable. Such additives maybe marketed as liquid extractsof livestock manure or otherorganic residues.

2) Mined mineral deposits thatare unprocessed except forgrinding. Again, the composi-tion of these materials can behighly variable, but mayinclude granite, glauconite (a mineral high in unavailablepotassium), and gypsum orsand.

3) Mined humates or humicacids. These are prehistoricorganic deposits in theadvanced stages of transfor-mation into coal which arenormally discarded duringmining. Liquid humates alsohave been marketed and are,presumably, a concentrate ofhumic acids.

4) Various inorganic solids suchas evaporated sea water orsulfates, which may be com-bined with organic extractsof materials such as kelp (seaweed) or whey.

Humates and/or humic acid aregood examples of non-traditionalsoil conditioners, and a number of

*Assistant Professor and Extension Soil FertilitySpecialist,Associate Professor and ExtensionAgronomist, and Assistant Professor andExtension Agronomist - Peanuts and Cotton,The Texas A&M University System.

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research trials across the UnitedStates have evaluated their effectson soil properties and cropgrowth. Studies conducted inKansas (Table 1) showed thathumate did not significantlyimprove corn grain yields over a 3-year period (1). Similar resultswere observed in research on arelated material called leonardite,an organic, coal-like deposit report-edly high in humic acid (2).Research in Illinois (3), NorthDakota (2) and Canada (4) showedno significant improvement inyields of corn grain, corn silage,wheat, barley and field beans whenvarious soil conditioners wereapplied alone or in combinationwith commercial fertilizer. In con-trast, most studies showed consis-tently improved yields with theaddition of irrigation water and tra-ditional commercial fertilizers.

Soil ActivatorsSoil activators are marketed on

the basis that they stimulate exist-ing soil microbes or inoculate thesoil with new beneficial organisms.

Some manufacturers suggest thatsuch products may improve soilphysical properties (increase struc-ture, reduce compaction), increasefertilizer and soil nutrient uptake,improve crop yields and/or quality,correct soil “toxicities” (such assalinity), and provide disease andinsect resistance (5). Most soilmicrobiologists agree that to signif-icantly increase the activity of soilmicrobes for more than a fewhours, a minimum of several hun-dred pounds of organic materialmust be added to the soil.However, these products often areapplied at rates of only a fewpounds per acre, which may add aslittle as 1 pound of microbes tosoil that already contains 2,000 to4,000 pounds of microbes per acre(6).

Numerous studies have beenconducted across the United Statesto evaluate various soil activators.In general, these studies haveshown no significant beneficialeffects of these products on cropyields or quality. Table 2 presents

results of field studies conductedin Texas using two soil activatorproducts (5). In both fertilized andunfertilized plots, neither productincreased yields of grain sorghumor cotton above the check plot.Laboratory evaluations of theseproducts also indicated that theydid not increase the numbers oractivity of soil microbes and thus,would not be expected to increasethe rate or extent of crop residuedecomposition.

Other field trials using thesetwo products were conducted onforages, peanuts, rice, soybeans andtomatoes by researchers in Texas,Alabama, Louisiana and Oklahoma(5).These studies consistently indi-cated that neither product signifi-cantly affected yields of the vari-ous crops under the different soiland climatic conditions. This workis extremely important, particularlybecause it included 22 differentsoil series ranging from fine sandsto clays (pH range 4.8 to 8.4), andbecause the work was continuedat the same locations over a 2- to 3-year period to verify results.

Certainly, inoculation to stimu-late the development of certaintypes of beneficial microogran-ismsis not uncommon. In certainsewage treatment processes andcomposting operations, a portionof the treated material may be usedto provide “seed” organisms tounprocessed material. An examplein agriculture is inoculation of seedwith Rhizobium bacteria to pro-mote good nodulation in legumecrops. However, these biological

Table 1. Effects of humate on yields of irrigated corn.1

Grain yield (bu./acre)Treatment 1978 1979 1980 Average

Control (no fertilizer) 211 152 170 178

50 lbs. 18-46-0/acre 213 149 177 180

50 lbs. 18-46-0/acre +250 lbs. humate/acre2 208 162 172 181

50 lbs. 18-46-0/acre +500 lbs. humate/acre2 210 162 172 1811Adapted from Lawless et al., 1984 (see References).2Rate of humate reduced by one-half in 1979 and 1980 applications.

Table 2. Grain sorghum and cotton yields at three locations as affected by application of two soil additivesand fertilizer.1

Sorghum grain yield (lbs./acre) Cotton lint yield (lbs./acre)Fertility treatment Beeville McGregor Temple McGregor El Paso Lubbock

Unfertilized

Check 175 2057 2218 194 806 290Product A 140 1854 2233 199 842 301Product B 217 2036 2202 193 777 310

Fertilized

Check 1110 2543 2237 265 743 393Product A 900 2514 2352 240 766 370Product B 1041 2365 2352 240 749 397

1Adapted from Weaver et al., 1974 (see References).

processes have been thoroughlyinvestigated and the potential ben-efits reasonably well documented.

Wetting AgentsWetting agents and surfactants

have long been used in agriculturein combination with herbicidesand insecticides.Their primaryfunction is to reduce the surfacetension of water droplets andimprove leaf surface coverage byfoliar sprays. How-ever, many relat-ed products are marketed on thebasis that they will loosen tight orcompacted soils, improve waterinfiltration and retention, enhancenutrient availability and increasecrop yields. Some research hasshown that certain non-ionic soilwetting agents do in fact increasewater infiltration rates onhydrophobic (water-repelling)soils. However, these materials haveeither no effect or an adverse

effect on normal (wettable) soils(7). Obviously, using results fromone type of soil to predictresponse on another soil is ofteninappropriate.

Studies in Wisconsin evaluatedthe effects of three wetting agentson growth and yield of corn, soy-beans and potatoes (7). Each prod-uct was evaluated over a 2- or 3-year period and at up to three dif-ferent locations. Table 3 shows theeffects of two products on corngrain yields. Both products weresoil applied according to label rec-ommendations either preplant orpreemergence. In both studies,plots were carefully installed toinclude checks with and withoutfertilizer, in addition to plotsreceiving the wetting agents. Inthis way, the response of the cropto fertilizer and to the wettingagents could be compared.There

was no increase in grain yieldsfrom the addition of wettingagents, whereas adding commercialfertilizer significantly increasedcorn grain yields compared to theunfertilized plots. Leaf nutrientcontent (N, P, K) also was notincreased by soil application of thewetting agents.

In several other states, researchon the effects of various wettingagents on the growth and yields ofpotato, soybean, wheat and grainsorghum (8, 9) has shown no sig-nificant benefits. However, onefield study in Kansas (10) did report a significant yieldresponse in 1 year of a 4-yearstudy.

Making DecisionsSoil scientists and agronomists

are often asked to provide recom-mendtions on the use and effec-tiveness of new and non-traditionalproducts. However, many suchproducts have not been scientifi-cally evaluated. As a result, the bestadvice that can be given to grow-ers is to evaluate new productscarefully and insist upon local orregional research data (not testimo-nials) demonstrating product effec-tiveness and value. If there are nosuch data, consider conductingsmall-scale field trials on your farm.Figure 1 shows an example layoutfor a product trial. The followingfactors should be considered whenevaluating new products in farmand ranch production systems:

1) Use a small area, but one ofadequate size to obtain reli-able harvest data.

Table 3. Effects of two wetting agents on yields of corn grain over a 2-year study period.1

Treatment Grain yields (bu./acre)Nitrogen

fertilizer rate Product A rate(lbs./acre) (qts./acre) Year 1 Year 2 Average

0 0 140 126 1330 2 131 107 119

200 0 183 167 175200 2 171 155 163

Treatment Grain yields (bu./acre)Nitrogen

fertilizer rate Product B rate(lbs./acre) (qts./acre) Year 1 Year 2 Average

0 0 140 126 1330 1 139 120 130

200 0 183 167 175200 1 182 166 174

1Adapted from Wolkowski et al., 1985 (see References).

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Figure 1. Example plot layouts for small-scale product or management practice comparisons.

2) Select a field or a locationwithin a field that is uniformin soil, slope and managementhistory.

3) Always compare the plotsreceiving the amendment tocheck plots that are not treat-ed.

4) Install at least three or fourreplications (separate plots)of each plot or treatment.

5) Manage all plots in exactlythe same way during the sea-son, except for the differencein treatments.

6) Monitor crop growth anddevelopment during the sea-son to detect treatment differ-ences.

7) Harvest each plot separately.Compare the yields for allreplications of a particulartreatment to look at variabili-ty. If yields for a particulartreatment are not consistent,it may not perform consis-tently, or the test site mayhave hidden variation.

8) Finally, use the average value(crop yield or quality) foreach treatment to comparethe different treatments toeach other. Then, evaluateinput costs for each treat-ment compared to anticipat-ed returns.

If product and application costsapproach or exceed returns, thetreatment may not be a soundinvestment.

The purpose of this publicationis not to suggest that all currentand/or future non-traditional soiladditives are of no value. As newinventions and new products aredeveloped they may have thepotential to improve crop yields,crop quality and/or production

economics. However, properproduct testing and evaluationare critical to verifying the poten-tial benefits of new and unprovenmaterials.

Farm managers should under-stand the requirements of theirlands and crops, and thoroughlyassess the benefits and costs associ-ated with various production prac-tices. Achieving “maximum eco-nomic yield” depends upon usingonly those inputs which will, withreasonable certainty, provide areturn on that investment.

References1. Lawless, J. R., H. D. Sunderman,

F. L. Lamm and L. D. Robertson.1984. Report of researchresults. Supplement 1.Compendium of researchreports on use of non-tradition-al materials for crop produc-tion. NCR-103 Committee.Iowa State Press, Ames, Iowa.

2. Bauder, J.W. 1976. Soil condi-tioners - A problem or a solu-tion? North DakotaAgricultural ExperimentStation. Reprint No. 869. FarmResearch. 33:21-24.

3. Egli, D. B. and J.W. Pendleton.1984. Progress report of agro-nomic field studies withleonardite. Compendium ofresearch reports on use of non-traditional materials for cropproduction. NCR-103Committee. Iowa State Press,Ames, Iowa.

4. Elegba, M. S. and R. J. Rennie.1984. Agrispon: microbial andelemental analysis and evalua-tion of its effect on the growthof wheat, barley, field beansand corn. Canadian Journalof Soil Science. 64:621-629.

5. Weaver, R.W., E. P. Dunigan, J. R.Parr and A.E. Hiltbold. 1974.Effect of two soil activators oncrop yields and activities of soilmicroorganisms in theSouthern United States.Southern Cooperative SeriesBulletin No. 189. JointRegional Publication by theAgricultural ExperimentStations of Texas, Alabama,Florida, Georgia, Kentucky,Louisiana, North Carolina andOklahoma.

6. Miller, R. H. 1978. Ecologicalfactors which influence thesuccess of microbiological fer-tilizers or activators.Developments in IndustrialMicrobiology. 20:335-342.

7. Wolkowski, R. P., K. A. Kellingand E. S. Oplinger. 1985.Evaluation of three wettingagents as soil additives forimproving crop yield and nutri-ent availability. AgronomyJournal. 77:695-698.

8. Laughlin,W. M., G. R. Smith andM.A. Peters. 1982. A multipur-pose wetting agent,WEX, and acultured biological product,Agrispon, leave potato yieldsunchanged. American PotatoJournal. 59:87-91.

9. Fenster,W., G. Randall,W.Nelson, S. Evans and R.Schoper. 1978. Effect of WEXon nutrient uptake and cropyields. Compendium ofresearch reports on the use ofnon-traditional materials forcrop production. NCR-103Committee. Iowa State Press,Ames, Iowa.

10. Sunderman, H. D. 1983. Soilwetting agents. AES KeepingUp with Research. No. 73.Kansas Experiment Station.Manhattan, Kansas.