Texas AgriLife Extension Service

of leaf matter to root area is necessaryto regenerate the food stores neces-sary to protect plant stands from sub-sequent stress, and avoids having tobuild all of the top growth at the ex-pense of food storage reserves. Someleaves must be maintained to collectdew and condense moisture to sustainregrowth. Closely-grazed plants withweakened root systems may perma-nently wilt when there is still significantmoisture in the soil. An adequateamount of leaf area must be main-tained in a well-established stand inorder to maintain efficient water use.

Soil Water Supply

Water must enter the soil before it canbe stored for later use by plants. Rain-fall either penetrates the soil surface(infiltration) and moves into the soil pro-file (percolation), runs off the surface,or pools and is lost to surface evapora-tion. Under ideal conditions, the soilprofile is fully recharged with water andsome percolating water passesthrough the soil to recharge an aquifer.Surface runoff, water infiltration andsoil water storage are affected by vege-tation, litter and rock cover, soil charac-teristics, surface crusting, soil texture,slope and rainfall intensity.

How much runoff occurs depends onthe vegetation on the site. Good vege-tative cover enhances water infiltrationbecause plant growth and residuesbreak the velocity of the rain droplets,thus reducing surface sealing and com-paction. Bunchgrass pastures losevery little precipitation as runoff be-cause they have more vegetativecover, standing crop and mulch accu-mulation. In contrast, sodgrasses pro-vide less soil surface protection(looser, smaller crowns and litter cover)than needed to encourage infiltration.Soil erosion is generally higher onthose sites.

Compaction and Hardpans

Root growth (expansion, penetrationand distribution) is greatly affected bysoil compaction, Compacted soils arevery dense and lack sufficient spacesbetween soil particles to hold air and

water. Tight soils prevent the verticaland lateral movement of water withinthe soil, At the same time they hinderroot expansion and penetration, sowhat little moisture is in the soil islargely unavailable to the plant. Com-paction is not visible and is often unde-tected except through the observed ef-fects of lower production, moreundesirable plants, greater surfacerunoff and increased soil erosion.These restrictions to effective soilwater storage and use reduce the ef-fectiveness of sound managementpractices such as fertilization and over-feeding. Compaction can reduce for-age production as much as 80 percent.

There are at least three primary typesof compaction on range and pasture-land: surface traffic compaction; “tillagepans;” and subsurface hardpan layers,Surface compaction results from sus-tained equipment or livestock traffic,particularly when soils are wet. Mostdamage is to the upper 2 to 3 inches ofsoil, and roots have difficulty penetrat-ing the pan. Growth is limited, espe-cially for young seedlings. Such standsof grass will mat on the surface and areprone to stress early in a drought andmay fail in an extended drought. Sur-face compaction is easily corrected be-cause it is shallow and can be brokenwith a light disking or shallow renova-tion tool. If corrected early, productionmay be fully restored within the samegrowing season.

Tillage pans (hardpans) also restrictroot growth and water movement onimproved pastures. Tillage pans arecaused by repeated implement use atthe same depth, This type of compac-tion is frequently attributed to plow, diskor chisel points and the tractor used topull this equipment. Soils with restric-tive layers have very low permeabilityrates, seal rapidly, and pack tightly withonly basic equipment use. A hardpanis an impermeable barrier to rootgrowth. Since roots cannot growthrough the hardpan, they have accessonly to the moisture and nutrientsabove the barrier, Soil water below thehardpan cannot move upward to re-plenish the soil moisture around theroot system. Rainfall can saturate thesoil only above the hardpan; it cannot

move downward to replenish the entiresoil profile. As a result, plants havemalformed root systems and are verysusceptible to drought.

Many natural hardpans have devel-oped over long periods of time asleached minerals and clays are depos-ited at a specific soil depth. Unlesshardpans are broken and thoroughlymixed with porous soil, they have atendency to reform after a few seasons.Breaking the hardpan is useful only if itallows plant roots to reach moisture ata greater depth.

I Renovation Techniques

Compacted soils can be broken withcommon cultural practices. Most plowswill create enough lateral fractures tocorrect surface compaction. Soil perfo-rators and aerators also fracture thesurface while adding multiple pocksand depressions to trap rainfall. Trafficand tillage pans can be easily correctedwith deep tillage equipment operatingjust below the compacted layer.

Chemically altered subsurface hard-pans (e.g. calcium carbonate) are gen-erally more difficult to correct. If thehardpan is thin (less than 2 inches andnonuniform), subsoiling may disturbthe pan enough to restore water perco-lation. Thicker layers of impervious soilwill soon revert to their former state,sometimes within the same year. Whileaeration, chiseling and shallow renova-tion will reduce compaction and” in-crease water storage above the sub-surface layer, more aggressivesubsoiling is required for subsurfacepans (i.e., with a parabolic subsoiler orV-ripper). The paratill plow shatterscompaction using a Iift/fall principle; itmay satisfactorily alter the subsoil,even if for short periods,

Sod renovators, aerators and light chis-els can be used to open the soil forwater storage without burying or dis-placing surface litter. As a surfacemulch, plant residues improve waterinfiltration and decrease soil erosion.Of the deep subsoilers, the paratill plowis currently the least destructive to sur-face residues, The best time to use asubsoiler is when perennial plants are

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dormant and the soil is moist enough torenovate without clodding, but not sowet as to smear or stick to the equip-ment.

Renovator points should be placedonly 1 inch below the compacted layer.This minimizes the energy costs andhorsepower requirements. Perforators,sliding chisels and lifting plows reducecompaction by cutting and creatingsmall displacements of soil, or some-times by lifting and fracturing entirelayers of soil. Frequently, the degree ofrenovation achieved is directly propor-tional to the type of equipment usedand the horsepower required to pull it.It is important to consider costs andchoose renovation equipment cor-rectly. Compacted layers usually canbe identified and their depth deter-mined by probing the soil with a smoothsteel rod. Equipment can then be lev-eled and properly adjusted for depth.

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Grass Responsesto Renovation

During drought, it has been observedthat grasses on renovated land con-tinue production and remain green 2 to3 weeks later than grasses on com-pacted soils. Likewise, the nutrientquality of the forage is higher. In fieldtests, yields of Coastal bermudagrass,buffelgrass and kleingrass increased100 to 300 percent over various peri-ods of evaluation (Table 1). Four yearsafter renovation, forage differences be-tween renovated and non-renovated

clay soils were negligible. Deep reno-vation of a loose soil with no compac-tion layers does not increase vegeta-tion, however.

Renovation Equipment

Several methods can be used to reno-vate ranges and pastures and increasewater use efficiency. These includeplowing, deep subsoiling, chiseling,disking and aeration.

Plowing

The strong points of the moldboard, orturning plow, center on its ability tocompletely invert the plowed layer ofsoil. It is useful to plow before applyingfertilizers and herbicides. Plowing bur-ies weeds and incorporates importantresidues such as animal manures andlegume crops. The turning action of theplow almost completely fractures theroot zone, removes most compactionand reduces weeds to a manageablelevel,

There are disadvantages to moldboardplowing, however. One is that the loss

Of surface residue increases the risk oferosion. Also, the design of the plow tipand “slide” create compaction justbelow the point. Not much lifting actiontakes place since gangs of plows usu-ally are pulled under their own weight.Thus, plowing at the same depth forseveral years creates subsurface com-paction that restricts root growth andsubsurface water movement. In thepast it was believed that the best way

Table 1. Average annual weights of additional forage (air dried) obtainedwith different renovation tools in South Texas, 1986-1992.

Forage yields (lbs./a)Over non-treated pastures

Renovation Coastaltool’ bermudagrass Kleingrass Buffelgrass

Subsoil 2,026 1,167

PIow 2,266 711 IChisel 1,412 3,539 1,275 IDisc 751 2,059 IAerator 1,000 3,864

1Representative tools are listed to illustrate typical advantages from renovation;duration of these studies varied; tool types are grouped into similar categories.

to eliminate such compaction was toplow at ever greater depths. However,once shallow soils have severelyeroded and most of the topsoil is gone,plowing simply brings up and incorpo-rates undesirable (acidic, poorly struc-tured or sterile) subsoil material into theroot zone. Sometimes deeper tillage isnot possible because of buried rock,caliche outcrops or high equipmentpower requirements.

Subsoiling

The first subsoilers were functional, butwere relatively awkward, power inten-sive and highly disruptive to the fieldsurface. These subsoilers createdlarge clods which required disking andsurface leveling before routine forageproduction could be resumed. Eventoday, many subsoilers create largeclods so that subsequent leveling isnecessary before haying equipmentcan move safely over the land. Fre-quently subsoiling uncovers largerocks, buried wood and other materialshazardous to plows.

Because of the excessive power re-quirements for subsoiling (deep tillage)and the potential for undesirable sur-face roughness, the best time to do it isin winter when grass is partially or to-tally dormant and the soil is more likelyto be moist. This may not be importantfor pastures or rangeland being totallyreestablished, but it is important to therenovation of old rangeland sites andhayfields.

Subsoiler legs or shanks can fracturecompacted soil layers and producesmaller clods and less upheaval if thesoil is neither too wet nor too dry. Theland surface can be restored to accept-able smoothness with one, or perhapstwo, diskings. Poor equipment designand minimum lift sometimes create ad-ditional compaction at a deeper level,but this is not as critical to water stor-age. Structural damage is possible ifsoil is too wet. The engineering of sub-soilers and subsoiling plows hasevolved to include coulters and liftingpoints, which has reduced surfaceroughness (Figure 2).

Subsoiling is easiest when a pasture isbeing reestablished and saving surface

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water percolation through the soil.

plants and seed from burial is not anissue. Subsoiling is important to sus-tained forage production, All surfaceequipment and livestock ultimately cre-ate compaction and the need for sub-soiling is inevitable under most inten-sive agricultural production systems.

Chiseling

Chiseling is accomplished by draggingshanks, with or without blades, in thesoil at various depths and spacings.Chiseling usually is shallower than sub-soiling. Typically, shanks are on 24-to36-inch spacings and are inserted 4 to12 inches into the soil. Chiseling is afaster process than plowing, leaves re-sidue on the surface between shanks,and can be used to break deeper com-paction areas if required. Since sodand residues are left between shankrows, there is still adequate erosionprotection. Chiseling can be used forsod and some hardy bunch grasses.Chiseling does leave the surface fairlyrough, so a followup disk harrowing ordragging may be required (Figure 3).

Disking

The farm disc is commonly used onpastures to break up surface compac-tion to a depth of 4 to 5 inches, How-ever, heavier discs (1 ,500 pounds ofweight per running foot) with 36-inch

Figure 3. Chisels pull shanks through thesoil at various depths to fracture hard pansand compaction layers.

blades are often used for brush man-agement and seedbed preparation onrangeland (Figure 4). These heavydiscs renovate soil to a depth of 12 to18 inches, promote water infiltrationand, ultimately, improve grass produc-tion. It is best to disk in late winter,before peak rainfall and the beginningof spring growth. Repeatedly disking atthe same depth may also cause hardpan development.

Aeration

Aerators use knives, blades, spikes orcleats to create pocks or cut furrows inthe soil, This fractures surface crustsand compaction layers (Figure 5).Aeration loosens soil, increases thespace between particles and increaseswater and air movement,

Summary

Many rangelands and pastures withundesirable soil and vegetation char-acteristics have such low water storagecapacities that plant stress is inevitablewhen rains do not occur frequently,Renovation may be necessary to elimi-nate compaction layers and plowpansor to loosen the soil at specified levelsin the profile. Renovation increases thepenetration of water into the soil profile,decreases surface runoff, aerates thesoil for better root development andgas exchange, and ultimately in-creases plant production, Renovationpractices must be carefully plannedand integrated into the total ranchingmanagement system,

IFigure 4. Disking breaks up surface crusting.

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utrientsto infiItrate the SOIL

I Acknowledgements

Funding for this publication wasprovided by the Extension Service –United Sates Department of Agricul-ture under the USDA Water QualityInitiative, EWQI04400. The authors ap-preciate the typing skills of Ms. SylviaGarza and Pam Tulles and the review-ers of the manuscript, Dr. Don Dorsett,Dr. B. L. Harris and Mr. Wesley New-man. This publication is a contributionof the Comprehensive Ranch Manage-ment for Profit project, a South TexasIntegrated Resource Management pro-gram.

Additional Readings

McGinty, AlIan, Thomas L. Thurow andCharles A. Taylor Jr., “ImprovingRainfall Effectiveness on Range-Iand.” L-5029, Texas AgriculturalExtension Service,

Welch, Tommy G., Robert W. Knight,Dan Caudle, Andy Garza and JohnM. Sweeten. “Impact of GrazingManagement on Nonpoint SourcePollution,” L-5002, Texas Agricul-tural Extension Service.

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