Water is probably our least understood natu-ral resource. The earth has virtually the sameamount of water today as it did whendinosaurs roamed the planet. Water coversnearly three-fourths of the earth as rivers,lakes and oceans, but only about 3 percent ofthe planet’s water is fresh, and two-thirds ofthat is ice. About 0.6 percent of the earth’swater is in the earth’s underground aquifers,and a small but very important amount (0.003percent) is contained in plants, animals andthe soil. Over four trillion gallons of water fallon the United States daily in the form of pre-cipitation, but much of that disappears inevaporation or runoff. The amount that soaksinto the soil determines, in part, plant life andproductivity. The hydrologic cycle (Fig. 1) isthe continuous process bywhich water is transportedfrom the oceans to the atmos-phere to the land and back tothe sea. Water evaporates fromwater bodies such as oceans,ponds and rivers and is movedacross the earth as water vaporby wind currents. Soil, plants,people, animals, factories andvehicles also contribute to thisvapor. Water vapor condensesand falls to earth as rain, sleet,snow or hail depending on theregion, topography, climate andseason. A large portion of theprecipitation returns to theatmosphere as vapor throughthe evaporation process as itfalls. Evaporation also occursfrom plant, soil and water sur-faces. Precipitation that reachesthe ground either evaporates,

infiltrates into the soil or runs off downstreamto ponds, lakes or oceans. Part of the soil andsurface water is used by plants and animalsand returns to the atmosphere through tran-spiration and respiration. That which perco-lates through the soil profile seeps into under-ground streams or reservoirs. The amount ofwater on the earth is constant; it is alwayssomewhere in the cycle.Because the total quantity of water availableto the earth is finite and indestructible, theglobal hydrologic cycle is a closed systemwith any water problem being a distribution(quantity, time, location) or pollution (quality)problem. However, the hydrologic cycle in ariver basin, a state like Texas, a county, or aranch is open. The amount of water received

E-168

Soil and Vegetation Management:Keys to Water Conservation on Rangeland

Joseph L. SchusterProfessor and Extension Range Specialist

Texas AgriLife Extension Service • Zerle L. Carpenter, Director • The Texas A&M University System • College Station, Texas

Figure 1. The hydrologic cycle.

is not a constant. Water disposition within aranch is influenced by climate, geology andvegetation on the ranch. The water budget ofa ranch depends on precipitation receivedand the amount of water lost over a giventime. The water storage capacity of the soiland the losses through evaporation and tran-spiration (evapotranspiration) influence thechange in storage over time. Actual waterlosses vary depending on the seasonal patternof rainfall, individual storm intensity andduration, the soils, and the kind, amount anddistribution of vegetation.

Evapotranspiration represents the largestwater loss from arid and semiarid landsbecause runoff and groundwater recharge arerelatively minor losses. Evapotranspirationaccounts for 90 to 95 percent of waterloss from Texas rangelands.Therefore, efforts to retain asmuch water as possible onsite should theoreticallyconcentrate on reducingevaporation and transpi-ration losses.

Soil and vegetationmanagement is the keyto increasing wateravailability on range-land. We can do little toalter the overall watercycle so our supply ofwater is fixed, dependingupon local climate, seasonand current weather patterns.

Effects of Vegetationon Hydrologic Processes

The fate of each drop of water falling on theland depends largely on the kind of soil andthe vegetative cover. Experience and researchhave provided land management practices formanaging soil and vegetation resources toincrease water use efficiency. Adequate vege-tation cover prevents erosion by breaking theimpact of raindrops and slowing overlandflow. Plant cover reduces soil erosion in rain-drop splash by intercepting raindrops andabsorbing their energy. Effectiveness of reduc-ing soil splash is proportional to how muchcover is present at the time rain occurs.Research has shown that effective control

(95 percent) of raindrop splash energiesrequires approximately 2,000 pounds per acreof sodgrass or 3,500 pounds of bunchgrass.Soil-protective values decline rapidly as coverdeclines below these levels.

Plant cover also interrupts the travel of rain-drop splash and overland flow thus reducingerosion. Soil movement caused by surfaceflow depends on the energy of the runoff, thesusceptibility of the soil to detachment andtransportation, and the protection afforded byvegetative cover. Plant cover protects soilfrom erosive action of runoff water by offer-ing resistance to the movement of water andshielding the soil from its effects. Protectionfrom erosion is obtained through resistance ofvegetation to the energies of rainfall and

runoff. Generally however, a combina-tion of plant cover andmechanical measuresdesigned to meet the specific

combination of erosion fac-tors operating on a particu-lar land area is necessaryfor effective erosion con-trol.

Within a particular cli-mate, water loss throughtranspiration is propor-tional to the leaf area (tran-

spiring surface) and theavailability of water in the

rooting zone. The less thetranspiring surface and theshallower the root system the

less water is lost through transpiration.Soil water content is generally greater undergrass cover, due to lower evapotranspirationlosses. It is also higher under herbaceouscover than under mixed-brush and herba-ceous cover. On the other hand, vegetativecover greatly reduces the amount of runoffwith grasses generally decreasing the runoffmore than forbs or shrubs. Therefore, wateravailability should increase if vegetation con-version is from brush to grass unless someunderground geologic layer disrupts normalsoil water movement. An impermeable layerat a shallow depth might keep water withinreach of the shortest rooting plants.

The type of vegetation, because of differencesin structure, area and texture of plant sur-faces, also influences how much water clingsto vegetation and evaporates before passing

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We can, however, manageand conserve water whereand when it falls and by con-trolling the kind of vegeta-tion make the fullest use ofthe water that falls. It isoften our management ofthe vegetation that deter-mines if we have both thequantity and the quality ofwater needed, when andwhere we need it.

through the canopy to the ground. Relativeinterception losses increase from low sod-grasses, to bunchgrasses, to shrubs and trees.For example, estimated annual interceptionlosses are 10.8 percent from curly mesquite(sodgrass); 18.1 percent from sideoats grama(bunchgrass); and 46 percent from liveoakbrush and trees. So, converting from brush ortrees to grass should increase the percentageof incoming precipitation available in the soilfor use by forage plants.

Conversion from brush to grass on rangelandwill also theoretically yield more waterdownstream because infiltration is less undergrass than under brush, and runoff is poten-tially increased if infiltration is reduced.Generally, the amount of cover (biomass), andhence the rate of infiltration, is greatest undertrees and shrubs, followed in decreasingorder on sites dominated by bunchgrasses,shortgrasses and bare ground (Fig. 2). Inwestern Texas grass cover – especially bunch-grasses – provides the most desirable groundcover because it is the most water use effi-cient. Bunchgrasses also do an excellent job incontrolling erosion by holding soil on site andyielding more water off-site than shrubs.

Effects of VegetationManagement Practices on

Water Availability

Soil water increases due to vegetation man-agement ultimately depend on whetherrunoff and deep drainage increase by anamount equal to the reduction in evapotran-spiration. Several factors can affect this,including:

■ whether shrub biomass is replaced bygrass biomass (if herbaceous coverreplaces shrub cover in equal amountsthere will be little difference in transpira-tion),

■ speed of percolation of water in the soilprofile (restrictive layers may slow waterpercolation and allow more transpira-tion),

■ high rainfall areas that get more waterthan replacement plants use,

■ whether transpiring tissue of grasses isless than the trees or shrubs it replaces,and

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Figure 2. Vegetation type greatly influences what happens to incoming precipitation. Bunchgrass type vegetation is themost water use efficient on the Texas Agricultural Experiment Station in Edwards County, Texas. Adapted fromBlackburn, et al. 1986.

■ storm characteristics. Vegetative surfacescan hold only a certain amount of waterat a given time. Large storms account forthe major portion of runoff and deepdrainage in the Southwest.

Vegetation management practices can affectboth on-site and off-site water through theireffects on vegetation composition and soilsurface characteristics. The amount and quali-ty of increased soil water depend on the origi-nal vegetation, soils and climate. Also itdepends on the range management practiceused in conversion of the vegetation and itseffects on vegetative composition and soilsurface characteristics. Any practice thatincreases standing vegetation and litter willdecrease runoff and sediment production.

Vegetation ManagementPractices

Range management practices directly affect-ing vegetation are: (1) grazing management,(2) range revegetation and (3) brush andweed management.

Grazing ManagementAbility to control kinds and numbers of ani-mals and when they utilize the rangeland isabsolutely essential in regulating the effects ofgrazing on vegetation. Of all the range man-agement practices and technologies available,proper stocking or control of forage utiliza-tion is most important. Continued excessivedefoliation is the major cause of range deteri-oration. Deteriorated range means morerunoff and erosion (Fig. 3). Without control ofanimal numbers, the season of use, and distri-bution of animals, other practices are usuallyof limited value in maintaining desirable veg-etation cover. Any grazing management strat-egy that enhances vegetative cover improveswater use efficiency and conserves the soilresource. Grazing management should bethe first consideration in developing watermanagement strategies. (Fig. 4 and 5.)

Range RevegetationArtificial revegetation utilizes agronomicpractices to restore native plant communitiesor to introduce desired species. It is an expen-sive and ecologically disruptive process, par-ticularly risky in arid and semi-arid areas.Artifical revegetation should not be attempt-ed unless natural revegetation through graz-ing management will not restore the range to

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Figure 3. Good ground cover means less runoff and erosion and better water use efficiency. (Adapted from R. W.Bailey and O. L. Copeland, Jr. 1961. Low flow discharges and plant cover relations on two mountain watersheds inUtah. International Association of Science Hydrology Publication 51:267-278.)

See “Improving Rainfall Effectiveness onRangeland” (L-5029) for more information.

the desired condition within an acceptableperiod. In general, artificial revegetation isnot recommended if 10 percent or more of thevegetative cover is made up of desirablespecies. Revegetation may also not be feasiblebecause of poor soil conditions, erosion haz-ard or economic considerations. Seeding inconjunction with land surface modificationtechniques such as water spreading, waterharvesting, contour furrowing, pitting anddiking will enhance the probability of successfor reseeding and managing water use.

Seeding should be considered on severelydepleted ranges and where vegetation modi-fication practices call for a change inspecies. It is a valuable practice in replacingone plant cover with another to provide thedesired forage or water management (Fig. 6).

Brush and Weed ManagementDevelopment of ecologically sound land man-agement practices requires a clear under-standing of how the practices affect thehydrology of the site. Reducing the density ofundesirable species increases the availabilityof moisture and nutrients for more desirableforage species. Also, water yields shouldincrease if brush removal reduces transpira-tion losses. Control methods include burning,mechanical control, herbicidal control andbiological control. The hydrological impact ofall the methods has not been studied specifi-cally, but many studies allude to increasedon-site moisture availability. Others reportincreased downstream flow. Each methodaffects the water regime differently.

Herbicidal ControlDefoliation of plants with herbicides immedi-ately affects evapotranspiration losses. Whenplants defoliate, transpiration is reduced andlitter is added to the soil increasing soil aggre-gation and water infiltration. Dead stems androots decay and leave organic matter on thesurface and in holes created by decomposingroots. The total impact is that both the on-siteand off-site water regime is enhanced withoutrisk of erosion or increase in sediment loadsdue to physical disturbance. Replacement ofbrush species with herbaceous species, espe-cially grasses, provides water conservationplus forage. As much as a 500 percent in-crease in forage production has been recordedafter herbicidal control of brush (Fig. 7).

Herbicidal control of undesirable vegetationis applicable where:

1. vegetational change to more desirablespecies is needed,

2. the undesirables are susceptible to theherbicides, and

3. the terrain does not lend itself tomechanical methods.

Mechanical ControlMechanical methods such as axing, shreddingor roller chopping add litter to the soil withrelatively little soil disturbance. These meth-ods are applicable on nonsprouting species orwhere retreatments can be applied (Fig. 8).Dozing, root-plowing, grubbing or chainingremove plants from the soil and create con-siderable soil disturbance. Bulldozing andgrubbing create pits where trees and roots areextracted (Fig. 9). These pits act as watercatchments which concentrate water nutrientsand enhance moisture infiltration.Evapotranspiration is reduced making morewater available for replacement plant use ordeep percolation. However, the reduction willnot be maintained unless another vegetativecover is established. Erosion is a hazard untilherbaceous vegetation is re-established.

These methods are applicable on most non-rocky soils and where vegetative cover canbe replaced.

Chaining, cabling or dragging usually doesnot increase runoff and erosion if debris andlitter are left in place to protect the soil andthe herbaceous vegetation is re-established.Generally, soil moisture and runoff are muchhigher on chained areas than unchained areasthroughout the year. These differences aredue to changes in the microclimate, mulchingeffect of the litter and differences in wateraccumulation.

Innovations that make chaining even moreeffective include the disk chain and disk-chain-diker (Fig. 10).

Chaining and dragging are applicable onlarge acreages and work best with moist soilconditions and single stem non-sproutingspecies. Chaining, dragging and cablingshould be considered temporary and fol-lowed in due time with repeat applications orother follow-up methods of control.

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igure 8. Roller chopping reduces noxious brush and increases for-ge production through its influence on the water availability.

Figure 4. Overstocking results in deterioratedrangeland and poor water use efficiency.

Figure 5. Proper stocking benefits livestock production, wildlife,aesthetics and the water regime.

Figure 6. Seeding into pits created by grubbing noxious brushand burning periodically changed woodland back to grasslandat the Texas Agricultural Experiment Station near Sonora.

Figure 7. Control of noxious brush provides morewater and nutrients for forage species.

Figure 9. Power grubbing removes water-using brush and createsbasins which concentrate water and nutrients for forage plants.

Figure 10. The disk-chain diker designed by Harold Wiedemann, Texas AgriculturalExperiment Station, Vernon, Texas, reduces brush and creates pits which concen-trate water and nutrients for forage species.

Figure 11. Contour furrows reduce runoff andincrease soil water storage.

Figure 12. Creating pits in the soil, either by roller chopping,aerating or with a specially designed pitter increases wateravailability and forage yields on deteriorated range.

The relative impact of any plant control tech-nique on the water regime depends on sever-al factors:

■ severity of the soil disturbance;

■ the response of the herbaceous vegeta-tive;

■ effectiveness of the control method inremoving brush;

■ the impact of the practice on litter andground cover; and

■ time since implementation of the prac-tice.

Soil Modification Practices

Soil modification practices used for rangeimprovement generally bring about improve-ments in range productivity throughincreased conservation of water and wateruse efficiency. Many farming techniques andimplements have been adapted for range use,and some have been developed specificallyfor range use.

Contour FurrowingContour furrows are grooves or ditches madein the soil by various implements (plows,chisels, furrowers, etc.). The furrows shouldbe placed on the contour to collect runoffwater and increase soil water storage. Furrowdimensions vary considerably from grooves 4to 6 inches wide and 3 to 4 inches deep to asmuch as 2 feet wide and a foot deep. Inter-rupting the furrows with dams at intervalsincreases their effectiveness in ponding waterand increasing infiltration.

Contour furrows have been used successfullyin semi-arid regions to reduce runoff andimprove infiltration for increased forage pro-duction (Fig. 11). Contour furrowing of poorcondition range has been shown to reducerunoff and conserve more than one inch ofwater annually in the Great Plains. Increasedherbage production follows improved waterretention and storage and the transport ofnutrients from surface layers to lower depths.

Contour furrowing is applicable on produc-tive soils of restricted permeability on longuniform slopes with simple contour pat-terns. They are most effective when rainfall

intensities do not greatly exceed the hydraulicproperties of the furrows.

TerracingTerraces differ from furrows in that they arelarger and applied on the grade to allow con-trolled runoff. They are designed primarilyfor flood control and reduction of runoff andsedimentation on moderately steep slopes.Although terraces have been widely used inrestoring critical watersheds in the West, theiruse is generally impractical except as a water-shed treatment practice on rangeland.

PittingThe creation of small basins or pits to catchand hold precipitation on the site has beenused since the dust bowl days of the 1930s.Known as pitting, it is often used in conjunc-tion with reseeding to enhance seedlingestablishment by concentrating nutrients andwater.

Tools used for pitting vary widely. Almostany equipment capable of gouging, diggingor in some way creating pits in the soil sur-face can be used. The most commonly usedimplements are: (1) modifications of disk-plows, and (2) spike-toothed pitters. Modifieddisk-plows gouge out long shallow pits whilethe spike type pitter creates small basins.Modifications of spike-tooth pitters are calledaerators. Aerators use spikes or cleats to cre-ate pits and aerate the soil increasing waterand air movement (Fig. 12).

Pitting has been effective in increasing forageproduction by as much as 100 percent, pri-marily due to enhanced water relations. Thedisturbance and better water relationsincrease productivity of the remaining vegeta-tion and, through plant succession, make bet-ter plant communities. The value of pits inwater retention depends on their density, size,depth and soil permeability. The pit effective-ly serves as a basin to collect water and allowsoil penetration.

Pitting is best suited to medium texturedsoils with less than 8 percent slope. Its valueis limited on sandy, rocky or brush coveredsoils.

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RippingRipping on rangeland is synonymous withchiseling or subsoiling on farmland. It is doneto fracture compacted soil layers to allowwater and root penetration. Implements usedinclude chisel-type plows capable of penetrat-ing to depths below soil hardpans to 36-inchdepths. However, 12 inches or less is the mostcommon depth of ripping on rangeland. Be-cause of the soil disturbance and furrowingeffect, ripping increases soil water penetrationand can dramatically increase forage produc-tion.

Ripping can reduce surface runoff dramatical-ly. It is applicable on medium to fine tex-tured soils with compacted soil layers.Ripping should be done on the contour, andunder dry soil conditions. Forage yieldincreases of 100 to 300 percent have beenobtained from chiseling or aerating coastalbermudagrass, kleingrass and buffelgrass insouth Texas (Fig. 13).

Water Harvesting Practices

MicrocatchmentsCollecting runoff water by creating smallbasins or microcatchments is practiced in aridand semi-arid regions throughout the world.

The goal of microcatchments is to catch waterand allow its storage in the soil rather thanrunoff. The water stored can be used for plantgrowth or ground water recharge. The basinsconcentrate water in a small area and provideextra water for plant establishment. Onceplants are established, the catchment contin-ues to collect water and nutrients for plantgrowth. The water that can be stored dependsupon the size of the microcatchment and ulti-mately the effective depth of the soil profile(Fig. 14).

Microcatchments have been used successfullyto establish saltbush and enhance establish-ment of herbaceous vegetation in the TransPecos region of Texas.

They are applicable in semi-arid regions onmedium to fine textbook soils and on slopesof less than 5 percent.

Water SpreadingWater spreading was developedin arid regions receiving limitedrainfall that falls during short,intense storms resulting in runoff.Water spreading is a simple irriga-tion method whereby floodwaters are diverted from theirnatural course and spread overadjacent flood plains. Ditches,dikes, small dams, rock, brushand wire fences are used to divertflood flows and spread the waterover the flood plain to allow infil-tration (Fig. 15a and 15b). Thewater that penetrates is then avail-able for plant growth or deep per-colation.

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See “Renovation Practices to ImproveRainfall Effectiveness on Rangeland andPastures” (L-5077) for more information.

Figure 14. Schematic of a microcatchment. Microcatch-ments consist of a catchment area and an infiltrationbasin.

Figure 13. Chiseling or aerating coastal bermudagrass, kleingrass and buffel-grass may increase forage yield by 100 to 300 percent.

Water spreading is applicable whereephemeral streams are dry most of the timebut flooding occurs during the growing sea-son following heavy rains or snow melt. Ithas been applied effectively in semi-aridregions such as the Trans Pecos region ofTexas.

Summary

The earth’s water cycle is a closed systemwith a finite but indestructible quantity. Thewater budget of a particular ranch, however,is open and depends upon how much precipi-tation is received and how much water leavesthe ranch.

The kind, amount and distribution of vegeta-tion are the major variables affecting wateruse and loss from a range site. Within a par-ticular climate, water loss through transpira-tion is proportional to the leaf area and theavailability of water in the rooting zone.Grasses, especially bunchgrasses, provide themost desirable ground cover because they arethe most water efficient, control erosion verywell, and yield more runoff water off-sitethan shrubs.

Soil water content is greater under herba-ceous cover, especially grasses, than undermixed-brush and herbaceous cover. Wateryield increases resulting from vegetationmanagement ultimately depend uponwhether runoff and deep drainage water losses exceed transpiration losses.

Range management practices can affect bothon-site and off-site water through their effectson vegetation composition and soil character-istics. The amount and quality of increasedwater availability depend on the original veg-etation, soils and climate. Range improve-ment practices such as grazing management,revegetation, brush and weed management,and soil modification techniques directlyaffect the water regime.

Proper stocking should be the first considera-tion in range water management. Any graz-ing management strategy that enhances vege-tative cover improves the water regime bothin the pasture and down stream. Range seed-ing should be considered on severely deplet-ed range and where vegetation modificationpractices call for a change in species. Seedingin conjunction with land surface modification

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Figure 15a. Water spreading should be considered inarid regions with thunderstorm type rainfall. Floodwaters are diverted from the stream channel and spreadacross the flood plain.

Figure 15b. A low wire fence across a wash in the TransPecos spreads water for better infiltration.

techniques will enhance the probability ofsuccess.

Brush control with herbicides reduces tran-spiration losses, adds litter to the soil surfaceand increases water infiltration. Mechanicalbrush control methods enhance the waterregime by creating soil disturbance, reducingtranspiration and increasing infiltration. Boththe on-site and off-site water regimes areenhanced.

Soil modification practices generally bringabout increases in range productivity throughincreased conservation of water andimproved water use efficiency. Practicesapplicable to Texas rangelands include con-tour furrowing, pitting, ripping, microcatch-ments and water spreading. Water harvestingpractices such as microcatchment and waterspreading systems collect runoff water thatwould otherwise be lost.

Additional Readings

Bailey, R. W. and O. L. Copeland, Jr. 1961.Low flow discharges and plant cover rela-tions on two mountain watersheds in Utah.International Association of ScienceHydrology Publication. 51:267-278.

Blackburn, W. H., T. L. Thurow and C. A.Taylor, Jr. 1986. Soil erosion on rangeland.Proceedings of Symposium on Use ofCover, Soils and Weather Data inRangeland Monitoring. Society for RangeManagement, Denver, CO. pp. 31-39.

Branson, F. A., G. F. Gifford, K. G. Renard andR. F. Hadley. 1981. Rangeland Hydrology.Range Science Series No. 1, Society forRange Management, Denver, CO. 340 pp.

Hanselka, C. W., S. D. Livingston and D.Bade. 1994. Renovation Practices to ImproveRainfall Effectiveness on Rangeland andPastures. Texas Agricultural ExtensionService Leaflet L-5077.

McGinty, A., T. L. Thurow and C. A. Taylor, Jr.1991. Improving Rainfall Effectiveness onRangeland. Texas Agricultural ExtensionService Leaflet L-5029.

Welch, T. G., R. W. Knight, D. Caudle, A.Garza and J. M. Sweeten. 1991. Impact ofGrazing Management on Nonpoint SourcePollution. Texas Agricultural ExtensionService Leaflet L-5002.

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