Desert wheatgrass, (Agropyron desertorum (Fisch.) Schulte) an introduced
perennial grass, is widely used to improve the forage resources
in semi-arid regions of the western United States and
Canada. The use of this species is based on trials that have shown
that it provides early forage, is drought tolerant, often produces
greater yields and animal gains, and is able to withstand heavier
use than many native species. The nutritional attributes of this
species are compared to those of certain other grass species in
this paper

Mayland, H.F.

Murray, R.B.

Van Soest, P.J.

Northwest Irrigation & Soils Research Laboratory Publications

Seasonal Changes in Nutritional Quality of Agropyron desertorum Compared with Six Other Semiarid Grasses

USDA - ARS - NWISRL

Edited by:J. R. GoodinDavid K. NorthingtonARID LAND PLANT RESOURCESProceedings of the International Arid Lands Conferenceon Plant Resources, Texas Tech UniversityEditorsJ. R. GoodinDavid K. NorthingtonSponsored byCommittee on Deserts and Arid Zone Research, Southwestern and Rocky MountainDivision, American Association for the Advancement of Science (CODAZR)International Center for Arid and Semi-Arid Land Studies (ICASALS), Texas TechUniversityAgency for International Development, United States Department of StateUnited States Forest ServiceNational Science FoundationOrganizing CommitteeJ. R. Goodin, Texas Tech University (Co-Chairman)D. K. Northington, Texas Tech University (Co-Chairman)J. Rzedowski, National School of Biological Sciences, MexicoM. Kassas, University of Cairo, EgyptM. P. Petrov, Leningrad State University, RussiaF. Nicknam, Bureau of Soil Conservation and Watershed Management, Iran0. B. Williams, Division of Land Resources Management, CSIRO, AustraliaE. S. Ayensu, Office of Biological Conservation, Smithsonian InstitutionManuscript EditorPrabhu PonkshePublished byInternational Center for Arid and Semi-Arid Land StudiesTexas Tech UniversityLubbock, Texas 79409, U.S.A.July 1979Seasonal Changes in Nutritional Quality of Agropyron desertoruMCoMpared with Six Other Semi-Arid GrassesR. B. MURRAYU.S. Sheep Experiment Station,Dubois, Idaho 83423H. F. MAYLANDUSDA, SEA-AR, Snake River Conservation Research Center,Kimberly, Idaho 83341andP. J. VAN SOESTAnimal SCiente DepartmentCornell UniversityIthaca, New York 14850Desert wheatgrass, (Agropyron desertorum (Fisch.) Schulte) an in-troduced perennial grass, is Widely used to improve the forage re-sources in semi-arid regions of the western United Statea andCanada. The use of this species is based on trials that have shownthat it provides early forage, is drought tolerant, often producesgreater yields and animal gains, and is able to withstand heavieruse than many native species. The nutritional attributes of thisspecies are compared to those of certain other grass species inthis paper.In southern Idaho, where this study was conducted, the nativesagebrush-grass range was converted to a nearly pure stand ofcheatgrass (Bromus tectorum L.) by repeated burning and heavygrazing. Desert wheatgrass was planted in the fall of 1959 on aportion of this cheatgrass range following a wildfire that summer.This afforded us an opportunity to compare the nutritional qualityof desert wheatgrass with an introduced annual and five nativeperennial grasses on a common site.Our objectives were to compare the trends (over the April - Novembergrazing season) in nutrient content and digestibility for seven539species {desert wheatgrass, streambank wheatgrass (Agropyron riparium Scribn. & Smith.), cheatgrass, Great Basin wildrye(Elymus cinereus Scribn. & Merr.), Sandberg's bluegrass (Poasandbergii Vasey), bottlebrush squirreltail (Sitanion hystrix (Nutt.) Smith), and needle-and-thread grass (Stipa comata Trin. &Rupr.)}, and to develop equations which describe these trends andenable prediction of dates of probable mineral deficiencies.The above species were selected for comparison because they are theprincipal grass species found in the study area. Their abundanceon the range, except for desert wheatgrass, is dependent upon thedegree of grazing abuse.Experimental AreaAll data were collected at the Saylor Creek Experimental Range lo-cated 15 km southwest of Glenns Ferry, Idaho. The range lies atan elevation of 957 m. This area is characterized by winter andspring precipitation periods and dry or low rainfall during thesummer and fall. It receives less than 10% of annual precipitationduring July, August, and September. Annual precipitation variesfrom 125 mm to 480 mm and averages 240 mm based on long-term re-cords from Glenns Ferry. Winter temperatures may reach -32°C andsummer temperatures frequently exceed 39°C.Remnants of the original vegetation still present on some of theexperimental range indicate that the former vegetation for thearea was a Wyoming big sagebrush-needlegrass (Artemisia tridentata spp. wyomingensis-Stipa thurberiana) type. On sandier soils,needle-and-thread grass probably replaced Thurber's needlegrass inthe climax. Natural invasion of cheatgrass, fire, and subsequentheavy grazing of native species have altered the type drastically,leaving a range dominated by cheatgrass-bluegrass with varyingamounts of other species.Soils of the experimental range were developed on gently undulatingtopography from Black Mesa gravels and aeolian sources (Malde andPowers, 1962). These soils are considered to be in the Minidokasilt loam series, a member of the course silty, mixed, mesic XerollicDurorthid family and are calcareous throughout the profile.ProceduresPlant material for forage quality characterization was harvestedperiodically at a 2 cm stubble height from random clones in thesame nongrazed pasture between mid March and November during the1962 through 1968 period. Plant material was oven dried 24 to 48hours at 70°C and ground to pass a 40-mesh screen. Forage mois-ture content was determined on some samples.540Total nitrogen (N), with the salicylic acid modification for N-Nand N-0 linkages, was determined by semi-microKjeldahl procedures.Nitric-perchloric acid (3:1) digestion of forage samples preceededanalysis for phosphorus (P), sulfur (S), calcium (Ca), magnesium(Mg), potassium (K), sodium (Na), zinc (Zn), manganese (mn), copper(Cu), and iron (Fe). Phosphorus was estimated colorimetricallyfollowing the ammonium molybdate-ammonium metavanadate procedure.Sulfur content was determined by the modification of the turbidi-metric procedure. All other elements were estimated by atomicabsorption spectrophotometry.Forage samples were also analyzed for neutral detergent fiber (NDF),and true dry matter digestibility (TDDM) following the proceduresspecified by Goering and Van Soest (1970). Rumen fluid inoculumwas obtained from a donor cow maintained on a timothy grass (Phleum pratense L.) hay diet.Linear and curvilinear regression techniques were used to summarizeforage water, forage mineral concentrations, and forage qualitydata. All forage mineral and nutritive data were fit to eachof the following curve forms: a + bx, axb , a + b/x, aebx , x/ (a+bx),1/(a+bx) and a + bx + cx 2 , where x = Julian date. The curve formselected was the one yielding the largest sum of the r 2 values forthe seven species tested. Data are presented to illustrate theprobable dates of mineral deficiency for the seven species. Morespecific data are given in Murray et al. (1978).Results and DiscussionForage moisture, certain mineral components, and certain ratiosexhibited trends with advancing plant maturity. Forage moisture,N, P, S, K, Zn, Cu, N:S, and K/(Ca+Mg) declined. The Ca-P ratioincreased, even though Ca contents were not related to foragematurity.In most species Ca, Mg, Na, Mn, and Fe contents were not relatedto date of maturity. Iron concentration of the field collectedplant tissue was much higher than can be attributed to ironabsorption, and high levels are attributed to dust contamination.Forage Moisture Cattle grazing cheatgrass and desert wheatgrass pastures earlyin the spring generally gain less than in the late spring. Thedifference in gains may be attributed to the relatively highforage moisture content that restricts the animal's ability toingest sufficient dry matter. Table 1 shows that five of theseven species had moisture contents in excess of 200% (33% drymatter) on April 15. Basin wildrye maintained a relatively highmoisture content through July 15, whereas cheatgrass was completelydry by that date. Desert wheatgrass, in contrast, had a highmoisture content early in the season, but dried slowly and reached83% (55% dry matter) on July 15.541Table 1. Predicted forage moisture contents on a dry weight basisfor the seven grass species. Species were collected onperiodic dates for five years of a seven year period.Prediction	 DateSpecies 4/15 5/15	 6/15 7/15Per cent 	Desert wheatgrass 220 175	 128 83Streambank wheatgrass 187 150	 112 75Cheatgrass 296 190	 81 0Basin wildrye 298 234	 168 104Sandberg's.bluegrass 168 117	 64 13Bottlebrush squirreltail 238 176	 113 51Needle-and-thread grass 154 122	 90 58In one out of four years, adequate precipitation and moderatetemperatures permit regrowth of perennial grasses and germinationof cheatgrass in the fall. When this occurs, forage moisturecontents and mineral contents increase to levels similar to thosefound in the spring.Nitrogen In all species, the total N content exceeded 3% (18.8% protein)in April, then declined exponentially to less than 1% (6.2% pro-tein) by the end of the grazing season. According to NAS-NRC(1976), lactating cows require 1.47% N (9.2% protein) in theforage.Nitrogen levels in desert wheatgrass fell below the maintenancelevel by early July; streambank wheatgrass reached that levelin late July (Table 2). All species provided insufficient pio-tein by August, indicating that protein supplements might beused to advantage after that date on desert wheatgrass pasturesor on native rangelands.Fig. 1 shows the trend of N content in desert wheatgrass andillustrates the variability in N content over time.542Phosphorus The pattern of declining phosphorus levels in plant tissue wassimilar to that of N, but P levels were lower by a factor of 10.Cows with calves require forage containing 0.28% P (NAS-NRC, 1976).In most species and years the P level was below that recommendedbefore the end of June. Table 2 shows the predicted dates when Pwould be expected to reach 0.28%, indicating that P levels reachthe maintenance level before the first of May in all species.Calcium and Ca:P Ratio A better measure of the P requirement is the Ca:P (%/%) ratio.The ratios should be 2:1 under normal circumstances, but can be aswide as 7:1 when sufficient vitamin D is present (NAS-NRC, 1976).Calcium concentrations were extremely erratic with time, but theCa:P ratios tended to be less erratic and increased with plantmaturity. Generally, the Ca:P ratio of 7:1 was exceeded by mid-August in all species, except for cheatgrass and desert wheatgrass(Table 2). The latter two species maintained satisfactory levels'throughout the grazing season. Trends are shown for desert wheat-grass and needle-and-thread grass in Fig. 2.Yearling cattle given added P did not show an increase in weight(Olsen, 1971), but P supplements may be helpful for lactatingcows grazing on native ranges.Surfur and N:S Ratio Sulfur contents varied from 0.25% to 0.05%, declining most rapidlybetween April and June. NAS-NRC (1976) requirements are listedas 0.1% in the forage. Table 2 shows that dates of probable Sdeficiencies may occur as early as late May in cheatgrass. TheS levels may remain above the minimum level through Septemberin needle-and-thread grass. The trend of S in desert wheatgrassis compared to that of annual cheatgrass in Fig. 3.Allaway (1969) believed that the S requirement for ruminant animalswas best expressed as the ratio of N:S in forage, with the optimumrange between 10:1 and 15:1. When the ratio is wider or narrowerthan 10 - 15:1 the animal may have a reduced protein conversionefficiency. The data indicate that for some species (desertwheatgrass, needle-and-thread grass, and bottlebrush squirreltail)the N:S ratios are narrower than those presumed to be adequatebefore the end of the grazing season. The trends are shown - forN:S ratios in desert wheatgrass and cheatgrass (Fig. 4).Potassium The K concentration in early spring varied considerably amongspecies.Table 2. Probable date when forage mineral content or ratio falls out of range of the require-ment for lactating cows (based on prediction equations and NAS-NRC (1976) requirementlevels). Desert wheatgrass (Agde), Streambank wheatgrass (Agri), Cheatgrass (Brte),Great Basin wildrye (Elci), Sandberg's bluegrass (Posa), bottlebrdsh squirreltail(Sihy), and needle-and-thread grass (Stco).Mineral RequirementSPECIESAgde Agri Brte ElciDate 	Posa Sihy StcoN 1.47 % Jun 08 Jul 25 May 31 May 27 June 03 Jun 15 Jun 09P 0.28 % Apr 12 Mar 25 Apr 28 Apr 26 Apr 04 Apr 10 Mar 26S 0.10 % Jul 04 Jul 12 May 25 Jun 21 Jun 13 Jul 17 Sep 29K 0.60 % Oct 05 All yr Jul 20 Aug 13 Jul 04 Sep 12 Oct 05Zn 20 ppm Mar 30 Mar 23 Apr 20 May 02 Mar 09 Apr 03 Apr 20CA:P > 7:1 Never > 7:1 Aug 01 Oct 27 Aug 16 Jul 27 Aug 07 Aug 06N:S >15:1 Jun 02 May 19 May 28 Jun 16 1/ May 23 Mar 30N:S <10:1 Jul 19 Aug 24 Sep 21 Sep 15 1/ Jul 25 Jun 18TDDM <65%2/ Aug 21 Sep 03 Nov 29 Aug 02 Nov 17 Aug 02 Sep 131/Correlation of N:S with Julian date was not significant.2/This is equivalent to 50-52% TDN. Fifty-two % TDN is required by lactating beef cows.544AGROPYRON DESERTORUMTOTAL N, % a —1.34 +440/XR SQR n 0.90••• •O JANIMAR	 MAY	 JUL	 SEP	 NOVFigure 1. Nitrogen content of desert wheatgrass.— AGDE- BRTEa.U0 JAN	 MAR	 MAY	 JUL	 SEP	 NOVFigure 2. Trends in the Ca:P ratios of desert wheatgrass andcheatgrass.430z-Jg 201—1AGDE--- BRIEU)zMAR	 MAY	 JUL	 SEP	 NOVTrends in N:S ratios of desert wheatgrass andcheatgrass.5450.2AGDE- BRIE0ui0.I%ow0 JAN	 MARFigure 3. Trends in sulfur contents of desert wheatgrass andcheatgrass. IMAY     JUL SEP NOV546Basin wildrye had values in excess of 4%, whereas needle-and-threadgrass contained less than 2% K. The decrease in the K level wasrapid and by late July, most species had values of less than 1 percent.Table 2 compares the dates when the K level would be expected toreach the 0.6% requirement level. With the exception of Sandberg'sbluegrass and cheatgrass, most species contained adequate K throughmost of the grazing season.Magnesium & K/(Ca+Mg) Ratio Levels of magnesium in plant tissue varied between 0.1 and 0.2%and most samples were below the NAS-NRC (1976) requirement of0.18% for lactating cows. Trends were erratic in all species exceptcheatgrass which showed an exponential decrease in Mg content withplant maturity.When the ratio of K/(Ca+Mg) on an equivalent basis is wide and Mgis less than 0.2%, grass tetany may become a problem (Allaway,1969). There are few incidences of tetany when the ratio is lessthan 2.2:1 according to Kemp and 't Hart (1957).Both desert wheatgrass and basin wildrye have ratios of K/(Ca+Mg)wider than 2.2:1 during the early spring. Grass tetany problemshave been experienced when cattle graze desert wheatgrass pasturesin the spring, but few problems have arisen on cheatgrass or nativerange.Other Minerals Sodium, Mn and Fe concentrations in forage were erratic with res-pect to maturity, but were above the recommended levels (500 ppmNa, 20 ppm Mn, and 80 ppm Fe) in most samples.Copper exhibited downward trends in all species except cheatgrassand streambank wheatgrass. Nearly all samples contained greaterthan the recommended 4 ppm (NAS-NRC, 1976) forage tissue levels.When molybdenum (Mo) is in excess of 6 ppm in the tissue, the Curequirement is increased two to three times. However, a fewsamples analyzed for Mo were found to contain less than 3 ppm;therefore, it is not likely to be a problem with these speciesat this location.NAS-NRC (1976) suggests that forage Zn be at least 20 ppm to beadequate. Only in the very early spring (Table 2) were Zn valuesin excess of 20 ppm, and by May all species were below that level.Supplementing Zn on cheatgrass range results in increased calfgains (Mayland, 1975 unpublished). The trend in Zn concentrationbetween desert wheatgrass and cheatgrass is compared in Fig. 5.Digestibility Components The methods of Van Soest (1966) lead to a measure of digestibledry matter.32M 24a. -a.N1640AGDE– BRTEnn547JAN	 MAR	 MAY	 JUL	 SEP	 NOVFigure 5. Trends in Zn contents of desert wheatgrass andcheatgrass.We present data for neutral detergent fiber (NDF) and total di-gestible dry matter (TDDM). 	 The NDF is a measure of total fibercontent, whereas TDDM is a measure of the digestible cell wallcontents and digestible lignified cell wall corrected for silicacontent.The NDF % in all species increased with plant maturity. The rateof increase among species is similar, and by mid-June reachesapproximately 60 percent. However, Great Basin wildrye reachesthis level 15 days earlier, whereas desert wheatgrass does notreach the 60% level until early July.	 This indicates that forthis fraction, desert wheatgrass maintains its quality for alonger period than do other species. On the other hand, TDDMdecreases linearly with plant maturity and by September is gen-erally less than 65 percent. 	 This is equivalent to about 50-52%TDN (total digestible nutrients.)The levels of NDF and TDDM probably differ among species becauseof changes in the proportion of heads and stems compared toleaves.	 For example, cheatgrass and Sandberg's bluegrass areboth fine leaved and stemmed compared to the other species which0548could account for the fact that they maintained higher TDDM levelsthroughout the grazing season (Table 2).Conclusions and RecommendationsPlants growing in regions receiving winter and spring precipitation,but having dry summers, cure as soil moisture content declines inthe summer. Under these conditions, the nutritive quality of de-sert wheatgrass and other native species declines as the seasonprogresses. In the Northern Great Plains where summer moistureis prevalent, desert wheatgrass provides more nutritious forageduring the summer grazing season.Desert wheatgrass in many areas of southern Idaho provides theonly forage for livestock. In such situations, desert wheatgrasswas generally planted to displace cheatgrass. The latter speciesinvades burned and abused ranges. The yield of cheatgrass fluctuateswidely from year-to-year depending on available moisture, is afire hazard, and reaches maturity earlier than desert wheatgrass.Desert wheatgrass is more dependable in that its yields fluctuateless widely than cheatgrass.In this study the nutritional quality of desert wheatgrassparalleled that of cheatgrass and the native perennial grasses.For most species, mineral contents were below the requirementfor lactating cows before the end of the grazing season. Thedata suggest that mineral supplements should be a part of thegrazing management program on desert wheatgrass pastures and onnative ranges in this climate to maximize animal performance.Literature CitedAllaway, W.H. 1969. Trends in the mineral composition of feeds.Proc. Cornell Nutr. Conf. for Feed Manuf., Oct. 21-23 Buffalo,N.Y. p. 12-16.Goering, H.K., and P.J. Van Soest. 1970. Forage fiber analyses(apparatus, reagents, procedures, and some applications).U.S. Dept. Agric. Agric. Handb. 379, 20 p.Kemp, A., and M.L. 't Hart. 1957. Grass tetany in grazing milkingcows. Neth. J. Agric. Sci. 5: 4-17.Malde, H.E., and H.A. Powers. 1962. Upper cenozoic stratigraphyof western Snake River Plains, Idaho. Geol. Soc. Am. Bull.73: 1197-1220.549Mayland, H.F. 1975. Personal communication.Murray, R.B., H.F. Mayland, and P.J. Van Soest. 1978. Growth andnutritional value to cattle of grasses on cheatgrass range insouthern Idaho. USDA Forest Service Res. Paper INT-199, Feb. 1978.National Academy of Science-National Research Council. 1976.Nutrient requirements of beef cattle. No. 4. 5th rev. ed. Nat.Acad. Sci.Olsen, T.E. 1971. Utilization and supplementation of cheatgrassin southern Idaho. M.S. Thesis, Univ. Idaho. 52 p.Van Soest, P.J. 1966. Non-nutritive residues: a system ofanalysis for the replacement of crude fiber. J. Assoc. Offic.Agric. Chem. 49: 546-551.

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Seasonal Changes in Nutritional Quality of Agropyron desertorum Compared with Six Other Semiarid Grasses

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