2013. Plant Management Network. This article is in the public domain.Accepted for publication 5 September 2012. Published 21 January 2013.

Alfalfa and Forage Kochia Improve Nutritive Value of Semiarid Rangelands

Michael D. Peel, Blair L. Waldron, Kevin B. Jensen, and Joseph G. Robins, USDA-ARS, Forage and Range Research Laboratory, 695 N. 1100 E., Logan, UT 84322-6300

Corresponding author: Michael D. Peel. Mike.Peel@ars.usda.gov

Peel, M. D., Waldron, B. L., Jensen, K. B., and Robins, J. G. 2013. Alfalfa and forage kochia improve nutritive value of semiarid rangelands. Online. Forage and Grazinglands doi:10.1094/FG-2013-121-01-RS.

AbstractObtaining quality forage on semiarid rangeland is challenging. This study compared mid-summer crude protein (CP) and neutral detergent fiber (NDF) of ‘Vavilov’ Siberian wheatgrass (Agropyron fragile), ‘Mustang’ Altai wildrye (Leymus angustus), two alfalfas (Medicago sativa), and two forage kochias (Kochia prostrata) in monocultures and binary mixtures at plant densities on 0.25, 0.50, 0.75, and 1.00-m centers. Crude protein of alfalfa averaged 8.7%, forage kochia 9.6%, Vavilov 4.3%, and Mustang 7.9%. The CP of individual species components within mixtures was similar to their respective monoculture. The CP of forage kochia in both mixtures and monocultures increased 2.1% with increased plant spacing. The CP concentration of the total alfalfa-grass mixtures averaged 1.2% higher than grass monocultures and 2.5% higher for the forage kochia-grass mixtures. Forage kochia, alfalfa, and grass NDF concentration averaged 45, 50, and 63%, respectively. The NDF of individual species components was similar regardless of monoculture or mixture and plant density. However, NDF concentration of the total mixture decreased with increasing plant spacing in mixtures that included Vavilov. Under semiarid conditions, CP and NDF concentration of the material tested is influenced more by species composition and less by differences in plant density, or neighboring plants.

IntroductionOf the 336 million ha of grazinglands in the United States, 161 million ha is

in rangelands, much of it concentrated in the semiarid western states (7,11). According to Spaeth et al. (16), two thirds of US rangelands could benefit from improved management to improve forage production. The use of commercial nitrogen fertilizer will increase productivity particularly of grass monocultures; however, use of commercial fertilizers is not economically viable on the vast grazinglands of western US rangelands. Even so, productivity and forage nutritive value are improved with the utilization of the appropriate plant materials.

Improved yield and quality of grazinglands has been demonstrated in multiple studies (13,14,15,18,19,20). Many of these have focused on improvement through utilization of legumes and demonstrate that grass-legume mixtures usually have greater yield and have superior forage nutritive value than grass monocultures (14,15). Legumes, particularly alfalfa, are used as forage for livestock due to high protein content from fixed atmospheric nitrogen. Some of the fixed nitrogen from the legume is cycled into the soil pool and is available to surrounding plants (8). These studies, where water is often not a limiting factor, typically report harvesting forage on a schedule that optimizes forage nutritive value. Similar reports are available for alfalfa on grazinglands where both the forage yield and forage nutritive value are measured on alfalfa harvested at 10 to 40% bloom (9,15), whereas much of the semiarid rangelands of the western US are grazed late when most forages are past their prime for nutritive value.

Rangelands of the semiarid regions of the western US experience temperature extremes, drought, and fire which all restrict the plant species that can be grown with any chance of success. In addition, they are often not grazed

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until mid summer, fall, or winter when forage nutritive value is diminished. When utilized during this time, forage from the drought tolerant grasses often does not meet minimum crude protein (CP) requirements for ruminant livestock (>7%) (5,10,18). Requirements can be met through supplementation, but meeting requirements through species management is likely more cost effective. Waldron et al. (18,19) report that forage kochia is one such species that maintains CP and will meet or exceed the minimum requirements during the late season.

Recently it was shown that plant density has an impact on productivity of mixed plantings on dry rangelands, in particular alfalfa and forage kochia (13). Under drought stress conditions, growth is limited by available moisture and competition for resources. It is reasonable to suppose that such competition by neighboring plants for resources will impact forage nutritive value. This study was designed to compare mid-summer forage nutritive value parameters of CP and neutral detergent fiber (NDF) of two cool-season grasses (Siberian wheatgrass and Altai wildrye) in monocultures and in binary mixtures with two alfalfa sub-species and two forage kochia sub-species at four plant spacings.

Research Design and Study SitePlant materials included in the study were: ‘Mustang’ Altai wildrye (AW) (6)

a tall statured grass; ‘Vavilov’ Siberian wheatgrass (SWG) (2) a more drought-tolerant, but shorter grass; ‘Don’ falcata type alfalfa (ALF) (12); BB04B, an experimental, rhizomatous, sativa type alfalfa; ‘Immigrant’ forage kochia (FK), a virescens subspecies (17); and S-Select, an experimental forage kochia, grisea subspecies type that has a larger stature than the standard Immigrant FK. All plants were started in a greenhouse in Ray Leach Cone-tainers (Stewe and Sons, Corvallis, OR) and transplanted to the field in May of 2004 to the Nephi Experimental Farm, near Nephi, UT. Each plot consisted of 30 plants arranged in five rows of six plants each. Each species was planted in a monoculture and in a binary mixture with each other species. All monocultures and mixtures were established at four plant spacings. The spacings consisted of 0.25, 0.50, 0.75, and 1.00 m between each plant within their respective plot. In plots containing mixtures, the two species components were arranged as alternating plants within a row and in alternating rows arranged such that the same species was never adjacent to itself. As is typical with rangeland plantings in the region, no fertilizer was applied. The experimental design was a randomized complete block with four replications in a split plot arrangement, where the whole plot was plant spacing and the sub-plot was the species component.

Forage harvests were completed on 6 August 2005 and 30 July 2006. At harvest, the alfalfa and grass both had mature seed while the forage kochia was flowering. To eliminate border effects, outside rows of each plot were not harvested. All plants were harvested by hand with a cutting height of 8 cm, and within mixtures, each species was harvested separately to determine the CP (nitrogen content of the forage × 6.25) and NDF of each as an independent component of the total mixture. Comparison of percent CP and NDF concentration for the mixtures was determined using a weighted average based on yield data previously published (13). Following harvest, forage samples were dried to a constant weight at 60°C, ground to pass through a 1-mm screen and scanned with a Foss Model 6500 near infrared reflectance spectroscopy instrument (Eden Prairie, MN). System software was used to select samples to calibrate existing equations for each species. Validations of the equations were determined from a different subset of samples for CP and NDF. The r2 values from the validations for CP and NDF were 0.92 and 0.81 for alfalfa, 0.98 and 0.97 for the grasses, and 0.92 and 0.73 for the forage kochia, respectively. Samples used for calibration were analyzed for nitrogen using a LECO CHN-2000 Series Elemental Analyzer (LECO Corp, St. Joseph, MI). NDF was determined following the methods of Goering and Van Soest (4) as modified for use in ANKOM fiber analyzer procedures (ANKOM Technology Corporation, Macedon, NY) (1). All data were subject to analysis of variance using SAS (SAS

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Institute Inc., Cary, NC). Fisher’s protected LSD (P ≤ 0.05) was used for mean separation.

The study site (39°38’31"N, 111°52’34"W, elevation 1594 m) located near Nephi, UT, has an average annual precipitation of 32.8 cm (1903-2006). July is the driest month of the year receiving 1.8 cm of rain annually and March and April are the wettest months receiving about 3.9 cm of rain annually. July is the hottest month with average daily high and low temperatures of 33.8° and 14.4°C, respectively. Average frost free days (0°C) are 120. Soil at the site is a Nephi silt loam (fine-silty, mixed, mesic Calcic Argixerolls).

Species and Mixtures EffectCrude protein of the alfalfa and forage kochia was within 0.4% of each other

when grown in monocultures (Table 1). In comparison, CP of Mustang AW was less than Immigrant FK and the alfalfas, but no different than S-Select FK; however, Vavilov SWG CP averaged 3.6 percentage points less than Mustang AW and less than half that of either the alfalfa or forage kochia. This was consistent regardless of whether it was in a mixture or in a monoculture. The CP of each species component remained much the same regardless of whether they were grown in a monoculture or in a mixture (Table 1). However, two exceptions occurred. First, CP of BB04B ALF was higher when grown in a mix with Vavilov SWG than in mixtures with the other species. Second, Immigrant FK averaged one percentage point higher CP when grown in mixtures as compared to the monoculture. Furthermore, Immigrant FK averaged nearly 1% higher CP (P = 0.057, data not shown) than S-Select FK across all mixtures. It has been shown previously that S-Select FK has much higher yield than Immigrant FK (13) suggesting that S-Select FK is putting more energy into biomass production. Even so, the CP of S-Select FK is more than sufficient to meet the nutritional requirements for ruminant livestock (10).

Table 1. Crude protein (CP) concentration of Don falcata-type alfalfa, BB04B sativa-type alfalfa, Vavilov Siberian wheatgrass, Mustang Altai wildrye, Immigrant virescens-type forage kochia, and S-Select grisea-type forage kochia when grown in monocultures and in binary mixtures with each other.

In reports comparing nutritive value of mixtures with monocultures, the CP of the grass-legume mix is generally accepted as being greater than that of grass alone (9,15). However, previous work has not separated the components of the mixtures and measured the nutritive value separately, and furthermore, their harvests were made to optimize forage nutritive value whereas this study was harvested to coincide with mid-summer grazing. In this study, the fact that no differences in CP of the grasses were observed between monocultures and mixtures, particularly with alfalfa, suggests the increased CP in a grass-legume mixture is reflective of the legume component and not necessarily any change in CP of the grass.

Don BB04B Immigrant S-Select Vavilov MustangLSD

(0.05)

Percent CP

Monoculture 8.9 8.9 9.2 8.8 4.4 8.1 0.7

Don mix. − − 10.4 8.8 4.7 8.3 0.8

BB04 mix. − − 10.2 9.6 4.4 8.1 0.8

Immigrant mix. 8.6 8.4 − − 4.1 6.9 0.7

S-Select mix. 8.6 8.7 − − 4.1 8.0 0.7

Mustang mix. 8.6 8.2 10.1 9.3 − − 0.8

Vavilov mix. 8.6 9.3 10.1 9.5 − − 0.7

LSD (0.05) ns 0.47 0.88 ns ns ns −

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The large differences in CP between the two grasses indicate that the grass component of any rangeland planting can play a major role in the quality of forage. Waldron et al. (19) report CP of crested wheatgrass at 5% and lower during a winter grazing study, which is below the 7% CP required to maintain beef cattle, but when combined with forage kochia at 9% CP, the animal requirements were met. The Siberian wheatgrass used in this study similarly would not meet the minimum requirements of beef cattle, but either the alfalfa or forage kochia would compensate. Furthermore, some grass species may meet the nutrient requirements of ruminant livestock, such as the Altai wildrye shown in this study to have higher CP than the Siberian crested wheatgrass. In a previous study, CP levels in Mustang AW harvested in November ranged from 2.4 to 3.5%, indicating that in this species CP may decline from August to November (5).

Crude protein of the combined mixtures differed in large measure with respect to Vavilov SWG (Table 2). The ALF-Mustang AW mixtures averaged 2.1% more CP than the ALF-Vavilov SWG mixtures. In the same comparison of FK-grass mixtures the difference was less at 1.2%. A comparison of the ALF-grass with the FK-grass mixtures reveals that the latter averaged 1.2% greater CP concentration. While these differences seem small they can have overall significant impact, particularly when considered in the context of any increase in forage production realized from the mixtures as previously reported (14).

Table 2. Crude protein (CP) concentration of two alfalfas, two cool-season grasses and two forage kochias in monocultures and binary mixtures at four plant spacings when grown under semi-arid conditions in 2006 and 2007.

Differences (P < 0.001) were present among the species for NDF concentration. In the monocultures, forage kochia NDF averaged 46% followed by alfalfa at 50% and the grasses at just over 62% (Table 3). Generally, the NDF of each individual species component was no different when grown in a monoculture or mixture (Table 3). The exception was Vavilov SWG which had slightly higher NDF in the mixture with BB04B ALF, but was no different in the other mixtures as compared to the monoculture. Overall, Immigrant FK had lower (more favorable) NDF than Don ALF and both grasses. While the CP of

Entry/mixture

Spacing between plants (m)

meanLSD

(0.05)0.25 0.50 0.75 1.00

Percent CP

Don Alf 9.1 8.5 9.0 8.8 8.9 ns

BB04B Alf 9.2 8.8 8.8 8.8 8.9 ns

Immigrant FK 8.3 8.8 9.4 10.1 9.2 1.2

S-Select FK 8.1 8.3 9.3 9.5 8.8 1.9

Mustang AWR 8.7 7.4 8.2 8.1 8.1 ns

Vavilov SWG 5.1 4.1 3.6 4.6 4.4 ns

Don-Mustang 9.1 8.3 8.1 8.6 8.5 ns

Don-Vavilov 5.2 5.6 6.0 7.2 6.0 1.0

BB04B-Mustang 8.6 8.8 8.2 8.6 8.5 ns

BB04B-Vavilov 5.5 6.7 6.9 8.0 6.8 0.7

Immig.-Mustang 8.5 9.7 9.3 10.2 9.4 1.7

Immig.-Vavilov 6.8 7.3 9.0 9.4 8.1 0.9

S-Select-Mustang 9.3 8.8 8.8 9.5 9.1 ns

S-Select-Vavilov 7.1 7.7 8.6 9.0 8.1 1.6

LSD(0.05) 0.7 0.6 0.5 0.4 0.2 −

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Mustang AW was better than Vavilov SWG, NDF of the two did not differ in either monocultures or mixtures, and the NDF of both grasses was much higher (less favorable) than that of the alfalfa and forage kochia. Furthermore, when the grasses were grown with either the alfalfa or the forage kochia, the actual NDF concentration of the grass component did not change.

Table 3. Neutral detergent fiber (NDF) concentration of Don falcata-type alfalfa, BB04B sativa-type alfalfa, Vavilov Siberian wheatgrass, Mustang Altai wildrye, Immigrant virescens-type forage kochia, and S-Select grisea-type forage kochia when grown in monocultures and in binary mixtures with each other.

The NDF concentration in the total mixtures differed with respect to the alfalfa or forage kochia in the mix, but not the grass (Table 4). The NDF of the forage kochia-grass mixtures were lowest, averaging just less than 50%, with the

Table 4. Neutral detergent fiber concentration of two alfalfas, two cool season grasses, and two forage kochias in monocultures and binary mixtures at four plant spacings when grown under semi-arid conditions in 2006 and 2007.

Don BB04B Immigrant S-Select Vavilov MustangLSD

(0.05)

Percent NDF

Monoculture 51.9 48.5 44.9 47.6 61.4 62.9 3.4

Don mix. − − 43.2 48.8 62.4 63.1 2.3

BB04 mix. − − 43.7 46.5 64.5 64.2 2.8

Immigrant mix. 51.7 49.2 − − 63.4 65.2 2.5

S-Select mix. 52.6 47.5 − − 63.5 62.8 2.2

Mustang mix. 51.8 50.4 42.7 46.6 − − 3.1

Vavilov mix. 51.3 46.6 43.0 46.8 − − 2.3

LSD (0.05) ns ns ns ns 2.11 ns −

Entry/mixture

Spacing between plants (m)

meanLSD

(0.05)0.25 0.50 0.75 1.00

Percent NDF

Don Alf 51.1 53.7 51.6 51.6 51.9 ns

BB04B Alf 48.7 48.6 48.7 47.9 48.5 ns

Immigrant FK 45.8 45.5 45.7 42.6 44.9 ns

S-Select FK 47.9 49.7 45.8 46.6 47.6 ns

Mustang AWR 59.5 66.4 62.7 63.3 62.9 5.4

Vavilov SWG 60.8 64.7 62.1 57.8 61.4 5.0

Don-Mustang 56.9 57.8 58.5 57.6 57.7 ns

Don-Vavilov 60.4 61.2 58.1 55.7 58.9 3.6

BB04B-Mustang 53.4 52.0 54.3 54.0 53.4 ns

BB04B-Vavilov 60.5 56.0 55.8 51.0 55.8 3.4

Immig.-Mustang 46.7 46.0 49.2 47.0 47.2 ns

Immig.-Vavilov 51.7 51.5 48.3 46.0 49.4 2.5

S-Select-Mustang 48.0 49.6 49.2 48.8 48.9 ns

S-Select-Vavilov 54.8 52.0 49.6 48.4 51.2 4.2

LSD(0.05) 2.8 2.7 3.3 3.1 2.6 −

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Mustang-Immigrant mix at 47.2%. The BB04B ALF-grass mixtures did not differ from each other and were the next most favorable. The same was observed for the Don ALF-grass mixtures where they did not differ from each other but averaged 4.5% higher NDF than those with BB04B ALF. The significantly higher NDF of both Vavilov SWG and Mustang AW relative to the other species suggest a likely decrease in dry matter intake and lower utilization compared to any of the mixtures or non-grass monocultures.

Plant Density EffectThe CP of Immigrant and S-Select FK tended to increase with increased

plant spacing (lower plant density), with the exception of S-Select FK grown with Mustang AW (Fig. 1). This trend was the most pronounced for Immigrant FK where the overall CP average ranged from 8.7 to 11.2% CP for the 0.25 to 1.00-m spacing, respectively. In general, S-Select FK showed the same trend for higher CP with increasing plant spacing except in the mixture with Mustang AW. The change in CP for S-Select FK ranged from 8.6 to 10.4% for the 0.25 to 1.00-m spacing, respectively.

The effect of plant spacing on CP within the grasses was variable (Fig. 1). Mustang AW CP in a mixture with S-Select FK decreased from 9.9 to 6.5% for the 0.25 to 1.00-m spacing but did not differ by spacing within the other mixtures or monocultures. Vavilov SWG CP did not differ with spacing in the monoculture or in mixture with Don ALF; however, in the three remaining mixtures, differences in CP were present among the plant spacings (Fig. 1).

The CP concentration of all combined mixtures containing Vavilov SWG increased with decreasing plant spacing (Table 2). This increase averaged 2.2% from the 1.00 to 0.25-m spacing, and the increase was similar for all mixtures. The CP concentration of the Immigrant FK-Mustang AW combined mixture also increased 1.7% for the same comparison. In the remaining combined mixtures containing Mustang AW, the CP did not differ with plant spacing.

The effect of plant spacing on NDF was generally not significant for the forage kochia and alfalfa monocultures (Table 4). The exception was Immigrant FK (P = 0.02) and S-Select FK (P = 0.044) when grown in mixtures with Vavilov SWG, where the NDF of these components of the mixture decreased (improved) with increasing plant spacing. The overall change was from 46 to 39% and from 49 to 43% for Immigrant and S-Select FK, respectively. Vavilov SWG decreased in NDF 10 percentage points from the 0.25 to 1.00 spacing, but this decline was not statistically significant (P = 0.13). No consistent trend was detected for changes in NDF that corresponded to plant spacing for the individual components of mixtures. Interestingly, NDF of the entire mixture among the plant spacings for all mixtures that contained Vavilov SWG declined, with an average decrease of 5.5% from the 0.25 to 1.00-m spacing (Table 4).

SummaryThe data presented here indicate that under semiarid conditions differences

in forage CP and NDF were more reflective of the plant species itself rather than the influence from plant density or the other plant species grown with them. When measured in the mid summer, forage kochia and alfalfa have better nutritional value than the dormant grasses, and forage kochia can have better nutritional value than mature alfalfa. While the alfalfa, forage kochia, and Mustang AW were in the 8 to 10% CP range, Vavilov SWG was consistently around 4% CP. CP of each species remained largely the same whether in a monoculture or mixture, except Immigrant FK which was slightly higher in the mixtures. Generally, plant density had little or no impact on CP of the alfalfas or grasses, but a consistent trend was present for increasing CP with decreasing plant density in the forage kochias. The higher NDF value of the grasses compared to alfalfa and forage kochia, particularly in Vavilov SWG when combined with its low protein demonstrates a deficiency in nutritive value. The tendency for lower NDF in the forage kochia highlights an ability to maintain forage nutritive value later than the other species, particularly when combined with CP, and supports previous observations (19,20,21).

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Fig. 1. Crude protein concentration of Immigrant forage kochia (A), S-Select forage kochia (B), Mustang Altai wildryegrass (C), and Vavilov Siberian wheatgrass (D) in monocultures and binary mixtures at plant spacings of 0.25, 0.50, 0.75 and 1.00 m. Columns within a monoculture or mixture group labeled with different letters are significantly different (P = 0.05) for plant spacing.

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While it has been shown that alfalfa or forage kochia grown in mixtures with grasses typically improve production (9,13), this research suggests that a nutritive advantage will also be realized from their use in a mixture. This is particularly true if consideration is made of the total CP produced per unit area of a grass-monoculture with that produced when forage kochia is present due to the dramatic yield advantage previously demonstrated (13). Furthermore, the nutritive value of the total forage, CP in particular, can be impacted by the choice of grass, since it was shown that Vavilov SWG has significantly lower CP than Mustang AW. The influence of species on the total forage nutritive value has important ramifications for management decisions, particularly when reseeding a rangeland that will be used for fall and winter forage. To meet livestock nutritional requirements, it is advisable to evaluate species choices, both grass and non-grass options. Furthermore, it may be advisable to manage plant densities of forage kochia for higher CP that will compensate for deficiencies in associated grasses, rather than managing for highest yield as previously demonstrated (13).

Acknowledgment and DisclaimerContribution of the USDA-ARS Forage and Range Research Lab. Mention of

a trademark, proprietary product, or vendor does not constitute a guarantee or warranty of the product by the USDA.

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