Report for Forage Web Site, TTU

 

January 24, 2005

 

Optimizing Water Use for three Old World Bluestems in the Texas High Plains

 

Summary

Agriculture in the Texas High Plains is challenged by rapid depletion of ground water.  Warm-season grasses offer opportunities for grazing but information is needed on comparative water use efficiencies (WUE).  Three old world bluestems (Bothriochloa caucasica, ‘Caucasian’; B. ischaemum, ‘Spar’; and B. bladhii, ‘Dahl’) were grown under dryland and low, medium, and high irrigation levels to determine water use efficiency, yield, and nutritive value during 2001 to 2003.  Amount of water applied in the high treatment was 100% replacement of potential evapotranspiration (PET) minus precipitation.  Medium and low treatments were calculated as 66 and 33% of the high treatment; the dryland treatment received no irrigation (0%).  Caucasian had higher WUE than Spar under all water treatments in 2001 and under all irrigation levels in 2003, including Dahl.  Additionally, Caucasian and Dahl consistently outyielded Spar by about 30%.  Maximum yields resulted from a high irrigation level but forage nutritive value was higher under low irrigation.  These data provide information for optimizing water use, nutritive value, and for selecting an optimum between irrigation water invested and total nutrient yield. 

 

Introduction

Water use efficiency (WUE) of forage grasses is crucial in determining species suitable for implementation into forage/livestock systems in semi-arid environments.  Previous researchers have defined WUE as dry matter (DM) yield per ha divided by the amount of water added to achieve that yield.  Other authors have inferred WUE from plant-physiological parameters such as gas exchange and leaf water relations.  Old world bluestem species are widely grown in the semi-arid Texas High Plains but information is lacking concerning their water use – yield relationships under semi-arid conditions when compared at one location.

Previous research has suggested a 10 to 20% higher productivity of Caucasian bluestem compared with B. ischaemum types. The more recently released old world bluestem WW-B. Dahl showed higher DM yields under dryland conditions than a variety of warm-season grasses in central Texas.  With rising concerns regarding sustainability of agricultural systems dominating the Texas High Plains due to a declining supply of irrigation water, introduced warm-season grasses such as Bothriochloa species may offer alternatives for designing viable crop/forage/livestock systems.  A variety of old world bluestem species, primarily B. ischaemum types, were grown widely on Conservation Reserve Program land to minimize soil erosion and degradation.  Previous research showed that Dahl can serve as a key component in functioning crop/forage/livestock systems while reducing water and fertilizer needs.  This species has been shown to support higher animal gains than B. ischaemum types (unpublished data, Texas Tech University).  Also, Caucasian is perhaps more cold tolerant given its origin and could be an alternative for areas further north in the Southern High Plains. 

Declining water reserves in the Ogallala Aquifer require research efforts to find solutions for alternative agricultural systems.  The Southern High Plains of Texas may be environmentally well suited to establish forage-based systems while reducing overall water use.  However, little is known regarding the water use of old world bluestems grown under conditions of the Texas High Plains.  Thus, our objective was to test Caucasian, Spar, and Dahl regarding their WUE, DM yield, and nutritive value. 

 

Objectives

The overall objective was to determine forage growth and nutrient yield per unit of added water (water use efficiency) for three warm-season perennial grasses in Southern High Plains. 

 

Specific objectives included:

To determine the influence of dryland, and low, medium, and high irrigation levels on dry matter (DM) yield, water use efficiency (WUE; kg DM ha-1 mm-1 water), nutritive value, plant morphology including percentage live/dead and leaf/stem ratio of Caucasian, Spar, and Dahl bluestems.

 

Results

Data are shown comprehensively in graphs that follow immediately this report, and findings will be discussed only briefly here. 

Results suggested that WUE of all species, water treatments, and years varied between more than 20 kg DM ha-1 mm-1 and 5 kg DM ha-1 mm-1 as lower level.  Except in year 1 where irrigation treatments started in late June, WUE appeared to be higher under low and medium irrigation than under dryland and high irrigation level.  Moreover, maximum WUE were measured in 2002 with above-average precipitation, and minimum WUE were observed in 2003 that was the second driest year on record.  Differences may have been due to increased evaporation of irrigation water when applied with surface drip irrigation. 

Maximum DM production in 2001 was observed in Caucasian bluestem under a high irrigation level (100% replacement of PET) with 11.7 Mg ha-1, followed by Dahl with 11.3 Mg ha-1, and Spar with 7.9 Mg ha-1 at the same irrigation levels.  Observed yields under dryland conditions averaged 3.2, 2.4, and 1.5 Mg ha-1 for Caucasian, Spar, and Dahl, respectively.  In 2002, maximum DM production was again observed in Caucasian bluestem with 22.3 Mg ha-1, followed by Dahl (21.5 Mg ha-1) and Spar (18.5 Mg ha-1) under the high irrigation.  Dry matter yields obtained from dryland sites were 4.6, 3.0, and 4.2 Mg ha-1 for Caucasian, Spar, and Dahl, respectively.  In the last year of our research, Caucasian averaged 19.8 Mg ha-1 in dry matter yield under a high irrigation level; Spar generated 11.3 Mg ha-1 and Dahl 12.7 Mg ha-1.  Under dryland conditions, Caucasian averaged 4.1 Mg ha-1, while Spar generated 4.0 Mg ha-1, and Dahl averaged 1.7 Mg ha-1. 

Concentration of crude protein was higher in Dahl bluestem compared with the other old world bluestems tested averaged over all irrigation levels and dryland.  Fiber concentrations in investigated species were affected by irrigation levels.  Neutral detergent fiber increased with increasing amounts of irrigation during all three years of research.  Similar observations were made regarding ADF.  Dry matter digestibility was higher under low irrigation compared with all other irrigation levels and dryland.  Total DDM (kg ha-1) was higher under a high irrigation level compared to all other water treatments.  Leaf/stem ratios were affected by water treatments, showing that with increasing irrigation, plant maturity also increased and, thus, leaf/stem ratios decreased.  Live/dead ratios increased with increments in irrigation. 

 

 

Graphs Water use and dry matter production

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Text Box: Precipitation, mm 

 

 

 

 

 

 

 

 

 

 

 

 


 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 1. Precipitation during yr 2001, 2002, and 2003 at site of comparison of three old world bluestems grown with varying water supply. 

 

     

 

 

 

 

 

 

 

 

 

Text Box: Seasonal dry matter production, Mg ha-1
 

 

 


 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 2.  Total seasonal DM yield-evapotranspiration (ET) functions for Bothriochloa caucasica, B. ischaemum, and B. bladhii during yr 2001, 2002, and 2003.  Seasonal dry matter (DM) refers to above-ground DM.  Water use includes precipitation, irrigation, and soil water depletion.  L, Q Denotes linear and quadratic shape of the regressions, respectively.  Functions with the same lowercase letter within one general regression shape are not different (P > 0.05). 

 

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Text Box: WUE, kg ha-1 mm-1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 3. Water use efficiency (WUE) of Bothriochloa caucasica, B. ischaemum, B. bladhii as influenced by dryland and irrigation levels of low, medium, and high during years 2001, 2002, and 2003.  Years 2002 and 2003 were averaged.  Means with same uppercase letter among species within one water treatment and year are not different (P > 0.05).  Likewise, means with the same lowercase letter among water treatments within one species are not different (P > 0.05).  No species differences (P > 0.05) were found in 2002.  †SE = standard error of the mean. 

 

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Text Box: Total seasonal DM yield, Mg ha-1

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Figure 4.  Total seasonal dry matter (DM) yield as influenced by Bothriochloa caucasica, B. ischaemum, and B. bladhii under dryland and irrigation levels of low medium and high during yr 2001, 2002, and 2003.  Species denoted with the same letter within a water treatment are not different (P > 0.05).  †SE = standard error of the mean. 

 

 

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Text Box: Mean monthly forage mass, Mg ha-1 (dry basis)

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Figure 5.  Forage mass of Bothriochloa caucasica, B. ischaemum, and B. bladhii as influenced by dryland and irrigation levels of low, medium, and high during yr 2001, 2002, and 2003.  Data were averaged across months (May-October).  Species denoted with the same letter within a water treatment are not different (P > 0.05).  †SE = standard error of the mean. 

 

 

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Text Box: Forage mass (dry matter), Mg ha-1

 

 

 

 

 

 

 

 

 

 

 

 

 

 


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Figure 6.  Forage mass of Bothriochloa caucasica, B. ischaemum, and B. bladhii as influenced by dryland and irrigation levels of low, medium, and high during yr 2002 and 2003.  a, b Indicates quadratic and cubic effects of water treatments within month and species, respectively (P < 0.05).  †SE = standard error of the mean.

 

 

Graphs Forage nutritive value and morphology

 

 

Text Box: Neutral detergent fiber, g 100 g-1

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Text Box: Acid detergent fiber, g 100 g-1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 7.  Neutral (A) and acid (B) detergent fiber as influenced by dryland and irrigation levels of low, medium, and high averaged across Bothriochloa caucasica, B. ischaemum, and B. bladhii.  Data were averaged across yr 2001, 2002, and 2003.  Above-ground biomass was removed during last wk of July at an 8-cm cutting height.  a, b Indicates quadratic and cubic effects of water treatments within a month, respectively (P ≤ 0.05).  †SE = standard error of the mean. 

Text Box: Crude protein, g 100 g-1

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Figure 8.  Crude Protein as influenced by species (A) and by dryland and irrigation levels of low, medium, and high averaged across Bothriochloa caucasica, B. ischaemum, and B. bladhii (B).  Data were averaged across yr 2002 and 2003.  Above-ground biomass was removed during last wk of July at an 8-cm cutting height.  a, b, c Indicates linear, quadratic, and cubic effects of water treatments within a month, respectively (P < 0.05).  Means with the same letter among species and within a month are not different (P > 0.05).  †SE = standard error of the mean. 

 

 

 

 

 

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Text Box: Total nonstructural carbohydrates, g 100 g-1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


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Text Box: Dry matter digestibility, g 100 g-1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 9.  Total non-structural carbohydrates (A) and dry matter digestibility (B) as influenced by dryland and irrigation levels of low, medium, and high averaged across Bothriochloa caucasica, B. ischaemum, and B. bladhii.  Data were averaged across yr 2001, 2002, and 2003.  Above-ground biomass was removed during last wk of July at an 8-cm cutting height.  a, b, c Indicates linear, quadratic, and cubic effects of water treatments within a month, respectively (P ≤ 0.05).  †SE = standard error of the mean. 

 

 

 

 

Text Box: Total digestible dry matter, Mg ha-1 

 

 

 

 

 

 

 

 

 

 

 

 

 


 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 10.  Total digestible dry matter production as influenced by Bothriochloa caucasica, B. ischaemum, and B. bladhii, averaged across dryland and irrigation levels of low, medium, and high during 2002 and 2003.  Above-ground biomass was removed during last wk of July at an 8-cm cutting height. 

 

 

Text Box: Digestible dry matter, Mg ha-1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


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Text Box: Dry matter digestibility, g 100 g-1
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Figure 11.  Digestible dry matter (A) and dry matter digestibility (B), during the growing season, as influenced by dryland and irrigation levels of low, medium, and high.  Data were averaged across Bothriochloa caucasica, B. ischaemum, and B. bladhii, and averaged across yr 2002 and 2003.  Means with the same letter are not different (P > 0.05).  †SE = standard error of the mean. 

 

 

 

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Text Box: Leaf:stem ratio, g g-1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Text Box: Live:dead ratio, g g-1
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Figure 12.  Leaf:stem (A) and live:dead (B) ratios as influenced by dryland and irrigation levels of low, medium, and high averaged across Bothriochloa caucasica, B. ischaemum, and B. bladhii.  Data were averaged across yr 2001, 2002, and 2003.  Above-ground biomass was removed during last wk of July at an 8-cm cutting height.  a, b, c Indicates linear, quadratic, and cubic effects of water treatments within a month, respectively (P ≤ 0.05).  †SE = standard error of the mean.