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FORAGE & GRAZINGLANDS

Yield and Nutritive Value of Forage Bermudagrasses Grown Using Subsurface Drip Irrigation in the Southern High Plains

^a Extension Plant Sciences Dep., Agricultural Science Center at Clovis, New Mexico State Univ., Clovis, NM 88101
^b Dep. of Plant and Soil Science, Texas Tech Univ., Lubbock, TX 79409. Approved by the Dean of the College of Agriculture and Natural Resources, Texas Tech Univ., Publ. no. T-4-571. Supported in part by a grant from Agricultural Enterprises Corp., Oklahoma City, OK

^* Corresponding author (marsalis{at}nmsu.edu).

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Bermudagrass [Cynodon dactylon (L.) Pers.] forages are potential alternatives to traditional row cropping in the Southern High Plains. Early persistence of certain bermudagrass selections and economic potential and nutritive value of known, improved cultivars in semiarid West Texas are uncertain. A 2-yr study was conducted to evaluate hay productivity and nutritive value of 10 cultivars and two selections of bermudagrass grown with subsurface drip irrigation. Grasses were irrigated with 312 mm of water from 1 May through 31 August in 2002 and 2003. Precipitation amounts during the growing season (May–September) were 195 and 184 mm for 2002 and 2003, respectively. ‘Tifton 85’ yielded the highest total annual biomass (20.4 Mg ha^–1) and resulted in high irrigation water use efficiency (IWUE; 65.2 kg ha^–1 mm^–1). ‘World Feeder’ and ‘Macho’ performed poorly with respect to yield when compared with the other 10 grasses. Although Tifton 85 exhibited high acid detergent fiber (ADF; 349 g kg^–1) and low total nonstructural carbohydrates (TNC; 93 g kg^–1), in vitro dry matter disappearance (IVDMD) was greatest (622 g kg^–1) when contrasted with the mean of all other cultivars. Yields were similar for sprigged and seeded types. Results indicate that several bermudagrass cultivars maintained high yields and adequate nutrition 2 yr after establishment and, based on IWUE, may be an economically sound alternative to the existing cotton (Gossypium hirsutum L.) monoculture in the region.

Abbreviations: ADF, acid detergent fiber; CP, crude protein; IVDMD, in vitro dry matter disappearance; IWUE, irrigation water use efficiency; NDF, neutral detergent fiber; TNC, total nonstructural carbohydrates.

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
CURRENT IRRIGATION practices in the Texas High Plains with no new water management strategies implemented will result in water shortages due to demands exceeding supplies (Texas Water Development Board, 2001). Decreasing groundwater availability has increased the use of land for pasture and rangeland for livestock production. Forage systems and integrated crop–livestock systems are potentially viable, more sustainable alternatives for the region (Allen et al., 2005). The beef cattle industry has become more prominent on the Texas High Plains in the past 25 to 30 yr (Llano Estacado Regional Water Planning Group, 2001), and improved grazing and haying systems are needed to complement conservative water use systems. Drought-tolerant and water-use-efficient forages are required in limited irrigation systems to meet the needs of livestock industries. Bermudagrass [Cynodon dactylon (L.) Pers.], because of its tolerance to drought and high water use efficiency (Doss et al., 1962), may qualify for such situations.

Research involving the yield and nutritive value of improved bermudagrass cultivars has been extensive in other areas of the USA (Taliaferro et al., 2000, 2004; Evers et al., 1994, 2001; Hill et al., 2001; Baker, 2002) but little is known about the production potential of forage bermudagrass (sprigged or seeded) on the Texas High Plains, particularly with respect to value (both economic and nutritional) of the hay product. Thus, testing to determine its suitability to the unique environmental conditions of the region and to limited irrigation situations is warranted.

The overall objectives of this research were to determine if improved, forage bermudagrass cultivars are persistent and are productive enough to contribute to economic sustainability and soil and water conservation efforts 2 yr after establishment in the Texas High Plains when supplemental irrigation is restricted to about 300 mm annually. Specifically, the forage yield and nutritive value of bermudagrass grown with subsurface drip irrigation and harvested at 28-d hay-cutting intervals were of interest.

	MATERIALS AND METHODS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Grass Establishment
A small-plot experiment with subsurface drip irrigation was conducted at Texas Tech University Northeast Lubbock County Field Research Center, New Deal, TX (33°45' N, 101°47' W; 993 m elevation) to determine biomass productivity and forage nutritive value of 12 bermudagrass cultivars from 2002 to 2003. All 12 cultivars (eight sprigged and four seeded types; Table 1) were planted on 11 May 2001 in 1.2- by 1.5-m plots in a Pullman clay loam (fine, mixed, superactive, thermic Torrertic Paleustoll). Soil was tilled on 10 May for planting preparation. Sprigged types were planted in three rows within each plot (rows 30.5 cm apart) to give a sprig planting rate of 3.0 m³ ha^–1 and covered with soil to about 5 cm, and the soil was compacted with a roller for moisture retention and soil–sprig contact. Seeded cultivars were broadcast at a rate in excess of 15 kg ha^–1 to ensure good establishment. Typical recommendations for planting rates are 1.8 to 3.5 m³ ha^–1 and 5.5 to 11.0 kg ha^–1 for sprigged and seeded types, respectively. Seeds were raked into newly disturbed soil and compacted.

Fertilizer components and rates were based on soil test results, and recommendations issued for forage bermudagrass by Texas A&M University, Oklahoma State University, and New Mexico State University. Soil samples were obtained before planting and at the beginning of each subsequent growing season from depths of 0 to 15 and 15 to 30 cm from each plot and were combined to give an average fertility measurement at each depth range. Before planting, plots received 67 kg N ha^–1 as urea and 45 kg P₂O₅ ha^–1 as triple superphosphate. Other macro- and micronutrients applied included Fe as FeSO₄ and S as (NH₄)₂SO₄ at rates of 7 and 40 kg ha^–1 of Fe and S. All fertilizers were watered into the soil by hand to prevent losses from wind or volatilization.

Spread of bermudagrass stolons beyond individual plots was suppressed by glyphosate [N-(phosphonomethyl) glycine isopropylamine salt; Monsanto, St. Louis, MO] to the edges of plots in amounts (at least 21% active ingredient) high enough to kill vegetative material quickly and not translocate into plots. Weedy grasses within plots were controlled by hand roguing. To control various broadleaf weeds in plots and alleys, Clarity herbicide (BASF Corp., Research Triangle Park, NC) was applied at 0.6% concentration of active ingredient (diglycolamine salt of dicamba [3,6-dichloro-2-methoxybenzoic acid]) with a pressure sprayer on 3 July 2001. All weeds were controlled in subsequent years by hand roguing without the use of chemicals.

During the establishment summer, all grasses were defoliated periodically to 5 cm to promote lateral expansion within plots and to eliminate inflorescences for prevention of spread outside of plots. Growth was allowed to accumulate into autumn to promote buildup of total nonstructural carbohydrates (TNC) for dormancy survival and subsequent spring growth. Thatch was left on the plots throughout the winter to provide insulation from wind and cold temperatures. One harvest of forage was obtained on 14 Sept. 2001 because the bermudagrass was well established. Plant material was collected from a 0.24-m² quadrat randomly placed in each plot, cut to a height of 5 cm via hand shears, and oven dried at 55°C for 48 h. Once dry, grasses were weighed to estimate forage mass on a dry basis and ground to 1 mm using a Wiley mill (Comeau Technique Ltd., Vandreuil-Dorion, Quebec, Canada) and stored at room temperature for further analysis. Following hand clipping, plots were mowed (collection bag attached) to a uniform height of approximately 5 cm and fertilized with 67 kg N ha^–1.

Production
After the establishment year, plots were irrigated through the drip irrigation system as described above at a rate of 2.54 mm d^–1 throughout the months of May, June, July, and August to supply a maximum of approximately 78 mm mo^–1, or 312 mm yr^–1 (Fig. 1). This daily watering schedule was maintained despite precipitation events. Total annual precipitation was 324, 458, and 277 mm for 2001, 2002, and 2003, respectively (Fig. 1). Growing season (May–September) total precipitation and irrigation averaged 502 mm for the 2 yr. Mean long-term (1911–2002) annual precipitation for the area is 470 mm with about 75% occurring from April through October (Fig. 2). The plot area received greater than normal amounts of precipitation for the 2 yr in June, October, and December, but below-normal amounts for all other months. Temperatures were near average for the 2 yr; however, June was a particularly cool month when compared with the long-term mean (Fig. 2).

View larger version (19K): [in this window] [in a new window]   Figure 1. Monthly precipitation and irrigation amounts at New Deal, TX, from 2001 to 2003. Bermudagrass was planted 11 May 2001 and experiment was terminated 11 Sept. 2003.

View larger version (19K): [in this window] [in a new window]   Figure 2. Mean monthly (2-yr) and long-term (1911–2003) precipitation and temperature (1971–2000) at experimental location at New Deal, TX.

Ground forage from quadrat clippings at harvest was analyzed by near-infrared reflectance spectroscopy (NIRS) absorption techniques and was scanned with a spectrophotometer (Model no. 5000, NIRSystems, Silver Spring, MD) to predict concentrations of acid detergent fiber (ADF), neutral detergent fiber (NDF), crude protein (CP), and TNC. Absorption characteristics from the spectrophotometer were determined by NIRS 2, Version 3.10 software. A subset of the sample population was analyzed by conventional wet chemistry procedures. The calibration subset was analyzed for ADF, NDF, cellulose, hemicellulose, and ash by methods described by Van Soest (1965), Goering and Van Soest (1970), and Van Soest et al. (1991). Crude protein was estimated by a Leco FP-2000 Nitrogen/Protein Determinator (Leco Corp., St. Joseph, MI) and verified with Kjeldahl procedures described by AOAC International (1995). Total nonstructural carbohydrate percentages were obtained from modified procedures (Marsalis, 2004) described by Mounsif (1986). In addition, in vitro dry matter disappearance (IVDMD) (Tilley and Terry, 1963; modified by Barnes, 1966) was determined to obtain an estimate of how digestible bermudagrass forages were in July (6 July 2002 and 17 July 2003) of each year at 4 wk of growth. July harvests were selected because yields were greatest for most cultivars and peak production of bermudagrass occurred at this time.

Experimental design was a randomized complete block design with repeated measures analysis and four replications of each cultivar (Steel and Torrie, 1981). All forage nutritive value parameters and forage yield were analyzed using the GLM procedure in SAS that tested main effects of year, cultivar, month, and their interactions (SAS Institute, 1999). Differences among means were separated by the least significant difference test when F tests were significant (P 0.05; Steel and Torrie, 1981). Additionally, the mean of all seeded cultivars was compared with that of sprigged cultivars for each parameter. A specific contrast of ‘Tifton 85’ with the mean of all other cultivars was analyzed for IVDMD because of information reported in the literature concerning the high digestibility of Tifton 85 compared with other improved cultivars (Mandebvu et al., 1999; Hill et al., 1993; Taliaferro et al., 1996).

	RESULTS AND DISCUSSION

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Forage Mass, Yield, and Irrigation Water Use
Significant date x forage x year interactions led to interpretation of forage mass results on a monthly basis within each year (Table 2). Interaction was probably a result of the effect of the July harvest on forage mass production (Fig. 3). In 2002, forage mass increased for all cultivars from June to July; however, in 2003, forage mass during this period declined in all grasses except ‘Giant’ and ‘Cheyenne.’ Reduced forage production in July of 2003 may have been due to a lack of precipitation. In contrast, July 2002 received >40 mm of rain (Fig. 1).

View larger version (24K): [in this window] [in a new window]   Figure 3. Seasonal distribution of forage mass of bermudagrass cultivars grown in 2002 and 2003. Data are the means of four replications. Bars indicate the LSD (P < 0.05) for within-harvest comparisons.

View larger version (9K): [in this window] [in a new window]   Figure 4. Two-year seasonal distribution of forage mass of bermudagrass grown with subsurface drip irrigation. Sprigged = mean of all sprigged cultivars except Tifton 85; Seeded = mean of all seeded cultivars.

Irrigation Water Use Efficiency
Irrigation water use efficiency by the grasses was variable and mirrored closely total annual yield (Table 3). Tifton 85 used irrigation water most efficiently, with an IWUE greater than all cultivars except ‘Coastal’ and ‘Cheyenne’. Dry matter production of Coastal bermudagrass at New Deal was similar to yields attained at Tifton, GA, under normal rainfall conditions (Burton and Hanna, 1995). At Tifton, GA, with annual precipitation of 1010 mm, Coastal bermudagrass has produced as much as 22 Mg ha^–1 when fertilized with 400 kg N ha^–1 (Burton and Hanna, 1995). Results from New Deal, TX, indicated that with 680 mm of water (368 mm mean annual precipitation during the study plus 312 mm of irrigation), Coastal yields averaged 18.2 Mg ha^–1 when fertilized with 403 kg N ha^–1.

Estimated annual water applied (irrigation plus precipitation) to produce 1 kg ha^–1 of biomass at New Deal was 0.037 mm, but this estimation does not account for soil moisture depletion or water lost through evaporation, leaching, or runoff. Doss et al. (1962) reported a transpiration ratio for bermudagrass of 0.026 mm water kg^–1 dry matter (DM) ha^–1. In this experiment, if only irrigation is considered, Coastal required 0.017 mm (IWUE = 58.4 kg ha^–1 mm^–1) of water to produce 1 kg ha^–1 of DM. With an IWUE of 65.2 kg ha^–1 mm^–1, Tifton 85 required only 0.015 mm of irrigation water to produce 1 kg ha^–1 of DM. Mean IWUE for all 12 bermudagrass cultivars was 54 kg ha^–1 mm^–1. If this IWUE is used to predict the value of bermudagrass hay per millimeter of irrigation water, a value of $5.20 mm^–1 results from a conservative hay pricing of $0.10 kg^–1. By comparison, Cook et al. (2003) reported an IWUE range of 2.2 to 3.8 kg cotton (Gossypium hirsutum L.) lint mm^–1 during 7 yr of experiments with various cultivars of cotton. At a lint price of $1.21 kg^–1, a 3.8 kg mm^–1 IWUE would result in a value of $4.60 mm^–1. Debate over the value of forages grown in the Texas High Plains exists and some have argued that producing forages is not an economically sound venture. In this study, at current commodity prices, the value of bermudagrass product per unit of irrigation water was greater than that of cotton lint product, particularly if Tifton 85 hay ($6.29 mm^–1) is considered. Furthermore, the commercial value of Tifton 85 hay generally exceeds that of bermudagrass due to its higher demonstrated nutritive value and value as a hay for horses (Hill et al., 2001; Rouquette, 2005).

Small-plot yield results often are greater than those observed under field conditions and these data should be interpreted carefully. High production of some of these bermudagrass cultivars may have been a result of the efficiency in which irrigation water was applied through subsurface drip tapes within the rooting zone of the grasses. Although N was applied to the soil surface, it is speculated that N application through the drip tape would have added benefits to yield. All bermudagrass cultivars yielded >13.5 Mg ha^–1 over both seasons and production included five harvests per year. It is important to note that no plots were lost due to winterkill or drought in the establishment year or during the 2 yr of production. This is especially meaningful as 2003 was the second driest year on record for the region and average total precipitation amounts during the growing season were <200 mm.

Forage Nutritive Value
Acid detergent fiber response to harvest date across both years and all bermudagrass cultivars varied and resulted in a cultivar x date x year interaction (Table 2). Although ADF of the grasses followed a similar general trend, differences in magnitude led to interaction significance, and the greatest variation from one year to the next occurred at the first and last harvests (data not shown). In general, minimum ADF was observed for bermudagrass at May cuttings in both years. This is probably related to physiological aging and lower proportions of stems and structural carbohydrates that are common in early growth compared with late-season growth (Forwood et al., 1988; Blaser et al., 1986).

Mean ADF concentrations of bermudagrasses were >300 g kg^–1 for all cultivars grown (Table 4). Two-year means indicated that ADF of Tifton 85 and ‘Hardie’ was higher than all other cultivars. High ADF did not affect adversely IVDMD values of Tifton 85, which is consistent with previous research on Tifton 85 (Mandebvu et al., 1999; Hill et al., 1997a, 2000). In fact, ADF of Tifton 85 peaked in July of both years. Estimations of IVDMD are probably a better indicator of digestibility than digestible dry matter (DDM) calculations using ADF values, as other constituents such as ferulic acids and lignin play a role in forage digestibility (Mandebvu et al., 1999; Casler and Vogel, 1999). Although not determined in this experiment, estimating DDM based on relative forage quality would probably have provided a better estimate than the older method of relative feed value (Moore and Undersander, 2002). ‘Sahara’ contained the lowest 2-yr mean proportions of ADF and was lowest in ADF in both years at the May cutting dates.

Mean TNC concentrations ranged from 93 to 124 g kg^–1 (Table 4). Tifton 85 TNC concentrations were lower than all cultivars tested except Macho. When analyzed by year and harvest date, TNC content in the bermudagrass cultivars was variable (Table 2). In both years, TNC levels declined sharply from the first cutting in May to the second cutting in June; however, this decline was more pronounced in Tifton 85 (data not shown). This may be an effect of three factors. Suboptimum temperatures for photosynthesis of C₄ grasses, such as those in April and May, combined with limited water may lead to carbohydrate accumulation while respiration rates are low (Walton, 1983). As temperatures rise, TNC levels in grasses may decline due to increases in respiration rates within the plant that are greater than those of photosynthesis. The influence of increasing water can result in the same declining effect on TNC concentrations of warm-season, perennial grasses (Walton, 1983; Philipp et al., 2005). Considering that irrigation had been applied 1 mo longer by the June cutting dates than at May cutting dates, it is possible that prolonged watering combined with increasing temperatures in late spring led to a decline in overall TNC levels.

Significant increases in forage mass by the second cutting perhaps best explains why proportions of TNC might have declined, as reductions of nonstructural carbohydrates may occur as proportions of structural carbohydrates rise with maturity. In both years, TNC levels of all cultivars declined from August to September. It is possible that the sudden decrease in TNC concentrations at the last cutting was due to increases in CP levels at the same time. Carbon skeletons that would have been used for carbohydrate synthesis may have been allocated to protein synthesis instead, thereby causing TNC levels to decline. We speculate also that sustained warm temperatures from late August to mid-September, combined with shortening day length, may have caused photosynthesis to decrease at a greater rate than respiration. This net respiration effect would lead to lower TNC percentages.

In vitro dry matter disappearance determined for July was consistent across years and cultivars. Contrast analysis showed that IVDMD of Tifton 85 (622 g kg^–1 IVDMD) was higher than the mean (581 g kg^–1) of all other cultivars (Table 4). This comparison was made because of the unique morphology and genetic background of Tifton 85, as a cultivar having the highly digestible Tifton 68 as a parent (Burton et al., 1993). In addition, recent genetic analyses indicate that Tifton 85 is in a separate genetic class apart from many other cultivars (Karaca et al., 2002). Results were consistent with previous research conducted with Tifton 85 digestibility (Hill et al., 1993; Taliaferro et al., 1996; Mandebvu et al., 1999). Most cultivars had IVDMD values <600 g kg^–1, which may have been due to the timing of harvest in the middle of the summer when TNC levels tended to be low. Moreover, growth beyond 4 wk of age in bermudagrass is reported to have lower digestibility than that grown for 4 wk or less (Hill et al., 1997b). Although the bermudagrass cultivars in this experiment were not grown beyond 30 d, when combined with high summer temperatures, this marginal growth duration may have been longer than optimum in the semiarid environment in which the grasses were grown and may have influenced IVDMD.

Comparison of Seeded and Sprigged Bermudagrass Cultivars
Sprigging bermudagrass is expensive and can cost up to $310 ha^–1 (Evers et al., 2001) due to the cost of sprigs, including shipping, and special mechanization for planting if a sprigging machine is used. Seeded cultivars oftentimes are more desirable than sprigged types in the western USA due to the ease of obtaining seed compared with the high costs associated with shipping sprigs from distant areas. The persistence, yield, and quality of seeded bermudagrass cultivars are still in question, however, and, in the past, have often been inferior to those of sterile hybrid types (Hill et al., 2001). Forage production and nutritive value parameters of seeded bermudagrass cultivars were compared with those of sprigged to determine if hybrid type had an effect on overall fitness of the grasses growing in this semiarid environment. Forage mass, total annual yields, and CP means of seeded cultivars were similar to those of sprigged types when analyzed across the 2 yr (Table 5); however, both NDF and ADF estimates of seeded bermudagrass cultivars were lower than those of sprigged, and TNC concentrations were higher in seeded cultivars. In spite of this, seeded IVDMD was lower than that of sprigged; this discrepancy between the two establishment types was a result of high IVDMD associated with Tifton 85. When Tifton 85 was removed from the analysis, sprigged cultivars did not differ from seeded with respect to IVDMD. Assuming costs are reduced by using a seeded type, it is unknown whether these initial savings will carry over into subsequent years or if savings would exceed annual profits sustained from selected sprigged cultivars.

	CONCLUSIONS

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

	ACKNOWLEDGMENTS

 
We would like to gratefully thank Agricultural Enterprises Corp., Oklahoma City, OK, for contributing to the funding of this research. Sincere gratitude is expressed toward the following individuals for their assistance in the development and execution of the research: R.B. Mitchell, Dep. of Range, Wildlife and Fisheries Management; C. Fedler, Dep. of Civil Engineering; K. Pond, M. Galyean, and M.D. Abney, Dep. of Animal Science and Food Technology; D. Philipp, W. Cradduck, T. Duch, D. Niemann, B. Mueller, J. Collins, and L. Owen, Dep. of Plant and Soil Science, Texas Tech Univ., Lubbock.

	NOTES

TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.

Received for publication June 16, 2006.

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TOP NOTES ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 

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