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Agronomy Journal 94:792-797 (2002)
© 2002 American Society of Agronomy

PRODUCTION PAPER

Irrigation and Nitrogen Effects on Tall Wheatgrass Yield in the Southern High Plains

Leonard M. Lauriault*,a, Rex E. Kirkseya and Gary B. Donartb

a Agric. Sci. Cent. at Tucumcari, New Mexico State Univ., 6502 Quay Rd. AM.5, Tucumcari, NM 88401
b Dep. of Anim. and Range Sci., Box 30003 MSC 3-I, New Mexico State Univ., Las Cruces, NM 88003

* Corresponding author (lmlaur{at}nmsu.edu)

Received for publication March 15, 2001.

   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
Winter months in the Southern High Plains of the USA have the lowest precipitation. As a result, producers using tall wheatgrass [Agropyron elongatum (Host) Beauv.] may get higher production in the spring and possibly throughout the growing season with additional irrigation. Also, growers need information about interactions between soil moisture and N fertilizer to maximize productivity. In a split-plot study conducted at the New Mexico State University Agricultural Science Center at Tucumcari from 1997 to 1999, tall wheatgrass furrow-irrigated monthly from April to September was irrigated once, twice, or not irrigated during winter as the whole-plot treatment. For subplot treatments, tall wheatgrass annually received 168 kg N ha-1 split into two, three, or four equal applications. Tall wheatgrass irrigated in the winter yielded more dry matter (DM) over the 3 yr than unirrigated tall wheatgrass (11.72, 12.10, and 13.55 Mg ha-1 for tall wheatgrass not irrigated, irrigated once, or irrigated twice, respectively). Tall wheatgrass fertilized three or four times outyielded tall wheatgrass fertilized twice (11.08, 12.85, and 13.44 Mg ha-1 for two, three, and four N applications, respectively). No interaction occurred between the irrigation and N treatments. A year x harvest x N effect existed in which a mid-December N application, preceded and followed by precipitation, produced approximately 1 Mg ha-1 more DM than unfertilized tall wheatgrass in the first harvest the following year. Both supplemental winter irrigation and N application scheduling offer opportunities for tall wheatgrass producers to increase production in the Southern High Plains of the USA.

Abbreviations: DM, dry matter


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
TALL WHEATGRASS is well adapted to the Southern High Plains (Schuster and Garcia, 1973) and the Middle Rio Grande Valley of the USA (Jones and Hooks, 1976). It is widely used in year-round grazing systems during the early spring and fall when small-grains pastures are not available and before and after warm-season species are productive (Eck et al., 1981; Schuster and Garcia, 1973; Undersander and Naylor, 1987). Tall wheatgrass is also used throughout the summer in lieu of warm-season pastures. Although it performs best in areas having >450 mm yr-1 precipitation (Bleby et al., 1997), tall wheatgrass responds well to irrigation both in areas with high precipitation (Undersander and Naylor, 1987; Schuster and Garcia, 1973) and in areas with low precipitation (Jones and Hooks, 1976; Kirksey et al., 1993). There was an inconsistency in the results of these studies.

Undersander and Naylor (1987) clipped ‘Jose’ tall wheatgrass monthly from May through October at Bushland, TX, and measured total annual dry matter (DM) yields of 11.3 Mg ha-1. They used weekly sprinkler irrigations to supplement precipitation and promote growth during high water-use periods while applying 112 kg N ha-1 in February, April, June, and August. Schuster and Garcia (1973), near Bushland, clipped ‘Alkar’, Jose, and ‘Largo’ tall wheatgrass monthly throughout the year but measured only 3.8 Mg ha-1 DM after irrigating as needed and applying 63 kg N ha-1 in March and August. Jones and Hooks (1976) applied water as needed by furrow irrigation to tall wheatgrass grown at Los Lunas, NM, and measured 13.2 Mg ha-1 from two to three harvests annually using 146 kg ha-1 total N. Kirksey et al. (1993), harvesting two to three times per growing season at this station and using furrow irrigation monthly throughout the growing season, measured 4.8 Mg ha-1 annual DM of Jose tall wheatgrass by applying two N applications (April and June) per year totaling 230 kg N ha-1. This large variability in tall wheatgrass production may lie in the differences in climate (temperature and precipitation), irrigation type, and management used in the area where the tests were conducted (Frank et al., 1996; Power, 1980).

Sprinkler irrigation is more efficient and less labor intensive than furrow irrigation. Using automated sprinklers, a producer can apply as little as 25 mm at a time, whereas 75 mm is a small amount for a single furrow or flood application. Due to limited availability of water in canal or river systems and the cost of pumping ground water, furrow-irrigating forage crops as needed may not be feasible. Therefore, the tendency of many tall wheatgrass producers in the Southern High Plains of the USA is to furrow-irrigate, at most, monthly during the growing season. Some public irrigation systems, however, do not deliver water from 1 November to 1 April, which makes the monthly application of water to many cool-season species during their period of active growth practically impossible. Tall wheatgrass has an advantage over other perennial cool-season grass species in that it is later maturing (Cooper and Hyder, 1959; Dotzenko, 1961) and can still make considerable growth when irrigations are delayed in the spring (Undersander and Naylor, 1987).

There is considerable information about N fertility of other perennial cool-season grasses in the literature (Black, 1968; Campbell et al., 1986; Collins, 1991; Cooper and Hyder, 1959; Eck et al., 1981; Frame, 1991; Frank and Bauer, 1991; Power, 1980). Power (1980), however, mentioned that one of the more important factors affecting the response to N fertility was grass species. Moreover, Cooper and Hyder (1959) found that tall wheatgrass does not respond as well to N fertilization as other cool-season grasses. Dotzenko (1961) published the only information concerning the response of tall wheatgrass to different rates or schedules of applied N under the same conditions. In that study, N rates of 0, 90, 180, 360, and 720 kg ha-1 were applied in a single application in April to six perennial cool-season grass species harvested twice per year and furrow-irrigated four times per year. Total yields increased across N rates to achieve 11 Mg ha-1 at the 360 kg N ha-1 rate (Dotzenko, 1961).

Due to the variability of precipitation in semiarid environments and the cost of irrigations and other inputs, particularly N fertilizer, irrigated tall wheatgrass growers in the Southern High Plains need better information about interactions between available soil moisture and fertilizer to maximize productivity. The purpose of this research was to determine if tall wheatgrass would increase forage production with supplemental winter irrigation and the benefits of split N applications under the imposed irrigation regimes in the Southern High Plains of the USA.


   MATERIALS AND METHODS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 REFERENCES
 
The study was conducted at the New Mexico State University Agricultural Science Center at Tucumcari (35°12'0.5'' N, 103°41'12.0'' W; elev. 1247 m). On 5 Oct. 1995, Jose tall wheatgrass was sown at 22.45 kg ha-1 pure live seed using a disk drill fitted with a seed-metering cone. The tall wheatgrass was sown into a conventionally tilled seedbed formed into beds on 0.9-m centers for furrow irrigation. The soil was Canez fine sandy loam (Fine-loamy, mixed, thermic Ustollic Haplargid) with soil test levels of 67 mg kg-1 P (NaHCO3 extractant), 194 mg kg-1 K (ammonium acetate extractant), and a pH of 7.6. This soil has a rooting depth of approximately 1.5 m and a water-holding capacity of 25 to 30 cm (Ross and Pease, 1974).

Treatments included no supplemental winter irrigation, irrigated once during winter (mid-January), and irrigated twice during winter (mid-December and mid-February). Dates for the winter irrigations were selected as being evenly spaced between the final harvest of one year (30 October) and the anticipated availability of canal water in the next year (mid-April). The winter irrigation treatments were applied using well water and were in addition to monthly irrigations during the growing season when canal water was available (generally mid-April to 31 October). All irrigations were delivered through gated pipe and were of sufficient duration to completely wet the center of the beds for their full length. Historical irrigation flow-rate data, collected at this location as described by Ziska et al. (1985), was used to estimate that approximately 200 mm was applied with each irrigation. Individual plots were 7.2 by 10.7 m, with four replicates of each treatment arranged as a randomized complete block design. Two beds (1.8 m total) were used as a border between irrigation treatments to prevent lateral movement of water into the adjacent plot (Ziska et al., 1985). While irrigation treatments were initiated in winter of 1995–1996, no yield data were collected.

Due to the size of the plots, the following subplot treatments, each providing an annual total of 168 kg N ha-1, were commenced in the spring of 1997: 84 kg N ha-1 applied twice (mid-April and mid-June), 56 kg N ha-1 applied three times (mid-April, mid-June, and mid-August), and 42 kg N ha-1 applied four times (mid-April, mid-June, mid-August, and mid-December). Urea (46–0–0) was used as the N source for all applications. Fertilizer applications in April, June, and August were made immediately before irrigation. The December N application was followed by irrigation only in the whole-plot treatment watered in mid-December. Subplots were 1.8 by 10.7 m, of which the center 8.4 m2 was harvested. Once established, treatments were applied to the same plots for the duration of the study (1997–1999). No other fertilizers were applied.

Topgrowth was removed on five dates in 1996 and on 1 Apr. 1997 after which the test was managed as a spring, summer, and fall stockpiling system where harvests were taken in early May, mid-June, mid-August, and late October. Tall wheatgrass was vegetative at all harvests except mid-June when it was in the late boot–early head stage. Harvests were taken with a self-propelled sickle-type forage plot harvester equipped with electronic scales. Fresh weights were measured in the field. Immediately after weighing, a subsample of approximately 300 g was collected from each plot, placed in a paper bag, and sealed inside a plastic bag. The subsamples were weighed and plastic bags removed before drying for 48 h at 70°C. Subsamples were then reweighed to determine DM concentration, which was used to convert fresh harvest weights to DM yield.

The study was analyzed as a split-plot design with irrigation treatment as whole plot and N application rate as the subplot. Yield data for treatment effects of irrigation, N, and irrigation x N were subjected to analysis of variance and PROC GLM techniques (SAS Inst., 1996) for within-harvest comparisons. Repeated measurements were used to test year x treatment, harvest x treatment, and year x harvest x treatment interactions (SAS Inst., 1996; Snedecor and Cochran, 1980). Treatment means were separated using protected least significant differences (P <= 0.05).


   RESULTS AND DISCUSSION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
REFERENCES
 
The climate in the region is continental, characterized by cool, dry winters and warm, moist summers. Approximately 83% of the precipitation occurs as intermittent, relatively intense rainfall events from April through October. July and August typically have the highest precipitation. Weather data were collected from a National Weather Service cooperative station located at the Agricultural Science Center within 1 km of the study area. Mean monthly temperatures during the study were typical of the Southern High Plains region (Table 1) and within the range required for tall wheatgrass growth (Schuster and Garcia, 1973; Undersander and Naylor, 1987). The annual precipitation each year during the study period was also sufficient for tall wheatgrass growth (Table 1) (Bleby et al., 1997).


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  		Table 1. Monthly mean air temperatures and total precipitation at Tucumcari, NM from 1997 to 1999 and the long-term (1905–2000) means.

 
Mean annual yields measured in this study (Table 2) are consistent with those measured previously for tall wheatgrass in other studies at this location using similar and higher levels of irrigation and N (Kirksey et al., 1993). There were no interactions between the main plot treatment of irrigation treatments and the N rates. This is consistent with the findings of Eck et al. (1981), who measured similar N-rate response curves across years for tall fescue (Festuca arundinacea Schreb.) and smooth bromegrass (Bromus inermis Leyss.) at Bushland, TX, even when there was a change in application of a particular irrigation treatment between years.


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  		Table 2. The effect of winter irrigation and N application rates and schedules on annual and total dry matter (DM) yields of tall wheatgrass at Tucumcari, NM.

 
Tall wheatgrass yields declined each year of the study (Table 2). This and the significant year x harvest effect (Fig. 1) may be due to the distribution of precipitation within each year. Frank and Bauer (1991) and Sneva (1973) mentioned that forage production by cool-season grasses in semiarid areas was highly correlated with growing season precipitation and stored pre–growing season soil water supply. The lack of rainfall in May and June 1998 probably contributed to poor production in June of that year compared with June 1997 and 1999 (Table 1). In each year, the tall wheatgrass was harvested and irrigated by mid-May and harvested again on 13 June. Eck et al. (1981) reported that before summer dormancy, tall fescue and smooth bromegrass grew for about 3 wk after a flood irrigation of 120 mm. In the present study, the tall wheatgrass did not become dormant, but it did appear to suffer from moisture stress between irrigations whenever measurable precipitation did not occur as indicated by the depressed yields in June 1998.



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  		Fig. 1. Seasonal distribution of furrow-irrigated tall wheatgrass dry matter (DM) yields during 3 yr at Tucumcari, NM. Bars indicate the LSD (P < 0.05) for within harvest-date comparisons. Data are averages of irrigation treatments and N rates.

 
Tall wheatgrass responded to irrigations applied in the winter. Differences between irrigation treatments were measured in total yields in 1997 and 1998 and for total DM produced over the 3 yr of the study (Table 2). While the year x irrigation treatment effect was not significant, there was an apparent decline across years in the magnitude of the differences within years. However, a significant harvest x irrigation treatment effect occurred (Fig. 2) , caused by a difference in the first harvest when tall wheatgrass irrigated twice in winter produced more herbage than tall wheatgrass irrigated only once or not at all. The effect may be related to irrigation timing rather than the actual amount of supplemental water. The nonirrigated treatment did not receive any supplemental water from mid-September to mid-April, the single irrigation treatment was watered in mid-January, and plots irrigated twice received water in mid-December and mid-February. Although it cannot be determined whether the effect is due to either or both of the irrigations (mid-December or mid-February), water applied before mid-February may no longer be available for plant use when tall wheatgrass begins growth in early March (Undersander and Naylor, 1987) due to evaporation from the soil surface.



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  		Fig. 2. Effect of winter irrigation regime on the seasonal distribution of furrow-irrigated tall wheatgrass dry matter (DM) yields at Tucumcari, NM, from 1997 to 1999. Bars indicate the LSD (P < 0.05) for within harvest-date comparisons. Absence of an LSD on a date indicates no significant difference among treatments. Data are averages of N rates and years.

 
Tall wheatgrass also responded differently to equal annual rates of N when applied in different increments and frequencies (Table 2). Nitrogen applied in three or four equal increments resulted in greater DM production than N applied twice at a higher rate. This is in contrast to the literature for other species and moisture situations (Collins, 1991; Eck et al., 1981; Power, 1980). But Collins (1991) also found that under rainfed conditions, in 1 of 3 yr having significantly less-than-average precipitation, yields were depressed in both tall fescue and perennial ryegrass (Lolium perenne L.) when application rates of N increased from 42 to 84 kg ha-1.

A buildup of soil N can occur when total water applied does not exceed the infiltration rate, water-holding capacity, and plant uptake (Black, 1968). The soil used in the present study had a high enough water-holding capacity to keep all water applied naturally or by irrigation available for plant use (Ross and Pease, 1974). Bleby et al. (1997) reported that tall wheatgrass produced roots to a depth of 3.5 m, even in a poorly drained, saline soil. They found that tall wheatgrass had the capability of avoiding waterlogged soil and salinity zones by extracting water from different depths. Thus, the depression in yield when 84 kg N ha-1 was applied in the present study may be related to a buildup of soil N resulting in an increase in soil salinity (not measured) that may limit water uptake by tall wheatgrass. This indicates that, to an extent, the N rate and application frequency are more important in limited-moisture environments than total N applied.

Differences in the 8 May 1998 harvest led to a significant year x harvest x N treatment interaction (Fig. 3) . Note that the yields when N is applied in two or three applications were similar to, or only slightly higher than, those of the previous year. It is the yield produced when the total annual N was split into four applications that is exceptional, being even higher than that of 13 June 1997 when the tall wheatgrass was in the early heading stage. There is only one possible explanation for this: The N application on 16 Dec. 1997 was preceded by precipitation earlier in the month (Table 1) that may have encouraged growth by the tall wheatgrass (Frank et al., 1996) regardless of irrigation treatment. Another 51 mm of precipitation, falling as snow during 20 to 22 December, probably infiltrated in its entirety, moving the N into the soil and providing sufficient moisture to continue tall wheatgrass growth, again without regard to irrigation treatment. During the winter of 1997–1998, the soil temperature at Tucumcari never fell below 0°C. The upper surface of the snow may have protected against volatilization while the melting lower layer promoted N infiltration.



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  		Fig. 3. Nitrogen rate effects on the seasonal distribution of furrow-irrigated tall wheatgrass yield in each of 3 yr at Tucumcari, NM. Bars indicate the LSD (P < 0.05) for within harvest-date comparisons. Absence of an LSD on a date indicates no significant difference among treatments. Data are averages of irrigation treatments.

 
Others have observed a benefit from fall-applied N on early spring yields of established perennial cool-season grasses (Campbell et al., 1986; Sneva, 1973). Cool-season turfgrasses also are known to benefit from fall-applied N through stimulation of root growth, which helps in winter and subsequent summer survival and early spring green-up (Turgeon, 1991). It is possible that the precipitation before the December 1998 fertilizer application encouraged active growth by the tall wheatgrass, allowing it to more efficiently respond to the applied N, and thereby increase use efficiency of the precipitation following the N application (Frank and Bauer, 1991; Frank et al., 1996; Power, 1980). Campbell et al. (1986) applied N to cold, moist, but unfrozen soil in October and November and measured increased cool-season grass DM yields the following year. However, when N was applied to frozen, snow-covered ground in December, no yield benefit was measured. In the present study, the 8 May 1997 harvest could not have shown this effect because no N had been applied in December 1996. The 8 May 1999 harvest would not have shown it because precipitation in December 1998 was well below average (Table 1).

If this scenario is correct, producers in semiarid regions using flood or furrow irrigation may benefit from applying N fertilizer and an irrigation shortly after a significant rainfall event that stimulates growth of tall wheatgrass. In December 1997, 13 d elapsed between the bulk of the precipitation and the N application. It might also be possible to increase yields by applying N after irrigation if significant precipitation is imminent. If sprinklers are used, a light irrigation, followed by the N application and a heavier irrigation, may give equivalent results. Otherwise, water may not be available for multiple flood or furrow irrigations. It is likely that some time [speculatively 3–7 d (Frank et al., 1996)] should be allowed between the first precipitation event or irrigation and the N application to activate tall wheatgrass growth.

Based on the information gathered from this study, two furrow irrigations of 200 mm each during winter, in addition to monthly irrigations during the growing season, improved yields of tall wheatgrass. The timing of those irrigations, however, may have played a role in their effectiveness. Additionally, N applied at the same annual rate but in more frequent, split applications of lesser rates produced more total annual tall wheatgrass forage than fewer applications at higher rates (>56 kg N ha-1) in this semiarid environment where water is applied infrequently. Finally, a late-fall or early-winter application of N, preceded and followed by precipitation or irrigation, may lead to higher DM production by tall wheatgrass in the next spring.


   ACKNOWLEDGMENTS
 
We gratefully acknowledge the technical and field assistance of George Arguello, Eutimio Garcia, and Leslie Robbins.


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
Contrib. of the New Mexico Agric. Exp. Stn., New Mexico State Univ., Las Cruces.


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




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