SEEDING FORAGE KOCHIA ONTO CHEATGRASS-INFESTED RANGELANDS

Transcription

1 SEEDING FORAGE KOCHIA ONTO CHEATGRASS-INFESTED RANGELANDS Stephen B. Monsen Dale Turnipseed ABSTRACT 'Immigrant' forage kochia was spring planted at four locations in southern Idaho on unprepared seedbeds infested with annual weeds. Each site was seeded with either 4.0 kg/ha or 7.0 kglha pure live seed. Successful establishment was achieved at each location, but distribution of shrub seedlings was erratic at three of the four locations. The number of seedlings that established ranged from 0.95 to plants per square meter. Establishment of shrub seedlings was not related to cover density of annuals, suggesting that forage kochia can be used to seed sites infested with weeds. Shrub seedlings established with minimal site preparation, demonstrating that the plant can be used to seed inaccessible areas where extensive weed control measures cannot be used. INTRODUCTION Rangelands infested with cheatgrass (Bromus tectorum) are difficult to restore through management practices (Evans and Young 1978; Piemeisel1938) or artificial seeding (Hull and Pechanec 194 7). Direct seeding into cheatgrass-dominated sites without prior site preparation or weed control has not proven successful as the seedlings of most seeded species fail to compete with the aggressive annual (Evans and Young 1978; Hull1963; Hull and Pechanec 1947; Robertson and Pearse 1945; Rummell 1946). Areas dominated by cheatgrass or other exotic annual weeds normally require intensive site preparation toreduce competition and allow seeded species to establish (Evans and Young 1984). However, it is difficult to control or reduce cheatgrass competition. Abundant seed crops are produced annually even during years oflow rainfall (Mack and Pyke 1983; Young and others 1969). Seeds often germinate in the fall if moisture becomes available, and persist as winter annuals (Hulbert 1955). Regrowth begins early in the spring at quite low temperatures, usually before regrqwth or seedling emergence of most other species. In addition, some germination occurs in the spring from seeds that did not fall germinate. Consequently, site preparation treatments must be designed to control fall and Paper presented at the Symposium on Cheatgrass Invasion, Shrub Die Off, and Other Aspects of Shrub Biology and Management, Las Vegas, NV, April 5-7, Stephen B. Monsen is Botanist, Shrub Sciences Laboratory, Intermountain Research Station, Forest Service, U.S. Department of Agriculture, Provo, UT Dale Turnipseed is Regional Wildlife Land Manager, Idaho Department offish and Game, Jerome, ID spring germination and remove live plants. Control measures must also be successful in reducing or eliminating the seedbank. One-time tillage does not always control cheatgrass, unless weed seeds are deeply buried. Chemical treatments can be effective in reducing seedling survival (Eckert and Evans 1967), but present other problems. Deep plowing or use of chemicals may control the weed but may also eliminate most other species. Selective measures have not been developed that can be used to control the annual grass and yet retain desired plants. Tillage, fire, or chemical weed control practices have been successful on some areas, but are difficult to conduct on inaccessible sites where cheatgrass has invaded. Few rangelands have uniform terrain and can be easily treated. Partial reduction of cheatgrass density does not proportionally reduce competition. Reduction in numbers of cheatgrass individuals is usually compensated by an increase in vigor and stature of the remaining plants. Consequently, reduction of 80 to 90 percent of cheatgrass plants may not significantly reduce the competitive influence of the few remaining individuals. Thus, control measures must be thorough to allow desirable species a chance to establish. Cheatgrass possesses other characteristics that hinder the establishment of desirable species. Most important, cheatgrass seeds are able to germinate under a wide range of temperatures, including conditions where day- and night-time regimes may fluctuate between 1 and 15 c (Buman and Abernethy 1988). Seedlings that are able to establish at such low temperatures are able to utilize soil moisture during warm periods in the winter and early spring months. In addition, seedlings and young plants grow rapidly. Buman and others (1988) reported that 6-week-old seedlings of cheatgrass produce roots that exceed 43 em in length. Conversion of cheatgrass ranges to more desirable species, including most natives, has been hindered by the inability of planted species to compete as small seedlings with the annual grass. Seedlings of only a few species have the ability to compete with cheatgrass, particularly under semiarid conditions. The success of 'Hycrest' crested wheatgrass (Agropyron desortorum) (Asay and Knowles 1985), and mountain rye (Secale montanum) (Buman and others 1988) has been most notable. Seeds of mountain rye germinate at slightly cooler temperatures than cheatgrass (Buman and Abernethy 1988), and the growth rate of this perennial exceeds that of cheatgrass (Buman and others 1988). When grown in direct competition, the perennial grass prevails (Monsen and Shaw 1984). Few other perennial species express similar traits. The conversion of cheatgrass ranges to more productive, less fire-prone 66 This file was created by scanning the printed publication. Errors identified by the software have been corrected; however, some errors may remain.

2 plant communities will depend, in part, on the development of species with improved seedling vigor and establishment attributes. The selection and release of 'Immigrant' forage kochia (Kochia prostrata) for seeding semiarid sites resulted, in part, because of the promising establishment attributes of this species (Stevens and others 1985; Stevens and VanEpps 1984). Some initial plantings resulted in erratic stands, due in part to the use of poor-quality seed and improper planting practices. Forage kochia seeds have a postharvest dormancy period of approximately 5 months (Balyan 1972), and no successful method for circumventing afterripening has been developed (Allen 1985). Improper harvesting, cleaning practices, and storage practices can and have resulted in reduced viability and seed quality. Young and others (1981) reported that forage kochia seeds are relatively poor germinators, with less than 50 percent germination at moderate seedbed temperatures. However, the percent of nonviable seed included in their studies was not reported. More recent studies indicate that seed samples contain a number of small and naked seeds that are not viable and should not be included in germination tests (Allen 1985). Preliminary studies indicate that this plant can be established with limited site preparation (Stevens and VanEpps 1984), and that it competes well with weedy species (Ferguson and Frischknecht 1983; Frischknecht and Ferguson 1984; McArthur and others 1974). However, planting without some means of weed control would not appear to be advisable. This study was instigated to evaluate the effects of site preparation and seeding rates on seedling establishment of forage kochia when seeded into existing stands of cheatgrass and other annual weeds. METHODS Field plantings were established at four locations in southern Idaho on lands owned by the Idaho Fish and Game Department. Study sites are located in Jerome, Minidoka, and Gooding Counties, but are within 18 km of the city of Jerome. Plantings were established on farmlands that had been abandoned within the last 4 to 5 years, but are currently being managed for upland gamebird habitat. Each site was occupied by several species of annual weeds, and some native perennials. The annual precipitation and climatic conditions at each site are quite similar (table 1), and before disturbance the areas supported mixed stands of Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) and perennial bunchgrasses. Soils at each site are similar, and differ only slightly in texture and depth of the solum. Soils at Highway 25, Highway 93, and Crestview are very deep (greater than 1.5 m), have a silt loam texture, and are well drained. Soils at the Niagra location are 1.1 m deep, ofloamy sand texture, very well drained, with moderate to low water-holding capacity. Plantings were made in the spring of 1988, using an Amazon NT 375 No-Till grain drill to plant all sites. The drill is designed to plant small-seeded species and trashy seeds like forage kochia (Canadian Ministers of Agriculture 1985). Direct seedings of forage kochia were made into existing weedy stubble without prior site preparation. Two study locations, Crestview and Highway 93, were seeded at a rate of 7.0 kg of pure live seed (PLS) per hectare. Forage kochia was seeded at a rate of about 4.0 PLS/ha at the Highway 25 and Niagra locations. Seed was planted at 19-cm row spacings, and placed at a depth of about 1 em. Seed of 'Immigrant' forage kochia harvested in the fall of 1987 was used in all plantings. Prior to seeding, germination tests were conducted to determine seeding rates. The seed lot had 38 percent germination and 67.8 percent purity, equating to 25.7 percent PLS. The number of seeds or utricles per kilogram (PLS) was 749,575. Two hundred 30- by 60-cm plots were randomly located at each study site in late August 1988 to determine density, height, and crown spread ofkochia seedlings. In addition, the percent ground cover of all associated species was recorded. Daily precipitation and temperature data were obtained from the Jerome weather station throughout the period of seedling establishment (February to May). Differences in seedling density ofkochia plants among study sites were determined using Student-Newman-Keuls means separation tests. Pearson correlation coefficients were used to relate density ofkochia seedlings to the presence of associated species (SAS Institute 1987). RESULTS Precipitation received during the March to May period was above normal, amounting to 11.9 em of moisture (table 2). Seedlings emerged soon after planting in late February and early March before a 2-week period when approximately 4 em of moisture was received. In late May another storm event provided 3.2 em of moisture. Little or no precipitation was recorded for June, July, and August (fig. 1). Daily temperatures remained relatively cool for approximately 2 weeks after planting. Freezing temperatures Table 1-Ciimatic conditions and seeding procedures at four southern Idaho study sites Stud~ sites Crestview Highway 25 Highway93 Niagra Mean annual precipitation (em) Frost-free days Site preparation None None None None Seeding rates (kg/ha) (PLS) Seeding date 3/19-3/20 3/11 3/10 2/19-2/20 Row spacing (em)

3 Table 2-Mean monthly precipitation and monthly precipitation received in , the year of seedling establishment at Jerome, 10 Departure from Month Mean normal October 0.2 November 3.5 December 3.7 January 3.3 February 2.6 March 2.6 April 2.3 May 2.1 June 2.2 July.6 August 1.2 September 1.6 Total Centimeters T -.6 T were recorded throughout the latter part of February and mid-march; thereafter the temperatures rose above freezing and no serious frost occurred that would damage young seedlings. All sites were dominated by annual competition, consisting of cheatgrass, Russian thistle (Salsola pestifer), and tumblemustard (Sisymbrium altissimum). Seeds of all species spring-germinated at approximately the same time; little fall germination occurred for any weedy species. At the time of field rating, cheatgrass plants were dead and dry as were most other species. Plants of all weedy species were able to mature and develop some seed, but were stunted due to intense competition and dry summer conditions. However, the broadleaf weeds remained green much later into the summer than did cheatgrass. In late August the density of forage kochia seedlings ranged from 0.95 to 16.9 plants per square meter (table 3). The greatest number of seedlings was recorded at the Highway 93location planted with 7.0 kg/ha PLS. Sites seeded at the high rate, 7 kglha PLS, generally produced more Temperatures in Degraes +20 Centigrade II,I II n Precipitation In Centimeters 0.5.se March April Figure 1-Daily maximum and minimum temperatures and weekly precipitation recorded February through May 1988 at Jerome,

4 Table 3-Mean number of live and dead forage kochia seedlings recorded at four study locations and percentage of planted seeds 1 that developed into live seedlings. Means followed by the same letter are not significantly different (P > 0.05) Seeding success Planting Plants/m 2 Plants/hectare Planting Percent site Live Dead Live Dead rate return kglha Highway ,605a Crestview ,595b Highway , 139bc 23, Niagra ,144c Seeding rate based on 749,575 seeds (with bracts) per kilogram. seedlings than those with the lower seeding rate, 4 kglha PLS. Within each planting site, seedling density varied considerably. However, the number of live seedlings at each planting site was relatively high. The frequency of occurrence of forage kochia seedlings varied among planting sites (fig. 2). As seedling density increased, frequency of occurrence also increased. Seedlings often appeared in multiples of two or more plants per plot. With the exception of the Highway 93 planting site, the frequency of seedling occurrence was less than 23 percent Dead kochia seedlings were recorded at only two planting sites, Highway 93 and Highway 25. Less than percent of all seedlings at the Highway 93 site succumbed, yet nearly 59 percent of all seedlings at the Highway 25 site failed to survive. No significant relationship was found between kochia seedling density and percent ground cover for any annual or perennial species or group of species. However, the percent ground cover of annual broadleaf weeds was quite high at the Highway 25 site where forage kochia seedling mortality occurred (table 4). Little cheatgrass existed at the Highway 25 site where broadleaf weeds were so prevalent. Nearly all forage kochia seedlings remained green and succulent throughout the entire summer. Seedlings that succumbed did so in early August. Forage kochia seedlings also attained maximum stature by mid August. Seedlings varied in height from 4.1 to 7.5 em, but were not significantly different in stature or vigor among the planting sites (table 5) '10 No. SeedUnga Figure 2-Frequency distribution of forage kochia seedlings at four study sites. Data represent percent of plots with none, one, two, or three or more seedlings No Plants [?J 1 Plant II 2 Plants 3or more DISCUSSION The Amazon drill operated satisfactorily throughout all areas where weedy stubble occurred. In addition, the drill was able to uniformly dispense the trashy seed of forage kochia. The furrower openers were also able to create a suitable seedbed for the shrub seed amid considerable surface debris. Forage kochia seeds were able to germinate, and seedlings established from early spring seeding on semiarid sites dominated by annual weeds. Shrub seedlings did not enter into early summer dormancy, but remained green and continued to grow until late August. Forage kochia seeds responded well to early spring moisture when surface seeded or planted at shallow depths. Seedlings appeared on sites where the presence of surface litter, including standing material, was very dense, and from observations seedlings appeared to benefit from accumulated litter. Seedling density of forage kochia varied among planting sites. Site variables affected seeding success, but planting designs were not adequate to fully evaluate the effects of the two seeding rates on seedling density. However, it appeared that seeding at the high rate, 7.0 kg/ha PLS, resulted in greater numbers and more uniform distribution 69

5 Table 4-Understory species composition, litter, and bare ground for each of four study sites Study sites Species Crestview Highway 25 Highway 93 Niagra Percent cover Cheatgrass brome Broadleaf annuals Broadleaf perennials Seeded perennial grasses Native perennial grasses Litter Bare ground Table 5-Shrub seedling size and vigor for each of four study sites. Means were not significantly different (P > 0.05) Highway 93 Crestview Highway 25 Niagra Mean height em Vigor ranking: 1-5 with 5 the highest. Vigor of seedlings than planting at 4.0 kg/ha PLS. The number of plants that established at all sites ranged from 0.91 to 16.4 seedlings per square meter. These are adequate numbers to produce full-dominating stands, but the distribution of plants at three of the four sites is erratic. Forage kochia spreads quite rapidly (Frischknecht and Ferguson 1984), and some areas may be interseeded and managed to allow for natural recruitment. However, it would not be advisable to seed at a low rate in weedy areas where full stands are desired to control weeds. Density of forage kochia seedlings was not positively or negatively correlated with the percent cover of any existing weedy species or group of species at any study site. Forage kochia plants established amid dense stands of annual weeds at all planting locations. Few shrub seedlings succumbed to annual weed competition during the summer growing period at three of the four study sites. Once seedlings emerged, they appeared able to compete with developing cheatgrass plants. Numerous shrub seedlings did succumb at the Highway 25 planting site where summer annuals were the only weedy species present. A high percentage of summer annuals also existed at the Crestview study site, but no dead shrub seedlings were encountered at this location. However, at the Crestview location cheatgrass and some perennial herbs also existed, and the summer annuals were noticeably less vigorous. At this location cheatgrass appeared to be gaining dominance from the summer annuals; at the Highway 25 site summer annuals dominated. Piemeisel (1938) reported that summer annuals first colonize sagebrush disturbances, but give way to cheatgrass within 2 to 4 years. This shift in understory composition may benefit kochia seedling survival. It appeared that forage kochia seedlings are more susceptible to competition provided by summer growing annuals than early spring developing species such as cheatgrass. Forage kochia seedlings died in the late summer at the Highway 25 location at the time when cheatgrass plants were dead. Thus, it would appear that early spring developing species had less effect on forage kochia seedling survival than summer-growing species. Forage kochia seedlings grew rapidly at all planting sites, attaining heights between 4.12 and 7.55 em. The presence of associated vegetation did not appear to depress growth of the surviving shrub seedlings. Few small or stunted seedlings were encountered at any site even though they grew in close association with annual weeds. CONCLUSIONS Forage kochia demonstrates unusual attributes that favor its establishment in semiarid environments. Seedlings are able to establish within dense annual competition without extensive site preparation. Seeding directly into unprepared seedbeds is possible using an Amazon drill that places the seed near the soil surface. The presence of litter that commonly accumulates with annual weeds was not detrimental to shrub seedling establishment. Shrub seedlings established from early spring plantings during a year of above-average spring rainfall. Although seeds germinate quickly, spring seedlings may not always be successful. Seeding forage kochia at a rate approximating 7.0 kg/ha of PLS is advisable when drill seeding into unprepared seedbeds. However, additional studies are needed to fully determine the most practical seeding rates. Summer annual weeds appear more competitive to forage kochia seedlings than cheatgrass, yet favorable stands developed in areas dominated by both types of weeds. The establishment attributes of this shrub favor its use in controlling annual weeds with minimal site preparation and planting. 70

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