Impact of Incorporation, Mulch, and Root Coating on the Establishment of Kura Clover from Rhizome Segments on Mine Spoils in Southeastern Kentucky

Chris D. Teutsch, Assistant Professor, Virginia Polytechnic Institute and State University, Southern Piedmont Agricultural Research and Extension Center, Blackstone 23824; Michael Collins, Professor and Department Head, Mississippi State University, Starkville 39762; and David C. Ditsch, Associate Professor, University of Kentucky Robinson Substation, Quicksand 41339-2215

Abstract

Kura clover (Trifolium ambiguum M. Bieb.) may have a place in surface mine reclamation, but low seedling vigor of currently available varieties limits establishment. The objectives of this study were to compare the effect of incorporation method, mulch, and a water-conserving mycorrhizal root coating (1998 only) on the establishment of kura clover from rhizome segments to a conventionally seeded control. Mulching increased plant density in sprigged treatments at the end of the establishment year (P < 0.05). Incorporation treatments that included disking increased plant density in Trial 1 but not in Trial 2. In Trial 2, the water-conserving mycorrhizal root coating negatively impacted sprig survival, resulting in lower plant densities one year after planting (P < 0.05). In fall of the establishment year, stand counts were higher for the conventionally seeded plots (P < 0.05). The following spring, seeded plots had more plants in Trial 1 (P < 0.05), but not in Trial 2. In Trial 2, competition from annual lespedeza [Kummerowia striata (Thunb.) Schindler] resulted in smaller seedlings at the end of the establishment year, and most likely contributed to the decreased ability of the conventionally seeded plants to over winter. Only the mulched-seeded treatment in Trial 1 had a satisfactory stand one year after planting.

Introduction

Commonly used pasture legumes, including red clover (Trifolium pratense L.), white clover (Trifolium repens L.), and alfalfa (Medicago sativa L.) do not persist well in pastures in the southeastern United States (23). Based upon data from other regions, kura clover, a relatively recent introduction originating in the European region of the former USSR, possesses the potential to persist under continuous grazing (23).

Kura clover is similar to most other perennial clovers in that it grows from a central crown, but dissimilar in that it possesses the ability to spread vegetatively via rhizomes (23). Once established, kura clover possesses a relatively deep taproot and vigorous rhizome system, which results in the formation of daughter plants (19). Collins and coworkers (2) found that two-year-old kura plants had on average 12.5 rhizomes per plant for a total rhizome length of 72 inch. In addition, approximately three-fourths of rhizomes possessed a daughter plant.

Kura clover has demonstrated the ability to be productive under various clipping and grazing systems. Sheaffer and Marten (16) found that kura clover stands thickened over time while alfalfa, red clover, birdsfoot trefoil (Lotus corniculatus L.), cicer milkvetch (Astragalus cicer L.), alsike clover (Trifolium hybridium L.), and crown vetch (Coronilla varia L.) decreased. Although kura clover produced less dry matter initially than alfalfa, cicer milkvetch, and birdsfoot trefoil, its persistence and high forage quality under a range of harvesting schedules indicate that it could be an important forage legume (16).

In another experiment, Peterson and coworkers (12) found that kura clover managed under a 5- or 6-cut system yielded less than kura clover under a 3- or 4-cut system. In addition, kura clover that was rotationally stocked produced more with a 28-day rest period than with a 14-day recovery period. Taproot total nonstructural carbohydrate (TNC) concentrations and persistence did not differ for any of the previously mentioned cutting or grazing treatments (13). The authors hypothesized that the extensive root and rhizome system of kura clover helped to maintain adequate TNC reserves and therefore persistence under varying defoliation schemes. Peterson and coworkers (12) concluded that since kura clover is tolerant of frequent and close defoliation and is high in forage quality it should be used as a pasture legume.

Kura clover has also shown the ability to grow on infertile and acidic soils (19). Daly and Mason (3) found that kura clover was twice as productive as white clover on a drought-prone hill soil at a pH of 5.7 and a phosphorus level of 32 lb/acre (Olsen). The authors concluded that the extensive root and rhizome system of kura clover was better able to extract limiting nutrients from the soil. Although kura clover is capable of persisting under low fertility, application of phosphorus has resulted in dramatic increases in dry matter production (1,4). Davis (4) found that increasing phosphorus fertilizer application rate from 45 to 714 lb/acre resulted in a seven-fold increase in yield.

Kura clover is adapted to a large number of environments ranging from high elevation subalpine areas to valley bottoms (19). It can be found on the dry hill topsoils of the Huna area in New Zealand, where its production was moderate compared to the lowland fertile soils of the Rangiora area. Although kura clover has been reported to be productive when soil moisture is limiting (19), under severe water stress, drought-induced dormancy has been observed (N. L. Taylor, personal communication). Native stands of kura clover have also been found on the poorly drained lowlands of the chernozem steppes in the southern Ukraine, with some ecotypes being able to withstand prolonged waterlogging (1,19). The winter hardiness of kura clover has been clearly demonstrated by its excellent persistence and productivity in the north central and northeastern regions of the United States as well as in Canada (19). Although kura clover persists in the southern United States, it is relatively unproductive south of the transition zone, which is located between the subtropical and temperate regions of the United States (23). In Kentucky, kura clover has been very productive under a 4-cut system provided moisture is adequate (23). Three years of testing showed that kura clover produced on average 3.0 ton/acre/year (24).

The wide range of ecological niches occupied by kura clover combined with the fact that it is tolerant of frequent and close grazing, would seem to make kura clover an ideal pasture legume for the Appalachian region. However, difficulty in establishing kura clover has limited its use in temperate pasture systems (19,22,23). Kura clover has poor seedling vigor when measured as relative shoot growth compared with other species (19,22,23). Kura clover has been shown to produce less shoot growth than red clover, white clover, birdsfoot trefoil, alfalfa, and crown vetch at 45 days after planting (20). Low seedling vigor results in slow stand establishment and intolerance to competition during establishment. However, while shoot growth of kura seedlings tends to be limited during establishment, root and rhizome production can be extensive. Spencer and Hely (20) found that kura clover produced three times more below ground biomass than white clover. Collins and coworkers (2) found that one-year-old kura clover plants grown on mine spoil had on average 55% of their total biomass below ground. The substantial root and rhizome system of kura clover stores nutrients and may convey tolerance to environmental stresses that reduce photosynthesis (21,23).

Scott and Mason (15), recognizing that slow stand establishment was limiting kura clover use, conducted a nine-year trial to determine if vegetative propagation from rhizome segments was a viable method for introducing kura clover into unimproved tussock grasslands. Factors affecting establishment from vegetative propagules included rhizome length, presence of a terminal bud, and fertilizer application. Rhizomes between 4 and 6 inches had an establishment success rate of 85% compared to 69% for those less than 2 inches in length. The presence of a terminal bud also affected establishment success. Application of 45 lb/acre of superphoshate annually increased the establishment of rhizome segments to almost 100% compared to 30% for the control. Scott and Mason (15) conclude that while this method of establishment is biologically viable, success and implementation depends on the development of equipment and methods that are capable of successfully harvesting and resowing the rhizome fragments.

The ability of kura clover to grow and persist on infertile and acidic soils along with its potential to persist under a wide range of grazing and clipping regimes, makes it a logical choice for reclaimed mined land pastures in Appalachia. The prolific rhizome production of kura clover, and the work of Scott and Mason (15), suggest that vegetative propagation may be a viable method of stand establishment. The objectives of this study were to compare vegetative propagation and conventional seeding methods for establishment of kura clover, to evaluate the effect of mulch on the establishment of kura clover, and to evaluate the usefulness of a water-conserving mycorrhizal root coating in the vegetative propagation of kura clover on mine spoils.

Research Design and Procedures

Plots were established on 24 March1997 and 17 March1998 on reclaimed mine spoil in Breathitt County, KY. Spoil material was sampled to a 6-inch depth and results are summarized in Table 1. Phosphorus, K, Ca, and Mg were extracted using Mehlich III extractant and quantified by inductively coupled plasma emission spectrometry (9,18). Soil solution pH was determined from a 1:1 (wt/wt) soil and water paste (17). "Rhizo" kura clover sprigs were harvested with a mechanical sprig digger and refrigerated overnight (Fig. 1). Sprigs are defined as segments of rhizome, which may or may not contain a crown. The sprigs used in this study were on average 7.1 inches in length (SE = 2.3 inches), had 6 nodes per sprig (SE = 2.2 nodes), and 57% possessed a crown. Plots were roto-tilled and disked prior to application of the treatments.

Fig. 1. Digging kura clover sprigs from an established stand at the University of Kentucky's Robinson Station, Jackson, KY.

Table 1. Initial spoil characteristics for 1997 and 1998 trials.

Trial	pH	P	K	Ca	Mg
Trial	pH	(lb/acre)
1997	5.5	32	144	1223	579
1998	6.2	74	206	2461	1492

The experimental design was a randomized complete block with a split-plot treatment arrangement and four replications. Whole plot treatments were either mulched with 3.0 ton/acre of wheat straw or left unmulched (Fig. 2). Split plot treatments were 785 lb/acre of sprigs (approximately 1 sprig per ft²) incorporated by disking only, disking and cultipacking, and cultipacking only, or conventional seeding using a cultipacker type seeder at 12 lb/acre of inoculated seed. In 1998, a fifth treatment consisting of a water-conserving mycorrhizal coating of sprigs, incorporated by disking and cultipacking, was added (Fig. 3). This coating was designed to reduce desiccation and to inoculate sprigs with vesicular arbuscular mycorrhizae (RTI, Monterey, CA). Sprigs were broadcast by hand uniformly over the 5-×-20-ft plots and mechanically incorporated (Fig. 4).

Fig. 2. Plots mulched with 3.0 ton/acre of wheat straw in 1998.


	Fig. 3. Applying the water-conserving mycorrhizal coating to kura clover sprigs in 1998.		Fig. 4. Broadcasting sprigs onto plots at a density of approximately 1 per square foot.

Stand density was determined on 24 April 1997, 1 May 1997, 15 May 1997, 5 June 1997, 1 July 1997, 24 July 1997, 6 August 1997, 18 September 1997, and 18 April 1998 for Trial 1 and on 4 April 1998, 23 April 1998, 30 April 1998, 16 May 1998, 22 May 1998, 3 June 1998, 16 June 1998, 24 June 1998, 2 September 1998, 30 September 1998, and 10 May 1999 for Trial 2, by counting plants in 4 ft² of plot area in sprigged plots or by counting 8 ft of row in the seeded plots. All stand counts are expressed as plants per ft². Above-ground biomass was measured approximately one year after seeding by clipping an 80-ft² area to a 2-inch stubble height. A subsample of the harvested vegetation was separated into kura clover and weeds. Weed-free yields of kura clover are expressed on a dry matter basis.

Stand count data were transformed using a square root transformation before being analyzed as repeated measures (6). A combined analysis over years, excluding the water-conserving mycorrhizal coating treatment added in 1998, was conducted (Fig. 3). Since densities of conventionally-seeded plots were substantially higher, data for the sprigged treatments were also analyzed separately using repeated measures analysis of variance. Untransformed means are reported. Treatment means were separated using Fisher’s protected least significant difference derived from the analysis of the transformed data (6).

The combined analysis over years indicated significant treatment × year interactions (P < 0.05); for this reason the two trials were analyzed separately. No significant seeding method × mulch interactions were found for either trial. Therefore, the main effects for mulch and seeding method are presented.

Impact of Mulch on Establishment

In both 1997 and 1998, mulching significantly increased plant density of sprigged plots (P < 0.01). The positive effect of mulch on the sprigged treatments became consistent by 100 days after planting (DAP) in 1997 and by 65 DAP in 1998 (Figs. 1 and 2). Rainfall was ample and well distributed for the three-month period following sprigging in 1998, and probably delayed strong expression of the mulch effect. The earlier observation of the mulch effect in 1997 was most likely due to drier conditions during the month following sprigging. The magnitude of the mulch effect increased with time after planting in both trials (P < 0.01). However, by 400 DAP in 1998, mulched treatments were equal to unmulched treatments.


Fig. 5. Mulch effects on stand density (plants per ft²) for the sprigged plots in Trial 1. Means within a sampling date followed by the same letter are not significantly different according to Fisher’s protected least significant difference (P < 0.05).		Fig. 6. Mulch effects on stand density (plants per ft²) for the sprigged plots in Trial 2. Means within a sampling date followed by the same letter are not significantly different according to Fisher’s protected least significant difference (P < 0.05).

The positive effect of the mulch was likely due to increased spoil moisture in the mulched treatments. Increased spoil moisture due to mulching has been shown to be a result of higher water infiltration rates and reduced evaporation, both of which increase plant available moisture (10,11). The beneficial effect of the mulch observed in the present study is similar to that seen by Schuman and coworkers (14) who found that surface-applied mulch increased stand density for the establishment of big sagebrush (Artemisia tridentata Nutt.). Work by McGinnies (10) also showed that straw mulch increased soil moisture and resulted in improved stands of seeded species.

Impact of Planting Method on Establishment

Conventionally seeded plots consistently had higher plant densities than sprigged plots (P < 0.01) with the exception of the last sampling in Trial 2 (419 DAP) in May of 1999 (Table 2). Plots where sprigs were incorporated by disking and disking plus cultipacking had higher plant densities in Trial 1 (P < 0.03), but not in Trial 2 (Table 2). Treatments involving disking probably resulted in a deeper incorporation of the sprigs into the spoil material than cultipacking alone, thereby creating a more favorable environment in terms of moisture status for sprig growth. Plant densities were generally greater in Trial 2, most likely due to more favorable moisture conditions during establishment and better spoil material (Table 1), which resulted in a seedbed more conducive to sprig root growth.

A negative aspect of ample and well-distributed rainfall in 1998 was the growth of annual lespedeza, which competed with the kura clover seedlings. This competition resulted in smaller seedlings at the end of the establishment year, and most likely contributed to the decreased ability of the conventionally-seeded plants to overwinter. Approximately 17% of the conventionally seeded plants present in the fall (197 DAP) were present the following spring compared to 45% survival for the sprigged plots. This may indicate that, under competitive conditions similar to those in Trial 2, plants established from rhizome segments can better withstand interspecies competition and environmental stresses during the establishment period. If this observation is true, then sprigging kura clover into established pastures may be a better alternative than renovation with conventional seeding techniques. The adverse effects of interspecies competition on kura clover establishment observed in this study for the seeded treatment agree with the comments of Taylor and Smith (23) that kura clover does not tolerate competition during establishment. These authors also concluded that control of all potentially competitive plant species was required for successful establishment of kura clover from seed.

In the spring of 1998 for Trial 1 (389 DAP), and in the fall of 1998 for Trial 2 (197 DAP), an increase in plant density was observed for the sprigged treatments compared with earlier stand evaluation dates (Table 2). This increase in plant density indicates the production of daughter plants. However, even with the formation of daughter plants, none of the sprigged treatments had developed acceptable stands in either trial a year after planting. The earlier formation of daughter plants (169 DAP) in Trial 2 was most likely due to better growing conditions in 1998 and superior spoil material (Table 1). In another study conducted on mine spoil, Collins and coworkers (2) found that 75% of newly established seedlings possessed daughter plants by 150 DAP.

Plots established using Myco-Dip (RTI, Monterey, CA) treated sprigs and incorporated with disking plus cultipacking had lower plant densities on most dates than plots established using the same incorporation treatment without Myco-Dip (Table 2). The basis for the negative effect of the coating needs further investigation. However, one may postulate that the root coating negatively affected water relations of the treated sprig. In dry soil, the highly hygroscopic coating may have drawn water from the sprig tissues or may have restricted movement of soil water to the sprig. An investigation by Henderson and Hensley (7) found transplant survival and growth was not improved by using a hygroscopic root dip. In fact, transplants treated with the root dip had lower plant water potentials. However, a number of studies conducted with barefoot tree seedlings have shown increased survival rates when a root dip was employed (5,8). Magnussen (8) found that root dip increased seedling survival by 24% under mild drought stress that did not extend beyond two weeks. A study by Echols and coworkers (5) also found that root dip improved seedling survival only under short-term drought stress. In more stressful environments, no significant influence on long-term seedling survival was found. Echols and coworkers (5) concluded that root dip effectiveness is uncertain and decreases with extended drought stress.

Kura Clover Yield for the Year Following Establishment

Only the mulched-seeded treatment in Trial 1 developed a harvestable sward one year after establishment. The total DM yield for the year following establishment for the mulched-seeded treatment in Trial 1 was 1427 lb/acre, which was approximately 40% that of an adjacent red clover study (unpublished data). Similarly a study in Minnesota showed that initial yields of kura clover were less than that of other common legumes; however, in the second and third year, kura clover yields were similar to those of other top-yielding legumes (16). In the current study, no treatment in Trial 2 produced a harvestable yield during the year following establishment. This was most likely due to severe competition imposed during establishment by annual lespedeza.

Conclusions

Findings from the current study confirm that kura clover establishment is possible using vegetative propagation. However, success is highly dependent upon thorough incorporation of the sprigs into a well-prepared seedbed and adequate initial moisture, both of which can be difficult to achieve in mined land reclamation. Results from Trial 2 indicate that kura clover seedlings established from rhizome segments may be more tolerant of interspecies competition during establishment; however, these observations need to be confirmed. Although kura clover possesses many desirable characteristics in terms of persistence and stress tolerance, its use in mined land reclamation is limited by poor stand establishment.

Acknowledgments

We thank Tracy Hamilton, Mary Rose Jones, and Wade Turner for their technical assistance. We would also like to thank the Robinson Forest Trust for funding this research.

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