Northern Prairie Wildlife Research Center
Success in the establishment and maintenance of seeded grasslands is closely correlated with soil type, slope, moisture regimes, and other site factors. In the Dakotas, the best stands of introduced cool-season grasses and legumes have been established on Class II or III soils (USDA-SCS 1978b) on level to gently undulating terrain with slopes of 0 to 10%. Good stands have been attained in some areas on Class IV soils with steeper slopes. Sites purchased for some wildlife management areas often do not meet these criteria and special attention should be directed at establishment methods. Introduced cool-season grasses and legumes will probably eventually require periodic rejuvenation by tillage. Thus, this type of cover is best suited to areas where soil erosion from cultivation is slight. Class VI lands should normally be seeded to native grasses.
Soils on which tall, warm-season native grasses grow best are moderately deep to deep, well-drained, and medium to moderately fine textured. Permeability of these favorable soils is moderate and available water capacity is usually high or very high.
Additional planning considerations for restoring cropland to seeded grassland communities within the limits of current technology and available seed sources are presented in the section entitled Seed Sources.
The type of site preparation to be used is associated with soil texture and slope. The tilled seedbed method is preferred for most seedings and may be used on fine (clay-silt) to moderately textured soils. Coarse textured (sandy) soils should be planted to an annual grain crop in 1 year and the grass seeded directly into clean, standing stubble.
Control measures to reduce or eliminate undesirable vegetation should be planned during site preparation and well in advance of the grass seeding. Fields that have not been tilled recently and contain quackgrass (Agropyron repens), smooth bromegrass (Bromus inermis), Canada thistle (Cirsium arvense), leafy spurge (Euphorbia podperae), or perennial weeds may require one or more years of intensive cultivation, herbicide treatment, or both. If only tillage is used, numerous tillage operations may be required to suppress competing vegetation. A final tillage just before freeze-up in the fall has been effective in killing rhizomes of undesirable perennial grasses and weeds. Several tillage methods have been designed to keep plant residue on the soil surface and thus reduce runoff, evaporation, and erosion. Selective herbicides are available and should be carefully evaluated as alternatives to tillage.
It is essential to adequately control competing vegetation before attempting to establish seeded grasslands. Inadequate weed suppression is the cause of grass seeding failures more than any other single factor. A field at the Northern Prairie Wildlife Research Center near Jamestown, North Dakota, provides an example of what can be accomplished with good site preparation and proper seeding techniques. The site had been previously cultivated and was vegetated for 15 years primarily with quackgrass. Procedures followed to establish an excellent stand of tall, warm-season native grasses were (1) quackgrass was killed by intensive summer fallowing (six to eight cultivations were made annually for 2 years and a final cultivation just before freeze-up); (2) the seedbed was packed very firmly; and (3) seeding was done on 30 May with a special grass drill so that the seeds were placed in the compacted soil at the proper depth. Adequate rainfall during June and July provided excellent conditions for germination and growth of the grasses. Big bluestem, indiangrass, and switchgrass attained heights of 4 to 5 feet and produced seed during the year of establishment.
Bryan and McMurphy (1968) reported excellent seedling vigor of native grass cultivars on a weed-free seedbed. Cornelius (1946) stated that reseeding was superior to natural secondary succession in revegetating abandoned cropland. Experience of land managers in western Minnesota and at some sites in the eastern Dakotas has shown that good stands of tall, warm-season, native grasses can be attained in those areas.
Seedbed condition is a very important factor in successfully establishing perennial grasses and legumes. Clean-cultivated seedbeds may be prepared with conventional tillage equipment. Another importent factor in successful establishment of grasses is the degree of compaction of the seedbed. After tillage, the soil should be packed firmly with a spike-tooth harrow or corrugated roller. The soil has been compacted to the desired firmness when a man's footprint in it is less than 1/2 inch deep. Fine-textured soils (or "clayey soils" ) should not be tilled when they are wet because this results in a cloddy or puddled condition.
The protective-crop method of seedbed preparation can be applied on medium- and coarse-textured soils or steep slopes where wind and water erosion are problems. A protective crop includes a planting of an annual grain crop that is harvested to leave a stand of stubble. The protective crop can be planted after site preparation that includes clean-tilled summer fallow. Delay planting of the protective crop in spring until one or more crops of annual weeds have germinated during year 1 and have been killed by shallow tillage. One option is to prepare a firm seedbed and plant close-drilled sudangrass (Sorghum sudanense) between 15 June and 1 July. Spring-seeded annual crops such as oats (Avena saliva), barley (Hordeum vulgare), flax (Linum usitatissimum), grain sorghum (Sorghum bicolor), or millet (Panicum miliaceum) provide satisfactory cover crops. Mow and remove the vegetation leaving a 12- to 15-inch stubble (USDA-SCS 1978a).
Drill perennial grasses directly into the standing stubble without disturbing the soil. Planting into rye (Secale cereale) stubble is not recommended because this crop is very competitive and produces volunteer plants for 2 to 3 years. An application of the herbicide glyphosate before planting or prior to emergence of grasses may be used to control volunteer weed growth. Refer to Extension Service recommendations and follow the manufacturers instructions on the label. The standing stubble method provides an excellent seedbed for fall-dormant or spring plantings using either cool- or warm-season grasses. Warm-season grasses should not be planted in fall. The microclimate created by the standing stubble reduces evaporation and crusting or compaction of soils. However, in northern latitudes, soil temperatures in April and most of May are lowered, partially offsetting the advantages of seeding into stubble to establish warm-season grasses.
The seeding of flax, some small grains, or other crops as companion crops is not recommended with native grasses. The use of companion crops with introduced grasses and legumes is optional. If companion crops are used, flax is the least competitive and other small grain companion crops, such as oats and barley, should be seeded at 1/3 to 1/2 normal rates and mowed at a height of about 15 inches when the grain is beginning to form seed. Use of wheat (Triticum aestivum) or rye as companion crops is not recommended. Genest and Steppler(1973) studied the effects of oats, barley, and wheat as companion crops on grass establishment and found that best results were obtained by not using any companion crop.
The primary requirements for planting perennial grasses and legumes include (1) uniform distribution of seed at the proper rate per acre, (2) placing the seed at the proper depth, and (3) firming the soil around the seed. Drills designed to plant a wide range of native and introduced grass and legume seeds are commercially available. They are equipped with special seed boxes, agitators, depth bands, and packer wheels to meet the primary requirements of planting perennial grasses.
Ground vehicle and aerial broadcast seeding of grass seeds are not recommended. However, we recognize that it is possible to establish good stands of seeded grasslands by broadcasting under optimum moisture conditions. Wilson et al. (1970) compared drill and broadcast methods for crested wheatgrass (Agropyron cristatum) and found that drilling gave much better results because of more constant moisture and temperature relations for seedlings. Bement et al. (1965) obtained the best results in grass establishment from drilling on fallowed soil. If it is necessary to use a broadcast method, then double the seeding rate and pack the soil surface firmly with a corrugated roller or spike-tooth harrow after seeding.
Proper depth of planting is essential to successful stand establishment of seeded grasses and legumes. The kind and size of aced, soil texture, and moisture conditions are the principal factors that influence seeding depth. Seeds should be planted at a depth of 1/2 to 3/4 inch in medium- to fine-textured soils and approximately 1/2 to 1 inch and never more than 1-1/2 inches-in coarse-textured, sandy soils.
Grasses and legumes should be seeded when soil moisture and temperature conditions are optimum for germination of the various species. Cool-season grasses and legumes will germinate and emerge at lower temperatures than warm-season native grasses. Three alternative times are acceptable for seeding cool-season introduced grass: (1) early spring before 1 May; (2) late summer to early fall, 10 August to 10 September if soil moisture is adequate for germination; or (3) late fall dormant seedings after 20 October. Late fall seedings should be so late that germination cannot occur and seeds remain dormant over winter. Preferred seeding dates are before 15 May for cool-season introduced or native grasses and 1 to 15 June for warm-season native grasses. All factors considered, spring plantings by drilling on seedbeds adequately prepared by tillage, preferably summer-fallowed, are most likely to result in the best stands of seeded grassland. Optimum seeding dates for introduced cool-season grasses and legumes, native cool-season grasses, and native warm-season grasses are shown in Table 1 and Table 2. Seeding rates of 20 to 40 pure live seeds (PLS) per square foot are needed to establish adequate stands of perennial grasses in the glaciated prairie pothole region.
Our discussion of the PLS concept is adapted from Kinch (1964). The seeding rate should be adjusted for each species, variety, or seed lot in the mixture. The optimum seeding rate is an interaction of the seed, field condition, and climate. The inherent genetic factors, expressed as percentage germination and seedling vigor, interact with environmental factors-soil, site, moisture, and competition-to determine stand establishment. Seed germination is influenced by stage of maturity at harvest time, age, and storage conditions. Seed origin, size, and mechanical damage have also been correlated with seedling vigor. Moisture and weed competition are two important environmental factors limiting the successful establishment of seeded grasslands. A seeding rate of 40 PLS per square foot is recommended for seeding native grasses in the tallgrass prairie portion of Iowa, Minnesota, eastern South Dakota, and North Dakota including Major Land Resource Areas 56, 102A, 102B, and 103 (Fig. 1), and other sites further west where moisture is adequate. The higher (i.e., +40 PLS) seeding rates are designed to allow more effective competition with annual weeds and to accelerate the rate of establishment.
A seeding rate of 30 PLS per square foot is considered optimum for the mixed-grass prairie transition zone (Major Land Resource Areas 53B, 53C, 55A, and 55B) and 20 PLS per square foot for the drier mixed-grass prairie of central and western portions of South Dakota and North Dakota (Major Land Resource Areas 53A and 54).
A seeding rate of 20 PLS per square foot is recommended for seeding the mixture of tall wheatgrass, intermediate wheatgrass, alfalfa, and sweetclover in all major Land Resource Areas in the area of applicability (Fig. 1).
Pure live seed is a single expression derived by multiplying the purity times the germination. The label on each bag or lot of seed provides information about the kind and quality of the seed. Two important items are the pure seed (purity) and germination percentage.
A big bluestem seed tag shows 82.45% pure seed and 73% germination. To determine the PLS, multiply the pure seed percentage (82.45%) by the germination percentage (73%) and divide by 100.
82.45 x 73.00/100 = 60.18% PLS
The PLS shows that 60% of the material in the bag is viable big bluestem seed and that 40% is inert matter and other seeds.
The PLS values can be used to compare seed lots to determine which is the higher quality. Minimum PLS standards can be established for different kinds of seed to ensure specified quality of seed (Table 3). All seed should have a current germination and purity test. Pure live seed rates may be converted to bulk pound seeding rates by multiplying by the factor indicated for purity and germination of the seed lot (Table 4).
Two methods can be used to select drill calibration and assist with establishing seeding rates.
Seeds per foot method.-Refer to Table 3 to determine the number of seeds per linear foot for various row spacings on PLS basis for recommended seeding rates. The number of seeds have to be increased to adjust for germination of seed. Select the conversion factor for the germination percentage of your seed lot from the full seeding rate column. Multiply the number of seeds per foot of row (Table 3) by this conversion factor. Run the drill over a hard ground surface, concrete floor, or tarpaulin; measure a foot of row, and count the number of grass seeds. Adjust the drill until it is delivering the approximate number of seeds per foot as calculated above. When mixtures are being seeded, use the percentage of each species in the mixture to calculate the number of seeds per foot of row. Seeds per foot for other row spacings not listed on the chart can be interpolated (multiply the figure in the 6-inch column by the ratio spacing used [inches] divided by 6 inches).
Weight method.-Jack up one end of the drill and measure the circumference of the drive wheel (Table 5). From Table 5 determine the number of revolutions of the drive wheel (R) using row spacing and wheel circumference (C) for the drill.
Put some seed into the box and turn the drive wheel until all seed spouts are feeding well. Place a container under the correct number of seed spouts (from Table 5) and turn the drive wheel the number of revolutions previously determined. Weigh the sample in grams, multiply this weight by 0.5, and the result is pounds per acre at that setting. Make adjustments in the drill setting and continue trials until the desired seeding rate is obtained. Weights used in this method are based on seeding rates of the bulk weight of commercial seed.
Seed mixtures to provide a stand of cover with introduced cool-season grasses and legumes include about 8 pounds of tall or intermediate wheatgrass, or both, and 1 pound of alfalfa per acre. Results have been variable from the inclusion (i.e., with, or in place of, alfalfa) of sweetclover in the mixture. Experience indicated that rates of 2 or 3 pounds per acre created too dense a stand the second year and suppressed grasses. If sweetclover is used, not more than 0.5 pound per acre is recommended. Canopy cover in an established stand of introduced cool-season grasses and legumes should be composed of about 75% grasses and 25% legumes. On many sites, poor stands result from having too much alfalfa in the stand. Stands should contain a large amount of standing and partially lodged dead vegetation from previous years. Green vegetation contributes increasingly to the overall cover during May and June due to the cool-season growth characteristics.
Use of Soil Information. The following planning considerations are designed to facilitate the establishment of seeded grassland communities on cultivated soils within the limits of current technology and available seed sources. Soil surveys include valuable information and interpretations that can be used to achieve the proper management of selected lands for wildlife habitat.
Soil surveys are an inventory of the soil resources of an area. Maps are available showing the distribution of soil phases in relation to other physical and cultural features.
Procedures to follow in determining seeding mixtures and rates are explained in the following three steps:
Step 1. Use a soil survey to determine soil mapping unit, land capability class, and range site.
Soil mapping units represent the kinds of soil in a survey area. Each map unit is given a symbol or number that identifies the soil on the detailed soil maps. The soil description includes general facts about the soil and a brief description of the soil profile.
An evaluation of the soil characteristics-texture, depth, permeability, water-holding capacity, soil reaction (pH), salinity,-and topographic features (length and degree of slope)-will assist in determining the type of vegetation needed to meet the desired habitat management objectives.
Capability classes are generalized groupings of soils rated I to VIII which indicate progression of greater limitations and narrower choices of the soils for different uses. These classes can be used in determining suitability of sites for conversion from cropland to grassland by using introduced or native species. Classes I to VI include most of the agricultural lands within the prairie pothole region.
Soils differ in their capacity to produce natural vegetation. Range sites are used for purposes of classifying range resources. A range site is a distinctive kind of rangeland that differs from other kinds in its ability to produce a characteristic natural plant community. A range site is the product of all the environmental factors responsible for its development, especially the soils. Therefore, certain specific soils are generally associated with a given range site (USDA-SCS 1976).
Range condition refers to the present state of a range site relative to the potential plant community for that site. The site is in excellent condition if 76 to 100%, by weight, of the stand consists of the plants of the potential plant community; good condition if it is 51 to 75%; fair if it is 26 to 50%; and poor if it is 0 to 25%. These terms also apply to the seeding and establishment of native plant communities.
Step 2. Consult the SCS Technical Guide Standards and Specifications for guidelines to the potential natural plant community for a specific range site and vegetation zone. Then design the seeding mixture based on the relative frequency and occurrence of each species. If published guidelines are not available, make a survey of the kind and frequency of each major species on a similar site in climax or near climax condition in the same vegetation zone. Ideally, a different species mixture should be developed for each range site. For a practical management operation this may be difficult to achieve, because seeds of some species are not available. In evaluating the kinds and proportions of species to be included in a potential plant community, the initial array may be considered as approximate, subject to change along environmental gradients associated with differences in soil, moisture, topography, and climate. Plant community boundaries are distinct where changes in soils, topography, or moisture conditions are abrupt. Boundaries are broader and less distinct where plant communities change gradually along broad environmental gradients of relatively uniform soils and topography.
Step 3. Use Table 6 to determine seeding rates for each species.
Table 7 provides an example of the method of calculating the seeding rate for tall, warm-season mixtures of big bluestem, indiangrass, and switchgrass on sites where these are suitable.
Table 8 provides a seeding rate for a native mixed-grass planting on a silty range site (Major Land Resource Area 55B; Fig. 1). The application of this planting plan is based on the ability of the technician to identify the range site from the soils map and in the field, to load the drill with the designated grass mixture, and to plant at the proper rate. Additional species diversity may be achieved by applying high-quality native prairie hay as a mulch to the selected areas. A protective cover is essential on sites where erosion is a problem. Companion crops are not recommended with native grass seedings.
Table 9 illustrates a similar procedure for establishing a stand of tall wheatgrass, intermediate wheatgrass, alfalfa, and sweetclover.
The origin, or location where collected, of native strains or released varieties of grasses is important in determining where the plant will be adapted. Also, an understanding of the inherent variability within individual populations of a species is essential to select varieties for seeding. The USDA-SCS, in cooperation with other agencies, has established numerous field evaluation plantings to determine the adaptation and performance of several species and selected varieties of native grass.
When strains of grasses from northern sources are moved southeastward from the point of origin, they mature earlier, are shorter, produce less herbage, and are more susceptible to leaf and stem diseases. When strains from southern sources are moved northward they generally mature later, are taller, and produce more herbage. Experience has shown that southern strains moved too far north may not be winter-hardy and may be damaged or killed during the year of establishment or under adverse conditions caused by climatic or management factors in later years.
The varieties of native plants in commercial seed production are selected to exhibit superior performance within a proven area of adaptation. The use of these superior varieties is encouraged. The alternative is to use seed harvested from natural grasslands. Purchased seed from native grassland harvests is often not identified to a specific point of origin, but if the seed can be harvested in the vicinity of the area of proposed planting it can be used locally with confidence. The area of adaptation for selected varieties of native grass species follow the principles of those of native ecotypes. Experience of the SCS (Cooper 1957) indicates that an ecotype can be moved as far as about 300 miles north or 200 miles south of its origin without having serious problems of winter hardiness, longevity, and disease. Movement of ecotypes east or west is affected by changes in annual precipitation and elevation. Generally, an increase of 1,000 feet in elevation is equivalent to a move of 175 miles north.
Guidelines in the above paragraph do not apply to introduced species but each introduced species or cultivar has a greater though definite range of adaptation (Thornburg 1981). Use of certified seeds of selected varieties known to be adapted to specific areas is recommended for the latter reasons (Table 10).