Establishing a new pasture requires some management to get the forage growing quickly and vigorously. Here are some of the key factors involved in establishing or renovating a pasture:
Key factors involved in establishing pastures for grazing.
- Soil testing
- Seedbed preparation
- Species selection
- Seeding methods
- Seeding time
- Seeding rates
- Sowing depth
- Seed quality
- Seed dormancy
- Seed treatment
- Propagation methods
- Pasture grass-forage legume intercropping
- Fertilizer requirements
- Soil testing
A soil test refers to analysis of a soil sample to determine nutrient content, composition, and other characteristics such as the acidity or pH level (acidity or alkalinity of a solution). A soil test should be done before sowing in order to correct any mineral deficiencies.this provides a simple, affordable and fast way of scanning soil samples for Nitrogen, Phosphorus, Potassium and pH with a Soil Scanner. Based on a quick scan with spectography, a farmer can get within 10 minutes an advice on what will grow well on your soil and what kind of fertilizers you might need.
- Seed bed preparation
Good seed-to-soil contact is essential to maintain adequate moisture near the seeds. The moisture is necessary for germination and for the small root systems of young grass seedlings. The best type of seedbed preparation depends on the type of equipment available and whether a new pasture is being established or an existing pasture is being renovated. Characteristics of a good seedbed are:
(a) uniformly firm soil to depth of about 10 cm,
(b) adequate soil moisture, and
(c) weed free.
- Species selection
Selecting the right species or species mixture is extremely important. When establishing a pasture, it is important to match pasture species to the site, soil type, and purpose of feeding (fattening) and animal species. Good pastures must have the following characteristics:
(a) tolerance to grazing,
(b) resistance to drought,
(c) high nutritive value,
(d) high palatability and,
(e) high biomass forage production.
- Seeding methods
The ideal seeding method depends on the type of equipment available and whether you plant on a no till or a conventional seedbed. To ensure good soil-to-seed contact, seed germination, and timely emergence, different seeding methods are available. Some of these methods include
Broadcasting or sowing in swards means that the seed is spread in the field while considering the direction of the wind for even distribution.
A farmer broadcasting seed in the field
For hand broadcasting, the seed should be mixed with a ballast of a similar specific gravity such as sand and weighed out into lots for specified areas; the field is then marked by temporary pegs so that each area is covered by one seed lot. Marking out the land and weighing the seed into lots is especially important when using people who are not experienced. Seed is very expensive, so the extra care is usually well recompensed by reducing the common mistake of too dense sowing in the first part of the field and no seed left for the last.
Broadcasted seed must be covered lightly using a branch of a tree to avoid damage by birds or being washed away in case of heavy rains. Sowing in swards or broadcasting has a disadvantage of using a higher seed rate. However, it has advantages of producing more pasture for livestock and of controlling soil erosion.
- Row planting/drilling
Row planting or drilling cuts a thin furrow in the soil, deposits the seed, then covers it and firms the soil with press wheels. A good rule is to plant the seed three to four times as deep as the diameter of the seed. The seeds are hand drilled into furrows of about 2 cm depth. Pasture crops are planted in rows or straight lines to enhance maximum yields as well as for convenience. The spacing between lines is 30 to 60 cm depending on the pasture type. The seed germinates in 1-7 days.
Row planting method
Row planted Rhodes grass pasture
Advantages of sowing pasture seed in rows:
- A lower seeding rates is used;
- Harvesting is usually a lot easier;
- Light exposure is maximized. Conversely, the excessive shading effect of other plants is minimized thus favouring more efficient photosynthesis and improved crop yield;
- Access through the inter-rows facilitates cultivation, weeding, and other farm operations including hauling;
- Movement within the crop area is more convenient and allows close inspection of individual plants;
- Visibility is enhanced; and
- It is easy to calculate or count the plant population in a given farm area.
Under-sowing is establishing pastures under a nurse or a cover crop such as maize. The nurse crop is grown together with pasture for economical land use. The nurse is harvested after maturity and the pasture left for 2 to 3 years. The grain is harvested and the sward develops thereafter. This saves a season and cuts out the tillage for one crop. The cereal is sown in the usual way and then the pasture seeds are broadcast or row-planted more after the last weeding. Rhodes grass and molasses grass (Melinis minutiflora) are some of the pasture species that can be established under maize. The seed is broadcast or planted in rows under the maize after the last weeding. The stover must be removed immediately the crop is harvested, and a slashing to remove tall weeds is desirable. The crop is not grazed until after the onset of the next rains.
Oversowing is the technique of sowing forage legumes and/or grass into existing pastures without preparing a traditional ploughed and cultivated seedbed. There are two factors crucial to oversowing success:
(a) availability of soil moisture for germinating seedlings.
(b) controlling competition. Graze tightly after sowing – do not set up sward for cutting for hay or silage.
- Seeding time
Seeding on the correct date is also very important for the success, longevity and productivity of a pasture. Optimum sowing time varies greatly with local conditions and farming systems. Pasture seeds planted at the beginning of the rain season have plenty of moisture for germination, but they sustain increased weed pressure. The shorter the rain season, the more critical is early sowing. Where the dry season is short, pasture can be sown late in the rains. The peak of the rainy season is best avoided.
- Seeding rates
Proper seeding rates depend on: (a) pasture species and, (b) seeding method. To obtain a good establishment, use seed that is pure, has a high germination rate, and has not been stored for a long period of time. High quality, certified seed is recommended. Seed cost could be a major portion of the total establishment cost, but buying less expensive seed does not always translate into savings. Table 1 shows recommended seeding rates for common pasture species.
Table 1: Recommended seed rates of common pasture species
|Pasture type (Common name)||Scientific name||Seed rate
|Signal grass||Brachiaria brizantha||10-15 bags|
|Napier grass||Pennisetum purpureum||18 bags|
|Rhodes grass||Chloris gayana||10 kg|
|Guinea grass||Panicum maximum||10 kg|
|Greenleaf Desmodium||Desmodium intortum||1-2 kg|
|Centrosema seed||Centrocema (pubescens)||molle||3-4 kg|
|Siratro||Macroptilum atropurpureum||2-4 kg|
|Lablab||Lablab purpureus cv Rongai||7-10 kg|
|Alfalfa||Medicago sativa||4 kg|
- Sowing depth
Seed is usually placed on the surface and lightly covered with soil. To achieve the best strike with most pasture grasses and legumes do not bury the seed deeper than 10 mm. However, lucerne, purple pigeon grass and silk sorghum can be planted as deep as 25 mm.
- Seed quality
Poor quality seed will lead to poor and prolonged pasture establishment. Seed germination and contamination with weeds should be checked. Seeds should not be stored for too long, they should be planted as soon as possible to ensure a high germination rate. Seed quality affects germination of the seed.
Seed viability is a measure of the percentage of seeds that are alive after storage. The greater the viability of your seeds, the fewer seeds will be needed to establish a desired number of plants in the field or nursery.
A simple viability test:
- Randomly take 100 seeds from the seed you intend to use.
- Put the seed on a wetted container such as a blotting paper or a perforated plastic plate.
- Make sure the seeds get enough light and water.
- After 7 days, count the number of seeds that have germinated.
Percent (%) germination = Number of seeds that have germinated x 100
Good pasture seed should have a germination percentage of over 30% for grasses and over 70% for legumes. Get good quality seed from reliable sources.
Seed longevity, vigour and viability depend on genetic and physiological factors as well as storage conditions. The most important factors that influence storage are temperature, moisture, seed characteristics, micro-organism geographical location and storage structure.
- Seed dormancy
Seed dormancy is defined as a state in which seeds are prevented from germinating even under environmental conditions normally favorable for germination. These conditions are a complex combination of water, light, temperature, gasses, mechanical restrictions, seed coats, and hormone structures. Storage of pasture grass seed for 3-6 months in a cool dry and well ventilated place overcomes this. The major reasons of seed dormancy are: (a) immaturity of embryo, (b) impermeable seed coat and, (c) hard seed coat and, (d) seed inhibitors.
- Seed treatment
Pasture legumes such as Centrosema, Siratro and Stylosanthes have a high proportion of seeds with impermeable seed coats which do not absorb water and which, therefore, do not germinate when sown but can lie dormant in the soil until such time as the seed coats loses its water-resistance; such seeds are said to be “hard.” This is an excellent character for survival in areas of unreliable rainfall, but is not desirable when rapid establishment of a fodder crop is wanted. Germination of hard-seeded forage legumes can be improved by (a) scarification; (b) hot water treatment; and (c) innoculation.
This is involves rubbing gently small quantities of forage legume seed between two sheets of sand paper held in the palm of the hand. For larger amounts, a mechanical scarifier (e.g. a cement mixer containing some gravel) can be used.
(b) Hot water scarification
This can be done in small to medium quantities of seed.
- Boil one litre of water (depending on the quantity of seed).
- Put 1-2 kg of seeds into a piece of cloth bag and dip it into boiled water (removed from boiling place) for 2 minutes. All the seeds must be submerged and in contact with the boiled water.
- Soak the seed in cold water for 12 hours.
- Dry the seeds for 1-2 hours.
- Treated seed should be sown soon after treatment.
Inoculation of pasture legume seed
Pasture legumes form a symbiotic (mutually beneficial) association with specific soil bacteria (rhizobia) to meet their nitrogen requirements. Nodules develop on the plant roots and house millions of rhizobia that convert nitrogen from the air into a form the plant can use in a process known as nitrogen fixation.
The association between the host plant and its rhizobia is very specific and pasture legumes must be inoculated with the correct rhizobia strain (or Group) for maximum nitrogen fixation. Techniques to successfully inoculate pasture legume seeds are described here. If the specific Rhizobium is not available, then the soil from rhizosphere of nodulating plants of the same species should be mixed with the seed.
Types of inoculants
Inoculants come in four different carriers:
- freeze dried powders
- a pre-coated seed form, with inoculum as part of the pellet.
Improved survival is obtained by using an adhesive or sticker to attach the inoculum to the seed. The most readily available form of sticker is a 10% sugar solution (i.e. 10 gm. sugar in 100 ml water). Seed is wetted with the solution and the peat culture mixed with the seed and allowed to dry in the shade – direct sunlight will kill the rhizobium. The following should be noted when inoculating and handling inoculated seed:
- Make sure that the seed has not been treated with a chemical and that containers used do not contain toxic substances such as oil, petrol, chemical pesticides.
- Do not mix inoculated seed with acid fertilisers such as superphosphate.
- Ensure that the peat culture used is within the expiry period.
- Store inoculum in a refrigerator for up to 2 months.
- Sow inoculated seed into moist soil.
- Spraying a peat/inoculum mix onto established legumes during cloudy weather can partially or completely overcome nodulation failure.
There are many factors affecting forage legume component in the pastures. The most important but controllable factors are the defoliation, grazing/cutting management and fertilizer. The optimum level of legume content in the pasture grasses should be about 30%.
Pasture crops can be propagated using: (a) vegetative materials or (b) seed.
- Vegetative planting
Some pasture grasses are sometimes propagated vegetatively, usually cuttings, stoloniferous or rhizomatous species. It is done where seed is expensive, not available or difficult to produce or where clonal material is used (e.g., some cultivars of pangola grass (Digitaria decumbens) and Kikuyu grass (Pennisetum clandestinum).
- Sowing from seed
Direct sowing means that you start planting seeds in the field, rather than raising seedlings indoors earlier and transplanting them outside.
Why is sand needed when sowing small pasture seeds?
Tiny pasture seeds such as Green leaf desmodium, Rhodes grass, Siratro and Centrosema are difficult to handle. It is easy to end up with the entire packet of seed in a pile on your field. This wastes seed, reduces germination rates and increases the time spent thinning. One of methods you can use to solve this problem is to mix the seed with sand, or other fine material. Mixing seed with sand spreads the seed out and makes it less likely you will drop too many seeds in any one spot.
- Mix a packet of seed with about 4 times as much sand.
- Drop the seed/sand mixture sparingly along the row or area where you want to plant.
One of the commonest causes of failure in establishment of small-seeded species is sowing too deeply. Thus, the timing, rate and depth of sowing are critical. Since most pasture plant seeds are relatively small, they are generally sown on the surface of the soil or incorporated to not more than 1 cm depth.
- Pasture grass-forage legume intercropping
Successful meat production is dependent on forage programs which supply large quantities of adequate quality, homegrown feed. A major percentage of the feed units for beef cattle come from pastures. In addition, pastures supply over 60% of the nutrients consumed by beef cattle.
To maintain high productivity and forage quality for beef cattle, it is recommended to intercrop forage legumes with pasture grasses rather than rely on nitrogen fertilizer.
Pasture grass mixed with forage legumes
The role of forage legumes as the cheapest potential source of soil, crop and animal N in different beef cattle farming systems include:
(a) Higher yields
The total yield of forage per acre is increased by over 30 percent.
(b) Improved quality
Adding forage legumes to grass fields improves forage quality over grass alone. This added quality includes increases in palatability, intake, digestibility, and nutrient content. In terms of meeting the nutrient requirement of beef cattle, all forage types will likely be limiting energy and protein content during some point of the forage plants life cycle. The maturity (or stage of growth) of the forage is typically the largest determinate of the crop’s nutritive value. As the plant enters the reproductive stages of growth, it develops a higher proportion of fibrous stem material which lowers the overall concentration of digestible energy and protein the animal will receive from the plant. In general, forage legumes tend to have higher concentrations of protein and digestible energy than grasses when compared at a similar stage of growth
(c) Extend the grazing season
Most forage legume species are less prone to the hot, dry conditions that restrict growth of other species due to their large tap root systems that allows the plant to access soil moisture deeper in the soil profile.
(d) Legumes vs. Nitrogen fertilizers
The concentration of Nitrogen provided by the soil is low and insufficient to support regular plant growth. Forage legumes are capable of providing their own source of Nitrogen through a symbiosis with Rhizobia. These bacteria infect the legume host’s root system and produce an enzyme that converts (or “fixes”) inert, atmospheric Nitrogen into active, plant available forms. As portions of the forage legume plant decompose or are redistributed as manure following the consumption by livestock, the fixed Nitrogen slowly becomes available for use by other species in the pasture.
(e) Weed management
Weeds can reduce the quantity and the stand life of desirable forage plants in pastures. Weeds can also diminish the quality and palatability of the forage available for livestock grazing, and certain weed species are potentially poisonous to grazing animals. The aesthetic value of a pasture is also impacted by weeds. Forage legumes when intercropped with pastures grasses can serve as cover crops, control weeds and conserve soil moisture.
Established pastures should be monitored to assess the need to address a developing soil nutrient issue. Soil nutrient issues may be identified through visual assessment, plant tissue tests and soil tests. Which fertiliser is best suited to a particular situation requires local knowledge and it is often advisable to seek professional assistance.
(a) Pasture grasses
Nitrogen is the main nutritional determinant of pasture grasses and split applications after one month of sowing and at flowering, each of 50-100 kg/ha Nitrogen, are commonly used based on the fertility of the soil. This implies that after application of the two split doses, the total application rate of Nitrogen will range between 100-200 kg/ha. Single dose application of Nitrogen is discouraged as the plant will not have adequately developed to effectively utilize all the applied nitrogen. As such, much of the Nitrogen is often wasted and is not channeled into vegetative and seed production. At times, the grass benefits from application of phosphate fertilizers at sowing if phosphorus is limiting. However, a farmer is advised to consult a local extension staff before such a decision is taken.
(b) Pasture legumes
Nitrogen is often not limiting in pasture legumes because the Nitrogen fixing bacteria found in the root nodules of pasture legumes have the capacity to utilize atmospheric Nitrogen and fix it into soil. The fixed Nitrogen is then utilized by the leguminous plants. Ensuring adequate availability of phosphorus is crucial if adequate fodder yields are to be realized. It should be noted that the rate of application will depend on the phosphorus content and pH condition of the soils. When the soils are strongly acidic, application of phosphorus is merely a waste as most of it is simply fixed and rendered unavailable for plant uptake. Under such conditions, amendment of the soil with lime shall improve the soil pH conditions and hence prevent fixation of applied phosphorus.
One should be successful in establishing a new pasture if all of the requirements for establishment are met in a timely manner.
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