ABSTRACT

Ever since it’s inception in New Zealand during the 1950’s, coated seed has been seen to best advantage in the type of stress conditions found in many land reclamation areas in North America. These areas are often dry and unfertile, making legume and grass establishment difficult. Legumes can be more difficult to establish than grasses, as many land reclamation areas are devoid of the native rhizobium populations necessary to cause effective nodulation. In addition, the NEED for inoculation is often overlooked. Coated seed is designed to remove the necessity for inoculation of legumes prior to seeding and to assist in overcoming other typical land reclamation stress conditions.

INTRODUCTION

Although coated seed has been available in North America for many years, numerous people are not aware of the benefits it offers especially in relation to land reclamation work.

The history of coated seed goes back a long way. Coatings of an organic nature were used by farmers of earlier times with notable success and recorded references to coated seed can even be found in the Bible. Modern day coated seed was pioneered in New Zealand in the 1950’s where the rugged hill country proved to be an ideal testing ground. The successful establishment of clovers and grasses on many thousands of acres of the South Island high country was mainly due to aerial applications of coated seed.

The coating technology was soon extended to cover other legumes as well as a wide range of forage and turf grasses. Gradually, the original technology spread from New Zealand to North America and Europe, where virtually any type of seed that the market requires is now available in coated form.

THE REASONS WHY WE COAT SEED

The six most important reasons why we coat seed are:

l. Pre-inoculation of legumes

2. Nutrient benefits

3. Protection from stress conditions

4. To improve ballistic properties and simplify seeding

5. Safe application of agricultural chemicals

6. Protection from rodents, birds and the harmful effects of some fertilizers

THEORY

Seed coating is a process designed to create a nutritious environment in the immediate vicinity of the germinating seed and to provide a "boost" for the seedling in its critical early phase of development. This is particularly important under the type of stress conditions found in many land reclamation projects.

Phosphorus is the main nutrient supplied by the coating to the seed. The type of phosphorus used in the coating varies with the different manufacturers. As it is placed in the immediate vicinity of the seed, it is utilized by the growing plant before being fixed and becoming "relatively unavailable".

In the past, many people have expected coated seed to allow them to ignore good seeding techniques at planting time and to provide large yield increases as well. Coated seed does provide major advantages but good cultivation and planting techniques should still be followed wherever possible.

Today coated seeds benefit the plant in its critical seedling stage ensuring early vigor and in the case of legumes, fast, effective nodulation. There is obviously some "carry over" effect from this increased seedling vigor, but once the plant has nodulated and the fertilizer in the coat has been assimilated by the plant, the coating cannot directly benefit the plant in its future development. The increased use of agricultural chemicals and slow release fertilizers may offer additional benefits in the future. However, present economical, nutritional and bacterial benefits make coated seed worthwhile in most land reclamation projects today.

The need for nodulation is obvious. Effectively nodulated legumes can fix large amounts of nitrogen from the atmosphere. This nitrogen is utilized not only by the legume but also by other plants growing in association with it. Pure alfalfa stands  are capable of fixing approximately 150 kilograms of nitrogen per hectare per year.

In the past, seed has been inoculated using a variety of methods, many of which are unsatisfactory. One of the more effective methods of inoculation is by spreading a sticker over the seed and sprinkling dry peat based inoculant onto this. This method will result in effectively nodulated plants providing it is done immediately prior to seeding. However, this is not always possible, especially when aerial seeding or hydroseeding remote land reclamation sites. Pre-inoculation is the obvious answer. It ensures that the rhizobia are "in the right place at the right time".

Seed coating was initially the subject of some controversy when it was first introduced to North America, however, one statement was always made without fear of contradiction. That was and still is that "seed coating is the most effective method of pre-inoculation available in North America today".

1. PRE-INOCULATION

This is the single most important reason why legume seeds are coated and it is particularly important in areas where the legume being seeded has not been grown previously.

Pre-inoculation is the addition of nodule bacteria (rhizobia) to the seed, weeks or even months in advance of sowing. It ensures that the bacteria are in close proximity to the roots of the germinating seedling and thus in a position to cause fast, effective nodulation. Increasing numbers of people are now recognizing the need for legume inoculation, particularly when seeding in the harsh conditions prevailing in most land reclamation areas. The need for inoculation is very important in the case of trefoil, as there are few, if any, native populations of the rhizobium necessary to induce nodulation in trefoil present in North American soils.

It is true that many soils in North America do have large populations of rhizobium meliloti and that in many cases, un-inoculated alfalfa seed would nodulate when sown in these soils. It is also true that the yields of many of the plants infected by these native bacteria have been significantly greater had they been infected by the far more effective strains of rhizobium used in modern seed coating processes.

Large amounts of money are spent by Agriculture research scientists each year in an attempt to develop new stains of rhizobium which can utilize the rhizobium/legume association far more effectively than many of our native rhizobium strains.

2. NUTRIENT BENEFITS

Seed coating creates a nutritious environment around the germinating seed. This increases seedling vigor during its critical early development. Up to 20% of all grass seed coatings and 9% of the legume coating is phosphatic fertilizer. Phosphorus is essential for plant growth and is especially critical for young seedlings, as it ensures normal root development and vegetative growth during the critical early stages of establishment. Even on soils with phosphorus levels sufficiently high to sustain normal growth, localized placement is very beneficial. It is particularly desirable from the standpoint of accessibility to the establishing seedling and in order to reduce fixation. Phosphorus does not travel in the soil, therefore, the nearer it can be placed to the seed, the easier it can be utilized by the seedling.

Lime, an important component of the coat, can have a beneficial effect in low pH soils and in addition, it combines with the phosphorus to form an excellent carrier for rhizobia. Although coated seed does have significant nutrient benefits it should be emphasized here that the coating does not negate the need for normal cultivation and fertilization techniques at seeding time whenever possible.

3. PROTECTION FROM STRESS CONDITIONS

The fact that seed coating offers the seed significant protection from the typical stress conditions found in many land reclamation areas is a very important factor in its use in such areas. The principal means by which the various stress conditions are overcome are:

a. Moisture Stress. Bare seeds which find a successful germination site can draw small but sufficient quantities of moisture, particularly overnight from soil or foliage, thereby initiating germination. Such seedlings may die in large numbers where moisture availability remains insufficient to sustain growth such as during a week or two of dry weather following over-sowing. When coated seed is used and moisture conditions are good enough for coat penetration to the seed within, it is less likely that subsequent germination will fail from absolute moisture deficiency of soil or foliage.

b. Wind and High Temperatures. Wind and high temperatures are particularly harmful to over-sown legume seeds. This is because the death rate of rhizobia is increased dramatically by the drying effects of such conditions. It has been shown that even under controlled climatic conditions, rhizobia on bare seed suffer a severe decrease in viability in as little as 2-4 hours after inoculation. The coating around the seed offers protection for the rhizobia and ensures their survival, which in turn ensures an effectively nodulated legume plant.

c. Nutrient Deficiencies. The benefits available to the seed from localized placement of fertilizer are well known. Seed coating is a means of placing fertilizer in the immediate vicinity of the plant where it is most effective. Most coatings contain phosphorus, however, other nutrient deficiencies in the soil can be overcome by the use of slow release fertilizers which have been shown to have a significant effect several months after seeding.

To be able to utilize these fertilizer benefits it is essential that soil pH be as near optimum for nutrient uptake as possible. Although seed coating will not replace the need for liming, it has been shown that the lime in the coat has a pH buffer effect which helps to protect the seed from acidic soil conditions.

4. BALLISTIC PROPERTIES

Most coated grass seeds are at least twice as heavy as bare seed. This factor is particularly important when land reclamation sites are being aerial seeded. Bare seed is much lighter with poor ballistic properties thus it frequently fails to penetrate foliage to a satisfactory soil germination site. On the other hand, the increased weight of coated seed substantially increases its aerial velocity. This allows penetration of the foliage and often results in improved germination.

5. PROTECTION FROM RODENTS, BIRDS AND THE HARMFUL EFFECTS OF FERTILIZERS

Rodents and birds often fail to recognize coated seed as food. This may be due in part (particularly in the case of birds) to the increased size of the seed but more often can be attributed to the taste of the phosphorus and lime in the coating.

Mixing bare seed with some fertilizers can have serious effects on both the germination of the seed and in the case of legumes, will destroy the rhizobium on the seed. These two factors are both overcome by the protective effect of the coating, which allows all seeds to be successfully mixed with fertilizers prior to seeding.

6. AGRICULTURAL CHEMICALS

The use of agricultural chemicals is particularly important in North American agriculture. Coated seed has been utilized as a carrier for fungicidal treatments such as Captan and Thiram for some time. Seed coating is a safe, reliable and economical method of applying agricultural chemicals to the seed, especially when these chemicals are available in flowable formulations.

DISCUSSION

Coated seed has a very important part to play in land reclamation projects in North America. Many of the reasons for this have been discussed earlier in this paper.

The concept of coated seed and especially "hydrocoated" seed is still relatively new  and requires further research.

The following are examples of land reclamation projects where Coated seed has been used in North America:

1. Northern Alberta - Tar sands reclamation

2. Northern Manitoba - Conversion of native bush to pastures

3. Cape Breton Island - Mine land reclamation

To ensure that coated seed can be used in such reclamation projects, several different types of coat have had to be developed, including a "hydroseeding coat". Coated seed normally breaks down very quickly in water. In the past, it could not be hydroseeded as the coat dissolved and all its benefits, including the pre-inoculation system, were lost. Technology has been developed that produces a coated seed which will withstand at least 40 minutes vigorous agitation in the hydroseeder tank and still retain its coat. Laboratory and plot trials with this coating material show no reduction in germination compared to conventionally coated seed. Further modifications to the process have allowed it to be used on legume seeds without any harmful effects to the rhizobia

Many land reclamation projects involve the use of aerial seeding. Coated seed is particularly valuable for this purpose. One rather interesting aspect of aerial seeding is the reclamation of large areas of native bush in Northern Manitoba. This operation involves spraying the trees with herbicides and following this up by over-sowing with coated seed. Several areas in Manitoba were seeded this way and after the bush died had a very good covering of grasses and legumes and eventually became excellent grazing land.

Coated seed is not the answer to every seeding problem either on land reclamation sites or in good pasture lands, however, it does have its role to play in North American agriculture.

This role is best suited to the unique land reclamation problems that exist in Canada. The single most important problem in many of these areas is the lack of effective native strains of nodule bacteria. Coated seed undoubtedly offers the best pre-inoculation system for legumes under the stress conditions found in these areas. This reason alone is sufficient to warrant its use in most land reclamation projects.

next article >>