Seed :: Pulses :: Cowpea

QUALITY SEED PRODUCTION IN COWPEA

Selection of land for seed production

The selection of land is the first and foremost task for a seed producer. The seed production plot must be selected carefully. A fertile and healthy seed plot will certainly produce quality seed. The field selected for seed pro­duction must not have been sown. with cowpea in the previous season. This is done to avoid volunteer plants that cause admixture. Fields continuously cultivated with cowpea may harbor root rot or wilt pathogen. Hence, such fields must be avoided. Also, following crop rotation will help to reduce endemic pathogen.

Seed production field

Soil with neutral pH must be selected. Loam or clay loam soils are best suited. Higher organic matter will lead to production of vigorous seed.

What are volunteers?

Volunteers are plants that grow in the field from the seeds already found in the soil. These seeds should have been fallen from previous season crop. They germinate without sowing or they volunteer to grow by themselves, hence the name volunteer plants.

Isolating the seed crop to avoid genetic contamination

The quality seed must be genetically and physically pure. Genetic purity can be maintained by preventing cross pollination with other undesirable varieties. This is achieved by isolating the seed crop.
Isolation is the act of growing the seed crop away from a contaminant such that cross pollination is prevented. The cowpea seed crop must be grown 5 M (15 feet) away from another variety of cowpea.

Frequently we come across seed farmers complaining that they are not able to isolate seed crop. Under such condition five rows of maize can be raised all around seed crop to pre­vent contamination.

Selecting the right season

Seed is very sensitive to weather. A grain crop can be sold for a lower price even if it is damaged by rain. But a seed crop, if affected will lead to reduced seed vigour. Hence selecting the right season is important. Generally, the seed should mature in cool dry climate. Seasons are selected with this idea in mind. In Tamil Nadu, the best seed crop growing season is February – March.

Preparation of land

The land is thrown into ridges and furrows of one and half feet wide or beds and channels of 4' x 6' depending on the cultivation practices.

Fertilizer

Ten cartloads (5 tonnes) of well decomposed compost is spread along the field with basal application of 45kg urea and 120kg super phosphate per acre.
 
Selection of seeds

Seeds used for sowing must be from an authentic source. An authentic source is one with high genetic purity and other aspects of physiological and physical quality of seed being sown. Seeds used for sowing must also be vigorous only then you can expect a good field stand. Seeds must be checked for hard seeds, diseased seeds, immature seeds, shrunken and de­formed seeds.

It must be noted that any farmer can take up certified seed production. The Agricultural Officer of the area will be of help. The certified seed crop will be taken using Foundation seed and Foundation seed crop using Breeder seeds.

Seed rate

Depending on the variety the seed rate varies from 8 -10 kg per acre.

Seed treatment

Text Box: Hard seeds- What are they?  	Pulse seeds normally harbour hard seeds. These are seeds that do not absorb moisture when soaked in water. As a result they fail to germinate thus causing gap in the field. Certification does not allow gap filling in seed production plots. Hence, sowing seeds with more than 10% hard seeds is not advisable.    How to identify hard seeds?  	Take 100 seeds and place them in a small vessel. Fill the vessel with 100ml of water. Wait for 2 hrs and at the end count the number of seeds that have swollen upon imbibition. The number of seeds not imbibed are termed as hard seeds.    How to reduce hard seed content?  	As mentioned earlier, if the hard seed content is more than 10% the seeds can be given acid treatment. Seeds possessing hard seeds are treated with 10% commercial sulphuric acid. The seeds are placed in plastic bucket and acid is added at 100ml per kilo of seed. The acid added seed is stirred with wooden stick for 2 minutes and then immediately washed with water three times to remove acid completely. The seeds are then dried in shade for 4 hours.

Before sowing, the shrunken, shriveled, fungal infected and bruchid infected seeds must be removed and only good seeds must be sown. Some time hard seeds can occur in some varieties due to initial dormancy. Such variety seeds must be identified and treated with acid.

Seed treatment using Rhizobium     
           
Two packets of Rhizobium (500gms) will be needed to treat seeds of one acre. In order to make the rhizobium stick to the seeds, we need a binder. The binder is prepared using rice gruel. This is prepared by adding 100 gm of rice to 500 ml of water and boiled until the rice becomes sticky. Three hundred milliliters of rice gruel is needed for preparing the rhizobial inoculation. The prepared rice gruel is then cooled under shade for 5 hrs. To this cooled rice gruel, two packets of rhizobium are added and stirred into a black sticky mass. The eight kilos of redgram seeds are placed in bucket. The rice gruel-rhizobial mixture is then poured over the seed and seeds are mixed well using a stick or hand. After assuring that the redgram seeds are coated evenly by rhizobial inoculum, the seeds are spread over gunny and dried under shade for 6 hrs. The dried seeds are then used for sowing within 24 hrs of inoculation.

Seed treatment using fungicide

Seeds must be treated with seed treating fungicide to reduce infection by fungal pathogens found in the soil. Cowpea seeds are treated with Bavistin 2g for every kilo of seeds. Now-a-days organic fungicide like Trichoderma viridi is recommended for pulses at the rate of 4g per kilogram of seed.

Sowing

The seeds are sown at 2 cm depth with a plant - to - plant spacing of 20cm and 45cm between rows.

Irrigation management

Seed crop is very sensitive to irrigation. Seed fields must be constantly monitored for drought conditions. If not irrigated properly, pulse crop shed flowers. Water starved plants produce seeds that are hard and small with low vigor. Hence, pulse seed crop needs regular and sufficient irrigation.
Water is applied immediately after sowing followed by life irrigation on the third day. Then, irrigation is done whenever, the fields become dry. Irrigation during flowering, pod formation and seed development are must.

Foliar feeding of fertilizers

Some times, basal application of fertilizers alone is not sufficient for the seed crop. It is necessary that we provide nutrition during the heavy growth and seed formation period when there is a huge demand for nutrients.
The nutrient needed by the rapidly developing pulse seeds are provided through foliar feeding. This provides rapid food source like sick humans are provided glucose fluid through intravenous method. We have to prepare a nutrient solution for spraying. This is done by soaking 2 kg DAP in 10 L of water over night. The next day the solution is filtered and the filterate is then sprayed to the seed crop. Half litre of the spray solution is mixed with 9.5 L of spray water and sprayed using power sprayer. Normally 15-20 tanks will be necessary to spray one acre of crop at vegetative phase. During pod formation phase 20 tanks may be needed. This nutrient solution is sprayed 25-35 days after sowing followed by another spray 40-50 days.

Cautions to be observed during spraying

  • Irrigate the crop immediately after spraying or ensure that adequate soil moisture is available.
  • Spraying should be done during evening hours.
  • Drench well the crop with spray solution.
  • DAP solution can be combined with pesticides.
  • Avoid spraying during peak flowering.

Weed control

The harm caused to farming operations by weeds need be emphasized. It is needless to say that seed crop must also be protected from weeds. Weeds not only smother the seed crop, they also harbour pest and diseases.  .
Immediately after sowing and irrigation, Basalin weedicide is sprayed by dissolving 2ml of Basalin per liter of water. The spraying of weedicide must be done within three days of sowing. If done later, it can harm the seed crop. Application of weedicide will control the early growing weeds; in or­der to control later emerging weeds, manual weeding can be done after 15 days. Some times, the 600ml of Basalin can be mixed with 20 kg sand (4 iron chatties of sand) and evenly spread on the field within three days of sowing. This reduces the cost of spraying.

Pest and disease control

Pests

In most part of the areas, the incidence of stem fly is very high. This pest affects the plant at the early stages leading to drying and withering of affected plants. During the growth phase major pests like aphids and Prodenia affect the seed crop. These pests can be controlled by spraying either Methyldematan, Dimethoate or Phosphomidan at the rate of 2ml per litre. During severe infection of Prodenia, the larva can be collected and destroyed.

Disease

During the growing phases of the seed crop incidence of aphid borne mosaic can be seen. The affected plants show crinkling of leaves and mottling. These plants can be rogued out as and when they appear. Controlling the vector i.e. aphid by application of Dimethoate (2ml/L) will also help in con­trol Root rot can also occur. This disease is visualized by the presence of drying plants in the field. The roots of these plants show blackening caused by fungus. These plants must be removed and the area can be drenched using 1 % Bavistin solution.

How to prepare 0.1% and 1% Bavistin solution?

Take one grams of Bavistin and dissolve it in one litre of water for preparing  0.1 % Bavistin solution and ten grams of Bavistin is dissolved in one litre to get 1 % Bavistin solution.

Tendril clipping in cowpea

Cowpea plants generally have the habit of forming tendril. Tendril, growth generally delays flowering thus leading to reduced seed producion. To avoid this, the tendril formation must be curtailed. This is using manual labourers who can nip the tendril.

Tendril clipping

Maintaining seed quality by thorough rouging

One of the most important aspects of seed production is thorough rouging. Rogue is defined as the presence of those plants that deviates from the characters described for the variety. Such rouges if left in the field, they tend to reduce the genetic purity of the seed crop and thus reduce the purchase value of resultant seed. Roguing is defined as the operation of removing rouges. In practice, all plants that do not obey the characteristics of the par­ticular seed crop are to be removed along with diseased plants, other crop plants, weeds, insect affected plants during rouging operation.

When to do rouging?
           
Rouging is more effective if done prior to flowering, since upon flow­ering there is very high possibility of cross pollination. Though cowpea is self pollinated, some extent of cross pollination is caused by bees. Rouging is also attempted during flowering, pod formation stage and prior to har­vest in case of pulse crop.

Rouging during vegetative phase

During vegetative phase i.e. during first 25 days, rouging is attempted based on plant characters like height of plant, leaf shape, size and venation. Plants showing tendril formation and those showing symptoms of root rot and mosaic are also removed.

Rouging during flowering phase

The rouges are identified based on flower characteristics. During this phase, when most of the plants are flowering, all those plants still in vegeta­tive phase are also removed along with plants severely infected with virus.

Rouging during pod formation phase

At this phase, the rouges are removed based on pod characteristics like length of pod, size, shape and colour.

Rouging during pod harvest phase

Rouging is done prior to harvest based on seed characteristics like col­our of seed, luster and size of seed.

Attention:

Varietal characteristics for various crop are given in Table  at the end to this lesson.

Caution!
           
All the rouges must be immediately removed from the seed field and desdestroyed.

Proper care during Harvest

The seed crop comes to harvest 70 - 80 days after sowing, this is generally 30 days from 50% flowering. At this time, the pods turn straw colour. First picking of the pods can be done followed by a second picking. Prior to harvest there is an important pest to be controlled. Bruchids are the major pests of stored pulse seeds.

Crop at maturity

Pre -harvest sanitation spray

Bruchids lay eggs on the surface, the grubs bore into the seeds and eat the cotyledon. The seeds thus store poorly and loose viability faster. It has been found that bruchids lay their eggs on the pods while in the field itself. Hence control of these pests must start from the field itself. The field carry-over of Bruchids can be controlled if the crop is sprayed using Quinalphos 25% EC (2 ml of insecticide per litre) ten days prior to harvest.
           
Upon ripening, the cowpea pods will turn from green to brown. This the right stage for harvest for seed purpose. Delay in harvest will lead to shattering of pods and infection by diseases, pests and sometimes seed vigor will be lost due to untimely rains.

In case of irrigated crop, the ripened pods can be collected in one or two pickings and dried on the threshing floor. The pods are then beaten using pliable sticks to prevent damage to seeds. After thorough beating, the seeds are separated from pods. The plant debris are removed and seeds cleaned by winnowing.
Cleaned seeds are then dried on tarpaulin on the threshing floor un­til the moisture content is reduced to 9 %. This is the safe moisture content for storing seeds and maintaining their viability.


Matured pods

Please Note

While drying the harvested cowpea pods or plants on thresh­ing floor, adequate distance must be provided between two varieties. Minimum ten feet must be provided and this is to reduce the admixture of two varieties caused by spreading of seed when pod bursts upon drying.

Processing to improve seed quality

One of the main characteristics of seed quality is the right size. Plumpy seeds are better than ill-filled puny seeds. Grading is one simple method by which we can separate the filled seeds from broken and puny seeds. Grading is done using round holed sieves. Such sieves are easily available in the market. Depending on the size of cowpea variety, the sieve size for cowpea is 3.50 for small seeded and 4.00 mm for bold seeded types. After sieving, those seeds that are broken, fungal infected, seed coat damaged seeds are removed.

Protecting seeds during storage

Seeds after harvest have to be stored so that they are viable and healthy for sowing during the ensuing season. Hence, proper after care during stor­age is very essential part of seed production. In this section, we will learn about the role of seed moisture content, seed treatment and proper methods of storage for prolonging seed viability.

Seed moisture content

Seed moisture is the most important physical quality. Seed moisture determines the length of seed storage life. Higher the moisture, the longev­ity of seed is reduced drastically. Seeds with moisture are attacked by fun­gal and other storage pests like Bruchids. Further, seeds being living organ­isms tend to utilize all their stored energy and loose vigor. Hence, reducing seed moisture is the first step in ensuring longer seed life.
The moisture content must be reduced to 9% for short term storage of 6-8 months. Seeds with 9% moisture can be stored in cloth bag or gunny bag. Seeds that have to be stored for long term i.e. 1-2 yrs, have to be dried to 8% moisture. Such seeds have to be stored in polythene bag.

Point to remember

Seeds stored in polythene bag have to be dried to moisture content below 8%. This is necessary because polythene bag do not allow moisture to move out and seeds if stored with high moisture will get damaged. Hence always store seeds with low moisture in polythene bags.

Seed treatment
                 
Seeds are generally affected by fungi during storage. To prevent, seeds are treated with fungicide before storage. Cowpea seeds are treated using Bavistin at the rate of 4g/kilo of seeds.

Seed packing

After seed treatment, seeds have to be stored in bags or containers. Choosing the right type of container is necessary. This depends on the quan­tity of seeds to be stored and storage environment. Seeds absorb moisture and even if the seed is dried to safe moisture content before storage, during storage depending upon the prevailing climatic con­ditions, seeds tend to absorb moisture. If the storage is attempted in an envi­ronment with high humidity, seed absorb moisture until they equilibrate with the atmosphere. Hence high humidity in the environment will lead to increase in seed moisture that is detrimental to seed storage. Such high hu­mid conditions exist at sea shores, near lakes and rivers. Most of the places of peninsular India are highly humid especially during the monsoon peri­ods between the months of June-December.

In order to store the seeds with any detrimental effect to vigor, seeds are to be stored. In case of short term storage, cloth bag can be preferred, Cloth bag is porous and hence it can hold seeds for short period. However, cloth bags are cheaper and easily made using local tailor. Large quantity of seeds can be stored in gunny bag. If the seeds are to be stored for longer period that thick polythene bags can be used.

Stacking seed bags

Seed bags can be stacked one upon other upto 6 layers. Stacking be­yond this will damage the seeds present in the lower layers. To prevent damage to seeds in the bottom layers, the layers can be rotated periodically by shifting the lower layers to the top and vice -versa. Stacking must also be done on dunnages. Dunnages are wooden rafts that keep the seeds above floor and allow aeration. Tarpaulins and thick plastic sheet can also be used.

Taking care of seeds during storage

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Good seed                                     Bruchid infested seed

Seed treatment is most effective in combating fungal pathogens. However, seed treatment alone will not be effective against storage pests like bruchids.                                

Grain cum pulse seed storage

Pulses are used both as seed and grain. Being of high protein value, pulse seeds have high demand as grain also. Farmers may be tempted to use them for grain as the market price for grain some times exceeds the seed cost. Under such circumstances the seeds can be treated with harmless sub­stances like activated clay, neem oil and vegetable oil.

What is activated clay?

Activated clay is ordinary white clay removed of moisture and acid washed to improve its ability to damage insect surface. It is very cheap and non-toxic to humans. Seeds treated with activated clay can be washed and reused for consumption, at the same time it offers protection against bruchid infection.
Activated clay is used to treat seeds at the rate of 100g per kilo of seeds. Activated clay has rough clay particles that cut the surface of bruchids. Such bruchid beetles then die as they loose moisture fast compared to unbruised ones.
          
Similarly pulse seeds can also treated using vegetable oils / neem oil at 3ml per kilo. These techniques are farmer friendly techniques and do not harm the environment also.

Seed Certification
                       
Seed certification guarantees the quality of seed as it ensures that the certified seed has the genetical, physical, physiological and seed health qualities. By genetical quality we mean that the seed has all the characteristics as desired by the breeder who had developed the variety, like short duration, higher yield, high protein etc. The physical quality entitles the seed to be free of stones, broken seeds, straw bits, leaf bits and has low seed moisture for better storage life. Physiological quality is measured by germination and seed health envisages free from pest and diseases. Only those seeds that possess the aforementioned qualities are certified by the certification agency.
           
The certification officials visit the seed field for quality inspection and only those seed fields that are maintained properly are alone accepted for certification. The accepted fields are then harvested and processed under the supervision of the certification agency and tested for germination and other seed qualities in the laboratory.
           
Only those seeds that possess the required quality are given certificate known as tag. This tag is blue for certified seeds. So, next time when you buy a seed see whether it has the blue tag.

Minimum seed certification standards prescribed for certified seed

Field standards

 

Rogues (maximum limit)

0.2%

Seed standards

 

Pure seeds (minimum limit)

98.0%

Inert matter (maximum limit)

2.0%

Other crop seeds (maximum limit)

10/kg

Weed seeds (maximum limit)

10/kg

Germination (minimum limit)

75.0%

(including hard seeds)

 

Moisture content

 

Moisture proof bag

8.0%

Moisture pervious bag

9.0%

Characteristics of cultivated varieties that can be used while rouging
(Plants possessing characters other than given for a variety must be removed)

Characteristics

 P152

C04

C06

Paiyur 1

Parents

Selection
from Iran
variety

Selection
from
Russian

Cross
MS 980 x
Cl52
bold

Selection
from
V.M.16

Duration of 50% flowering

45-50

40-45

35

75

Duration

90-95

85

65-70

90

Plant height (cm)

60

50

35

60-70

Colour of stem

Green

Green

Green, green
petiole pink wash

Dark

No. of branches

-

3-4

3-4

-

Leaf character

Dark green, Green
remains
green even
veins
on maturity

Green

Light Green
pods seen
above plan
canopy
Brown

green

Pod Colour

Green

Green

Light green pods seen above plant canopy

Green

Mature pod colour

Light brown to straw

White

Brown

Brown

Seed colour

Buff

Dark brown

Dull white

Brick red

100 seed weight(gm)

10.0

11.5

9.9

9.9

Seed yield (Kg)

900

960

670

900

 
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