Seed and Sowing

 

Seeds and Sowing 

B.Sc Agriculture 1st semester notes(Agronomy, AGR-111)

Based on ICAR 5th Dean

Plants reproduce sexually by seeds and asexually by vegetative parts. Good quality planting material is prerequisite to profitable crop production. The seed or planting material largely determines the quality and quantity of the produce because it is the basic source of genetic material of the crop. Seed Botanically, seed may be defined as a fertilized ovule consisting of intact embryo, endosperm (stored food) and seed coat which is viable and has got the capacity to germinate. Endosperm is the storage organ for food substance that nourishes the embryo during itsdevelopment. Seed coat is the outer cover that protects or shields the embryo and endosperm. Agronomically, seed may be defined as any planting material which is used for further propagation of the plant thus the agronomic definition of seed includes sugarcane sets, potato tubers and rooted slips of Napier grass. Difference between Seed and Grain: Grain is a ripened ovule used for economic purpose whereas seed is a ripened ovule used for further propagation. Characteristics of Good Seed or Qualities of Good Seed: 

A good quality seed must possess following characteristics. 1) Genetic Purity: Seed must be true to its type i.e. it must belong to the proper variety or strain of the crop which is proposed to be grown. 2) Physical Purity: it should be healthy (free from physical damage) and free from all inert materials and weed seeds. 3) Viability: Seed must we viable i.e. capable of germinating under favourable conditions. The germination capacity should be up to the standard mark. 4) Uniformity: Seed should be uniform in its texture, structure, and look. 5) Infection free: Seed must be free from seed borne diseases and pest infection.

 Types of seed A) Based on Storage Capacity: 1. Orthodox Seeds: These seeds are long lived and can survive drying (<10% moisture) and/or freezing(<10°C temperature). Orthodox seeds are therefore, also termed as desiccation tolerant seeds. These seeds can be stored at less than 10% moisture for longer period. The longevity or life span of orthodox seeds may vary from over a year to many hundred years depending upon the particular species and storage conditions. Most of the crop seeds belong to this category. 2. Recalcitrant Seeds: These seeds short lived and cannot survive drying (<10% moisture) and freezing (<10°C temperature). Most of the fruits with the large seeds like mango Jackfruit come under this category. Recalcitrant seeds are difficult to be successfully stored for longer period and their ex-situ conservation is problematic. It is because of their high moisture content that encourages microbial contamination and results in more rapid seed deterioration. Secondly, storage of recalcitrant seeds at freezing temperatures causes the formation of ice-crystals which disrupt cell membranes and causes freezing injury. B) Based on the Generation of the Seed: 

1. Nucleus seed 2. Breeder seed 3. Foundation seed 4. Registered seed 5. Certified seed 6. Truthfully labeled seed 1. Nucleus seed: It is the initial amount of pure seed of improved variety or parental lines of a variety produced by the original breeder/institute/university that has evolved that variety or hybrid from basic nuclear seed stock. The nucleus seed is genetically cent percent (100%) pure and does not contain other physical impurities. The nucleus seed is produced strictly under isolation so as to avoid both genetically and physical contamination. Nucleus seed should retain original vigour of the variety or parental line. Pedigree certificate is issued to this category of seeds by the producing breeder. This category of seed contains no tag. 2. Breeder seed: The progeny of the nucleus seed multiplied in large quantities under direct supervision of plant breeder is known as breeder seed. This is also hundred percent genetically and physically pure. This seed is used for production of foundation seed. A golden yellow colour tag is issued for this category of seed. 3. Foundation seed: The progeny of breeder seed or foundation seed itself produced by a recognized seed producing agencies like National Seed Corporation (NSC), Tarai Development Corporation (TDC) and State Seed Corporation (SSC) is known as foundation seed. Sometimes it is also called as ‘certified foundation seed’. A white colour tag is issued for foundation seed by seed certifying agencies. During the production of certified Foundation seed, the following guidelines shall be observed: (a) Foundation seed produced directly from Breeder seed shall be designated as Foundation seed stage-l; (b) Foundation seed produced from Foundation seed stage-l shall be designated as Foundation seed stage-ll; (c) Foundation seed stage-Il will not be used for further production of Foundation seed and shall be used only for production of Certified seed class; (d) Minimum Seed Certification Standards shall be the same for both Foundation seed Stage-| and II unless otherwise prescribed; (e) Certification tag shall be of white colour for both Foundation seed stage-I and II and shall contain the information as to its stage; (f) Production of Foundation seed stage-ll shall ordinarily be adopted in respect of such crop varieties provided, when it is expressly felt by the Certification Agency that Breeder seed is in short supply; Production of Foundation seed stage-| and II shall be supervised and approved by the Certification Agency and be so handled as to maintain specific genetic identity and genetic purity and shall be required to conform to certification standards specified for the crop/variety being produced. 4. Registered seed: Registered seed is produced by growing foundation seed that is grown either by seed producing agencies or by selected farmers under the strict supervision of seed certifying agencies. Purple colour tag is issued to this category of seed. This class of seed is not produced in India. 5. Certified seed: Certified seed is produced from foundation seed/registered seed or certified seed itself. It is produced by seed producing agencies like NSC are SSC or by selected farmers under the supervision of seed certifying agencies. After proper labeling, this category of seed is sold to the farmers for commercial cultivation. This class of seed bears azure blue colour tag. Generally certified seed is produced from foundation seed but it can be produced from certified seed itself provided: - this reproduction does not exceed three generations beyond Foundation seed Stage-l, - it is determined by the Certification Agency that genetic identity and genetic purity will not be significantly altered; - Certification Agency is satisfied that there is genuine shortage of Foundation seed despite all the reasonable efforts made by the seed producer. - Certified seed produced from certified seed shall not be eligible for further seed increase under certification. Certification tags for such production which is not eligible for further seed increase under certification shall be super scribed with, “not eligible for further seed increase under certification”. 6. Truthfully labeled seed: It is the category of seed produced by cultivators or farmers and private seed companies and sold under truthful label. It is not subject to inspection by the certification agencies but the field standards and seed standards should be maintained as per Seed Act. Seed producer or seller is responsible for the quality of this category of seed. This category of seed generally has no tag the label of seed is however, of Opel green colour. C) Based on the Effect of Germination on Light 1. Photoblastic seed: A seed whose germination is influenced by light is known as photoblastic seed. The response to light is apparently mediated by phytochrome- regulated production of the plant hormone gibberellin. This influence may be positive (i.e. stimulate germination) or negative (/.e. inhibit germination). Thus, the photoblastic seeds are of two types:  Positively photoblastic seeds and negatively photoblastic seeds. a. Positively photoblastic seeds: Seeds that are stimulated to germinate by presence of light are described as positively photoblastic seeds. e.g. lettuce, tobacco and Lotus (Nelumbo nucifera). Positively photoblastic seeds are commonly called as “photoblastic seeds”. b. Negatively photoblastic seeds: Seeds whose germination is inhibited by the presence of light and germinate only under dark conditions are known as negatively photoblastic seeds. e.g. Plox, Silence and Nemophilia. 2. Non-photoblastic seed: Seeds whose germination is not affected by the presence or absence of light are known as non-photoblastic seed. Example: most of the crop seed. Germination: Coming out (protrusion) of radical and plumule from the seed coat under favourable conditions is known as germination. Germination results in the rupture of the seedcoat due to imbibition of water and emergence of seedling from embryonic axis. Germination is of two types: Epigeal and hypogeal. 1. Epigeal: When the cotyledons of seed come out of the soil due to extension (faster growth) of hypocotyl, the germination is called Epigeal. e.g. cucurbits, mustard, French bean, caster, onion, etc. 2. Hypogeal: when the cotyledons of the seed do not come out from the soil, the germination is called Hypogeal. Example: rice, wheat, pea, gram, pigeon pea, maize, coconut, etc. Conditions Necessary for Germination or Factors Affecting Germination A) External factors: Moisture, oxygen and temperature. When the seeds do not get required moisture in the soil, the viability is lost, however, if the moisture is excess after germination, it will lead to rotting of the sprouts. Similarly, when temperature is above and below the optimum temperature required for germination, the germination rate will be affected. B) Internal factors: food, growth regulators, completion of resting period and viability. Dormancy: Dormancy is a physiological phenomenon due to which seeds remain alive but do not germinate even in favourable conditions. It refers to resting stage of seed which could be due to biochemical and physical factors. There are three types of dormancies found in seeds viz. enforced dormancy, innate dormancy and induced dormancy. A) Enforced Dormancy: Enforced dormancy is literally "forced" upon the seed by some limitation of the germination environment, in other words, enforced dormancy is due to absence of favourable environment for germination (i.e. absence of water, favourable temperature or deep placement in the _ soil).Seeds requiring light, alternating temperatures, or light/dark conditions fall into this category where, one or more of these conditions need to be satisfied for the seed to begin germination. This type of dormancy disappears once the missing condition(s) are supplied or favourable conditions re-appear. B) Innate Dormancy: Innate dormancy is due to genetic factors e.g. presence of hard seed coat, imbalance in growth promoters and regulators, etc. Innate dormancy is present within the seed when it reaches physiological maturity. It is imposed upon the seed by the mother plant and remains for some time after the seed is shed. Often, the seed need only go through an after-ripening period for it to disappear. But, it may also be combined in the seed with other types of dormancy so that the seed remains dormant after the innate dormancy mechanism is removed. C) Induced Dormancy: Induced dormancy is due to external environmental conditions like high temperature, low oxygen etc. It occurs when imbibed seeds are placed under extremely unfavourable conditions for germination. Seeds which acquire this type of dormancy do not require continuous unfavourable condition to remain dormant. It means seeds fail to germinate even if later placed under favorable conditions too, however remained viable and can germinate with specific treatment. Induced dormancy has also been referred to as secondary dormancy.

 Seed Treatment to Break Dormancy 

A) Physical treatment i. Scarification: Scratching of hard seed coat to remove the mechanical barrier to obtain uniform germination with better penetration of moisture into the seed. This can be done by rubbing the seed with sand or by pounding seeds in a large sized motor with pastel. This treatment is done to break the dormancy which is due to the presence of the hard seed coat. ii. Stratification: Treating the seed with heart or cold water to break dormancy and induce germination is known as stratification. In hard water treatment, seeds are soaked in the water at 40 to 45 °C for different durations. In cold water treatment, pre-soaked seeds are placed at 2 to 8 °C for 12 to 24 hours. Repeated alternate wetting and drying as well as alternate heating and cooling is also done in some seeds to break the dormancy. This treatment is done to break the dormancy which is mainly due to the embryonic factors; however, this treatment also softens the seedcoat. B) Chemical treatment: i. Keeping in dilute acid solutions (0.1-0.5%) of nitric acid (HNO3), hydrochloric acid (HCI) or sulfuric acid (H2SO,) for different duration. ii. Treating with 1-3% solution of Potassium Nitrate (KNO3), Ammonium Nitrate (NH,NO3) or Hydrogen Peroxide (H 03). C) Hormonal treatment: i. Treating with GA3 500ppm(soaking for 12 hours) ii. Soaking in kinetin 1-100 ppm solution for 12 hours. Methods of Sowing/Crop Establishment A) Direct Sowing/ Direct Seeding Direct sowing includes all those methods of planting in which the seeds/planting materials are directly sown in the main field in which the crop is to be taken. It includes broadcasting and line sowing. 1) Broadcasting: Broadcasting is the process of random scattering of seed on the surface of seedbeds. It can be done manually or mechanically both. When broadcasting is done manually, uniformity of seed depends upon skill of the man. Soon after broadcasting the seeds are covered by planking or some other devices. Small seeded crops are generally sown by this method. Mechanical broadcasters are used for large-scale work. Generally, broadcasting is done in a narrow strip on one go and the Sowing of whole field is completed in multiple strips. To ensure a good and uniform population, it is better to broadcast on either direction. This is called criss-cross sowing. If the seed is too small, it is mixed with sand to make a bulky one and for easy handling. e.g. Seasame seeds are mixed with sand at 1:15 or 1:10 ratio and sown. Broadcasting is the largest method of sowing followed in India, since; it is the easiest and cheapest and requires minimum labours. Disadvantages a) Seeds cannot be placed in desired depth and all the seeds broadcasted do not have contact with the soil; some seeds fail to germinate, therefore, enhanced seed rate is required. b) Uniform distribution of seeds in the field is not possible. c) Due to non-uniformity in spacing, intercultural operations are difficult. d) Intercropping is not possible as the seeds are not sown in lines. 2) Line Sowing Line sowing includes all the methods in which the seeds are sown in lines. Drilling, dibbling and sowing with the country plough come under this category. 

(i) Drilling (or) Drill sowing: Drilling consists of dropping the seeds in furrow lines in a continuous flow and covering them with soil. The number of rows planted (in one go) may be one or more. This method is very helpful in achieving proper depth, proper spacing and proper amount of seed to be sown in the field. Drilling can be done by (1) Bullock drawn seed drills (2) Tractor drawn seed drills. In this method, fertilizer can also be applied simultaneously with seed-cum-fertilizer drills. It is possible to take up sowing of inter crops also. It requires more time, energy and cost, but maintains uniform population per unit area. (ii) Dibbling: Dibbling is the process of placing seeds in holes made in seedbed and covering them. In this method, seeds are placed in holes made at definite depth at fixed spacing. The equipment used for dibbling is called dibbler. It is a conical instrument used to make proper holes in the field. Small hand dibblers are made with several conical projections made in a frame. This is very time consuming process, so it is not suitable for small seeded crops and for sowing in large area. This is done for wider spaced crops and medium to large seeded crops or for sowing in a very small area. 

(iii) Sowing with the country plough: Sowing behind the country plough is done by manual or mechanical means. Seeds are dropped in the furrows opened by the plough and the same is closed or covered when the next furrow is opened. The seeds are sown at uniform distance. In this method, either seeds are dropped manually behind the plough in open furrow, known as Kera method or below the plough shore through a hopper known as Pora method. The seed dropping hoppers are known as Pora or Goru or Guntakas. B) Transplanting Transplanting consists of preparing seedlings in nursery and then planting these seedlings in the prepared field (main field). In this method seeds are not directly sown in the main field. This method is commonly adopted for small seeded crops like tobacco, vegetable and flowers or in those crops whose seedlings very delicate and require intensive care. It is very time consuming operation. Equipment for placing plants in the soil is called transplanter. Age of seedlings is generally 1/4th of the total duration of the crop. If the total duration is 16 weeks, four week period (1 month) is under nursery beds. After the nursery period, seedlings are pulled out and transplanted. This is done on the main field after thorough field preparation or optimum tilth. The seedlings are dibbled in lines or in random. Closer spaced crops are mostly raised in random method even after nursery, e.g. rice and finger millet. For vegetables, desired spacing is required during transplanting. Transplanting shock is a period after transplanting, the seedlings show no growth. This is mostly due to the change in the environment between root and the soil. It is for a period of 5-7 days depending upon season, crop, variety, etc. Area required for nursery normally is 1/10" of the total area Advantages (i) Can ensure optimum plant population (ii) Sowing of main field duration, i.e., management in the main field is reduced (iii) Crop intensification is possible under transplanting Disadvantages (i) Nursery raising is expensive (ii) Transplanting is another laborious and expensive method. Depth of sowing: The seeds should be placed at optimum depth. When the seeds are placed at deeper layers they have to spend more energy for germination. When it is placed on soil surface, it will be taken away by birds/worked away. The thumb rule is to sow seeds to a depth of approximately 3 to 4 times diameter of the seed. The optimum depth of sowing for most of the field crops ranged between 3 and 5 cm depth. The seeds sown should be protected from rodents or birds before germination by employing labourers to scare the birds at least for three days after sowing. SEED RATE The required number of plants/unit area is decided by calculating the seed rate. The seed rate depends on spacing or plant population, test weight, germination percentage. The formula is as follows.

Seed rate (kg per ha) =

 Plant population (per ha) x Test weight (g) x 100 x 100