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The moisture content is the amount of water in the seed and is usually expressed as a percentage. It can he expressed on either a wet weight basis (where it is expressed as a percentage of the fresh weight of the seed) or on a dry weight basis (where it is expressed as a percentage of the dry weight of the seed). The seed moisture content is the most vital parameter, which influence the seed quality and storage life of the seed. Seed moisture content is closely associated with several aspects of physiological seed quality. For example, it is related to seed maturity, optimum harvest time, mechanical damage, economics of artificial seed drying, seed longevity and insect & pathogen infestation.

Fumigation is a method of pest control that completely fills an area with gaseous pesticides to suffocate or poison the pests within. It is utilized for control of pests in buildings, soil, seed, and grain produce. It is also used during processing of goods to be imported or exported in order to prevent transfer of exotic organisms. Fumigants are chemical compounds in gaseous form that enter the body of insect through the spiracles spread all over via trachea and tracheoles. The important fumigants are Methyl bromide, Ethylene dibromide, Aluminium phosphide, Ethyl formate, Hydrogen cyanide, Chloropicrin etc.

These materials include barrier coated paper bags, barrier laminated film bags, jute bags, PP woven box bag and cotton bags.
 
A: Paper Bags
    1.    Coated paper:  bags provide a barrier for leaking or staining of the product. This can be done by a greaseproof or claycoated kraftpaper.
    2.    Open-Mouth sacks:  can be manufactured using different types of paper. Simple kraftliner, glossy claycoated and lacquered outerliner are possible. These sacks can be supplied with liners and printed up to 8 colours.

The objective of seed pelleting is to provide an opportunity to package effective quantities of materials such that they can influence the micro-environment of each seed.
 
Process of Pelleting

Seeds are introduced into a coating drum or pan that resembles a cement mixer. An amalgam of pelleting materials (clays, limestone, calcium carbonate, talc, vermiculite) and cementing adhesives (gum Arabic, gelatine, methyl cellulose polyvinyl alchol) are used to form the pellet and other compounds such as inoculants, fungicides, etc. May be added to enhance seed performance.

Objective

    1.    Design drum priming (2-3 kg and drying unit with house hold or commonly available materials.
    2.    Standardization of time for seed priming for different crops.

Probable drum priming unit components

A] A vertical drum which need to be rotating
B] A motor which will rotate
C] A desktop assembly
D] A simple two way seed drier (Fig not given here)

Seed Priming is the process of controlled hydration of seeds to a level that permits pre-germinative metabolic actively to proceed, but prevents actual emergence of the radical. It is done to increase the speed and uniformity of germination particularly under adverse conditions of temperature, moisture and salinity conditions. In this condition, seeds go through all the essential preparatory processes of germination but prevent cell elongation and radical emergence. During the waiting period at the osmotic barrier the ‘slower’ seeds tend to catch up with the ‘faster ones’ so that the subsequent germination is more uniform, than that of untreated seeds. The duration of priming varies with the crop as well as method of priming such that priming is allowed for I and II stage of seed imbibitions without allowing radical protrusion.

Seed is the primary and essential starting point of a wide range of crops, including the majority of vegetables except those vegetative propagated (e.g- potato and sweet potato). Seedling emergence and field stand establishment is one of the problems facing the growers, especially in early planting where adverse conditions are prevailed (low temperature and high soil moisture). Seed germination and seedling emergence are affected by many factors such as: seed genotype, seed quality (seed viability and seed vigor) and the environmental conditions (moisture and temperature) prevailing during seed germination and subsequent seedling emergence, assuming that the seed is not dormant.

Objective: To study the seed treatment methods and equipments A key factor in achieving the few potential of good quality seed is the blanket treatment of the seeds with agrochemical in order to control or prevent diseases in the  crops.

Drying is an important unit operation in seed processing in order to maintain seed ability and vigor . it is advocated that seeds should be harvested soon after they attain physiological maturity to obtain better quality seeds and to minimize field losses. The traditional method of sun drying is inadequate, uncontrolled and time bound, which may not meet the high demand of quality seeds in time. Hence artificial drying, the effect of certain drying parameters like seed moisture content, drying air temperature, airflow rate, depth of seed loading and time of exposure on drying characteristics and viability of seeds are to be determined for safe and economical drying of seeds.

The use of seed processing equipments helps in improving the seed quality by inducing uniformity of physical properties of seeds. This help in achieving optimum plant population and desired economic yield. In certain crops like soya bean, standard seed processing may not give desired seed quality because of sensitivity towards moisture. As general practice seed need to be dried to its safe moisture content of 9 before processing. But in case of soya bean lower seed moisture may result higher mechanical damage after standard seed processing. Drier seed are more vulnerable for mechanical damage. In this practical w try to explore the importance of moisture in seed processing and also need of alternative processing equipments like spiral graders to minimize mechanical damage.

This practical in continuation of the practical no.10 explore the effects of screen sizes on different varieties. The screen sizes vary not with crops but with varieties also. To know the effect of screen sizes among the varieties we need to take the top and middle screens as standard or as recommended. These methods can be applied to any crop and to different varieties.

Seed size is an important parameter of seed vigor as it in influences the performance of seed in soil. Seed bulk at harvest contains a wide range of seed sizes but these may not all be of equal value for sowing. Farmers have always realized the necessary of using uniform seeds for good viability to obtain high emergence and growth. This will also help in getting optimum plant population and higher yields.
 
The influence of seed size on seedling vigor and crop productivity has already been proven since the days Hannaford who was considered as father of seed processing. To achieve uniformity in seed size this optimum sieve/screen size is very critical for optimum seed recovery and economical seed yield. Though the screen sizes are standardized for different crops but vary with different varieties. The shop floor should continuously explore and fine tune screen sizes for different varieties.

9.1 Magnetic seed separator

These machines use a magnetic force to separate damaged seeds or other particles from the good seeds. This is used to solve special problems in seed lots that can not be taken out with our other basic seed cleaning equipment. Most of the time it is used for vegetable and field seeds that have problems in seed damage (fish mouth in cucumber or melon seeds / cracked radish or cabbage seeds), insect damage (beetle holes in cotton seeds) or contamination with soil or plant parts (white plant parts in onion seed) etc.

The processing operations are carried out based on the principle of physical differences found in a seed lot.

Mechanical damage is inflicted on seeds during harvesting, threshing drying, processing and handling. Injury may occur from any kind of physical abuse. Threshing abuse probably is most serious but, seed conditioning and handling also contribute to seed injury. High temperatures during drying or drying too quick or excessively can cause injury. Susceptibility to mechanical injury increases as the moisture content of the seed decreases. Effect of all individual impacts received by the seed appears to be cumulative in total seed damage. Cereals are largely immune to mechanical injury presumably because of the protective outer structures, the palea and lemma. Large sized legumes are more suscepitable. Small seeds tend to escape injury during harvest and seeds that are spherical tend to suffer less damage than elongated or irregularly shaped ones.

Methods in Seed Blending

For good seed blending there are three methods and details of which given as below:

The physical properties of seeds are a basic activity for designing processing equipments and precision planters. Since these characters vary with crop or variety, one needs to have the data handy to be used on shop floor. This data also helps to quantify processing efficiency, presence of dormancy and suitability for seed treatments for all existing and new crops or varieties.

Seed processing is specialized activity and also a tool to improve seed quality further to an acceptable standard. Seed quality parameters like germination, vigour or genetic purity can be improved using processing. Say a seed lot having a minimum standard of 90% germination, but the competition in the market offering seed quality 92 or 95 % then to meet the market demand we can process the seed lots using re-milling or re-conditioning techniques. Also sometimes simple techniques like liquid density separation which uses specific density of the seed to separate good seed from inferior quality can be considered.

1.1 Problem
    1.    Compare the seed quality at different physiological maturity stages
    2.    Compare the seed recovery in acid and fermentation method

1.2 Materials
    ·    Tomato fruits – 4 batches
    ·    Plastic bucket/ Beaker
    ·    Water

Visit to a seed processing unit and attending the following questionnaire to know firsthand information on operations of shop floor