Seed Hardening: A Tool For Successful Crop Production In Drylands

Pre-sowing hardening of seeds is one of the methods for modifying the physiological and biochemical nature of seeds for favourable condition to induce drought tolerance in emerging seedlings. Soil moisture stress immediately after sowing affects germination and establishment. Seed hardening enables seedlings to survive this early moisture stress. It is the process of soaking seeds in chemical solution for specified time and drying to induce tolerance to drought. During seed hardening, seeds are subjected to partial hydration followed by dehydration before sowing. Seeds are soaked in chemical solutions of prescribed concentration. Soaked seeds are then dried in shade back to original moisture content. During soaking, seeds imbibe water and germination process is started but not completed. The hardened seeds are thus in a ready state for germination. When sown in moist soils, seeds germinate immediately. Such early germination helps in seedling emergence before surface soil dries up. The seed hardening is considered as low cost technology and is the most important requirement for pre-monsoon sowing.

Seed hardening is, therefore, done to overcome the adversity of moisture stress that is common in dry farming areas. When dry seeds are soaked in water/chemical solution, the quiescent cells get hydrated and germination initiated. It also results in enhanced mitochondrial activity leading to the formation of high energy compounds and vital bio-molecules. The latent embryo gets enlarged. When the imbibed seeds are dried again, the triggered germination is halted. When such seeds are sown, reimbibition begins and the germination event continues from where it stopped previously. As a consequence there will be multitudes of benefits, which make the plants prepared to resist the adverse weather if any.

Beneficial effect of seed hardening:

• The seed hardening accelerated rapid germination and ensures early germination by 2–3 days compared to untreated seeds.

• It induces better root development and rapid growth of seedlings, which enables absorption of more moisture.

• Germination and seedling emergence are completed before surface soil dries out.

• It induces drought tolerance by increasing the resistance to protoplasmic dehydration in young seedlings subjected to moisture stress.

• Quick germination of seedlings favour more effective competence with weeds.

• Hardened plant recover much more quickly from wilting than those from untreated plants, includes resistance to salinity.

• Seeds withstand higher temperature for prolonged period without loss of viability.

• Flowering is slightly accelerated in treated plants.

• Overall hardened seeds perform better and result in more yield.

Precautions:

• Hardened seeds can be sown immediately or within 30 days of treatment.

• For success in seed hardening, attention must be paid in selection of right chemical, its concentration, time of soaking, volume of solution and drying under shade to original moisture content.

Materials and chemicals used for seed hardening:

• Water

• Aqueous salt solutions like chlorides of sodium, potassium and calcium. Sulphates of sodium and ammonium. Potassium nitrate.

• Growth regulators like Gibberallic acid, chlorocholine chloride, kinetin, 2-chloroethyl phosphoric acid, Ascorbic acid.

• Vitamins like K3 Nicotin acid, pantothenic acid etc.

• Plant products like garlic extract, coconut water etc.

• Osmotic priming material like D-Manitol, poly ethylene glycotect

Uses in crops:

• Seed hardening with 2 per cent potassium di-hydrogen phosphate or potassium chloride.

• For cotton in black soils, pre-monsoon dry seeding is recommended at 2-4  weeks before commencement of monsoon, with a sowing depth of 5 cm and seed  hardening with CCC (500 ppm) or potassium chloride or DAP at 2% level.

Methods of seed hardening

Water treatment: seeds are soaked in water and allowed to absorb moisture up to 35% of their weight and kept in swollen condition for about six hours at 15 to 25^oC. The seeds spread as a thin layer under shed for 2-3 dyad to attain their original weight. The treatment may be repeated for 3-4 times which depends on type of crop and variety.

Chemical treatment: The treatment of alternate wetting and drying of seeds as in the case of water treatment has to be carried out with different chemical solution of varying concentration as recommended 

Table 1: List of chemicals or solutions used for soaking seeds.

Crop	Chemical and concentration	Soaking time	Volume of solution per kg seed
Rice	Potassium chloride1 %	Water-10 hrs chemical-10 hrs	1 litre
Sorghum	Potassium di-hydrogen phosphate 2 % Potassium chloride 1 %	6 hrs 5 hrs	350 ml 1 litre
Pearl millet	Potassium chloride 2 % Sodium chloride 3%	16 hrs	1 litre
Ragi	Calcium chloride 0.5%	Until visibility of embryo growth	1 litre
Sesame	Calcium chloride 0.2%	6hrs	1 litre
Sunflower	Zinc sulphate 2 %	12 hrs	1 litre
Cotton	CCC 1000 ppm KCl 2% DAP 2%	6 hrs 5 hrs 5 hrs	1 litre 1.6 litre 1.6 litre

 

Table 2:  Chemicals Recommended For Seed Hardening in Different Crops.

Maize	Cycocel (250 ppm) chemical
Sorghum	KH2PO4 (2%) or CaCl2 (2%)
Pearlmillet	NaCl (0.5%)
Paddy	KCI (1%)
Millets & cotton	KCI(2%)
Groundnut	CaCl2 (0.5%)
Pigeonpea	ZnSO4 (100 ppm)
Sunflower	GA3 (500 ppm) or MgSO4 (0.2 – 0.5%)
Greengram	MgSO4 ( 100 ppm)
Chickpea	KH2 PO4 (1%)

Author

Lokesh Kumar Jain

Assistant Professor, Agronomy

College of Agriculture Sumerpur

Email: jainlokesh74@gmail.com