Factors involved in Seed Sowing Management
This can be classified into two broad groups.
1. Mechanical factors – Factors such as depth of sowing, emergence habit, seed size and weight, seedbed texture, seed–soil contact, seedbed fertility, soil moisture etc.
(i) Seed size and weight: Heavy and bold seeds produce vigorous seedlings. Application of fertilizer to bold seed tends to encourage the seedlings than the seedlings from small seeds.
(ii) Depth of sowing: Optimum depth of sowing ranges from 2.5–3 cm. Depth of sowing depends on seed size and availability of soil moisture. Deeper sowing delays field emergence and thus delays crop duration. Deeper sowing sometimes ensures crop survival under adverse weather and soil conditions mostly in dry lands.
(iii) Emergence habit: Hypogeal seedlings may emerge from a relatively deeper layer than epigeal seedlings of similar seed size.
(iv) Seedbed texture: Soil texture should minimize crust formation and maximize aeration, which in turn influence the gases, temperature and water content of the soil. Very fine soil may not maintain adequate temperature and water holding capacity.
(v) Seeds–Soil contact: Seeds require close contact with soil particles to ensure that water can be absorbed readily. A tilled soil makes the contact easier. Forming the soil around the seed (broadcasted seeds) after sowing improves the soil–seed contact.
(vi) Seedbed fertility: Tillering crops like rice, ragi, bajra etc., should be sown thinly on fertile soils and more densely on poor soils. Similarly high seed rate is used on poor soil for non-tillering crops. Although higher the seed rate grater the yield under conditions of low soil fertility, in some cases such as cotton, a lower seed rate gives better result than a higher seed rate.
(vii) Soil moisture: Excess moisture in soil retards germination and induce rotting and damping off disease except in swamp (deep water) rice. Adjustment in depth is made according to moisture conditions, i.e., deeper sowing on dry soils and shallow sowing on wet soils. Sowing on ridges is usually recommended on poorly drained soils.
2. Biological factors – Factors like companion crops, competition for light, soil microorganisms etc.
(i) Companion crop: Companion crop is usually sown early to suppress weed growth and control soil erosion. In cassava + maize/yam cropping, cassava is planted later in yam or maize to minimize the effect of competition for light. In mixed cropping, all the crops are sown at the same time.
(ii) Competition of light: In mixed stands, optimum spacing for each crop minimizes the competition of light.
(iii) Soil microorganisms: The microorganisms present in the soil should favour seed germination and should not posses any harmful effect on seeds/emerging seedlings.
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