Crops and varieties selected should match the length of growing season during which they are not subjected to soil moisture stress. Climatological analysis helps to identify cultivars suitable for different regions. Feasibility for intercropping, sequence cropping and double cropping can also be known from such analysis.
For regions with cropping season less than 20 weeks, single crop during kharif or rabi is recommended. Regions with more than 30 weeks and above have no problem for double cropping. In regions with 20–30 weeks cropping season, double cropping may be risky. Such areas are ideal for intercropping.
Table: Length of effective Cropping Season in different Areas of India
Water balance for different agroclimatic regions has been calculated and water availability periods worked out. Regions with 350–600 mm rainfall having 20 weeks effective growing season are suitable for single cropping in kharif (red and shallow black soils) or rabi (deep black soils). Intercropping is possible in regions receiving 600–750 mm rainfall and having 20–30 weeks of effective growing season. Areas with more than 750 mm rainfall or with more than 30 weeks are suitable for double cropping.
Optimum population: Poor or suboptimal population is a major reason for low yields in rainfed crops. Establishment of an optimum population depends on seed treatment, sowing at optimum soil moisture, time of sowing, depth of sowing, method of sowing and crop geometry.
(a) Seed treatment: Seed treatment is done for many purposes such as protection against pests and diseases, inoculation of bio-fertilizers and inducing drought tolerance. Seed treatment with insecticides and fungicides is a low cost technology for protection against pests and diseases. In dry lands, spraying of chemicals for pest control is difficult due to scarcity of water. Hence, a preventive measure through seed treatment is very useful. Bio-fertilizers like azospirillum, rhizobium and phosphobacterium are applied through seed inoculation as a low cost technology for nutrient supply.
Table : Suitable Cropping Systems based on Rainfall and Water Availability Period
(i) Seed hardening: It is done to induce drought tolerance in emerging seedlings. It is the process of soaking seeds in chemical solution and drying to induce tolerance to drought. Soil moisture stress immediately after sowing affects germination and establishment. Seed hardening enables seedlings to survive this early moisture stress. During seed hardening, seeds are subjected to partial hydration followed by dehydration before sowing. Seeds are soaked for specified time 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 ensures early germination by 2–3 days compared to untreated seeds and induces better root development, 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. Hardened seeds can be sown immediately or within 30 days of treatment.
The seed hardening is considered as low cost technology and is the most important requirement for pre-monsoon sowing. 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. The seed hardening for various crops is given in Table 13.12. For pulses (black gram/green gram), 4 kg of wood ash is collected, powdered thoroughly to which 30% Acacia gum is added and mixed thoroughly so that wood ash-gum paste is obtained. 8 kg of black gram or green gram seed is spread over the Acacia-wood ash paste and mixed thoroughly so that all the seeds are smeared with the paste. The treated seeds are shade dried for 5 hours and then can be sown.
(b) Sowing at optimum soil moisture: An effective rainfall of 20–25 mm, which can wet a depth of 10–15 cm, is needed for sowing. Moisture stress at or immediately after sowing adversely affects germination and establishment of seedlings. To ensure adequate soil moisture at sowing, sowing has to be done as early as possible after soaking rainfall is received. Sowing methods and implements play a crucial role in this regard.
(c) Time of sowing: Optimum time of sowing is indicated by adequate rainfall to wet seeding depth and continuity of rainfall after sowing. The probable sowing time in a rainfed area is the week which has a rainfall of not less than 20 mm with coefficient of variability less than 100% and the probability of a wet week following wet week. Timely sowing ensures optimal yield besides it may also help pest avoidance.
Table : Seed Hardening for various Crops
Pre-monsoon dry seeding: In some regions, where heavy clay soils dominate, sowing after rains is impossible due to high stickiness of soil. Here, sowing is done in dry soil, 2–3 weeks before the onset of monsoon (pre-monsoon). Seeds will remain in soil and germinate only on receipt of optimum rainfall. The advantages of pre-monsoon dry seeding are early sowing, uniform germination and good establishment, utilization of first rainfall itself for germination instead of for land preparation in post monsoon sowing and early maturity before closure of monsoon and avoidance of stress at maturity.
For sorghum in black soils, pre-monsoon dry seeding is recommended 1–2 weeks before onset of monsoon with depth of sowing at 5 cm and seed hardening with 2% 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.
The success of pre-monsoon dry seeding depends on the following:
• It is recommended for bold seeds like cotton and sorghum only and not for all crops.
• Time of advance sowing must be fixed based on rainfall analysis for date of onset of monsoon and continuity of rainfall after sowing.
• Seeds must be hardened to ensure quick germination and drought tolerance.
• Seeding depth must be such that seeds will germinate only after receipt of rainfall to wet that depth is received. Surface sowing may lead to germination with less rainfall and death due to subsequent soil drying.
• Off season tillage is necessary to enable sowing in dry soil before monsoon.
• Seed damage by soil insects has to be prevented.
(d) Optimum depth of sowing: When seeds are sown on surface or at very shallow depth, germination and seeding growth are affected when surface soil moisture dries up. Sowing at a depth where soil moisture availability is adequate, ensure early and uniform germination and seedling establishment. Optimum depth of sowing varies with crop, especially seed size and penetration power of plumule. For e.g., it is 1–2 cm for sesamum, 2–3 cm for pearl millet and minor millets, 3–5 cm for pulses, sorghum and sunflower, 5 cm for cotton and maize, and 7 cm for coriander.
(e) Method of sowing: Sowing method is an important determinant of population. In dry lands, it is important to sow the seeds in moist soil layer to ensure proper germination and seedling emergence. It is therefore necessary to sow immediately after rainfall to avoid sowing in dry soil. It is also important to sow the seeds at correct depth, neither on the surface nor too deep. Establishment of an optimum population also depends on proper spacing between plants. The density, geometry, and depth of sowing are dependent on method of sowing. The sowing methods usually adopted in dry lands include broadcasting, sowing behind plough and sowing by seed drills. Dibbling of seeds and planting of seedlings are also adopted for some crops (Cotton, tobacco and chillies). Each method has advantages as well as limitations. The choice of sowing method depends on seed size, soil condition time available, cropping system, crop geometry, sowing depth, source of power, cost of sowing, etc.
Table : Merits and Limitations of Sowing Methods
(f) Crop geometry: It refers to the shape of land occupied by individual plants as decided by spacing between rows and between plants. It depends on the root spread and the canopy size of the crop and the cropping system.
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