DEPTH OF SOWING
• Uneven depth of sowing results in uneven crop stand.
• Shallow or deep sowing results in lesser plant population as all seeds do not germinate.
• Weed problem becomes severe under uneven plant population with large gaps.
• Optimum depth of sowing depends on size of seed, seed reserve, coleoptile length and soil moisture.
• Crops with bigger sized seeds like groundnut, castor, sunflower etc. can be sown even upto a depth of 6 cm.
• Small sized seeds like tobacco, ragi, gingelly have to be sown as shallow as possible.
• If seeds are sown too shallow, the surface soil dries up quickly and germination may not occur due to lack of moisture.
• Shallow sized seeds which are sown shallow should be watered frequently to ensure good emergence of crop.
• The thumb rule to sow seeds to a depth approximately 3 to 4 times their diameter.
• Optimum depth of sowing for most of the field crops ranges between 3 cm to 5 cm.
• For small seeds like gingelly, finger millet and pearl millet optimum depth of planting is 2 cm to 3cm.
• Very small seeds like tobacco are placed at a depth of 1 cm by broadcasting on the soil surface and mixing them by raking.
• Traditional tall varieties of wheat have long coleoptiles and Mexican varieties have short coleoptiles.
• Traditional tall varieties of wheat are sown deep in the soil with seed drill.
• Mexican varieties do not emerge when they are sown deep.
• Mexican wheat give higher yields compared to tall varieties only when they are sown at a depth of 4cm.
METHODS OF ESTABLISHING THE CROP
• Broadcasting is the most primitive method of sowing crops.
• In broadcasting seeds are spread uniformly over well prepared land and are covered by ploughing or planking.
• In broadcasting method seeds fall at different depths leading to uneven crop stand.
• It is common to observe plants from seedling stage to flowering in crops that are sown by broadcasting.
• Intercultivation is difficult in broadcasting as seeds fall randomly.
• Broadcasting is followed in fodder crops or crops where seeds are cheap or crops which can easily establish and suppress weeds.
• In drilling method seeds are sown in lines with seed drills.
• Drilling facilitates uniform depth of sowing resulting in uniform crop stand.
• Weeds can be controlled economically by inter-cultivation in line sown crops.
• In planting method, crops with bigger sized seeds and which need wider spacing like cotton, maize, potato, sugarcane etc. seeds or seed material is placed in the soil by manual labour or by machine.
• In transplanting method thumb rule for optimum age of seedlings is one week for every month of total duration crop.
• The depth of transplanting should be as shallow as possible for getting more number of tillers in tillering crops.
• Transplanting of rice seedlings more than 2 cm deep results in poor tillering.
TYPE OF SOWING
• Dry sowing is adopted in black soils where sowing operations are difficult to carry out once rains commence.
• Seeds are sown in dry soil around 7 to 10 days before the anticipated receipts of sowing rains.
• Wet sowing is the most common method of sowing crops.
• Minimum amount of rainfall necessary for taking up sowing is 20mm.
• Plastic mulch helps in increasing soil temperature by 1 to 5 oC.
• Providing light irrigation (20-40mm) preferably with sprinkler 5 to 7 days after sowing helps in good establishment of winter sown groundnut in south India, by increasing soil moisture and by marginally raising soil temperature.
• In olden days cotton seeds are rubbed with paste made of wet dung and earth and then dried to facilitate in sowing seeds.
• Fluff on cotton seeds can also be removed by treating the seeds with concentrated sulphuric acid for two minutes.
• Earth or sand is mixed with seeds of ragi, gingelly, tobacco etc. before sowing as seeds are minute to facilitate in sowing.
BREAKING DORMANCY
• Scarification is the process of breaking, scratching, mechanically altering or softening the seed coats to make them permeable to water and gases.
• In hot water treatment seeds are dropped in water of 75 to 100 oC.
• In acid treatment, concentrated sulphuric acid twice the volume of seed is added.
• Duration of acid treatment varies from 10 minutes to six hours or more depending on the seed coat of plant species.
• In leaching method germination inhibitors are removed by soaking seeds in running water or by placing them in frequent changes of water.
• Length of leaching time is 12 to 24 hrs.
• Treating the seeds with gibberellic acid (GA3) of 500 ppm for a period of 12 hours breaks the dormancy.
• Cytokinins and ethylene are also used to break dormancy.
• In priming seeds are soaked in water for 24 to 48 hours to induce incipient germination.
• American cotton is sown after soaking the seeds in water for 12 to 24 hours.
• Safe duration of soaking seeds is 24 hours for maize and rice, 12 hours for wheat and 10 hours for chickpea.
1000 SEED WEIGHT OF DIFFERENT CROPS
Crop Test Weight /Seed Index
Rice: 20-30 g
Wheat: 36-50 g
Barley: 35-40 g
Pearlmillet: 5-9 g
Grain Sorghum: 25-30 g
Finger millet: 1.0 – 4.5 g
Chickpea(Desi): 140-259 g
Chickpea (Kabuli): 260–450 g
Pigeonpea: 45-105 g
Lentil: 17-38 g
Blackgram: 36-49 g
Greengram: 20-70 g
Soybean: 80-150g
Cowpea: 100-250 g
Horsegram: 25-41 g
Groundnut: 200-250 g
Rapeseed and mustard: 3-5 g
Sunflower: 40-50 g
Safflower: 10-70 g
Castor: 100-150 g
Linseed: 4-8 g
Sesame: 2.85-4.06 g
Niger: 3-5 g
Tobacco: 0.05-0.12 g
Cotton (Seed Index or 100 seed weight): 7-10 g
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