Seed and sowing of sorghum

A healthy crop with good yields starts with the use of well selected seeds for sowing.
To get the required plant stand, healthy and good ear-heads with well-filled seeds need to be selected
at the time of harvesting. Seed from such ear-heads are stored in a well ventilated with low moisture conditions.
Use certified quality seeds of hybrids and improved varieties recommended for the area.

The seed should be treated with appropriate chemicals prior to planting to prevent seed-borne diseases as well
as soil pests which are common in the field during the earlier years.
The seeds are also treated with some biofertilizers for easy and enhanced availability of important nutrients like nitrogen and phosphorus.
Seed hardening is also practiced for better germination.

The following are the seed treatment practices:

Seed hardening is done by soaking the seeds in 2% (20 g in one liter of water) potassium dihydrogen phosphate solution for 6 hours. Use 350 ml of solution for soaking one kg of seed.
Dry the seed in shade to original moisture level.
The seeds of sorghum are treated with the 300 mesh Sulfur powder @ 4 gm of sulfur per kg of seeds for controlling the smut disease.
The seeds are soaked in 30% salt solution (3 kg of common salt in 10 liters of water). Ergot affected seeds which float are removed to avoid the incidence of ergot disease.
Seeds are treated with Carbofuran to prevent shoot fly infestation.
Treat the seeds with three packets each of Azospirillum (600 g) and Phosphobacterium to enhance the availability of nitrogen and phosphorus.
The seed treatment is done manually for small amount of seeds.

Large amount of seeds can be treated using a seed treating drum.

Three systems of sorghum sowing are followed:

• sowing on a flat surface,
• sowing on a ridge-and-furrow system,
• sowing on a broadbed-and-furrow system.

   
         Sowing on flat surface                      Ridge and furrow system

When seeds are sown using ridge and furrow system, the seeds are either sown at the bottom of the furrow or on the side or top of the ridge.

Planting on the side or top of the ride is practiced in heavy rainfall areas and under irrigated conditions.

The broadbed-and-furrow (BBF) system has an advantage over flat sowing in: 

• draining off excess water,
• providing more soil aeration for plant growth,
• greater in-situ moisture conservation.
• easier for weeding and mechanical harvesting.

       
         Broad-bed and Furrow                            BBF sown crop

The seeds are sown either by :

• sowing by broadcasting seed manually,
• Sowing behind country plough using pora,
• using an improved seed drill which may or may not be fitted with hoppers for fertilizer application,
• Using mechanical seed drills attached to a tractor.

Manual sowing by broadcasting the seed is practiced when the area to be sown is small.
After broadcasting, the seeds are covered by running a brush harrow.
The germination my not be uniform in hand sowing, and so one has to use a higher seed rate to get the optimum plant stand in the field.

Country seed drill

A country seed drill called pora i.e. a wooden hopper attached to a hollow bamboo (Fig.) is used to sow the seeds in the shallow furrows opened by the tines of a country plough.
A larger area can be covered with this method of sowing.

 

 

Seed cum fertilizer drill

The best method is to sow the hardened seeds of sorghum at 5 cm depth with seed cum fertilizer drill to ensure uniform depth of sowing and fertilizer application before the onset of monsoon as detailed.

   

Seed rate:
The amount of seed required per unit area depends on:

• Optimum plant stand required per unit area
• Plant type i.e. tall or short plants
• Weight of seed
• Quality of seed in terms of germination.

Seed rate should be determined based on the optimum number of plants required in unit area (acre or hectare or sq ft or sq m) for good yields.  The optimum plant population for sorghum can vary between 150,000 to 250,000 plants/ha. If the plant population is on the higher side of 150,000 plants, the reduced panicle and seed size is compensated by the higher number of panicles per unit area. The recommended plant stand for sorghum under normal conditions is 180,000 plants per ha or 15 plants per sq m or 72,000 plants per ac. Under irrigation or high levels of management on highly productive soils, a population of 225,000 plants/ha (100,000 plants per ac) is recommended. On extremely sandy, droughty soils, a population of about 90,000 plants/ha (40,000 plants per ac) is desirable. For rabi crop, the optimum population should be between 90,000 - 1,35,000/ha (36,000-55,000/ac). In case the soil moisture is low, it is advisable that the population should be 92,000 per hectare (36,000 per acre) and when the moisture is optimum the plant population should be 1,35,000/ ha (55,000/ac). Under irrigated conditions for summer crop, the optimum plant population should be 1,80,000 plants/ha.

Estimation of seed quantity per hectare:

Sorghum seed with 75% germination, 100-seed mass of 2 g, and the required plant population is 150,000 plants per ha. 

Step 1:

Since the germination percentage is 75, we need to adjust for this deficiency. Number of seeds needed to get 100 seedlings (100 x 100)/75=134

Step 2:

To get 100 seedlings, 134 seeds are required, then, the number of seeds required for 150,000 plants: (150,000 x 134)/100= 201,000 seeds. Thus, 201,000 seeds are needed to establish 150,000 plants per ha.

Step 3:

     The quantity of seeds(seed rate) required for 201,000 seeds, based on 100 seeds weight  of 3 g. (201,000 x 3 g)/100 seeds=6030g. Thus, 6 kg of seeds are needed per ha to establish 150,00 plants per ha. If germination % of seeds is not known, then the seed rate is determined by adding additional 20% of seeds to cover any seed germination problems.

Example: Sorghum 100-seed mass of 3 g, and the required plant population is 150,000 plants per ha.

Step1:

Based on 100 seed mass of 3 g (3 g X 150,000 plants)/100= 4500 g or 4.5kg. If germination % of seeds is not known, then the seed rate is determined by adding additional 20% of seeds.

Step 2:

Based on 20% more seed requirement for any seed germination problem i.e 120% required (120 X 4.5 kg)/100 = 5.4 kg of seed Thus, 5.4 kg of seeds are needed per ha to take care of any seed problem and to establish 150,00 plants per ha. The seed rate varies from 6 to 15 kg/ha. But the weight of seed planted is not a good measure of population since seed weight varies considerably i.e. 2 to 4 g per 100 seeds among various hybrids and improved varieties. Establishing optimum plant population in unit area is more important than the seed rate.

Sowing distance:

The distance between row to row of plants, and plant to plant within a row can be varied depending on the method of sowing. However it should be remembered that the sowing distance determines the optimum plant stand requirement. In general, if ridges are formed 45 cm apart, then the plants should be 15 cm apart within a row. If broad bed and furrow method is adopted, then the plant rows will be 60 cm apart on the bed and the distance between plants should be 10 cm to get the optimum population

Sowing time:

The sowing time of sorghum is important aspect in increasing the crop yield. This sowing time is also related with soil moisture and soil temperature, as well as incidence of shoot fly. The rainy season crop (kharif) should be sown immediately after commencement of monsoon and after having adequate moisture in the soil. The sowing should be completed before 7th July. Early sowing helps in minimum incidence of shoot fly and less damage to the crop. Delayed sowing after first week of July results in reduction of yield due to heavy attack of shoot fly. The seeds should be sown when there is moisture in the soil up to a depth of 5 to 7.5 cm. If irrigation facility is available, irrigating the field for sowing just before the onset of rainy season and thus advancing the sowing substantially increases sorghum yield. Rabi crop is sown between 25 September and 15 October. Late sowing beyond October may result in poor germination and plant stand due to low soil temperatures. Also, further growth of sorghum plants will be slowed down at low temperatures.