Agronomy Practical on Estimation of Seed requirement and plant population of field crops-calibration

Procedure and examples on calibration of seed requirement and calculation of plant population is presented by Dr.G.S.Tomar, Professor (Agronomy), IGAU, Raipur.

1. Agronomy Practical on Plant Population and Seed Requirement: Presented by
Dr.G.S.Tomar, Professor (Agronomy), CARS, Mahasamund (C.G.) for B.Sc.Ag.Students

Page 1 of 8

PRACTICAL
ESTIMATION OF PLANT POPULATION AND SEED REQUIREMENT OF
KHARIF CROPS

Seed rate is the quantity of seed of a crop that is required to sow in a unit area of land for
optimum plant population and crop production. Establishing a good plant stand in the field is
important to ensure good crop yields. Plant stand is expressed either as space between plants or
as an optimum plant population per unit area. We can determine the plant population if
information on plant spacing is provided. Similarly, if optimum plant population is given, then
inter-row and intra-row spacing can be determined. The required number of plants/unit area is
decided by calculating the seed rate. The seed rate depends on spacing or plant population, test
weight, germination and purity percentage.
Objectives
 To know the quantity of seed needed for sowing in advance.
 To prevent seed wastage from excess sowing such reduces the initial cost of production.
 To maintain optimum plant population in the field for higher yield harvest.
(a) Estimation of Plants Population per hectare
If the spacing of plants within the row and spacing between rows are known, then we can
calculate the number of plants in one hectare. For example, if the row width is 0.75 m and plants
are spaced 15 cm apart in the row, the final plant population assuming 100 % germination and no
plant mortality, would be (1 ha =10,000 sq m)
10,000 sq m
Plants population per hectare = -------------------------
Plant Spacing in sq m

10,000 sq m
Plants per hectare = ------------------------ = 88,888.88 plants/ha
0.75 m x 0.15 m
Likewise, if the crop is planted in hills the calculation made is:
10000 m2 x No. of seeds/hill
Plant population/ha=--------------------------------------------
Row width (m) x hill spacing (m)
Thus planting in 50 cm width with 50 cm between hills and two seeds are planted per hill will
results:

2. Agronomy Practical on Plant Population and Seed Requirement: Presented by
Dr.G.S.Tomar, Professor (Agronomy), CARS, Mahasamund (C.G.) for B.Sc.Ag.Students

Page 2 of 8

10000 x 2
=------------------------ = 80,000 plants/ha.
0.5 m x 0.5 m
(b) Estimation of Intra-row Spacing
We can calculate the spacing between the plants within a row, if row width and plant
population per ha are known. If row width = 0.75 m and plant population per ha = 150,000, is
given. Find the spacing between plants and within a row.
Step 1: Calculate the row length in hectare based on the row width.
= 10,000 sq m / 0.75 m = 13333 m
Step 2: Calculate the spacing between plants within this row.
150,000 plants are present in a row of 13333 m so, spacing between two plants =
13333 m /150,000 = 0.0888 m or 8.88 cm.
Therefore, if 150,000 plants are to be established per ha and a spacing of 75 cm is used
between the rows, then the plants are to be 8.88 cm apart in the row. Based on this spacing
between the plants, excess plants in a row can be removed.
(c) Determination of Seed Requirement
Seed rate for a particular crop determines the final plant population of particular crop.
Correct quantity of seed with good germination percentage (usually 95-98%) should be used to
maintain optimum plant stand for getting higher yield. The quantity of seed required per unit
area (seed rate) differs from crop to crop and it depends upon the spacing, test weight (1000 seed
weight for small seeds and 100 seed weight for large seeds), no. of seedlings per hill,
germination percentage, variety, cropping system and risk factors and soil fertility etc.
We can calculate the amount of seed required to establish a desired plant stand in the
field considering the quality of the seed. The seed-lot should be examined before sowing and
any deficiency should be adjusted by increasing the seed rate, to obtain the desired plant
stand. Seed rate for a crop depends upon seed size or test weight, desired plant population,
germination percentage and purity percentage of seed.
Area to be sown or plant population/ha.x No. of seeds/hill x Test wt. (g) x 100
Seed rate (kg/ha) =------------------------------------------------------------------------------------------
1000 x 1000 x Germination % x Purity %

3. Agronomy Practical on Plant Population and Seed Requirement: Presented by
Dr.G.S.Tomar, Professor (Agronomy), CARS, Mahasamund (C.G.) for B.Sc.Ag.Students

Page 3 of 8

Exercise-1: Calculate the seed rate for transplanted rice, if spacing 20 x 20 cm, seedlings per hill
=2, germination % = 90, purity % = 95, test weight = 26 g and damaged seedlings as % of
uprooted seedlings = 12 is given.
Solution:
Total no. of seedlings to be uprooted from nursery = no. of seedlings required for
transplanting + no. of damaged seedlings at uprooting + no. of seedlings required for gap filling.
10000 x No. of seedlings per hill
No. of seedlings required for transplanting/ha =-----------------------------------------
Hill spacing
10000 x 2
= ---------------- = 500000
0.2 x 0.2
Seedlings required for transplanting x 12 500000 x 12
Damaged seedlings =----------------------------------------- = --------------
100 100
= 60,000
Total no. of seedlings to be uprooted = 500,000 + 60,000 = 5, 60,000 seedlings
No. of seedlings required/ha x test weight x 100 x 100
Seed rate for transplanted rice =-----------------------------------------------------------------
1000 x 1000 x Germination % x Purity %
5, 60,000 x 26 x 100 x 100
=---------------------------------= 17.02 kg/ha seed is needed.
1000 x 1000 x 95 x 90
Exercise-2 : If rice is to be sown at 20 x 5 cm distance and seed possesses 95 % germination, 90
% purity with a test weight of 26 g. Damaged seedlings by birds to be replaced by seed is 11
seeds per sq m. Calculate the seed rate for direct sown rice.
Solution:
Total number of seeds required = Total no. of seeds required per ha + no. of seeds needed
for replacing damaged seeds.
10000 10000
No. of seeds required per ha =------------- = --------------= 1000000 seeds
Spacing 0.20 x 0.05
No. of damaged seeds per ha = 10000 x 11 = 11000 seeds
Total no. of seeds required = 10110000 seeds
Total no. of seeds/ha x test weight x 100 x 100
Seed rate kg/ha = ---------------------------------------------------------
1000 x 1000 x 95 x 90

4. Agronomy Practical on Plant Population and Seed Requirement: Presented by
Dr.G.S.Tomar, Professor (Agronomy), CARS, Mahasamund (C.G.) for B.Sc.Ag.Students

Page 4 of 8

1011000 x 26 x 100 x 100
=-----------------------------------= 30.74 kg/ha
1000 x 1000 x 95 x 90
Exercise-3 : Calculate the seed rate of sorghum for seeds having 70 % germination, test weight
of 2.8 g, and the required plant population is 250000 plants per ha.
Solution:
Since the seed germination is only 70 %, we need to adjust for this deficiency.
100 x 100
Number of seeds needed to get 100 seedlings = ------------------ = 142 seeds
70
250,000 x 142
Then, the number of seeds required for 250,000 plants =------------------- = 355,000
100
Thus, 355000 seeds are needed to establish stands of 250,000 plants per ha.
355000 x 2.8 g
The quantity of seed required per ha = ---------------------= 9940 g = 9.94 kg
100
Thus, 9.94 kg of seeds is needed per ha.
Exercise-4: Calculate the quantity of maize seed for sowing in one hectare area from the
following particulars
Spacing-75 cm x 30 cm, germination of the seeds-90 %, purity of the seeds-90%, seeds required
for gap filling-5 % by weight of seeds required for sowing and test weight of the seeds-250 g.
Solution:
10000 m2
Plant population =---------------------= 44444.44
0.75 m x 0.3 m=0.225
44444.44 x 250 x 100 x 100
=--------------------------------------------= 13.71 kg/ha
1000 x 1000 x 90 x 90 =810000
Quantity of seed required for gap filling at the rate of 5 % of seed weight
13.71 x 5
=-----------------=0.685 kg/ha
100
Total quantity of seed required for sowing/ha would be 13.71 kg + 0.685 kg
=14.39 kg/ha.
Exercise-5: Calculate the seed rate of groundnut in kg/ha from the following details: spacing-50
cm x 20 cm, germination of seed-92%, purity of seed-95%, test weight of kernels-200 g and
shelling percentage-60. The seed rate is to be calculated in terms of weight of kernels as well as
unshelled pods.

5. Agronomy Practical on Plant Population and Seed Requirement: Presented by
Dr.G.S.Tomar, Professor (Agronomy), CARS, Mahasamund (C.G.) for B.Sc.Ag.Students

Page 5 of 8

10000 m
2

Plant population=----------------------=100000
0.5 m x 0.2 m
100000 x 200 x 100 x 100
Seed rate of kernels (kg/ha)=----------------------------------------------= 22.88 kg/ha
92 x 95 x 1000 x 1000
Amount of unshelled pods needed for sowing (kg/ha)
Amount of kernels (kg/ha) x 100 22.88 x 100
=----------------------------------------------- =-----------------= 38.33 kg/ha
Shelling percentage 60
Ans.: Seed rate of groundnut as kernels= 22.88 kg/ha and as unshelled pods is 38.33 kg/ha.
Exercise-6: Calculate the seed rate of Green gram for sowing in one hectare of land from the
following: spacing-30 cm x 10 cm, germination-92 %, purity-85 % and 1000 grain weight-36 g.
Solution:
10000 m
2

Plant population=----------------------=333333.33
0.3 m x 0.1 m
333333.33 x 36 x 100 x 100
=-------------------------------------------=15.34 kg/ha
92 x 85 x 1000 x 1000
Exercise-7: Calculate the seed rate of Pigeonpea for sowing in one hectare of land from the
following: spacing-60 cm x 25 cm, germination-87 %, purity-86 % and 1000 grain weight-70 g.
Solution:
10000 m
2

Plant population=----------------------= 66666.67
0.6 m x 0.25 m
66666.67 x 70 x 100 x 100
=--------------------------------------= 6.23 kg/ha
87 x 86 x 1000 x 1000
Estimation of seed Quantity per row
Experimental plot size = 8 m x 4 m
Given: Sorghum seed with 70 % germination, 100-seed weight of 2.8 g and number of rows per
plot = 8, row spacing = 50 cm, seeds required per ha = 9.94 kg (as in previous example) and
population required: 250,000 plants per ha.
Based on the amount of seeds need to be used per ha, we can calculate the required seeds per plot
and per row for research plots.

6. Agronomy Practical on Plant Population and Seed Requirement: Presented by
Dr.G.S.Tomar, Professor (Agronomy), CARS, Mahasamund (C.G.) for B.Sc.Ag.Students

Page 6 of 8

9.94 kg x 1000 g/kg
Seeds needed per sq m = ----------------------------- = 0.994 g
10,000 sq m
Plot area = (8m x 4m) = 32 sq m. Thus, seed weight per plot =0.994 x 36 = 31.80 g.
Now, calculate the amount of seeds per row.
Single row area = length x width (spacing) = 8 m x 50 cm = 4.0 sq m
Seeds required per row =0 .994 x 4.0 = 3.997 g
Exercise-1: Suppose the required plant density Pigeonpea is 333 000 plants/ha, 100-seed weight
is 10 g and germination is 90 %. The seed requirement per ha and a plot of 15 m2 (3 m x 5 m)
with eight rows of 5 m length and 0.375 m between rows can be calculated.
Solution
(i) The seed required for 100 germinable seed for this lot is
100 seeds
-------------= 111 seeds
0.90
Therefore, to obtain 100 seedlings at least 111 seed should be sown as germination of the
seed lot was 90 %.
(ii) The seed required for 333 000 plants/ha
333 000 seeds/ha x 111 seeds
=......................................................= 369 630 seeds/ha
100 seeds
(iii) Mass (kg) of 369 630 seeds @ 10 g for 100 seeds will be
369 630 seeds x 10 g
=......................................= 36.9 kg or 37 kg/ha
1000 g/kg x 100 seeds
(iv) To sow 20 % additional seed the requirement will be
37 kg/ha x 1.20 = 44.4 kg/ha
(v) The seed required m
-2
will be
44.4 kg/ha x 1000 g/kg
=........................................= 4.44 g m
-2

10,000 m
2
or ha
(vi) The seed requirement for plot (15 m
2
) will be
= 4.44 g m-2 x 15 m
2
/plot = 66.6 g or 67 g/plot
(vii) The seed requirement /row will be
(The area of row is 5 m x 0.375 m = 1.875 m
2
/row)

7. Agronomy Practical on Plant Population and Seed Requirement: Presented by
Dr.G.S.Tomar, Professor (Agronomy), CARS, Mahasamund (C.G.) for B.Sc.Ag.Students

Page 7 of 8

(viii) Seed requirement/row = 4.44 g m-2 x 1.875 m
-2
/row
=8.32 g/row
Exercise-2 : Calculate the seed rate of hybrid cotton for one acre area with following
observation: Spacing = 67.5 X 30 cm, Test weight of fuzzed seed and unfuzzed seed is 140 and
150 g, respectively, Purity percentage = 90. Germination percentage = 80.
Solution
Purity % X Germination %
Real value of seed = -----------------------------------
100 x100
90 X 80
Real value of seed =---------------- =0.72
100 x100
Area in one acre
Plant population needed/Acre =-------------------------------
Plant spacing
4000 x 100 x 100
Plant population needed/ha =----------------------------- = 19753 plants
67.5 x 30
Plant population needed X Weight of one seed
Seed rate Kg/ac. =-------------------------------------------------------------------
Real value of seed X1000X100
19753 x 1.4 X 100
Seed rate (fuzzed seed) needed/ac =----------------------------- = 3.84 kg/ac.
72 X 81 x 1000 X100
19753 x 1.5 x 100
Seed rate (unfuzzed seed) needed/ac =-------------------------- = 4.115 kg/ac.
72 X 81 x 1000 x 100
Assignment
1.Work out the seed requirement of rice (in kg/ha), if
A.Transplanted Rice: Spacing of hills-20 cm x 20 cm, No. of seedlings/hill-3, Germination
of the seed-95 %, Purity of seed-90 %, Test weight-25 g, No. of damaged seedlings at the
time of uprooting-15 (as percentage of uprooted seedlings) and No. of seedlings required for
gap filling-12 per 5 m2 area.
Answer:25.92 kg/ha
B.Upland rice: Approximate spacing/plant-20 cm x 3 cm, Germination of the seeds-95 %,
Purity of the seed-90 %, Test weight-25 g and No. of damaged seeds by birds which need to
be replaced by another seed-10 seeds m2 area.

8. Agronomy Practical on Plant Population and Seed Requirement: Presented by
Dr.G.S.Tomar, Professor (Agronomy), CARS, Mahasamund (C.G.) for B.Sc.Ag.Students

Page 8 of 8

Answer: 51.66 kg/ha
2. Calculate the quantity of maize seed for sowing in one hectare area from the following
particulars
Spacing-75 cm x 20 cm, germination of the seeds-90 %, purity of the seeds-90%, seeds required
for gap filling-5 % by weight of seeds required for sowing and test weight of the seeds-250 g.
Ans.: 22 kg/ha.