This term is used to indicate the amount of seed that is needed to sow (or to “plant”) an
area of land. The seed rate is normally expressed in kilograms per hectare (kg/ha).
Example: a farmer has a 1 hectare field to sow and decides to grow only one crop. If he
decided to grow barley he would need about 50 kg of seed, but if he chose to grow pearl
millet instead he would need only about 5 or 10 kg.
The seed rate is determined by the desired target plant population. This is defined as
the appropriate plant population to achieve optimum crop performance. The seed rate is
calculated by first assessing the thousand grain weight (TGW), then considering the
likely percentage survival of the seeds to achieve that target population. Factors to
consider in this estimation include: sowing date, soil type and temperature, and the
farming system itself—for example, most organic systems require higher seed rates than
intensive regimes due to higher losses from insect pests and diseases.
Seed rate is similar to most aspects of food production—there are very few firm
rules to follow, and the seed rate for any one crop may vary enormously. With field
peas, for example, an early variety, with small seed that is planted in good time on
infertile soil in a dry region may need a seed rate of about 50 kg/ha. But a later maturing
variety of peas, with large seed and which is planted late in fertile soil in a region with
good rainfall may need a seed rate of 250 kg/ha.
Farmers very often increase the seed rate when they are sowing fields that are known
to be heavily infested with weeds in the hope that the weeds will be more crowded out
and shaded.
Effect of Germination Rate on Seed Rate
If the germination rate (discussed in the previous paragraph on germination) of the seed
to be planted is less than 100% it is obviously a good idea to plant correspondingly
more seed.
Some examples of seed rates (in kg/ha) of 3 crops with germination rates of between
60% and 90%+ are shown below:
Crop 90%+ 80–89% 70–79% 60–69%
Sorghum
Soybean
Oats4–5
45–60
80–90
5–6
50–70
90–100
6–8
60–80
100–120
8–12
70–90
120–150
Hybrids are the offspring of parents, either plant or animal, of different species or
varieties (inbred lines). The second and subsequent generations which result from
growing hybrid seed are not regarded as being hybrids.
Hybrids can be either sterile or fertile; they are more likely to be sterile if the two
parents are very different genetically, such as with the mule, the result of a hybrid cross
between a horse and a donkey.