If plants are growing too close together (ie they are “too closely spaced”) they compete
with each other for light, water, nutrients and air, and produce small plants of low
quality which are more susceptible to attack by pests and diseases.
If plants are growing too far apart, the yield per unit area is reduced and also the
plants may become too large and/or woody for consumption or sale. Weeds are also
allowed to develop more aggressively in the open spaces between crop plants.
The plant population, or plant density or spacing, is more critical for some crops
than for others. Wheat, for example, can be planted at very different spacings without a
big effect on the yield per hectare, because wheat plants can compensate for different
plant populations. Compensation in plants is the ability to grow large or to remain small
in response to the amount of space available to them. Other plants such as maize
compensate very poorly and so must be planted at much more precise spacings.
Figures 2 and 3 illustrate the effect of plant population on the yield per hectare and
the cob weight of maize:-
Figure 2 shows how maize should be planted more closely together—ie at a higher seed
rate - in fertile or highly fertilised soils than in infertile soils or soils with a low or zero
D Fertiliser
Figure 3 shows how the cobs of maize become smaller and smaller as the plant
population increases, even though the total yield per hectare continues to increase, up to
a certain plant population.
Yield/ha0 Plant poupulation ('000'sper ha)Low NMedium NHigh N604 TONY WINCH
The effect of correct spacing of plants is also discussed on page 52 “Seed Rate”.Figure 2. Plant population/Yield per Hectare