Introduction

• Population ecology is a sub-field of ecology that deals with the dynamics of species populations and how these populations interact with the environment.
• It is the study of how the population sizes of species living together in groups change over time and space.

Interaction of crops with weeds

Crop weed competition occurs in two broad aspects-

1. Direct competition: for nutrient, moisture, light and space
2. Indirect competition: through exudation and or production of allelopathic chemicals.

The outcome of this competition is governed by various factors:

1. Period of weed growth in relation to crop emergence: 1 st third period is very critical.
2. Crop type and varieties
3. Density of weed populations
4. Weed species: tall morning glory is more competitive in cotton than sickle pod at similar weed densities. Annual broad leaved are more competitive than annual grass weed of same population.
5. Soil type
6. Soil moisture
7. Weed physiology; c4 plants have adaptive value in weeds

Measures to reduce the competition between crops and weeds:

1. Spatial arrangement of plants( narrow row crops)
2. Crop seeding rate( high seeding rate in annuals control weeds)
3. Date of planting
4. Crop rotation
5. Crop mixtures(inter-cropping)
6. Cover crops
7. Mulching

The benefits of weeds to the part of crop include:

1. Weeds protect soil surface from erosion
2. take up nutrients that might otherwise be leached
3. add OM
4. selectively inhibit development of more noxious species through allelopathy
5. Certain weeds should be regarded as important components of the crop community
6. because of the positive effects they have on populations of beneficial insects