THE PRINCIPLES AND PRACTICES USED IN AGRICULTURE
1A. PLANT GROWTH
Green plants need to have an adequate supply of water, warmth, light, air and nutrients
in order to grow properly and produce healthy crops. Food growers have some control
over all of these factors:
- Water and Warmth—the time of planting can be chosen so that plants at each
stage of their life are growing when the temperature and rainfall are as near to
optimum as possible. Irrigation can sometimes also be used—see pages 93–100. - Light and Air—farmers and other food growers can select the planting date and
plant spacing so that adequate light and air is available to the plants–discussed on
page 4 “Plant Population” and page 42 “Day length / Photoperiodism”. - Nutrients—see pages 11–29 “Soil” and pages 29–36 “Fertilizer”.
The following subsection on plant growth discusses five topics that are of particular
interest to food growers:
plant propagation, plant population, leaf area index, the root system and the Nitrogen
Cycle.
Plants reproduce themselves, or “propagate”, either sexually by means of seeds, or
asexually by various processes of vegetative reproduction, described on pages 40–41.
Some plant species, such as onions, can propagate themselves by both methods,
using either seed or bulbs ( sets ).
Seed, or
“
grain”, provides the biggest proportion of the world’s food, especially in
poorer countries and, as a result, seed is discussed at greater length in this book than
other plant food sources such as root and oilseed crops, fruit and vegetables.
Key to the terms used in the drawing of a flower, Figure 1 overleaf:Pollen—contains the male gametophytes, and is produced in the anthers. When mature,
pollen is released into the air and comes into contact with the stigma of either the same
flower, or flower of the same plant, in a process known as self-pollination. When the
pollen comes into contact with the stigma in a flower of another plant, this process is
known as cross-pollination.
Pollen Tube—a long hollow tube that provides a passageway for the male pollen,
containing two male nuclei, to the female ovule, entering via the micropyle.
Pistil—the female part of the flower, consisting of the ovary, stigma and style, around
which the other flower parts are arranged.
1
SECTION 1
AND HORTICULTURE
”
Sexual reproduction in plants, by which they produce seed, is represented in
Figure 1.