Crop Plants and Environmental Factors

Elements of the environment

The environment of a crop is everything around it that affects its life. Think of five groups.

• Light: gives energy for making food (photosynthesis). Day length also tells some plants when to flower.
• Temperature: every crop has a best range. Rice likes warm weather, wheat likes cool weather. Too hot or too cold slows the plant.
• Water: roots drink it; it also carries food up the plant and cools the leaves.
• Air: leaves take in carbon dioxide; roots need oxygen from air gaps in the soil.
• Soil and living things: soil gives support, water and minerals (nutrients). Earthworms, microbes, insects and weeds also live there.

Some factors are non-living (light, temperature, water, air, soil). Others are living (microbes, insects, weeds). A good farmer looks at all of them together.

The weakest factor decides growth

A plant needs all factors at once. If one is short, the plant cannot grow past that point, even if the others are perfect. This is the law of the limiting factor. In the 3D, put water at 1 and everything else at 6: growth stays low. Fix water and it jumps up.

Too much is also bad. Too much water drowns roots (no air). Too much fertiliser burns them. So each factor has a best range, not just "more is better".

Cycling of matter

Matter is not used up in a field; it goes round and round.

• Carbon: leaves take CO₂ from the air and build sugar. When plants or animals respire, or when dead matter rots, CO₂ goes back to the air.
• Water: rain falls, roots drink, leaves release vapour (transpiration), clouds form again.
• Nutrients (nitrogen, phosphorus, potassium and others): roots take them from soil. Fallen leaves, crop stubble and animal dung rot, and microbes put the nutrients back in the soil.

When we harvest and take the crop away, nutrients leave the field. If we never give anything back, the soil becomes poor. That is why farmers add compost, manure or fertiliser and rotate crops (beans put nitrogen back).

Cultivation techniques and the environment

Farmers cannot change the sun, but they can change the small environment around the crop.

• Tillage (ploughing): loosens soil so roots get air and water.
• Irrigation: adds water when rain is short. Drip pipes give water straight to roots and waste little.
• Mulching: a cover of straw or leaves keeps soil cool and moist and stops weeds.
• Spacing and sowing time: plants too close fight for light; sowing in the right season gives the right temperature.
• Shade net, windbreak, greenhouse: soften heat, wind and cold.
• Compost and crop rotation: keep the soil food cycle going.

Every technique changes one or more factors. Choose by asking: which factor is my weakest?

Try it: the bean pot test

Take 3 small pots with the same soil and 3 bean seeds each. Keep all in light. Give pot A no water after sprouting, pot B a cup a day, pot C a bucket a day (with no drain). After 7 days measure the height with a ruler. Predict first: which will be tallest? Then check. Pot B should win, because water has a best range.

Key formulas and definitions

• Growth is set by the weakest factor (law of the limiting factor)
• Factors: Light, Water, Nutrients, Temperature, Air
• Plants per hectare = 10 000 m² ÷ (row gap × plant gap in m)
• Water volume (m³) = area (m²) × depth (m)

Worked examples

Common mistakes

• Thinking more of anything is always better. Too much water or fertiliser harms the plant.
• Fixing the wrong factor. Adding fertiliser to a plant that is short of water does nothing.
• Forgetting that harvest removes nutrients, so the soil must be fed back.
• Mixing up non-living (light, water, soil) and living (microbes, insects, weeds) factors.