External or Environmental Factors – Water and Plant or Biotic factors
Functions of water:
1. Major component of the plant body (90%).
2. Act as solvent for dissolving the nutrients & nutrient carrier.
3. Maintains/regulates the temperature of plant & soil as well
4. Maintains the turgidity of plant cells.
5. Essential for absorption of nutrients & metabolic process of the plants.
Plant tissues constitute about 90% of water. Rain and ground water are the sources of the water. Ground H2O is reused for irrigation through well, tank or canal, etc. Erratic rains are to be conserved properly so that plants make best use of it. Rainwater is to be supplemented by irrigation to meet the water requirement of crops for bumper yields.
Water Present in the soil helps the plants in many ways:
1. Supplies the essential raw material for production of carbohydrates by photosynthesis.
2. Promotes physical, chemical & biological activities in the soil.
3. Gaseous diffusion in soil for proper aeration.
Water is the life of plant & must be supplied in proper quantity. Too much water may suffocate the plant roots & too little may not be able to sustain the plant. The water requirement of crops differs from crop to crop & variety to variety as well, depending upon the growth habit, genetically & physiological make up, duration of the crop, etc. For example, sugarcane, rice, banana, wheat, groundnut, etc. are the high water requiring crops & Jowar, Mung, udid, Tur, gram, bajara etc. are the low water requiring crops.
Plant /Biotic factors: Biotic factors include plant, symbiosis & animals.
Plant: The soil & water are two variables which either has to be suitably adjusted for the plant to grow or the plant should be so bred & selected that it will adjust to a given soil & water condition, growing season, climatic requirement, etc. Some of the crops grow on only rain while some required irrigation water, Plant breeders are constantly at work to evolve varieties which will suit the given soil & water condition e.g. drought resistant, disease resistant, more nutrients absorbing capacity etc.
The unwanted plants, ‘weeds’ compete with crop plants fro solar energy, water nutrients & also for space which need to be controlled for better crop growth & production at proper time & methods.
Symbiosis: There are the some organisms which have mutual relationship with each other & with the prevailing environment of the place. This biological inter relationship among the organisms is termed as symbiosis. The symbiotic relationship between legumes & Rhizobia which results in ‘N’ fixation is of great significance to crop production. The legume bacteria use the carbohydrates of their host as energy & fixes up atmospheric ’N’ which in turn used by host plants. The free living organisms (Azotobacter) acquire their energy from soil OM, fix the free N & make it a part of their own tissue. When they die the ‘N’ available in their body tissues is used by the crop plants.
Animals: Soil organisms:
The soil organisms include:
1) Soil flora (plant kingdom) & 2) soil fauna (animal Kingdom).
Soil flora is of two types: i) Macro flora e.g. Roots of higher plants ii) Micro flora e.g. Bacteria, fungi, actinomycetes & algae.
Soil fauna is of two types: i) Macro flora e.g. earthworm, moles, ants, and ii) Micro fauna e.g. protozoa, nematodes. The soil fauna including protozoa, nematodes, rotifers, snails, insects constitute a highly important part of the environment for plant roots. All these organisms contribute decomposition, when using the OM for their living. Among these insects, nematodes cause considerable damage as crop pests.
Beneficial organisms: Insects like bees, wasp, moths, butterflies, beetles help in pollination of crops. Burrowing by earthworm facilitates aeration & drainage and the ingestion of OM & mineral matter results in a constant mixing of these materials in the soil & tends to make better plant growth.
Small animals: Like rabbits, squirrels, rats cause extensive damage to field & garden crops.