Significance of humidity in Agriculture

A. Direct effects:

• Low humidity coupled with high temperature and high wind movement causes higher transpiration and desiccating effects.
• If low air moisture couple with low soil moisture, it induces water stress in plants unless extra water is supplied. In other word, irrigation is needed under low relative humidity condition.

B. Indirect effects:

I. Photosynthesis: High humidity interfere the incoming solar radiation resulting into reduced photosynthesis.

ii. Leaf growth: Leaf growth not only depends on synthetic activities resulting from biochemical process but also depends upon the physical process of cell enlargement. Cell enlargement occurs as a result of turgor pressure developed within the cells. Turgor pressure is high under high RH due to less transpiration. This is why leaf enlargement is high in the humid region.

iii. Pollination, fruit set and fruit color development: At high RH, pollen may not be dispersed from the anther. Relative humidity also affects fruit set. For e.g., bean (Phaseolus spp.) responded negatively to low humidity for fruit setting. Excessive humidity creates negative effect on fruit color development.

iv. Pest and disease occurrences: Incidence of the insect pests and diseases is high under high humidity condition. High humidity favor easy germination of fungal spores on plant leaves. Usually, three conditions are favorable for the attack of diseases and pests.

• High humidity with high temperature
• High humidity with very low temperatures
• Low humidity with low temperature.

For example, late blight of potato becomes severe under warm and humid days. Infestation of the diseases and pests is high in rainy season vegetable production plots.

v. Crop yield: So, optimum atmospheric humidity is favorable for crop production but their extremities are harmful. For example; in maize, high RH during maturity stage increased incidence of pests and diseases and thus reduced crop yield. Normally 60-70% RH is ideal for most of the crop. Very high RH also reduces evapotranspiration, leads to stomatal closure and increases the heat load of the plants.

vi. Important consideration for post-harvest storage of crops: Cold temperature and low RH is important for long-term storage of the grains (wheat, rice etc.). Similarly, cold temperature and high RH is important in order to prevent water loss from fresh fruits and vegetables (leafy vegetables, cucumber, apple etc.)