Relative Humidity on Plant growth

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Increase in RH – decreases the temperature. This phenomenon increases heat load of the leaves. Since transpiration is reduced – not much heat energy used. Excessive heat due to closure of stomata entry of CO2 is reduced. Reduction in transpiration reduces the rate of food translocation and uptake of nutrients.

Very high RH is beneficial to – Maize, Sorghum, Sugarcane (C4 Plants)

Harmful to – Sunflower, Tobacco.

For almost all the crops it is always safe to have a moderate R.H. of above 40%. 60–80% conducive for growth and development of plants. The humidity is not an independent factor. It is closely related to rainfall, wind and temperature. It plays a significant role in crop production.

• The humidity determines the crops grown in a given region.

• It affects the internal water potential of plants.

• It influences certain physiological phenomena in crop plants including transpiration

• The humidity is a major determinant of potential evapotranspiration. So, it determines the water requirement of crops.

• High humidity reduces irrigation water requirement of crops as the evapotranspiration losses from crops depends on atmospheric humidity.

• High humidity can prolong the survival of crops under moisture stress. However, very high or very low relative humidity is not conducive to higher yields of crops.

• There are harmful effects of high humidity. It enhances the growth of some saprophytic and parasitic fungi, bacteria and pests, the growth of which causes extensive damage to crop plants. e.g.,

(a) Blight disease on potato.

(b) The damage caused by thirips and jassids on several crops.

• High humidity at grain filling reduces the crop yields.

• A very high relative humidity is beneficial to maize, sorghum, sugarcane etc, while it is harmful to crops like sunflower and tobacco.

• For almost all the crops, it is always safe to have a moderate relative humidity of above 40%.

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