Agronomic Concepts of the Growing Seasons

Growing Seasons

Agronomically the growing season can be defined as the period when the soil water, resulting mainly from rainfall, is freely available to the crop. This condition occurs when the water consumed by the crop is in equilibrium with rainfall and water storage in the soil. The growing season for a rainfed crop involves three different periods during which the soil moisture conditions depend on the rainfall received.

(a) Pre-humid period: During this period the precipitation will always remain lower than the potential evapotranspiration for the corresponding period. This period corresponds to the sowing period of the crop. Sowing can be done when the precipitation during the week is > 0.5 PET.

(b) Humid period: During this second period the precipitation remains higher than the PET. The crops in this period will be in active vegetative and flowering phase and the water requirement will be at its peak. At the end of this period water balance is on the positive side and the water storage in the soil is on the increase, since the rainfall is higher than the water needs.

(c) Post-humid period: This period follows the humid period. During this period there is a gradual reduction in the water stored in the soil due to the utilization by the crop plants. The crops will also make use of the rainfall received. This period usually coincides with maturity stage of the crop.

A. Types of growing period There are four types of growing period.

1. Normal: In this type, rainfall is in excess during the humid period. At the end of the pre-humid period when precipitation is higher than the 0.5 PET sowing the crops are taken up. This type of growing season is prevalent in semi arid tropics.

2. Intermediate type: The precipitation is lower that the PET all round the year. The growing season is limited to the period when rainfall is in excess of 0.5 PET. Only drought hardy crops like pearl millet, castor, etc., can be grown. Dry farming is highly risky.

3. All year round humid: In this type, the precipitation is more than PET all round the year, indicating the moisture sufficiency for cropping. This type occurs in high rainfall areas and mostly perennial crops are raised.

4. All year round dry: The precipitation is lower than 0.5 PET throughout the year. Cropping is not possible in these areas. This type of growing season is found in extremely arid areas, mostly the deserts. The fluctuations in the crop yields depend on the following conditions.

• The length of the rainy seasons i.e., from sowing to the end of the rains.

• The quantity and distribution of rains during the pre-humid and humid periods.

• The excess rainfall during humid period should go to soil storage. It may cause water logging and crop lodging.

• The amount of rainfall received during post humid season, may supplement the soil moisture during maturity.

This may favourably influence the yield. In India, four cropping seasons have been identified by IMD in dry farming areas.

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