Growing Period Or Moisture Availability Periods
Length of the growing period is defined as the period during which the availability of moisture in the root zone of a crop is adequate to meet the water needs. Because the amount and distribution of rainfall varies considerably from year to year so does the effective growing period. The length also depends on the type of soil interacting with a given quantity on rainfall. In areas receiving rainfall for 2 months, the growing season may the 8 days in a coarse textured soils or 100 days in soils of clayey or day texture. Similarly in areas with 5 rainy months, the growing from 180 to 210 days depending upon soil texture and moisture tolding capacity (Virman – 1991).
Therefore, at a given location, the amount and distribution of rainfall, moisture storage capacity and the rate of Evapotranspiration determines the length and characteristics of the growing period. Soil moisture reserves have the ability a extend the growing period by as much as one to three months spending upon the soil texture and depth.
The soil moisture availability period determines effective cropping season. Based on the analysis of long term data in the arid and semi – arid areas of India effective cropping period have been delineated for a number of locations (Table 2). In arid areas, the effective cropping season is normally 11 – 17 weeks, which restricts the choice of crops and limits the farmer to a single crop in the rainy season. In semi – arid regions, the effective cropping season is normally longer (22 – 32 weeks) with exceptions of 8 weeks in Bellary (Karnataka) and 17 weeks in Bijapur (Karnataka) regions. Rainy season crops are grown on shallow to medium Vertisols at Bijapur, while post – rainy season
Table 2. Effective cropping season at various locations in arid and semi arid areas of India.
Growing Season (Weeks)
Monsoon (23 – 39 mm)
Rainfall (mm) Post – monsoon
(Source: Single and Sebba Reddy, 1988)
crops are commonly grown on deep Vertisols at Bellary. The rainfall pattern and soil depth together determines the choice or crops and cropping systems. On shallow to medium Alfisols and related soils, only single season cropping mostly during the rainy season is possible. The amount of pre-monscore ram received in May determines whether or not double cropping is possible on demo Alfisols.
The water balance for different dryland research stations of SAI. The India has been calculated (Sing – 1993) and water availability periods haven been worked cut. The water availability period ranges between as low as 105 days at Bijapur and Bejary and as high as 210 days at Bangalore (Table 3).
Table 3. Water availability period at different dryland research centers of the SAT in India.
1. Vertisols and related black soils :
25 – 44
25 – 48
25 – 52
25 – 52
25 – 52
23 – 46
33 – 47
33 – 47
39 – 05
(Source: Singh, 1993)
Rainfall at 75% probability on long term basis Based on the information of water availability seriods potential cropping system have been suggested for different situations. The selection of efficient cropping system is also influenced by selection of suitable crops and their cultivers passed on duration and water use efficiency besides.