Climate, Soils And Socio Economic Factors (Singh, 1993)

Climate, Soils And Socio Economic Factors (Singh, 1993)

Farmers have to adjust the cropping systems and crop management practices to the limitations imposed by the environment. The farming system which they have practiced has been developed by experience of generations without proper knowledge of agro climatic conditions, effective cropping pattern and schedule of supplemental irrigation can not be planned. For this study of moisture availability index (M.A.I.) is very important.

The cropping patterns are basically dependent on moisture availability index (M.A.I.). Hargreaves (1971) defined M.A.I. as there ratio of assured rainfall expected at 75% probability and estimated potential Evapotranspiration for the concerned period. However, Thormathwite and Mather (1965) calculated MAI by using water balance equation. Bistroni (1980) has defined M.A.I. as:

            AE
MAI = —-
            PE
Whereses,
AE = Actual Evapotranspiration
PE = Potential Evapotranspiration
For determining actual, Evapotranspiration (AE) following two conditions nave to be considered.
1) If P > PE, then PE = PE
2) IF P < PE, then ae = p + s
Where,
P = Precipitation
S = Change in soil moisture

Rainfall distribution over the country is highly erratic and  tooth in time and space and there by Moisture Availability Index (M.A.I.) also becomes very underlain.

Moisture Availability Index the prime factor for  especially in tropics waries both in time and space. The MAI   on the basis of average monthly rainfall (Roman and Marth, 1971 and planning was done. However, in such system the monthly MAI values where truly representative as month is a longer period for planning any operation,. Moreover, If there are dry spells in between causing failure, the monthly MAI may not represent it. Hence, there is need is weekly MAI for agriculture planning. For planning of majority of        crops the weekly MAI values would be most available.

Raskar (1994) determined crop growing period on the cases of availability index (MAI) of different rainguage stations of Pune, Ahmednagar districts of Maharashtra. In rainfall zone 1 to 3 of scarcity  of these districts, the crop growing period at 0.3 MAI ranged between 18 a 19 weeks and at 0.5 MAI between 13 and 17 weeks during that season and 0.3 MAI between 9 and 11 weeks and at 0.5 MAI between 7 and 9 weeks during rabi season (Table 4). The dry spells of 3 to 6 weeks duration were observed.

Table 4.  Weekly moisture availability period at 0.3 and 0.5 MAI in different soil type in various rainfall zone of scarcity tract of Pune and Ahmednagar districts.

(Source: Rasker 1994)
Main of 5 iccation ** Mean of 8 locations *** Mean of locations at different locations. Drop planning on the basis of MAI was suggested sorghum grown on conserved soil moisture is sown in 39 the week but analysis suggests that it is quite possible to sow the crop well ahead of the present practice i.e. by 39 mm, preferably by 35 mm itself, when the assured amount of soil moisture is available for sowing as indicated by MAI more than 0.5. This will help the crop to have sufficient moisture in latter active growth stages such as elongation, flowering and grain filling.