World Colleges Information

Introduction:

->  Assessing Length of Growing Period (LGP) on practical basis is very important, especially for dry lands, since this period supplies the required soil moisture to the crops raised. It is evidently proved from the past research that the potential yield of a crop was directly proportional to the crop’s evapo-transpitation to the Potential Evapo-Transpiration (PET) demand of that region.

->  In one of the studies (Das 1995), the duration of the crop-growing period for Madhya Pradesh was determined based on rainfall data recorded from 1901 to 1970 in respect of 160 weather stations. The assumption made was that, the ratio of weekly assured rainfall to weakly potential evapotranspiration should be at least 0.3 and this was considered as the beginning of growing season.

->  Similarly, at the end of the rainy season, the available soil moisture must be adequate to maintain an actual evapo-traspiration to PET ratio of 0.3/more and this was assumed to be the end of the growing season. The study indicated that growing season was shortest in the Northern part of MP and longest in the Central part of the State.

->  In another study, which was conducted to compute LGP for rain fed condition using moisture adequacy index for the Cooch Behar district of West Bengal, India, weekly rainfall data from 1967 to 1992 and PET values were used. The average LGP for sandy loam soil was 287 days starting from 16th April to 28th January, which could be effectively utilized for double cropping having aus [rice]/jute followed by pulses/oilseeds in upland and triple cropping having aus (cv. Parijat) followed by aman [rice] (cv. IET 4094) and rapeseed (cv. B 9) in medium land for increasing crop production under rain fed condition (Khan and Saha, 1996).

->  Sanbagavalli et al., (2001) made a study to determine the LGP for Coimbatore, Tamil Nadu, India, using FAO model. Rainfall data from IMD were collected for 52 standard weeks for 80 years (1905-85) and mean striked out for each week. Thirty and fifty per cent initial probable weekly rainfall were computed from the mean weekly data collected for each standard week. LGP refers to the number of weeks when 30 per cent probable rainfall exceeds 50 per cent PET and falls below 50 per cent PET + stored soil moisture support period.

->  The LGP was from 38th standard weeks to 50th standard week, if weekly mean rainfall were taken, while it was 38th week to 50th standard week for 30 per cent probable rainfall and 40th week to 46th standard week for 50 per cent probable rainfall. With respect to 30 per cent probable weekly rainfall analysis, a growing period of 12 weeks was recorded. If 50 per cent probable weekly rainfall was taken, the LGP would be around six weeks, which did not reflect the ground reality.

->  Hence, it is suggested to use 30 per cent probable weekly rainfall for computing LGP. The computed LGP for 30 per cent probable rainfall was similar to the result obtained from mean rainfall and PET. Crops like sorghum (cultivar Co 25 and Co 26), maize (cultivar,CoH 1 and CoH 2) and sunflower (cultivar, Co 1 and Co 2) were suggested.  

->  The water balance method of Thornthwaite and Mather (1955) was used by Abhijit Saha and Khan (2001) to determine the LGP for soils with different water holding capacity (sandy, sandy loam, loam, clay loam and clay soil) in respect of Malta, West Bengal, India. Data on daily rainfall for the period from 1901 to 1987, PET and available soil water holding capacity data were used.  LGP was determined through the Moisture Adequacy Index (MAI), which is the ratio of stimulated Actual Evapo-Transpiration (AET) and PET.

->  The first week, when MAI reaches a value of 0.5 and the last week when MAI value decreased to 0.33 were considered as the start and end of a crop-growing season, respectively. The total LGP varied from 168 days in sandy soil to 263 days in clay soil, with an increase of 10-12 per cent in LGP in sandy and clay soils over their coarser soil types. Depending on LGP values, crops like upland rice, transplanted rice, jute, black gram and green gram were recommended for the pre-kharif/kharif season, while mustard, pea, gram, lentil and linseed were recommended for the rabi season.

->  Climatic water balance for three agro climatic zones in Indian Punjab was assessed using weather parameters such as rainfall, temperature, elevation, net radiation, wind effect, relative humidity and vapor pressure. Statistical analyses indicated that annual, as well as seasonal water deficit was maximum at Bathinda, while it was minimum at Ballowal Saunkhari. Such analysis was helpful in working out the length of crop growing period, which can be used for contingent crop planning and crop diversification for judicial use of limiting water resources (Kingra et al., 2004).

->  Considering the usefulness of the studies made in the past as cited else where in this paper and also the semi-aridness nature of both Rajasthan and Andhra Pradesh, an attempt was made to fix the LGP especially for use under dry land farming.

Materials and Methods:

(*)  Mehabubnagar district for Andhra Pradesh and Udaipur district for Rajasthan were selected for the study purpose. Monthly rainfall data from 1960 to 2000 (41 years) for Mehabubnagar district of Andhra Pradesh and monthly rainfall data for 44 years (1960 – 2003) for Udaipur district of Rajasthan were obtained from IMD, Pune. Monthly PET data were also obtained from IMD, Pune for the study district. For finding out the LGP, FAO water balance model as prescribed by Higgins and Kassam, (1981) was used.

(*)  In this method mean monthly rainfall and 50 per cent PET values were plotted for twelve months of a year. Whenever, the monthly rainfall did cross the 50 per cent value of PET in a concerned month, that month was taken as starting period of the LGP. Similarly, when the mean monthly rainfall got down from the monthly 50 per cent PET value, that month was taken as termination of the LGP.

(*)  In addition, the stored soil moisture after the termination of the LGP was also taken into account to compute LGP. With respect to the two study districts, the LGP was computed individually for all the years of study and a normal value also computed, based on the mean rainfall arrived.  Root Mean Square Error (RMSE) was computed for the values of LGP for each district between normal and yearly LGP values obtained. Effective rainfall was computed based on the Gupta et al. (1972) model and used for arriving cropping system design for the particular monsoon season of the two districts of study.

Results and Discussion:

->  The results on computed LGP for Mehabubnagar and Udaipur and their comparison are presented in Tables from 1 to 3. The perusal of data presented in Table 1 revealed that for Mehabubnagar, the actual LGP found varied from 4 to 7 months across the study period from 1960 to 2000 with the mean value of 5.44 months of LGP. While the computed mean LGP for the mean rainfall obtained for the study period had six months of LGP. The attempt to find out RMSE between normal LGP and actual LGP of different years revealed a RMSE value of 0.88. Thus it is interpreted that a five-month LGP could be considered for Mehabubnagar of Andhra Pradesh State from July to October.

->  This conclusion is drawn based on the data presented in Table 4 wherein there was deficit of rainfall to PET up to 60 per cent during June while the deficit was 12, 9, 10 and 58 per cent respectively for July, August, September and October. Though the deficit was 58 per cent during October, since the crop would be under maturity stage for the proposed July sowing there might not be any stress impact on the crop’s productivity.

->  Thus, the study pointed out that intercropping system, by integrating one-long duration crop of 120 days and one short duration crop could be recommended to this district. First week of July rather than that of June can be considered for sowing. Sanbagavalli et al, (2001) also recommended crops based on LGP analysis for Coimbatore, Tamil Nadu, India.

->  With respect to Udaipur, the actual LGP found varying from two to six months between the years of study from 1960 to 2003, with the mean value of 4.09, while the computed mean LGP for the mean rainfall obtained for the study period had four months of LGP. The attempt to find out RMSE between normal length of growing period and actual length of growing period of different years revealed a RMSE value of 0.92. Thus it is interpreted that a three-month LGP from July to September could be considered for Udaipur of Rajasthan State for cropping.

conclusion:

(*)  This conclusion is drawn, based on the data furnished in Table 4, wherein, there was deficit of rainfall to PET up to 13 per cent during July, while the deficit was 11 and 44 per cent respectively for August and September. Inclusion of October month within the LGP would be a problem for this location, since the deficit was up to 92 per cent. On contrary to the recommendation given under cropping system for Mehabubnagar for Andhra Pradesh, at Udaipur a short duration crop of 90 days could be recommended with the sowing week to be fixed on the first week of July. Crop suggestions were given based on the study by Jain et al (2003) for Gujarat agro ecological zones based on the LGP study.  

(*)  The RMSE values computed both for Mehabubnagar and Udaipur districts are presented in Table 3. Interestingly, it is observed that as compared to Udaipur district of Rajasthan, Mehabubnagar of Andhra Pradesh had lesser statistical error, indicating the usefulness of LGP studied across years.