Assessing climatic water balance and growing period length for crop planning under rainfed condition

Abstract

An agroclimatic study was conducted at Pusa, Samastipur region of Bihar using database of 45 years (1968–2012) to assess water balance and length of growing period for efficient crop planning under rainfed condition. The average annual rainfall computed was 1226.7 ±388.9 mm. More than 30 mm rainfall week−1 was found to occur during 24 Standard Meteorological Weeks (SMW) to 39 SMW and more than 50 mm rainfall week was available during 25–39 SMW, except 38 SMW. Total water surplus estimated was 487.3 mm during 24 to 43 SMW, as against the total annual water deficit of 75.4 mm during the corresponding period. Under average rainfall condition, actual evapotranspiration (AET) was more than 0.25 of potential evapotranspiration (PET) during the period from 18 to 50 SMW, whereas it was more than 50% of PET during 24 to 44 SMW. Chi-square test showed that Weibull distribution was the best fit distribution for annual and monsoon rainfall, whereas for non-monsoon season, Cauchy distribution was found to be appropriate. Out of annual average rainfall of 1227 mm, the surplus and effective rainfall were 39.7 and 60.3%, respectively. The average effective rainfall was 739.4 ± 89 mm. The effective rainfall, which was calculated by subtracting surplus water from rainfall, was equal to rainfall during 1 to 23 SMW and 44 to 52 SMW and lesser than rainfall during 24 to 43 SMW, which coincided with the surplus period. Year-wise lengths of growing periods (LGP) were worked out based on moisture adequacy index (Ima). Mean LGP based on Ima, was 217±46 days, with 60% of the total years recording LGP > 200 days. Crop planning based on LGP has been suggested for the region for sustainable crop production under rainfed condition.