Climate Change in Relation with Productivity of Rice and Wheat in Tarai Region of Uttarakhand

Abstract

The rice-wheat cropping system is a very important and popular cropping system being followed in the tarai area of Uttarakhand. The area, characterized by shallow water table and moist soil regime, lies within a narrow east-west strip of 8–25 km wide, on an outwash plain, gently slopping (<1%) southwards below the Bhabar tract along the foot hills of the Himalayas. The entire area is dissected by a number of small streams originating as springs from the junctions of Bhabar and tarai belts. In India, about 10.0 million hectare area is under rice-wheat cropping system and of this 4.8 m ha falls in the tarai area of Uttarakhand. The sowing of wheat after rice is being followed since about more than five decades after bringing the area under crop cultivation since its deforestation in 1950. In rice-wheat cropping system a complete recommended set of agronomic practices is followed including timely control of pests and diseases, proper integrated nutrient management, application of balanced fertilizers and crop residue management, recommended tillage practices after harvesting of rice crop and control of weed flora over a time period under different conditions and crop stages. In-spites of these the yield of wheat after rice in the area has declined by about 20–30% after the green revolution. It was thought that this decline in tend may follow the change in climatic conditions specially the air temperature and the rainfall pattern in the area. Crop productivity can be affected by climate change in two ways, one directly due to changes in climatic variables mainly temperature and precipitation and indirectly through changes in soil, distribution and frequency of infestation by insects, diseases or weeds. In the present investigation, the productivity and sustainability of rice-wheat cropping system has been evaluated by analyzing the impacts of temperature and rainfall over past 45 years on yields of rice and wheat crops recorded at G.B. Pant University of Agriculture & Technology, Pantnagar (29° N latitude, 79° 30′E longitude and altitude 243.84 m amsl) located in tarai and bhabar agro-climatic zone of Uttarakhand. The rice yields for 45 kharif wet seasons from 1961 to 2005 and wheat yields from rabi seasons of 1961–1962 to 2005–2006 was collected from the Pantnagar University Farm where these crops were grown using all standard & recommended agronomic & plant protection practices to maximize crop yields. The maximum and minimum temperatures as well as rainfall data of the same duration were collected from meteorological observatory situated within the University Campus. Five year averages of the yields and climatic variables were worked out from 1961 to 2005 and then the changes in yields and rainfall and temperature change trends were calculated and finally, the simple regression equation of the type as well as curvilinear regression analysis (Ezekiel and Fox 1959) were employed to develop regression equations between yields of rice and wheat with changes in climatic variables using statistical programs. The following curvilinear regression equation for change in yield of rice as a function of change in rainfall and maximum, minimum and mean air temperatures during the kharif season was developed:

$$ {\hbox{Y}} = { 6}.{344} - {1}.0{2 }{{\hbox{X}}_{{1}}} + { 3}.{45 }{{\hbox{X}}_{{2}}} - 0.0{157 }{{\hbox{X}}_{{3}}} - {4}.0{73 }{{\hbox{X}}_{{4}}},{ }{{\hbox{R}}^{{2}}} = { }0.{712} $$

This shows that in this area about 71.2% variations in rice yields are due to variations in south-west monsoon rainfall and temperatures. However, for wheat in rabi season, following regression equation between change in wheat yield and climatic variables was obtained:

$$ {\hbox{Y}} = {12}.{767} - {1}.0{8}0{ }{{\hbox{X}}_{{1}}}\,{ + }\,0.{261 }{{\hbox{X}}_{{2}}}{\ + }\,{ 1}.{917 }{{\hbox{X}}_{{3}}}\,{ + }\,{1}.{632 }{{\hbox{X}}_{{4}}}, {{\hbox{R}}^{{2}}} = { }0.{924} $$

This indicates that in this area about 92.4% variations in wheat yields are due to variations in winter rainfall and temperatures. Results of this studies showed that there has been a gradual increase in mean seasonal air temperature. The average seasonal change in maximum temperature and minimum temperature was found to be are 0.4°C and 0.2°C, respectively during kharif wet season. However, the rainfall variability is within 10–30% during kharif season (from June to October) over last 45 years at tarai & bhabar agroclimatic-zone of Uttarakhand. There have been changes in rice yields as well. The Rice yields were found to increase over the years due to introduction of high yielding varieties and adoption of improved cultivation technology and irrigation facilities in last two decades. Data also showed that the years in which rainfall is very high, the rice yields are low due to more incidences of diseases in crop in the area. Results of analysis for rabi seasons from 1961–62 to 2005–06 over last 45 years showed that the average seasonal change in maximum temperature and minimum temperature were 0.4°C and 0.4°C, respectively, and rainfall variability is within 8–40%. However, the wheat yields have also been found to change depending upon the rainfall distribution and rainfall variability except some variations. Results also indicate that in years in which winter rainfall was excessive, and then wheat yields were found to decline may be due to lodging and insect problems. However, in years of low winter rains, there has been response of irrigation in maximizing wheat production in the area. It has also been observed that in years in which mean monthly air temperature in the month of March is 1–2°C below the normal value, there has been delay in wheat maturity by 7–10 days and an increase in wheat yield is by 4–6 quintal per ha have been observed more compare to other years. As a conclusion it can be said that in this irrigated area, the effective beginning and end of rice growing season is determined by temperatures and rainfall distribution. For getting maximum yields it is necessary that the rice must be planted at the time i.e. in last week of June where optimum temperature conditions are met and since then the flowering will reach the date before night temperature falls below 20°C. The results further showed that, over the years in wheat for each degree rise in air temperature and lack of winter rains, there has been reduction in yields by 5–10% in timely and late sown wheat. However, there has been reduction in yields by 10–20% in early and late planted rice due to early withdrawn of monsoon and decrease in air temperature in the month of October. So in general, it can be said that there has been impacts of climatic variability on rice and wheat crops grown even using standard agronomic practices and control measures. Early rise in air temperature in the month of March due to lack of winter rains adversely affects the wheat yields in many years in the area. This type of study will be of immense use for other location as well, if the long range weather forecast for important climatic variables such as rainfall and temperature are available well in advance, the productivity of rice and wheat can be assessed for that location and it will promote in deciding the optimum sowing dates of Rice and also of wheat after rice and will help in deciding irrigation schedules & for taking control measures for maximizing their production.