ADAPTATION AND SELECTION OF CROP VARIETIES FOR HOT ARID CLIMATE OF RAJASTHAN

Abstract

Arid region occupies nearly 3,17,090 sq km area in India, of which 2,46,790 sq km is hot arid region. About 80% of the hot arid area falls in the eleven districts of Rajasthan. These areas are characterized with low, erratic rainfall with high coefficient of variation and high mean maximum temperatures. Soils are mostly sandy with a low organic matter content (0.1 to 0.45 per cent) and with poor moisture holding capacity and high infiltration rate of 9 cm/hour. Crop plants suited to arid regions are those that survive and produce in spite of arid/dry conditions. Sorghum and pearl millet are traditionally grown as rainfed crops mostly in environments characterized by a combination of the above listed stress factors, which become too marginal and unproductive for maize. Sorghum is a drought tolerant species, and pearl millet is even more drought tolerant with higher water use efficiency than sorghum. Similarly, pearl millet is even more salt tolerant than sorghum and is the second most salinity tolerant major cereal after barley. Pearl millet is better adapted to dry nutrient deficient soils and is thus cultivated under extreme harsh conditions of high temperature, low erratic rainfall and on soils with poor water holding capacity. It also has strong deep root system and short life cycle and can grow rapidly when moisture is available. As a result, it can survive and reliably produce small quantity of grain where mean annual precipitation is as low as 250 mm as compared to minimum water requirement of 400 mm for sorghum and 500-600 mm for maize. India is the largest producer of pearl millet, both in terms of area (9.3 m ha) and production (7.97 m t). Though a large number of pearl millet hybrids and some open pollinated varieties have been released for cultivation in arid regions, genetic differences in maturity and drought tolerance make some cultivars more suitable for dry regions. Early maturing cultivars escape terminal drought, making these more suitable for regions having extreme arid conditions, like western Rajasthan, parts of Gujarat and Haryana. Besides pearl millet, legumes are also cultivated in the arid western Rajasthan. These are moth bean (Vigna aconitifolius), mung bean (Vigna radiate), cluster bean (Cyamopsis tetragonoloba), horse gram (Macrotyloma uniflorum) and cowpea (Vigna unguiculata). Of these moth bean, guar and horse gram are highly drought tolerant and a number of early maturing varieties for cultivation in the arid regions have been identified. Climate change is occurring due to global warming and it is estimated that average temperature of the air above earth’s surface would rise by 1.4 to 5.8°C over the next 100 years. This will affect climate sensitive sectors like agriculture. For mitigating the effects of climate change, there is a need to develop heat tolerant, early maturing, drought tolerant, salt tolerant and disease, and insect pest resistant varieties. Pearl millet already has many of these traits that make it a well adapted crop for arid regions. Similarly, arid legumes which are adapted the harsh agroclimatic conditions of the arid region have several early maturing varieties. Further challenges of climate change can be tackled through development of varieties through biotechnology and genetic engineering approaches.