No abstract

Drought is one of the major constraints for sustainable crop production worldwide, especially in arid and semiarid regions. The global warming and climate change scenario has worsened the dilemma of water scarcity, creating an immediate threat to food security. Conserving water resources and exploiting various strategies that enable plants to withstand water deficits need to be urgently addressed. Drought adversely affects plant growth by modulating a range of physio-chemical, metabolic, and molecular processes inside the plant body, which ultimately reduces crop productivity. Besides developing drought-tolerant cultivars, better nutrient management could be a promising strategy to enhance drought tolerance in crop plants. Silicon, a quasi-essential element, is known to play a vital role in improving crop performance under a range of biotic and abiotic stresses. This review discusses the potential of Si application in attenuating the adverse effects of water-deficit stress. Silicon enhances plant growth by improving seed germination, cell membrane stability, carbon assimilation, plant–water relations and osmotic adjustment (by accumulating soluble sugars, proline and glycine betaine). It triggers the activity of antioxidants, promotes the biosynthesis of phytohormones, enhances nutrient acquisition and regulates the activity of vital enzymes in plants under drought stress. Silicon also induces anatomical changes in the plant cell wall through the deposition of polymerized amorphous silica (SiO2-nH2O), thereby improving stem and leaf erectness and reducing lodging. Further, Si-mediated physiological, biochemical and molecular mechanisms associated with drought tolerance in plants and future research prospects have been elucidated.

Onion is highly sensitive to water stress due to the absence of root hairs and shallow root system. Water stress at any growth stage of onion can result in severe loss of yield and profit. Moreover, fresh water availability for irrigation is continuously declining due to population explosion and global warming. There is a dire need to increase water productivity of irrigation systems. Although drip irrigation is highly efficient, its practical application is limited in developing countries due to high installation costs and lack of technical knowledge among farmers. The present research work was conducted in semiarid climate of Faisalabad, Pakistan to examine low cost irrigation methods for their profitability for onion production even under limited water availability. A field study was conducted using two onion cultivars (Dark red and Robina) with and without mulch under three irrigation methods (furrow, fixed furrow and alternate furrow) during two consecutive winter seasons (2012-13 and 2013-14). Results showed that profitability of onion bulbs produced under alternate furrow irrigation method with mulching was at par with bulbs produced by furrow irrigation without mulching (common method used by farmers). Among onion cultivars "Dark red" was found more consistent in generating a profit under limited water supply than "Robina". From the experimental results it may be concluded that under limited supply alternate furrow irrigation can be successfully used as an effective low cost substitute of normal furrow irrigation. The results showed that profitability of alternate furrow may be enhanced by the application of mulching.