Improving water use efficiency, nitrogen use efficiency, and radiation use efficiency in field crops under drought stress: A review

Raising temperature and increased drought events induced by a changing climate have increased the need for efficient use of natural resources and energy supplies. Producing sufficient food and fibers for the growing population with changing consumption patterns from ever decreasing resource base requires strategic plans for efficient use of natural resources such as water, nutrients, and photosynthetically active radiation (PAR). Water is considered as the second most limiting factor after land to increase food and fiber production. It is essential for various chemical and physiological reactions in plants and provides a medium where most cellular functions take place. Soil water-deficit significantly reduces crop yield and productivity through its adverse effects on nutrient uptake, net assimilation, and radiation use efficiency and subsequently on dry matter accumulation and production. Soil water affects nutrient transformation from unavailable to available form or vice versa, and thereby the total uptake amount. It also influences the availability of applied nutrients and efficiency through its effect on various nutrient loss mechanisms such as volatilization, nitrification, and/or urease hydrolysis. Soil nutrients and PAR are also key factors in crop production. Plants usually suffer from nutrient deficiencies and more importantly a reduction in net photosynthetic assimilation rate under water stress. Better inception of PAR is needed for higher biomass production and grain yield, which is also hampered under water-limited environments. The situation is expected to be further intensified in a future changing climate, which urgently calls for efficient adaptation strategies to mitigate the negative impacts associated with these changes on crop production, especially in dry areas. Therefore, improving the efficiency of natural resources use continues to escalate as a topic of interest for crop and soil scientists. This review presents an outline of defining water use efficiency, nitrogen use efficiency, and radiation use efficiency as well as their relationship under water-limited environments to identify agronomic- and physiologically-improved strategies for enhancing water, nutrient (nitrogen), and radiation use by field crops.