Agronomic Practices to Improve Water Use Efficiency

Abstract

Water scarcity, which already occurs for more than a billion people worldwide, will worsen further, and the water supply available for future generations, especially for use in agriculture, will be increasingly restricted (FAO, 2017). Above all, in arid and semi-arid regions, irrigated agriculture uses more than 70 to 80% of the total water available and is essential to increase food production in these regions, where the population is rapidly increasing (TURNER, 2004) [1]. The world’s population in 2004 was more than 6,000,000, of which around 5,000,000 were in developing countries, and 20% of this population has remained undernourished since the 1990s [2]. For this time, water management in agriculture, in the current era of scarcity, should be engaged to implement water use efficiency (WUE), spending fewer resources and producing less expensive plant protein [3,4]. In the past, during the post-war “green revolution”, the paradigm of agriculture was to modify the environment (heavy fertilization, irrigation, and mechanization, with energy expenditure) to adapt it to the plant, with the generation of so-called high-yield varieties (HYVs), with high harvest index (HI: Dry Weight [DW] of the organ harvested. plant DW-1), for mechanized harvesting and responsive to the application of fertilizers, which were cheap at the time [1], but less adapted to the stresses, which was mitigated by energy expenditure, in irrigation and mechanization, and fertilizers applied [5]. For example, in grasses, the induction of progressive tillering, as occurs in the millet and sorghum, is one of the mechanisms of escape from environmental stresses because each inflorescence will have a different period of fertilization increasing the chances of producing some viable panicles [5]. However, this characteristic would prevent mechanized harvesting, but small farmers in marginal areas of agriculture do not use mechanic harvesting. Marginal agriculture areas are frequently subjected to environmental stresses and have soils with poor nutrient content [3]. In the past, during the green revolution, it was always a characteristic undesirable for plant breeding programs to improve yield. In addition, the increase in HI was often obtained with a reduction of volume and root area, which is very important to implement the WUE [6]. Therefore, the genetic basis for the environmental adaptation of the most improved crop by man, such as maize, has been dramatically diminished. After the oil and energy crisis in the 1970s, the paradigm of agriculture has become to modify the plant to adapt it to the environment, with WUE, generating varieties with Low Technological Cost (LCVs) for agricultural production (Figure 1). This adaptation to environmental stresses can also be found in local landraces used by the small farmers living in marginal areas for agriculture, which needs to be better studied and recommended to increase food safety in these areas [3].