Increasing crop productivity when water is scarce—from breeding to field management

Abstract

To increase crop yield per unit of scarce water requires both better cultivars and better agronomy. The challenge is to manage the crop or improve its genetic makeup to: capture more of the water supply for use in transpiration; exchange transpired water for CO 2 more effectively in producing biomass; and convert more of the biomass into grain or other harvestable product. In the field, the upper limit of water productivity of well-managed disease-free water-limited cereal crops is typically 20 kg ha -1 mm -1 (grain yield per water used). If the productivity is markedly less than this, it is likely that major stresses other than water are at work, such as weeds, diseases, poor nutrition, or inhospitable soil. If so, the greatest advances will come from dealing with these first. When water is the predominant limitation, there is scope for improving overall water productivity by better matching the development of the crop to the pattern of water supply, thereby reducing evaporative and other losses and fostering a good balance of water-use before and after flowering, which is needed to give a large harvest index. There is also scope for developing genotypes that are able to maintain adequate floret fertility despite any transient severe water deficits during floral development. Marker-assisted selection has helped in controlling some root diseases that limit water uptake, and in maintaining fertility in water-stressed maize. Apart from herbicide-resistance in crops, which helps reduce competition for water by weeds, there are no genetic transformations in the immediate offing that are likely to improve water productivity greatly. Media summaryImprovements in water productivity will come from better agronomy and better genotypes tuned to each other so that the combination performs well in farmer's fields.

Ppd1, Vrn1, ALMT1 and Rht genes and their effects on grain yield in lower rainfall environments in southern Australia

“…For this study, southern Australia consists of the wheat-growing areas in the states of South Australia, Victoria, and New South Wales south of Parkes (Lazenby et al 1994). Climatically, this is a mostly Mediterranean-type environment with predominantly winter rainfall, but with an increasing proportion of summer rainfall with decreasing latitude in New South Wales and substantial seasonal variability in rainfall and temperature (Farrer 1898;Passioura 2006;Nidumolu et al 2012). Insufficient seasonal rainfall and high temperatures during grain filling can limit grain yield (Hochman et al 2009;Kirkegaard and Hunt 2010), as can soil constraints that limit root growth and access to soil water (Richards 2008;McDonald et al 2012).…”

Limits to maize productivity in Western Corn-Belt: A simulation analysis for fully irrigated and rainfed conditions

“…Therefore, quantifying the maximum yield per unit of available water supply, hereafter called the water-limited yield, is essential for identifying water management practices and policies to optimize water-use efficiency (Wallace, 2000). Boundary functions provide a robust framework to analyze water-limited productivity (e.g., French and Schultz, 1984;Passioura, 2006;Sadras and Angus, 2006). Yield is plotted against either: (i) water supply (stored soil water at sowing plus rainfall), or (ii) crop evapotranspiration (ET C ), on a seasonal basis, and a linear function is fitted to those data that delimit the upper frontier for yield.…”

“…Yield is plotted against either: (i) water supply (stored soil water at sowing plus rainfall), or (ii) crop evapotranspiration (ET C ), on a seasonal basis, and a linear function is fitted to those data that delimit the upper frontier for yield. The first approach, namely water productivity (WP), provides a benchmark to help farmers set target yields and identify other yield reducing-factors, such as nutrients, pests, and diseases (Passioura, 2006). The second approach based on ET C , namely water-use efficiency (WUE), provides a physiological frontier for water-limited productivity in which the slope represents the seasonal transpiration-efficiency (TE S ) and the x-intercept gives a rough estimate of seasonal soil evaporation (Sinclair et al, 1984).…”

Improving Water Sustainability and Food Security through Increased Crop Water Productivity in Malawi

“…With the ever growing world population, urbanisation and limited water resources, there is an increasing need worldwide for improved water resources management. Thus, producing more food per each drop of water is crucial to address both challenges of water scarcity and food insecurity [4,5]. Improving water use efficiency or enhancing crop water productivity is a critical response to increasing water scarcity, including maintaining sufficient water in rivers and lakes to sustain ecosystems and to meet the growing demands of cities and industries [6].…”