Digging Deeper for Agricultural Resources, the Value of Deep Rooting

Abstract

Recent studies have documented highly significant differences among current and potential crops, as well as genotypic differences, in the ability for deep rooting.Results have shown significant effects of deep roots on deep soil water and nutrient uptake.Technological improvements of nondestructive methods, such as rhizotron and image analysis based root observations, soil water sensors, and isotope tracers for uptake studies, allow combined and dynamic studies of root development and function.The quest for sustainable intensification of crop production promotes the interest in understanding and exploiting the potential contribution by deeper soil layers. Deep layers may contribute to resource supply for crop growth, reducing losses to the environment and deep C sequestration to mitigate climate change. In the quest for sustainable intensification of crop production, we discuss the option of extending the root depth of crops to increase the volume of soil exploited by their root systems. We discuss the evidence that deeper rooting can be obtained by appropriate choice of crop species, by plant breeding, or crop management and its potential contributions to production and sustainable development goals. Many studies highlight the potentials of deeper rooting, but we evaluate its contributions to sustainable intensification of crop production, the causes of the limited research into deep rooting of crops, and the research priorities to fill the knowledge gaps. In the quest for sustainable intensification of crop production, we discuss the option of extending the root depth of crops to increase the volume of soil exploited by their root systems. We discuss the evidence that deeper rooting can be obtained by appropriate choice of crop species, by plant breeding, or crop management and its potential contributions to production and sustainable development goals. Many studies highlight the potentials of deeper rooting, but we evaluate its contributions to sustainable intensification of crop production, the causes of the limited research into deep rooting of crops, and the research priorities to fill the knowledge gaps. The triple challenge to increase food and biomass production, adapt to and mitigate climate change, and reduce the negative impacts on natural capital and environment has been termed the perfect storm [1.Nelson G.C. The perfect storm.Significance. 2010; 7: 13-16Crossref Scopus (2) Google Scholar]. There are limited options to increase the area under intensive farming, and converting new land to agriculture would be at the expense of nature and biodiversity already under pressure [2.Springmann M. et al.Options for keeping the food system within environmental limits.Nature. 2018; 562: 519-525Crossref PubMed Scopus (1143) Google Scholar]. Agricultural activities currently cause nutrient loading to aquatic and terrestrial ecosystems, often exceeding ecologically tolerable levels, and also contribute to land use change, deforestation, freshwater depletion, and climate change [3.Campbell B.M. et al.Agriculture production as a major driver of the earth system exceeding planetary boundaries.Ecol. Soc. 2017; 22: 8Crossref Scopus (409) Google Scholar]. In addition, climate warming and greater weather variability increasingly challenge agricultural production systems, prompting calls for radical changes to sustain food production [4.Halberg N. et al.Eco-functional intensification and food security: synergy or compromise?.Sustain. Agric. Res. 2015; 4: 126Crossref Google Scholar,5.Campbell B.E. et al.Reducing risks to food security from climate change. Glob.Food Sec. 2016; 11: 34-43Google Scholar]. A neglected topic in the quest for sustainable intensification is better exploitation of deep soil profiles using novel crops, genotypes, and cropping systems with substantially greater effective rooting depth. 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