Manipulating root system architecture: deep fertiliser placement to improve drought tolerance in spring wheat (Triticum aestivum L.)

MSc Thesis - Research report written under supervision of Eric Visser

Wheat productivity in semi-arid regions may be improved through deep fertiliser placement by the development of a deeper root system, but more knowledge of both the benefits and possible drawbacks of this method is required to optimize crop system management. Therefore, the aim of this study was to determine the effects of deep fertiliser on wheat aboveground biomass under drought and irrigated conditions and how changed root system architecture links to this. Spring wheat either received deep (27-37 cm), shallow (5-15 cm), or homogeneously distributed (5-47 cm) combined NPK fertiliser and was either subjected to full irrigation or topsoil drought in a semi-randomly, full-factorial design with six replicates. In drought, deep fertiliser resulted in a 30% greater aboveground biomass (P = 0.007) and a deeper root system compared to shallow fertiliser placement (P < 0.0001). Moreover, in the absence of drought no drawback due to the increased seed-fertiliser distance was observed, reflected by similar growth rates and aboveground biomass in the different fertiliser treatments. Root diameter increased within zones of high nutrient concentrations, which was most prominent in dry soils. Greater aboveground biomass with deep fertilizer placement could be explained by an increase in photosynthesis rate and stomatal conductance. Belowground, roots responded strongly to fertiliser position and drouht by an increase in root diameter at greater soil depth (P = 0.03), an increase in root density (P = 0.03) and a decrease in specific root length (P = 0.04). Here we showed that deeper fertiliser placement can alleviate the negative effects of drought by the development of a deeper root system and did not inflict a yield penalty in the absence of drought. Deep fertiliser placement therefore can be a promising strategy to improve drought-tolerance, especially in crop systems where seasonal water input is minimal.