Relationship Between Root Biomass, Plant N, P and K Content, and Grain Yield in Wheat for the Second Green Revolution.

The First Green-Revolution wheats had small root systems, the result of parentage and selection in well-irrigated and well-fertilized conditions. This may have restricted grain yield. The 1RS rye translocation (Veery) increased root biomass by 30%, which increased water uptake and grain yield by 9% and 8%, respectively. We determined the effect of the root system on uptake of N, P & K in CIMMYT spring bread wheat ‘Pavon 76’ and its near isogenic translocation lines Pavon 1RS.1AL, Pavon 1RS.1BL and Pavon 1RS.1DL, grown in sand-tube experiments under optimum and low levels of nutrients for 2 years. Root, stem and leaves, and grain N, P & K content, and agronomic characters were measured. Leachate nitrate content was measured at early tillering, booting and early grain filling. Significant main effects for year, nutrient level and genotype were found for the characters. First and second degree interactions involving genotype were significant only for a few characters. Genotypic means averaged across years and nutrient levels are reported. Low levels of nutrients (40% reduction from optimum level) reduced mean root biomass, plant biomass, and grain yield by 27, 25, and 19% respectively. Translocation lines produced 31-46% more root biomass, 11-14%  heavier grains, and 6-8% greater grain yield than Pavon 76. The correlation coefficient between plant N, P & K content and root biomass (r = 0.81, 0.82 and 0.79, respectively), between plant N content and plant biomass (r = 0.83) and between grain yield and root biomass (r = 0.73) was significant. Leachate N content was highest during tillering (60 mg) and progressively decreased at booting (42 mg) and early grain filling (33 mg). The 1RS translocations, on average, had less lechate N content (42 mg) than Pavon 76 (53 mg). Multiple small application of N fertilizer during early plant growth with adequate irrigation water are recommended. Twenty-first century wheat plants may need a two to three-fold increase in root biomass to absorb sufficient water and nutrients to maximize grain yield and minimize nitrate leaching in the Second Green Revolution. Projected grain yields may reach 20 to 40% more than Pavon 76.