Root growth is important for the acquisition of nitrogen (N) and water in deep sandy soil profiles with high leaching potential. Root growth characteristics and the N uptake of wheat genotypes differing in early vigour were investigated in 2 glasshouse experiments. In both experiments the vigorous breeding lines Vigor18 and B18 and the well-adapted commercial cultivar Janz were grown in glass-walled growth boxes in a controlled-temperature glasshouse up to the onset of stem elongation. In Expt 1, rooting parameters and detailed measurements of root growth and proliferation were made at 2-day intervals using a root mapping technique. In Expt 2 the glass-walled growth boxes were segmented into upper (0–0.2 m), middle (0.2–0.7 m), and bottom (0.7–1.0 m) soil layers, and the contribution of N fertiliser uptake by roots from each soil layer to the total plant N uptake was determined by applying 15N-urea to a single soil layer each time. The accumulated total root length across the soil profile from the 1-leaf stage to the onset of stem elongation was 33–83% higher in the vigorous lines Vigor18 and B18 than in Janz. The roots of the 3 genotypes grew vertically down the soil profile at a similar rate, but the roots of vigorous lines branched earlier and grew horizontally faster and more extensively than those of cv. Janz, resulting in a greater root-length density and root number in the top 0.7-m soil layer. Uptake of N fertiliser by roots in the upper 0–0.2 m of the soil profile was 60–68% higher in the vigorous lines than in Janz. Roots of the vigorous lines located in the segment 0.2–0.7 m of the soil profile captured twice as much N fertiliser than those of Janz. Uptake of N fertiliser by roots in the lower 0.7–1.0 m of the soil profile was similar in the vigorous lines and Janz. This indicates that the early and more extensive horizontal growth of the roots in the 0.2–0.7 m of the soil profile was responsible for the superior uptake of N by the vigorous lines. The implications of these genotypic differences in root growth and proliferation and their relationship with the early acquisition of N are discussed with emphasis on their role in improving the efficiency of N fertiliser uptake and reducing nitrate leaching, particularly in the sandy soils of the Mediterranean climatic region of Australia.

A field trial, a lysimeter system study and a nutrient solution experiment were conducted to determine the genotypic differences in nitrogen (N) uptake among wheat (Triticum aestivum L.) genotypes differing in vigour of early growth. Plant growth and N uptake of Vigour 18, a breeding line with early vigour, and the commercial cultivars Westonia, Tincurrin, Camm and Janz were compared. Shoot biomass of Vigour 18 was higher than that of the other genotypes, except for Westonia at booting when 50 kg N ha -1 was applied 3 d after wheat emergence. Vigour 18 had significantly higher efficiency of fertiliser-N uptake than the other four cultivars at tillering when 50 kg N ha -1 was applied. Fertiliser-N uptake efficiency at booting was similar in Vigour 18 and Westonia, but significantly higher than in three other commercial cultivars. Vigour 18 had higher root dry matter, root-length density and root surface area than Janz when examined in columns of soil. The greater root growth of Vigour 18 occurred across all soil layers to a depth of 0.6 m. Differences in total N uptake between Vigour 18 and Janz were apparent from tillering (Z14,22) to booting (Z19,24,49). Vigour 18 also had significantly higher shoot biomass and N uptake than Janz when grown in nutrient culture. Nitrate reductase activity (NRA) expressed on a whole-plant basis was higher for Vigour 18 than for Janz, and was related to total N uptake. However, NRA expressed on a perunit-fresh-weight basis was not significantly different across the cultivars tested. It is concluded that vigorous early root and shoot growth in Vigour 18 was the main driving force for higher N uptake.

Highlight:Early vigour in wheat was shown to be a valuable trait for improving biomass accumulation and phosphate uptake from a low-P soil.

Seedlings from 198 wheat genotypes were screened in glasshouse trials for early biomass production (49 days after sowing, DAS) in a soil high in total phosphorus (P) but low in plant-available P. Fifteen hexaploid bread wheats were then examined more closely for early biomass production on 2 low-P soils: a highly P-fixing Ferrosol (1.3 mg resin-extractable P/kg) and a Red Kandosol (5.2 mg resin-extractable P/kg). The soils were either unamended for P or supplemented with sufficient P for maximum growth. Single lines of rye, triticale, and durum wheat were included for comparison. The plants were harvested at 21 and 35 DAS, and shoot biomass, root biomass, P content, and root length were measured. Shoot biomass was correlated with the P content of the seed in both unamended soils at the first harvest but only in the Ferrosol at the second harvest. There were no correlations between seed P and shoot biomass in the high-P treatments at either harvest. Genotypes were compared with one another by plotting shoot biomass from the high-P treatment against shoot biomass from the low-P treatment. Phosphorus-efficient genotypes were defined as those with relatively greater biomass at low P, while genotypes with a high biomass potential were defined as those able to accumulate relatively more biomass at high P. Two hexaploid wheats, Kukri and Vigour 18, were ranked as being P-efficient genotypes with a high biomass potential on both soils, while Halberd, CD87, and Katepwa were P-inefficient on both soils. Biomass accumulation for each genotype was compared with their root biomass, root : shoot ratio, specific root length and P-uptake efficiency. The strongest correlation across all treatments occurred between shoot biomass and root biomass. We discuss factors that may contribute to the variation in P-uptake efficiency among the genotypes.