Response of wheat genotypes efficient in P utilisation and genotypes responsive to P fertilisation to different P banding depths and watering regimes

Abstract

The capacity of wheat roots to lift water from subsoil with high moisture content into dry topsoil (hydraulic lift) and the subsequent impact on P uptake from dry topsoil are poorly understood. Two experiments were set up to test the capacity of 4 wheat genotypes differing in P efficiency to take up P from the fertiliser banded in dry topsoil (with wet subsoil). The interactions among genotypes, banding depths, and watering regimes (whole-profile or subsoil-only watering) were also characterised.

The root system increased soil water content from 64 to 90 g/kg soil around the P fertiliser band by taking up water in the subsoil and releasing it into the dry topsoil during the night. Phosphorus applied as a band at 20 mg P/kg soil in dry topsoil (5 cm deep) significantly increased P uptake and shoot weight compared with a nil P control. Westonia and Gutha genotypes (efficient in P utilisation, based on dry matter produced per unit of P taken up) had higher shoot weights than Aroona and Wawht 2074 (genotypes responsive to P fertilisation, based on dry matter produced per unit of P fertiliser applied). Greater growth of wheat genotypes occurred in the treatment with P fertiliser banded at a depth of 5 cm compared with 15 cm in the whole-profile watering treatment, but no difference between banding depths was noted in the subsoil-only watering treatment. Wheat genotypes responsive to P fertilisation increased P uptake and shoot weight at the 5-cm P banding depth and the whole-profile watering treatment compared with genotypes efficient in P utilisation. Phosphorus-utilisation-efficient genotypes increased shoot growth more than other genotypes in the subsoil-only watering treatment.

It can be concluded that roots of various wheat genotypes lift water from wet subsoil into the dry topsoil (hydraulic lift). Phosphorus fertiliser banded at 5-cm depth in dry topsoil increased P uptake and wheat growth due to the presence of hydraulically lifted water. Genotypes that are efficient in utilising P increased shoot weight more than genotypes responsive to P fertilisers in the subsoil-only watering treatment. In contrast, P-responsive genotypes increased shoot growth more than P-utilisation-efficient genotypes when P fertiliser was banded at 5-cm depth, and a whole-profile watering regime was imposed.