Rhizosphere and phosphorus acquisition

Phosphorus fertilisers play an important role in sustaining crop production in modern farming systems. However, global phosphorus reserves are finite and will deplete in the medium term.

On the other hand, the long-term application of fertiliser P in excess of that exported from the cropping system has lead to P accumulation in soils. The use of crop species that can access the transformed non-labile P pools would reduce P fertiliser use and improve P-use efficiency.

Our recent findings indicate that plant P acquisition from soil P pools depends on crop species, soil type, P fertilizer history and N form. In a Calcarosol with a long P-fertilizer history, both wheat and chickpea decreased P in all fractions including residual P in rhizosphere. In sand culture supplied with insoluble P compounds, wheat could utilise Al-P more efficiently than white lupin and cotton when N was supplied in Ca(NO₃)₂. In comparison, both wheat and chickpea were efficient in utilising Ca10-P when urea was added.

In a red Vertosol supplied with 150 mg P/kg of insoluble P sources, wheat was more efficient than white lupin in utilising Al-P. However, white lupin was more efficient than wheat and cotton in utilising Ca10-P, with P uptake by all species being slightly higher under NH₄ than NO₃ nutrition. Wheat and chickpea had ratios of L value to E value of 1.5-2.5 but canola had the ratio of <1 in Calcarosol and Vertosol. All three species had the ratio of <1 in Chromosol. Elevated CO₂ stimulated microbial activity and immobilized P in the rhizosphere in a Vertosol with P fertilizer history.

Contributors: Dr Xiaojuan Wang, Dr Guosheng Shao, Jian Jin, Nadrah Ashgar, Associate Professor Peter Sale, Professor Caixian Tang.

Collaborators: Associate Professor Petra Marschner and Dr Ann McNeill (University of Adelaide), Professor Roger Armstrong (DPI Victoria), Dr Chris Guppy (University of New England), Dr Rob Norton (Melbourne University), Profs. Fusuo Zhang and Jianbo Shen (China Agric University).

Funded projects:

• How do legumes improve phosphorus uptake of the following wheat? (Funded by ARC)
• Informing management options for enhancing soil phosphorus availability using rotations (Funded by GRDC)
• Subsoil nutrient management and stratification in cotton/grain rotations (Funded by Cotton Research and Development Corporation)
• Synchronising nutrient supply and crop demand in modern cropping systems (GRDC)