Enhancing nutrient use efficiency in agricultural soils is essential for sustainable production, particularly in the context of declining natural resources, such as phosphate rock and water availability. The use of organic wastes (e.g. composts, manures, biosolids) as soil amendments can potentially reduce the dependence on naturally available materials.
The Soil CRC’s ‘Unlocking soil nutrients with organic amendments’ project (3.1.006) is studying the effect of organic amendments on nutrient release in selected soils and cropping systems under different soil management practices.
Soil CRC Project Leader Dr Girish Choppala from the University of Newcastle said the project is exploring how organic amendments can unlock tightly bound soil nutrients, enhancing nutrient use efficiency.
“The project is also establishing innovative approaches to apply organic amendments in agricultural soils and examining ways to make the nutrients available for plants through moisture retention and nutrient mobilisation,” he said.
Project update
The project team has been investigating the impact of earthworm casting liquid (EL) and pyroligneous acid (PA) amendments on phosphorus (P) availability in Australian agricultural soils.
“Phosphorus is a crucial macronutrient for plants, significantly impacting their growth and productivity, so enhancing phosphorus use efficiency is critical for sustainable production,” Dr Choppala explained.
“We incubated 3 contrasting agricultural soils from Condobolin NSW with different levels (0%, 0.1%, and 1%) of EL and PA applications. Fourier-transform infrared (FT-IR) spectroscopy was used to observe the changes in functional groups, and sequential P fractionation, extraction of different fractions of iron oxides, and shifts in P-associated iron oxide analysis were conducted.”
The team found that both amendments appear to improve P availability in the selected agricultural soils (a red sandy loam, a red clay loam and a grey clay), specifically:
- both earthworm liquid and pyroligneous acid increased loosely bound P (Sol-P) and organic P (OM-P)
- earthworm liquid showed a stronger effect at 1% application
- in the red clay loam and grey clay soils, EL reduced Fe-bound P (Fe-P) and amorphous Fe levels, likely enhancing P availability by reducing Fe oxide sorption
- earthworm liquid reduced amorphous Fe (hydr)oxide content by 21.6% and 13.6% compared to controls
- FT-IR results suggest that amide and amine functional groups in EL may chelate and reduce Fe oxides
- 1% PA reduced calcium-bound P, potentially due to decreased soil pH and hydroxyl group chelation with calcium.
“By enhancing phosphorus availability in deficient soils and reducing phosphorus losses in rich soils, earthworm liquid and pyroligneous acid could provide practical strategies for sustainable nutrient management in some soils,” Dr Choppala said.
“This study reveals that these improvements in phosphorus use efficiency are achieved through complex interactions between the amendments and specific soil characteristics.”
The project team also expects to publish a paper on their review of recycled organics for improved productivity and is preparing a research manuscript on a recently completed soil incubation experiment.
Glasshouse pot experiments will begin soon, and the project is on track to wrap up at the end of 2025. Further findings will be shared on the Soil CRC website.
Project participants
- University of Newcastle
- Central West Farming Systems
- South East Water
- Primary Industries and Regions SA
- Australian Organics Recycling Association
- Herbert Cane Productivity Services
- Manaaki Whenua Landcare Research New Zealand