Addressing nutrient deficiencies key to lifting pasture productivity

This is being showcased in a trial being conducted at Bookham by Bookham Ag Bureau, Holbrook Landcare Network and South East Local Land Services as part of the SNSW Innovation Hub's Resilient Pastures project funded through the Future Drought Fund.

South East LLS senior agriculture advisor Fiona Leech said the trial site at Bookham is low fertility with a native perennial grass base consisting of Microlaena and Wallaby grass along with some annual grasses and subterranean clover.

"We know nitrogen, phosphorus and sulphur are key drivers of pasture growth and native pastures will respond to these nutrients," she said.

"In permanent pastures N supply is addressed by the legume component of the pasture. However, P and S are two major elements that must be addressed to build the legume component.

"So in order to lift pasture productivity a fertiliser containing P and S must be applied. It is important to address the micronutrient molybdenum which is also a critical requirement.

"The trial site has been chosen based on its low fertility with P and S constraining pasture growth by a similar extent."

Soil testing revealed the site has a base soil Colwell P of nine mg/kg and Ms Leech said they were using the Five Easy Steps P management program, developed by CSIRO and NSW Department of Primary Industries, to build soil phosphorus levels to near optimum over time.

The predicted optimum Colwell P for the site is 31 mg/kg.

The trial, which began in August 2023, is set to run for a five-year period with the aim of building the soil Colwell P test reading by 22 units - from nine to 31 mg/kg of P.

Using the Five Easy Steps approach it was determined that an average of 18.8 kg/ha P needs to be annually applied over 5 years.

Annual soil testing is being used to monitor Colwell P levels and determine how the levels are tracking compared to the target.

Three different fertilisers are being used to deliver the 18.8 kg/ha P including Single Super, TriplePluS and Agri-ash.

Ms Leech said further investigation is focused on understanding the management of sulphur in pastures.

Examination of the ratio of P to S delivered is being investigated in four of the treatments to help determine if adequate S is present to realise the optimum growth potential from the P applied.

Ms Leech said the treatments to watch in this space were Single Super with a nominal ratio of 1:1, TriplePluS approximately 2:1 and TriplePluS with Gypsum added a ratio of 1:2.

She said the ratio flipped with one phosphorus to two sulphur was the treatment to watch with the question being, will it lead to an improvement in soil S levels and pasture production?

Another element of the trial is experimenting with Agri-ash, a burnt sewage waste product, and whether there is adequate sulphur and how, along with gypsum, it performs relative to the Single Super treatment.

The trial site has a soil pH(CaCl2) of 4.4 with 29 per cent aluminium present in the topsoil layer (0 to 10 centimetres).

Lime has been included in a limited number of treatments to compare the production response with and without lime addition.

Soil testing will be conducted annually in spring to determine how well soil Colwell P and S are tracking, along with soil pH and a range of other soil chemical parameters.

Ms Leech said given the five by two metre plot size, annual soil testing would occur in the 0 to 10cm zone.

Deep coring to 50 centimetres was conducted at the commencement of the study and will again be conducted further down the track.

"A snapshot of pasture growth will also be measured for a period in the spring of each year when temperature and moisture are less likely to confound the pasture growth response to the soil nutrients applied," she said.

"The collaboration would like to acknowledge the generosity of the Hazell family in hosting the trial site."