Tropical grasses remedy ‘Sunday Country’


Tropical grasses improved poor soils during recent trials in northern NSW.

Researchers from Australia and Finland reported that tropical pasture roots might initiate favourable changes in difficult soils, ultimately resulting in increased fodder production.

The research, led by a team from The University of Queensland’s School of Agriculture and Food Sciences, compared the response of sodic-duplex soils to tropical and native pastures over 14 years.

Sodic-duplex soils are acidic and sandy in the topsoil, with heavier clay subsoil. Water can’t penetrate into the clay, leaving only the sandy surface to hold meagre amounts of moisture. These soils are often referred to as ‘spewy’ or ‘Sunday Country’ (too wet on Sunday – too dry on Monday).

The research compared soil structure and porosity; finding deeper and greater root abundance, improved stable subsoil structure and increased macroporosity under tropical pasture.

The researchers found that tropical pastures had nearly twice the abundance of roots as native pasture and markedly higher porosity, allowing ‘significantly’ greater potential water infiltration into the soil.

Soil chemistry analysis showed some leaching of nitrogen and phosphorus in the tropical grass pasture. The provision of nutrients to deeper layers in the soil allows soil fauna, fungi and roots to break up large soil structures into smaller aggregates.

Soil organic carbon (SOC) was 58 t/ha (native) vs 84 t/ha (tropical grass pasture) down to over 90cm. The greatest difference in SOC was in the top 20cm with up to three times more under tropical grass compared to native pastures.

Lead researcher Robert Banks explained: “Native pastures established on the region’s sodic soils are known for their limited agricultural production. Fertilised tropical grass pastures on these soils are reported to have much increased pasture production, deeper, more abundant root mass and greater soil profile moisture storage.

However, the subsoil physical differences between the two pasture types are not well-understood.

“Deeper roots from a more aggressive pasture appears to produce more dry matter to facilitate a process called the feedback loop of soil benefits. Roots assist in the movement of water and nutrients to deeper in the soil profile, which also assists in the development of much better soil structure. Improved soil structure means more root access and so the process continues.

“This research supports that tropical pastures have an important role in management of sodic duplex soils. The important findings show these pastures with winter legumes can substantially improve poorly structured soils as well as be more productive,” Dr Banks said.

He worked with UQ’s Kaye Basford, Laura Wendling from VTT Technical Research Centre of Finland and CSIRO’s Anthony Ringrose-Voase, with Vera Banks as the report editor. North West Local Land Services provided funding for soil chemistry testing and Meat and Livestock Australia provided funding for the research.

Source: Soil Research 58(2) 207-218

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