Author: Natalie Lee, GRDC

Date: 7th May, 2019

Widespread Western Australian field trials are generating information that will help grain growers decide which strategic tillage methods may be best suited to different soil types on their farms.

The first year of Grains Research and Development Corporation (GRDC) ‘Ripper Gauge’ trials showed deep ripping to a depth of 60 centimetres generally produced the highest grain yields on sandy soils, and more intensive tillage treatments tended to produce the best results on gravel-based soils.

The trials, that started in 2018, are being coordinated by the West Midlands Group (WMG) and conducted by local grower groups at 20 demonstration sites over three years in all WA port zones. A large range of soil types are being tested, including loamy sands through to gravel and sand duplexes, ‘forest gravels’ and clay soil types.

Treatments included ripping to 30cm, deep ripping to 60cm, ‘maximum’ tillage and a control (no amelioration). Machinery used varied according to what was locally available from growers.

This project will continue for the 2019 and 2020 cropping seasons to follow the impact of each amelioration treatment over time and in different seasonal conditions.

GRDC grower relations manager – west Lizzie von Perger said soil amelioration practices such as deep ripping, mouldboard ploughing and rotary spading could remove soil constraints and increase crop yields and had become increasingly popular on WA grain farms in recent years.

“However, knowledge is still limited about the benefit and longevity of these practices on a number of soil types,” she said.

“This project aims to evaluate and demonstrate the impact of soil amelioration on a wide range of soil types that are common in the WA grainbelt.”

WMG executive officer Nathan Craig said results from the first year of the project showed grain yield responses to soil amelioration methods tended to be associated with broad soil types, rather than with geographical areas.

“The sandy soils, including duplex and loamy types, mostly responded best to deep ripping treatments. Ameliorating the compacted soil layer of sandplain soils has already been shown to significantly increase yields in most seasons on WA grain farms,” he said.

“The gravel-based soils, that are often harder and shallower than the sandy soils, tended to be more responsive in the trials to maximum tillage treatments that had the greatest level and depth of soil disturbance.

“Maximum tillage treatments involved both ripping and aggressive disc tillage, in one pass, to loosen soil to a depth of about to a depth of about 30cm.”

Mr Craig said that there were some exceptions to these general rules, and some sites where treatments produced no grain yield responses.

“The soil types that did not respond to the soil amelioration methods were varied and located across different port zones but were generally in areas that experienced above average growing season rainfall,” he said.

Mr Craig said the treatments, especially the maximum tillage treatments, contributed to increased weed numbers at many of sites due to soil disturbance triggering weed germination.

“Increased weed numbers may have competed with crops, many of which were cereals, for soil moisture and nutrients to reduce the grain yield benefit of these treatments,” he said

“This sparked discussion from growers visiting the sites, with many suggesting that some canola varieties might be better to grow than cereals immediately following soil amelioration due to more robust herbicide packages being available for them.”

Mr Craig said the project also highlighted that gravelly and hard types of soils could significantly restrict how and when those soils could be ameliorated.

More information about addressing soil constraint and soil amelioration practices is available in GRDC videos and podcasts discussing outcomes from the five-year collaborative Soil Constraints – West initiative.

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