Acidic, light soil deemed useless no more thanks to research

Acidic, light soil deemed useless no more thanks to research


Cropping
Tropical grass Premier digit growing on the same light acidic country as the photo below. Addressing soil deficiencies plus growing in conjunction with serradella and other acid soil tolerant winter legumes is part of this success story.

Tropical grass Premier digit growing on the same light acidic country as the photo below. Addressing soil deficiencies plus growing in conjunction with serradella and other acid soil tolerant winter legumes is part of this success story.

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As recent research has shown if well managed, light soil can not only be productive but also build soil organic carbon.

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I commenced as NSW Coonabarabran district agronomist 52 years ago, and the advice from a senior departmental officer was "don't waste your time trying to solve poor productivity from the light acidic country in your district".

A lot of effort had been devoted by previous agronomists in this and other areas to improve light soils, but to little effect.

Such was the knowledge of acid soils, especially where acidity continued down the profile, at that time. However across the country an awakening of light soil potential was occurring.

Instance the Esperance WA development, where the discovery of trace element deficiency dramatically raised productivity of these very sandy soils. Similar was the success of the AMP development of the SA "90-mile desert", now regarded as one of the most productive in the state, but once regarded as near useless.

Surely there was hope for our light country, which represented about 40 per cent of farm land, as well as considerable areas of adjoining regions. State wise, more than 13 million hectares was designated acidic soils, with significant parts being acidic down the profile.

Success in finding solutions involved many research aspects included efforts of many researchers.

WA researcher Dr John Gladstones, first identified serradella, an annual pasture legume as extremely tolerant to soil acidity (especially aluminium toxicity). Within a few years we also established that serradella was persistent and productive on our poorest light soils. Other acid soil tolerant pasture legumes followed, including biserrula.

Typical unimproved native pasture on light country grows little feed, is easily overgrazed, and is rarely profitable.

Typical unimproved native pasture on light country grows little feed, is easily overgrazed, and is rarely profitable.

Prior to serradella, no winter legume responded to added major and trace elements, hence the belief that these soils were useless. Soil tests supported this belief.

Once an acid tolerant species was discovered soil nutrition research quickly discovered that sulphur and phosphorus were the main missing elements (also nitrogen but good legume growth with appropriate rhizobia solved that), and not necessarily high fertiliser rates were required.

Consol lovegrass was the next major breakthrough as an extremely acid soil tolerant spring summer and autumn growing perennial grass. If soil fertility was good its quality was also good and productivity and persistence excellent.

Bill Johnstone, of NSW Soil Conservation Service, responsible for Consol's release, supplied us with seed and again research showed we had another important part of a productive pasture complimenting a winter legume.

A few years later followed Premier digit grass and research showed us it was also acid soil tolerant, productive, long lasting and good quality. Especially important was that it is easier to grow with winter legumes than it is with Consol. Both perennial grasses also proved to be the answer to many light soil weed problems such as spiny burr grass and blue heliotrope.

Cropping research also found narrow leaf lupins and cowpeas as acid soil tolerant. Oats was generally acid soil tolerant but some varieties like Saia had outstanding tolerance.

Winter legume serradella growing in a tropical grass pasture on once regarded poor acidic soils.

Winter legume serradella growing in a tropical grass pasture on once regarded poor acidic soils.

The emergence of triticale as a man-made species (involving a cross between wheat and cereal rye) also provided a wide range of very acid soil tolerant winter crop varieties. Plant breeders have also developed an increasing range of tolerant wheat and even barley varieties.

Lime to correct top soil acidity has, since the 1980s, been widely adopted and is an integral part of many farm business. In many cases the top 0-10cm soil layer was the only acidity problem, although if not corrected in a farming situation it would spread to the sub soil if not addressed.

Lime will also commonly help where acidity is a problem down the profile but acid tolerant plants remain the major strategy.

Most light soils are fragile and vulnerable to wind and water erosion, as well as structural degradation if not sensibly managed. Zero till, stubble retention and careful grazing have all been important strategies for managing these soils.

As recent research has shown if well managed, they can not only be productive but also build soil organic carbon.

Next week: Summer crops in non-traditional summer crop areas. How to assess feasibility.

  • Bob Freebairn is an agricultural consultant based at Coonabarabran. Email robert.freebairn@bigpond.com or contact (0428) 752 149.
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