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Soil Acidity in the Coorong and Tatiara Districts

Soil Acidity in the Coorong and Tatiara Districts

The Coorong and Tatiara District Council covers a combined area of 1.54 million hectares. It is a productive area of SA with a total value of annual agricultural production of more than $490M (ABS, 2015-16).


Soil acidity (low soil pH) is becoming an emerging and significant problem throughout the area particularly on the sandy to sandy loam textured soils. It is a natural process but is accelerated with more productive and intensive farming practices. When the soil falls below pH 5.5 (CaCl2) the productivity of crops and pastures starts to decline. The area currently acidic or likely to become acidic in the next few years is approximately 334,500 hectares or 35.6% of the agricultural area with an estimated production loss of $5.3M.

KEY POINTS

- Soil acidity is becoming an emerging and significant issue throughout the Coorong and Tatiara District Council areas having a  major constraint on crop and pasture production
- Soil acidity can affect sub-surface and sub-soils
- Soil pH should be tested in paddocks on a regular basis at 5 cm increments to at least 15 cm
- Soil acidity can be treated with the use of lime and / or soil modifications (such as ripping, delving, spading and clay spreading) provided that the underlying clay is alkaline


Soil acidity and treatment in the Coorong and Tatiara District Council areas.

It is estimated that a further 375,000 hectares of agricultural land in the area has the potential to become acidic over the next few decades assuming that the current farming practices continue and that soils are not adequately treated.

ESTIMATED YIELD PENALTY

- When the soil pH falls below 5.5 (CaCl2) then yields of crops and pastures start to decline

- The estimated yield penalty for crops and pastures with increasing soil acidity has been sourced from research trials, observation and pH vs yield maps

- Commodity prices have been based on an average for example $260/ wheat and $700/lentils

- The total value of production losses are therefore conservative

Estimated Yield Penalty Area

RESOURCES

Through the Small Smart Farms Project- Understanding soil pH growth constraints funded by the Australian Government’s National Landcare Program with the support of the Tatiara and Coorong District Councils has allowed this work to improve our understanding of the impact of soil acidity on our region.

Please click on the links below to access further information about this project and Soil Acidity in the Coorong and Tatiara Districts

- Fact Sheet: Soil acidity and treatment in the Coorong and Tatiara Districts

- Report: Soil acidity and treatment in the Coorong and Tatiara Districts

For further information summarising;

- Soil acidity impacts

- Yield penalty, and

- Treatments, please keep scrolling

CAUSES OF SOIL ACIDITY

Soil acidity is a natural process accelerated by agriculture. It is caused by an accumulation of H+ ions:  (pH – logarithm of H+ ions)

-Ammonium nitrogen fertilisers - Ammonium nitrogen is  converted to ammonia and then nitrate and leaves H+ ions behind. If nitrate not used then it is leached leaving behind H+ ions
-Removal of plant and animal products. Most plant   material is slightly alkaline. Removal by grazing or   harvest leaves behind H+ ions. Most particular lucerne hay
-Build up of organic matter - Leaves behind H+ ions

EFFECTS OF SOILS ACIDITY

-Alters nutrient availability reduces calcium, magnesium, potassium, phosphorus and molybdenum
-Decreases mineralisation of N, reduces N fixation by legumes - rhizobia effected if pH (CaCl2) <5.2 for some legumes. Reduces micro organisms
-Toxicities - Aluminium toxic (pH (CaCl2) 4.8 or less)
-Decreases yields of plants with low tolerance lucerne, canola, barley, lentils, chickpeas etc

EFFECTS OF SOILS ACIDITY ON PLANTS

- Yields are falling, acid sensitive plants are struggling
- Uneven crop and pasture growth
- Poor plant vigour, poor nodulation legumes
- Reduced root growth, poor moisture use, reduced yield potential
- Reduced range of plants, variety differences
- Invasion of acid tolerant weeds eg. sorrell, ryegrass

Effect of Al Toxicity

Tolerance of crops and pastures to soil acidity

Tolerance of crops and pastures to soil acidity 2

TREATMENT OPTIONS 

- Acid soils can be treated with lime or through ripping, spading and clay spreading provided that the underlying clay is neutral or alkaline
- There are a number of lime sources in the SE
- Soil pH Veris® mapping is being used more and more as a technique to map soil pH on a broadacre scale to understand the extent and level of soil acidity

Further details on the economics of these treatment options is outlined in the following resources;

- Fact Sheet: Soil acidity and treatment in the Coorong and Tatiara Districts

- Report: Soil acidity and treatment in the Coorong and Tatiara Districts

IN SUMMARY

Soil acidity is a significant and emerging problem throughout the Coorong and Tatiara area especially on the sandy and sandy loam soils having a significant effect on crop and pasture yields

Monitor soils for soil pH on a regular basis approximately every 5 years. Sample at depths of 0-5 and 5-10 cm

Lime and or soil modification techniques such as ripping, spading, delving or clay spreading are options provided that the underlying clay has a neutral or alkaline soil pH

The pay back for liming is about 1 to 1.5 years. Clay spreading is in the order of 2.5 to 4.0 years

An example of soil pH mapping An example of soil pH mapping