|This page provides information on:|
Surface Soil pH
|Surface soil pH map|
Soil pH was mapped across Victoria using a statewide soil chemistry data set based on samples submitted from farms, vineyards and orchards between 1973 and 1994. Each sample was a composite of 20 to 30 cores representing the 0-10, 0-15 or 0-30 cm depth of soil taken from the main soil type in each paddock. Samples from national parks, urban land and sport and recreational turf were excluded from the data. Collated data included nearest location and pH (1:5 soil:water).
The map was generated by applying geo-statistical techniques (‘kriging’) to the mean pH of the locations. It indicates the geographic trends in the acidity and alkalinity of surface soils across Victoria's agricultural land. This map cannot indicate soil pH at the paddock scale and it should only be used as an indicator of likely pH at a regional scale. Considerable variations in soil pH will occur within a region. This map does not substitute for a soil test.
It is important to note that the map only considers surface soil pH. In many Victorian soils, pH will increase with depth.
|Acid Soil Action Kit|
The Acid Soil Action Kit is a publication intended as a guide for farmers, advisers and industry field representatives to help assess acid soil problems and decide on appropriate management strategies. The kit was designed and compiled by Carole Hollier (from Agriculture Victoria, Rutherglen) with the assistance of numerous colleagues in research, extension and industry. The kit was funded by the land and Water Research and development Corporation as part of the National Soil Acidification Program.
Kits can be obtained by filling in the attached Order Form:
Geographic trends in soil pH across Victoria
A number of Victoria’s soils are naturally acid while others are naturally alkaline. This is due to the effect of natural processes, (such as leaching, erosion, deposition) occuring over hundreds to thousands of years on the soil parent material. Consequently, areas of high rainfall such as those on the coast and mountains, have more acidic soils compared to more arid areas, due to the more intense leaching in wetter climates.
Surface soil pH is generally acidic in the Eastern and western Uplands, the Strzelecki and Otway Ranges and north-eastern Victoria. The acid soil conditions in these areas are known to limit plant production in agricultural industries. For example, crops and pastures such as barley, phalaris and lucerne have been limited by aluminium toxicity in north-eastern Victoria and the Central Highlands. Molybdenum deficiencies have limited pasture production in Gippsland.
Soil pH is high and alkaline in north-western Victoria, ie. Mallee and Wimmera. Field crops grown on these soils have experienced zinc deficiencies. Herbicide persistence has also occurred in the strongly alkaline soils.
Agricultural practices have also acidified soils. For example, soils under subclover based pastures, leguminous crops such as lupins, and where ammonium fertilisers are used. Management practices can be used to reduce the impact of acidification. These include use of perennial and deep rooted species (eg. phalaris), and avoiding acidifying fertilisers. Ultimately, application of lime will be needed to combat acidification.
In contrast, alkalinization has also occurred in some soils. Specifically, irrigation with alkaline bore water and fertilising with nitrate fertilisers will increase soil pH. Movement of an alkaline water table will also alkalinize soil. Of course, applying lime will alkalinize soil.
Significance of soil pH to plant growth
Soil pH affects the availability of soil constituents to plants and soil micro-organisms. For most plants, the ideal soil pH (water) test result is pH 6 - 7.5, although many will tolerate pH 5.5 - 8.5. However, the tolerance to extremes in pH varies between plant species and within species. Some plant species have quite different preferred pH ranges (eg. lucerne 6.0 - 8.5, celery 6.0 - 7.0, potatoes 5.0 - 6.0). Therefore, consideration of the need for soil amelioration will depend on individual circumstances.
Soil pH problems
The pH of the surface soils in Victoria ranges from pH 4 to pH 10. These extremes in alkalinity and acidity present problems for the production of many agriculturally important plant species and their symbiotic rhizobia. Due to the complexity of soil chemistry, it has often been difficult to confidently identify the cause of poor plant growth or nodulation. However, aluminium and manganese toxicities and molybdenum and phosphorus deficiencies are probable causes of poor production in many strongly acid soils. On the other hand, lime induced zinc and iron deficiencies often occur in alkaline soils.
|A portable kit (Raupach's Indicator) has been widely used to provide an indication of soil pH in the field. A small sample is collected and an indicator solution is added to form a paste. The paste is then coated with barium sulphate powder. The colour of the powder is then compared with a colour chart. This method is not as precise as the laboratory methods. The kits deteriorate with age and therefore should be discarded after 12-18 months.|
Ameliorating soil acidity
Lime is usually used to increase soil pH in strongly acid soils. The quantity of lime needed will vary between soils. Generally, coarse textured soils (eg. sands) need less lime than finer textured soils. Also, low organic matter soils need less lime than peaty soils. A lime requirement test will incorporate these affects when used to determine the amount of lime needed to raise soil pH. Other factors needed to determine an appropriate lime rate include target pH of the specific plant, lime quality, application method and economics.
Landholders assessing soil pH
at a soil pit field day