What Soil Amendments do I need?
This depends on several factors, all revolving around the pH of the soil and whether it is a clay, clay loam, silty loam, sand or has an imbalance of certain characteristics such as excess (leading to toxic levels) - Sodium (Na), Chloride (Cl), minor trace elements or heavy metals.
The way to check soil pH is by Soil Testing or using a portable pH meter. Major and secondary nutrients are most available at a pH of 6.5 to 7.0. Therefore, fertiliser dollars are not wasted when the soil is in this pH range. pH levels can be corrected by using Calcium Limestone (Calcium Carbonate) to raise the pH (the Carbonate is the part of the molecule that has acid neutralizing capabilities) and Gypsum (Calcium Sulphate) to lower the pH in soil.
Dolomite Lime also contains Magnesium, a minor nutrient that is also important for crop growth, therefore the application of Dolomite provides both Calcium and Magnesium (Mg).
Another local source of Limestone available is Earth Lime + Silica (Calcium Limestone with Silicon (Si).
Calcium Limestone, Earth Lime containing Silicate and Gypsum provide Calcium which is necessary in maintaining a desirable soil structure. Gypsum also provides Sulphur which is also an essential element in plant growth. Moisture and air movement through the soil is essential for plant growth - Calcium keeps the soil mellow and crumbly, encouraging plants to root deeper and grow faster.
From past trials in many crops (including sugarcane and a variety of horticultural crops) it has been proved that the correct regulation of Silicon assists nullify the deleterious effects of salinity and heavy metals.
The application of Calcium Silicate (earth lime + silicon) in sugarcane reduced the uptake and translocation of Sodium (Na), but increased Potassium (K) concentrations in roots and shoots. Chlorophyll contents and photosynthetic rate were also significantly improved by added silicate. Cane yield and yield attributes such as cane height, internode length, and number of tillers per plant was significantly higher along with juice characteristics such as Brix (% soluble solids in juice), Pol (% sucrose in juice), commercial cane sugar (CCS) and sugar recovery were significantly improved. Other trials demonstrated that a more vigorous root system developed with the addition of silicon in numerous crop types as well as adding to the plants natural immune system in controlling certain fungal and insect related diseases.
With the addition of the various soil amendments the soil becomes more open; it readily absorbs rainfall thereby cutting down run-off and erosion. This also helps eliminate wet spots that otherwise would remain after the rest of the ground becomes dry. The combination of near neutral pH and an open, well-aerated soil provides the best environment for microorganisms that decompose organic matter, convert fertilizers to usable nutrients, and fix nitrogen from the air to the soil. In Sodic soils (very high pH readings of 8 and 9+ also associated with high levels of Sodium and Chlorine) the applied Gypsum may be used up as the calcium replaces the sodium held on the clay-binding sites. The sodium can then be leached from the soil as sodium sulphate and soil structure is improved by providing openings in the soil to allow water, air, root and nutrient movement. The calcium in gypsum also works as a controller of the balance of especially the micro nutrients like iron, zinc, manganese and copper in plants, while heavy metal toxicity is regulated. If all the calcium is used up in displacing Sodium (Na) this can lead to a Calcium deficiency and using a mixture of Gypsum and Lime gives an adequate supply of Calcium for optimum plant growth.
A soil test (sample) is only as good as the sampling process and quality of information forwarded to the Laboratory with the sample. A number of important steps should be followed when soil sampling a block of land.
SOIL SAMPLING GUIDELINES
- Determinethe area that is to be sampled.
- Ensurethat the area being sampled does not exceed 10 - 20 hectares and that it is relatively uniform.
- Take notice if a block consists of more than one distinct soil type if it does, sample them separately.
- Avoid areas that differ in crop growth or where large amounts of mill mud or other amendments have been dumped (sample such areas separately if necessary).
- Infield sampling is best done with an auger (either a turning auger or a soil tube).
- Limit to a minimum of at least 10 or 12 'augerings' of soil should be collected from the area to a depth of about 20 cm using a zig-zag or grid pattern
- The basic principle is that more 'augerings' are better than fewer.
- Organise all the 'augerings' to be collected in a good-quality plastic bag or a clean plastic bucket to form a single composite sample.
- Proper care should be taken not to use a bucket with a galvanised handle as this source of zinc could contaminate the soil sample.
- Repeated mixing of all 'augerings' of composite samples is essential to ensure a uniform sample.
- Only dispatch a sub sample if the complete sample is greater than 1kg (500 g 1 kg is sufficient for dispatch to the laboratory).
- Forward this sample to a reputable laboratory for analysis.
- It is advantageous to supply as many details as possible on a label and on the sample bag to ensure that the sample can be easily identified, and that meaningful interpretation of the results is possible.
- The compilation of all information is important in that soil assays conducted by the laboratory correspond to those calibrated for the specific crop production required.
Inkerman Lime & Gypsum acknowledges that some technical information contained in this document has been sourced from publications available from several worldwide media sources.
What application rates should be used?
Generally speaking (this will be confirmed from soil test), apply 2.3 4.6t Limestone per ha for upward pH correction. This recommendation will be dependent on type of limestone or gypsum available and the severity of the pH level of the soil. Soils with a pH level of 5.9 or lower are considered critical and should be treated to increase the pH level to 6.0 or higher. Maintenance applications should consist of applying Limestone annually or with each full crop cycle. Similarly gypsum may be used at corresponding rates to lower pH reading or as advised from soil test. Gypsum and Limestone may be applied to the soil at any time; however the preferred time of application is several weeks prior to planting.
Many growers are opting for a maintenance 50/50 blend applied at 4t per ha to optimise the $ returns and having more friable and productive soils.
Speak to us regarding your anticipated requirements We have an Agronomist on hand, access to Soil Testing facilities and undertake to visit your farm this season whenever possible or as required.