Facts, Formulations and Fundamentals - Part 3
Part three of a series of three articles written by Kevin Timms Sports Turf Advisor NZ Sports Turf Institute on the Facts Formulations & Fundamentals of Fertilisers
- Soil test interpretation
- Fertilisers P - Z
Soil Test Interpretation
The most widely used method of soil analysis in the NZ sports turf industry is called the 'exchangeable bases method'. It is based on the standard method of soil analysis in New Zealand detailed in N.Z Soil Bureau Scientific Report 10A (1972).
The interpretation philosophy used is the BCSR (basic cation saturation ratio method).With this method the basic cations are expressed as percentage base saturation (%BS).The balance between the elements should be kept within a certain range for healthy plant growth.
IMPORTANT: This method is suited to dealing with sandy rootzones, often found in sports turf. Sand rootzones typically have low nutrient retention (low CEC) and typically require fertilizing on a 'little and often'. The BCSR method helps to discover any nutrient imbalances that may occur,
Another method of soil analysis is it utilizes the SLAN (Single Level Availability Nutrient) interpretation method. It indicates the amount of nutrient in the soil relative to an ideal soil where single nutrients are considered in isolation to one another it has the disadvantage that in sand all the figures will be low thereby suggesting that inappropriately heavy corrective fertilisation is needed. The SLAN method is principally suited to turf areas on soil based rootzones.
pH Soil analysis results for pH have an uncertainty of + or - 0.2 pH units. A soil sample testing pH 5.0 one day, could test pH 4.8 the next day, and pH 5.2 another day.
Phosphorous The Olsen phosphorus test is carried out to assess phosphorus levels. The test is taken at a pH of 8.5. The test only assesses the available phosphorus not the total phosphorus "present in the soil."
Potassium, calcium, magnesium and sodium These elements are the exchangeable bases. Soil analysis allows the balance between these elements to be determined and corrective measure taken.
Ca/Mg ratio An imbalance in the calcium with magnesium (Ca/Mg) ratio can potentially check plant growth but is not as important for turf grasses as the Mg/K ratio. A 3-8 parts Calcium to 1 part (3-8:1) Magnesium ration is a general guide for healthy turf growth However, in some soils (high shell content or soils rich in Magnesium) the ratio can be in the 3-8:1 range while still growing healthy turf.
Mg/K ratio The Mg/K ratio is more important. An imbalance can sometimes check growth. Adequate amounts of both nutrients are important for healthy turf growth. A ratio of 2-3 parts Magnesium to 1 part Potassium is a guide for healthy turf growth. In many turf soils (rootzones) a ratio of 1:1 or less is not uncommon due to high potassium fertilizer rates.
CEC (cation exchange capacity) This measures the cation exchange capacity of the soil, which indicates how well a soil retains nutrients (ions) such as potassium, calcium, magnesium, sodium, sulphate and ammonium
CEC figures below 12 are typical of sand root zones, 12-25 typical of mineral soils and 30+ typical of high organic matter soils. Low CEC soils (sandy soils etc) have low capacity to retain calcium, magnesium, potassium, sodium and nitrogen. Fertilizer needs to be applied 'little and often' to these root zones whereas high CEC soils may typically require feeding less often.
Base saturation The base saturation figure measures the percentage of the CEC that is occupied by the bases such as calcium, magnesium, potassium and sodium. The remaining places are occupied by hydrogen. Acidic soils typically have low base saturation figures. Alkaline soils (pH is greater than 7.0) have high base saturation levels.
Volume weight The sample is air dried, ground up and repacked into a standard volume to determine its weight. This figure bears no resemblance to soil density in the field. Figures of 1.0 or above are typical of sandy root zones. This figure is used when calculating the amount of soil nutrient present in the soil.
Click on the following link to view table of fertilisers :- Fact and Fundamentals of Fertilisers
Howard, D. New Zealand Sports Turf Institute.
Balance Agri-Nutrients. Nutrient handbook.
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