Agricultural and Horticultural Soil
Agricultural soils are tested to measure the soil quality and nutrient levels for monitoring fertiliser programmes and to assist with identifying nutrient deficiency or toxicity.
Why test soil?
Soil testing takes the guess work out of nutrient management and allows cost effective nutrient management. This is particularly important because most New Zealand pastoral soils are deficient in phosphorus, sulphur and to a lesser extent potassium and some trace elements can also be deficient. However, historical soil use will impact nutrient change with soils under intensive cultivation often having abnormal levels of some nutrients due to previous management practices and fertiliser programmes.
The value soil testing delivers
- Measure whether soil nutrient levels are high enough to sustain the desired level of plant growth.
- Indicate the existence of any deficiency, excess or imbalance of major nutrients.
- Provide a scientific basis on which to assess fertiliser and lime requirements of crops, pastures and turf.
- The Organic Soil Profile measures the soil quality, testing the soil organic matter, available nitrogen, total nitrogen and carbon:nitrogen ratio.
- The Hot Water Extractable Carbon test is recommended as a good indicator of microbial activity in the soil, as it is highly correlated with microbial biomass carbon and aggregate stability.
- A useful set of tests for assessing soil health would be Basic Soil, Sulphate-S, Anion Storage Capacity, Organic Soil Profile and Hot Water Extractable Carbon. Testing for heavy metal contaminants such as total cadmium and total copper may be important in some instances.
Soil tests measure only a fraction of the total pool of nutrients available to plants (immediate and long term) so it is important that standard New Zealand methods of sampling and soil analysis are used so the results are meaningful and can be related to plant growth under New Zealand conditions.