Soil Testing for General Agriculture
Why test soils
Most New Zealand pastoral soils are deficient in phosphorus, sulphur and to a lesser extent potassium and some trace elements can also be deficient. Soils under intensive cultivation may have abnormal levels of some nutrients due to previous management practices and fertiliser programmes.
Soil testing takes the guess work out of nutrient management and allows cost effective fertiliser programmes to be produced. Herbage tests of pasture complement soil tests and allow important trace nutrients like cobalt, selenium, copper and iodine to be adjusted for improved animal health.
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.
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 NZ methods of sampling and soil analysis are used so the results are meaningful and can be related to plant growth under NZ conditions. A single soil test is of limited value as it is essentially a snapshot in time of a dynamic environment. Trends in soil test values over time will give a better indication of how well your fertiliser program has worked. To obtain a more complete picture of farm nutrient status, soil testing should be complemented by plant testing which measures the mineral nutrients that the livestock are eating.
Even when soil nutrient status is at optimum levels other factors such as soil temperature, rainfall and compaction can influence the rate of uptake of nutrients by plants.
- For Pastoral Soils: a Basic Soil Profile and sulphate-S test are recommended. Where reactive phosphate rock (RPR) fertiliser has been used, the resin phosphorus (RP) test should be added.
- For Arable Crops like Maize: a Basic Soil Profile, sulphate-S and available-N are recommended.
- Other Soil Tests include: organic sulphur, total sulphur, the organic soil profile for soil quality, aluminium, boron, EDTA trace metals, Mehlich 3 trace metals and more.
For help choosing the right soil test and for help with their interpretation Soil Tests & Interpretation.