Our Vegetable Knowledge

Autumn soil tests and amendments

Soil testing is a vital tool for vegetable growers to monitor key soil properties and nutrient dynamics that influence upcoming crops. Autumn is an ideal time for sampling, not only because it is a quieter period for many operations, but also because soil moisture is usually optimal, making it easier to take samples. Results are also generally more reliable, as many annual cropping systems haven’t recently received fertiliser, which may skew results.

Sampling at the same time each year provides a consistent baseline for tracking trends over time, reducing variability. To capture further differences, consider splitting areas with distinct soil types or cropping histories into separate tests. Within each area, collect samples in a representative W or V pattern to account for variability.

Recommended tests for vegetable crops typically include pH, phosphorus, cation levels, cation exchange capacity, and base saturation. Soil organic matter (SOM) should also be tested, which is the single most useful metric to understand trends in soil health, being linked to nutrient availability, water retention, soil structure and microbial activity.

Nitrogen can be measured using the potentially mineralisable nitrogen (PMN) test, which shows both readily available nitrogen, and the portion likely to become available to the next crop. If nitrogen levels are high in autumn, a nitrogen-hungry service crop can capture excess before it is lost and make it available next season. Although useful to know in autumn, nitrogen levels are highly dynamic in soil. A spring PMN test prior to planting is more relevant. Conducting soil tests in autumn is important for planning and applying amendments such as lime or compost, giving them the necessary time to improve soil quality before the next crop.

For guidance on soil testing or interpreting results contact your local Fruitfed Supplies Technical Horticulture Representative.