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Using soil testing to ensure a productive farming system

Using soil testing to ensure a productive farming system

Using soil testing to ensure a productive farming system

Soil is the foundation of all life and protecting and improving its quality is fundamental for a productive farming operation. Understanding the health of soil enables you to make informed management decisions.

Soil health is made up of three main interrelated properties – chemical, physical and biological. When one of these is out of balance, it can affect the others.

Chemical properties include pH and nutrient availability which are important in plant health. Physical properties include soil texture and structure. Biological properties include mineralisable nitrogen and soil organisms. Good numbers of soil organisms cycle nutrients, help create good soil structure and break down organic matter.

Organic matter is understood to be one of the main indicators of sustainable farming as it affects soil water-holding capacity, soil aggregation, protection from erosion, nutrient retention and promotes biological and enzymatic activity. Management practices that aim to maintain or grow organic matter allow soil to be more resilient to the production demands of a growing system.

The amount of organic matter in the soil is dependent on land use, climate and soil type. Of these, land use is the only factor that can be managed to maintain or improve soil. While grasslands in permanent pastures have large and stable stores of soil organic matter, arable soils are at risk of organic matter depletion due to cultivation, removal of crops, residues and compaction from heavy machinery.

Soil carbon is the conventional measure to understand how land management changes are affecting soil organic matter. Changes in total soil carbon (tC) are generally slow over time.

The recently developed hot water extractable carbon (HWEC) test is sensitive to subtle changes arising from land, and therefore, soil management. Researchers1 have shown the HWEC test to correlate strongly with soil microbial biomass and aggregate stability, providing a good indicator for biological and physical soil properties. The HWEC test is an easily requested add-on to the standard soil quality tests.

Testing soil gives producers and growers the necessary information to monitor soil health and make informed management practice decisions. There are several different soil tests available.

Laboratory soil tests for soil pH, Olsen P, cations, cation exchange capacity, soil nitrogen and carbon provide a minimum set of soil quality indicators and have well-understood optimum levels for New Zealand soils and farm systems.

Like with any type of testing, collecting data over multiple years offers the advantage of understanding the long-term effects of chosen management practices on a farm system.

For more information on the various soil tests used to monitor soil health, contact your local PGG Wrightson Technical Field Representative.

1 Ghani, A., Dexter, M., & Perrott, K.W. (2003). Hot-water extractable carbon in soils: a sensitive measurement for determining impacts of fertilisation, grazing and cultivation. Soil Biology & Biochemistry 35 1231 – 1243.