Unlocking soil potential: Insights into soil sampling

Soil sampling is the cornerstone of successful crop farming, offering invaluable insights into soil health and guiding informed agricultural decisions. For famers in crop production fields, understanding their soil nutrient composition can be the difference between a bountiful harvest and a disappointing yield.

Hamond Motsi, a PhD candidate in soil science at Stellenbosch University, shares his expertise on soil sampling, explaining why it matters and how farmers can incorporate it into their practices.

Why soil sampling matters

Soil sampling is a very important part of farming, as it provides essential information about health and nutrition. It can tell you “what is it you need to add, what is it you need to reduce,” Motsi explains.

Regular soil testing informs farmers about their soil’s capacity to support crops, helping them manage fertility and prevent degradation.

When to sample and soil conditions

Motsi highlights two key periods for soil sampling:

Before planting: To prepare for the cropping season.
After harvesting: To assess changes in soil health and plan for the next cycle.

Sampling can also occur during various growth stages, however this depends on the farmer’s budget and needs. He clarifies that soil samples can be taken under any condition – wet or dry – since samples are dried before analysis.

Frequency and budget considerations

The cost of a full soil analysis, starting from a total of R750 at the Western Cape department of agriculture’s analytical services, for example, can deter small-scale farmers from frequently sampling. “If the farmer is working on a limited or a low budget, I would advise them just to make sure they sample on the fundamental periods, which are before they plant and then just after they harvest,” he suggests.

For farmers with more resources, Motsi recommends sampling at multiple growth stages to monitor changes in fertility.

Key indicators in soil analysis

Soil analysis reports provide vital information, including:

Nutrients: Major elements like nitrogen, phosphorus, and potassium, and secondary elements like calcium and magnesium.
Micronutrients: Zinc, copper, and others that support plant growth.
pH levels: Essential for determining soil acidity or alkalinity.
Salinity: High salt levels can inhibit plant growth and require specific management practices.

Soil degradation encompasses any process that diminishes the ability of the soil to support plant growth. While many people are familiar with soil erosion as a form of degradation, Motsi explains that other significant types include soil salinity, soil acidity, and most importantly, soil infertility where the soil’s capacity to supply essential nutrients is reduced. Farmers cannot visually identify specific types of soil degradation; instead, they must rely on soil sampling and analysis.

“Degradation can be defined as anything that can reduce the status of the soil to support the plants,” Motsi notes, urging farmers to prioritise understanding their soil’s nutrient balance and physical health.

Best practices for soil sampling

Accurate sampling is essential for obtaining reliable results. Motsi recommends:

– Use of proper equipment: An auger, a tool designed for sampling loose sandy soils, is ideal but farmers can use a hoe if necessary.

The auger is the ideal tool to use for soil sampling. Photo: Pixabay

– Depth of sampling: “The most required depth is from zero to 30 centimetres because that’s where you find a lot of roots and soil-plant interaction.”

– Sample different zones: For fields with variations in topography, Motsi advises sampling each region separately to account for differences in soil characteristics.

Farmers are advised to seek guidance from laboratories or extension officers to ensure that samples are collected correctly.

Technology and access

Emerging technologies, including GPS, drones, and earth observatory models, are transforming soil sampling. However, Motsi cautions that these are still in developmental stages and may not yet provide the accuracy required for consistent results.

For small-scale farmers, affordability remains a challenge. Research institutions, universities, and government programmes must be able to provide accessible solutions.

“Smallholder farmers don’t even know that [you] need to check your soil status before you plant. And that’s why yields are always low in those groups of farmers.”