Getting ready for farming season

Healthy soil is the starting point for every successful harvest.

In Eswatini, however, Soil Sci­ence and Plant Nutrition Research Officer in the Department of Agri­cultural Research and Specialist Services, Ministry of Agriculture Bongani Mvubu says that many fields are losing fertility due to erosion, overgrazing, nutrient mining, deforestation and chang­ing weather patterns.

“The good news is that farmers can reverse this trend by getting to know their soils better through soil sampling and liming.”

WHY TEST YOUR SOIL?

‘Just like people visit the doc­tor for check-ups, soil also needs a ‘health test’ before crops are planted’. Soil testing helps farmers to know:

• If the soil has enough nutrients for the intended crop.
• Whether the soil is too acidic or alkaline.
• How much organic matter and fertility the soil contains
• The right type and amount of fertiliser and lime needed.

Armed with this information, he mentions that farmers can avoid wasting money on unnecessary inputs while ensuring crops receive exact­ly what they need for strong growth.

TYPES OF SOIL TESTS

• Chemical soil tests: These fo­cus on soil fertil­ity and nutrient status.
• Physical soi l tests: These as­sess the physical structure and be­haviour of soil.
• Biological soil tests: These as­sess the activity and diversity of soil organisms.

SOIL SAMPLING

Soil sampling is the first and most critical step in the soil testing process. “Accurate and represent­ative soil samples are essential for obtaining reliable data about

 soil fertility, struc­ture and biological health. Incorrect sampling can lead to misleading test results and inappropriate management de­cisions that affect crop yields, soil sustainability and environmental quality.”

THINGS TO NOTE WHEN

SOIL SAMPLING

To ensure accu­racy, consistency and meaningful interpretation of soil test results, the following gen­eral guidelines should be followed:

Timing of soil sampling

Best time: Be­fore planting, dur­ing the dry season, or after harvesting when the soil is stable and not recently applied fertiliser.

Avoid sampling:

• After recent fertiliser or ma­nure applications.
• During extremely wet condi­tions (wet soils are harder to handle and analyse).
• From road edges, animal paths.

Soil sampling depths

Different depths reveal different layers of nutrient availability and soil conditions:

• Topsoil (0–20 cm): Most rel­evant for nutrient availability and crop root zone.
• Subsoil (20–50 cm or more): Important for deep-rooted crops, salinity and compaction assessment.

Number of samples

• Take 10–20 sub-samples ran­domly across each field or man­agement zone.
• Combine to form one composite sample per zone/field.

Soil sampling tools and ma­terials

• Soil auger or probe (preferred), or a clean spade.
• Clean plastic bucket.
• Sample bags or containers (clearly labelled).
• Trowel (to mix sample).
• Permanent marker, GPS or map for location tracking.
• Field notebook for recording data.

 Steps in soil sampling

Step 1: Divide the field into sam­pling units

• Determine whether the field is homogeneous or heterogeneous and categorise area into similar topography, management history and/or crop performance.
• Selecting appropriate sample collec­tion methods.
• Preparing all soil sampling tools and equipment.
• Then starting from one corner, take two steps in the field and have your first station or spot for sampling.

Step 2: collect soil sub-samples

• Use a zigzag or W-shaped pattern across the sampling unit.
• Take a sample every 15 paces along this path.
• Each place from which you take a sample is a ‘sampling station’.
• Before taking the soil from each soil station, it may be necessary to remove any plant debris and trash from the surface.
• Take soil samples within 5-20cm of the topsoil (root zone).
• If the field is ploughed, take sample from above, if not, remove top 5cm and take sample from 5 to 20cm below the ground using a spade or hoe or trowel to dig but preferable use a soil auger and put that soil into the plastic bucket.
• Follow a W pattern as shown in figure 1 and stop every 15 steps to take a sample. Thoroughly mix the collected soil in the bucket upon reaching the end of the field.
• From the thoroughly mixed soil, scoop a cup full of the mixture into a clean sampling bag or ice plastic bag to avoid contaminating the soil sample which may result to fault analysis, interpretation and conclu­sion. Tie the sample to avoid spilling.
• Finally, write all information about sampling area on soil sampling card or paper and stick the card or paper on the outside of the sample. “Avoid putting the paper in the soil directly as it might get wet and erase the information written on it.”

Step 3: Prepare a composite sample

• Mix the sub-samples thoroughly in a clean plastic bucket.
• Remove stones, roots or large de­bris.
• Place about 0.5 to 1kg of the mixed soil into a labelled sample bag.

Step 4: Label the sample and this includes:

• Farmer’s name and PIN.
• Plot or field name/number.
• GPS coordinates (if available).
• Date of sampling.
• Depth of sample.
• Crop history and management notes.

Step 5: Submit sample to the lab­oratory

• Send the sample to a certified soil testing laboratory as soon as pos­sible (Malkerns Research Station, Mhlume Laboratory and Triomf Laboratory Near Matsapha Airport)

If delayed, air-dry the sample in the shade before sending.