Preparing for planting season: Have you done a soil test?

With the onset of the rainy season, farmers are either started planting or are busy preparing their land. But due to the literacy level, the vast majority has failed to conduct a soil test on their farmlands to determine the nutritional value of the soil.

Knowledge on soil fertility through soil testing is important because soils can become sick after repeated use. A soil test helps the farmer to determine whether the nutrients present in the soil are in the right proportion to grow healthy crops.

Soil test not only helps the farmer to understand the soils on the farm, it also helps him to deal with the deficiencies and excesses and ensure that the soil nutritional content is correct.

Failure to conduct a soil test before planting usually leads to indiscriminate use of fertilizer by farmers who wrongly assume that the input is the solution to their desire for bumper harvests at all times. What they fail to understand is that different plants require different elements and when certain elements like iron and phosphorous are above their normal levels in the soil, they affect the growth of some crops like cabbage, maize, carrots or even potatoes especially on soils that do not require fertilizers.

 Unfortunately, such ignorant practice usually results in low yields and wasted efforts.

There are several soil tests, which include testing the soil pH. This checks on the acidity of the soil as the pH is a key factor in plant growth and it affects nutrients availability in plants.

When pH is maintained at the proper level for a given plant, nutrients are available at the maximum. Most plants prefer a soil pH of between 6.0-7.0 except for tubers like potatoes, which need a more acidic environment.

SAMPLE SOIL IMMEDIATELY AFTER HARVEST

When sampling, a farmer should divide the area to be sampled into different parts, collecting a minimum of 5-10 samples, then combines them and submits for analysis.

One should avoid sampling very wet soils or soils that have been recently fertilised, and samples should be at least 6-8 inches from the ground level. One should avoid areas of high erosion or those close to trees.

The best time of the year to sample is immediately after a harvest. Soil sampling can also be done during the growing season to help in identifying plant growth problems where soils are sampled when symptoms are present to ascertain the problem and take curative action during the current growing season.

The question on how often sampling should be done depends on individual crops where for perennial plants like the trees, testing should be done prior to planting and once every two to three years.

For annuals such as maize or beans, soils should be tested once every two years. For large-scale farmers who regularly use fertiliser, manure or other soil modifications, testing should be done more frequently to monitor changing soil conditions and prevent the build-up of excess levels of nutrients or salts.

Get the basics

A soil test should analyse the following:

1. The nutritional levels of the soil in terms of nitrogen, phosphorous, potassium, calcium, magnesium, sulphur and iron.

2. Soil pH, that is below 7.0 is acidic, at 7.0 is neutral while above 7.0 has high lime.

3. Organic matter, that is, the nutritional capacity of the soil.

4. The Cation Exchange Capacity. That is the soil’s ability to hold onto essential nutrients and provide a buffer against soil acidification.