Why it’s still not late to carry out a soil test

It is another time of the year when farmers are preparing their farms for the new planting season, with heavy rains expected in next few days.

However, as you plan to plant, the big question is, have you tested your soil? Even as the rains start in some areas, it is still not late to carry out the test before you plant.

Better yields can only be achieved from proper soil management and to do so, a farmer must know the status of their soils.

Now, before you collect a soil sample, you need to answer questions such as what are the benefits of soil analysis? What is the size of the sample and how is it to be collected? Where should I send the samples for analysis and what are expected costs?

Benefits of soil analysis

The soil analysis results informs the farmer of deficiencies or excesses, if any, of minerals. They also advise on the correct type and amount of fertiliser to apply. They also enlighten on the method and time of application of fertiliser.

The information lowers wastage due to application of only the exact amount and hence efficient utilisation of fertiliser.

Over and above these benefits, the farmer increases yields and hence income.

Soil sample size and the sampling method

To take a sample, one requires to have equipment that include an auger (special drilling instrument for this purpose), a bucket, collection bags, labels and a pen. An auger is highly recommended but in its absence, a panga can be used.

To make up one sample, take between 20-25 sub-samples from the entire field in a zigzag pattern, from the soil surface down to a depth of 20cm if one intends to plant shallow rooted crops or 0.5-1m for deep rooted plants.

The uniformity of the soils avoids hot spots such as anthills, manure heaps and crop residue.

When using a panga, dig a hole of the depth specified above. Slide the panga from the top layer to the bottom of the pit biting about an inch or two of soil all the way.

Repeat the exercise for the 25 sites and place the samples in a clean bucket.

Break the soil lumps (clods) and mix the sub-samples well and from the composite, fetch between 500 grammes and a kilogramme.

Place it in a collection bag, seal it and send it to the lab. Depending on the lab, you should get the results within a week.

Record your personal details and attach the form to the sample and send them to the laboratory. Note that the soil sample should not be taken when it is wet and it should also be submitted as soon as possible after collection.

Information to accompany the sample

The information to accompany the sample include your name, postal address, email and or telephone number; your county, sub-county, ward and village.

If you are a member of a cooperative, add its name. Also include the previous crop and the crop you intend to plant; size of the whole farm and size of the sampled field and its name if it has any.

The required tests should also be indicated. The tests could be fertility tests where macro-elements such nitrogen, phosphorus and potassium (NPK), calcium and magnesium and also micro-elements like manganese, copper, zinc and iron are examined.

Other factors include unfavourable soil characteristics which contribute to plant nutrient uptake and physical characteristics such as pH and soil organic matter.

The tests could also extend to examination of presence of disease causing germs.

Results interpretation

The samples can be delivered by hand or through the many courier firms. There are private and government soil analysis laboratories all giving good results.

All the laboratories not only give the results of the requested tests but also interpret the results and recommend corrective actions.

The charges depend on the test requested. For the fertility test, some laboratories charge between Sh500 and Sh1,300.
Kenya Agricultural and Livestock Research Organisation is one of the places you can take your soil for testing. A sample of the soil is tested at Sh1,000.

Correct sample collection and submission is very important and if one is not sure of his ability, it is better to request the services of an extension officer.

On-farm soil testing

The distances between the soil testing laboratories and the vast agricultural areas could be one of the limiting factors to soil testing?

To bridge this gap, some companies have come up with innovative methods of on-farm soil testing that include mobile laboratories and or specialised kits that one can use on the farm to get the desired results.

However, it is important to note that good kits are not affordable to smallholder farmers unless they pool resources to purchase one. Further, interpretation of results might still require an expert. Some kits might also require power like electricity though solar powered gadgets are also available. The range of tests might also be limited.

***

Dr Mwirigi is the Deputy Principal AHITI Nyahururu & a former Nyandarua ASDSP County Coordinator [email protected]