Healthy crops start from the ground up — literally. Before you decide what to plant, it’s important to understand the condition of your soil. Just like you wouldn’t start a long journey without checking your vehicle, you shouldn’t begin your planting season without knowing what’s happening beneath the surface. Soil testing is your “soil health check-up,” and it can make the difference between an average harvest and a thriving, abundant one.

Why test your soil before deciding what to plant?

Every soil is unique, and what grows beautifully in one place might struggle just a few kilometres away. Testing your soil helps you:

• Choose crops that are best suited for your conditions.
• Avoid wasting time and resources on plants that won’t thrive.
• Understand exactly what your soil needs to become more productive.

Planting without testing is like cooking without tasting; you won’t know if something is missing until it’s too late.

What do you test for?

A good soil test looks at several key factors:

• Soil texture – the proportion of clay, silt, and sand in your soil.
• pH level – how acidic or alkaline your soil is.
• Macronutrients – especially nitrogen (N), phosphorus (P), and potassium (K).
• Micronutrients – such as zinc, iron, manganese, and copper, which plants need in small but crucial amounts.

What does your soil texture tell you?

A soil texture triangle showing the proportions of sand, silt, and clay in different soils.

Your soil texture is simply the mix of sand, silt, and clay. This mix affects how much water your soil can hold, how quickly it drains, and how well it retains nutrients for your crops.

Here’s what it means for you:

Sandy soils – feel gritty, drain water fast, and lose nutrients quickly.

• Good for crops like watermelons, onions, or groundnuts that don’t like “wet feet.”
• Not good for cabbage or sukuma wiki unless you improve it with compost to hold water.

Clay soils – feel sticky when wet, hold a lot of water, and can become very hard when dry.

• Good for rice in paddies, which likes constant water.
• Not good for carrots or sweet potatoes, which need loose soil for their roots to grow well.

Silty soils – feel smooth, hold water and nutrients better than sand, but can get compacted.

• Good for maize and beans if mixed with loose organic matter.
• Can be bad for root crops if it becomes too hard after rain.

Rocky soils – drain very fast and have little space for roots.

• Only good for hardy crops like cassava, unless improved with compost and topsoil.

Why do you need an expert?

Even if your neighbour’s maize is doing well, your soil might be completely different. An agronomist or agricultural extension officer can test your soil and explain exactly how to manage its texture. They can show you:

• Which crops will do best in your soil.
• How to prepare your land so plants grow strong.
• How to avoid wasting money on seeds and fertiliser that won’t work for your soil type.

Remember: Guessing can lead to poor harvests — but getting the right advice can turn your soil into a source of steady, healthy crops.

Why does pH affect your crop?

The pH of your soil is a measure of how acidic or alkaline it is.

• A pH of 7 is neutral.
• Below 7 is acidic.
• Above 7 is alkaline.

The pH affects how easily your plants can take up nutrients from the soil. Even if nutrients are there, the plant roots may not be able to absorb them if the pH is too high or too low.

Nutrient availability at different pH levels

• Acidic soils (below 5.5) – Phosphorus becomes less available; aluminium and manganese can become too high and harm plants.
• Neutral soils (6.0–7.0) – Most nutrients are available; best range for most crops.
• Alkaline soils (above 7.5) – Iron, zinc, and manganese become less available, leading to yellow leaves and poor growth.

Crops and their preferred pH ranges

Expert tip: An agronomist can test your soil’s pH and advise you on the best way to correct it or help you choose crops that will thrive in your current soil conditions. This means you can get good yields even before making big soil changes.

Does your soil already have Nitrogen, Phosphorus, and Potassium?

When your soil is tested, one of the main things you’ll learn is whether it has enough of the three big nutrients that plants need most. Farmers call them NPK:

N = Nitrogen – makes plants grow green and leafy.

• If missing: leaves turn yellow, and plants grow slowly.
• Example: Maize will have pale leaves and small cobs.

P = Phosphorus – helps plants grow strong roots, produce flowers and seeds.

• If missing: plants are stunted, and leaves may turn purple.
• Example: Beans will have poor germination and low pod production.

K = Potassium – keeps plants healthy, strong, and resistant to diseases.

• If missing: leaf edges turn brown or yellow, and plants are weak.
• Example: Bananas will have small bunches and may get sick easily.

Plants need different nutrients at different stages

Just like people, plants have different needs at different times of life:

• Germination stage – needs more phosphorus to help roots develop.
• Vegetative stage (lots of leaves and stems growing) – needs more nitrogen for green growth.
• Flowering and fruiting stage – needs more potassium to produce strong flowers, fruits, or seeds.
• Senile stage (end of life) – nutrient demand is lower, as the plant is finishing its cycle.

Knowing these stages helps you feed your plants at the right time for maximum yield — but this is a topic for another conversation.

Why test for NPK?

If you don’t know what your soil already has, you may spend money on fertiliser your soil doesn’t need — or miss adding what it does need. For example:

• If your soil already has enough nitrogen, adding more may only make plants grow leaves but not produce well.
• If phosphorus is missing, seeds may sprout slowly, and you’ll lose time in the season.

Expert tip – An agronomist can explain your soil test results and advise:

• How much fertiliser or compost to add?
• Which type to use (not all fertilisers have the same mix of N, P, and K).
• How to rotate crops — for example, planting beans or groundnuts to add nitrogen naturally before maize.

Why guessing with fertiliser can harm your farm and the environment

Many farmers add fertiliser every season without knowing what their soil already has. This can cause two problems:

• Wasted money – If your soil already has enough nutrients, extra fertiliser won’t help your crop grow better.
• Pollution – Extra fertiliser can be washed away by rain into rivers, streams, or groundwater. This can harm fish, wildlife, and even drinking water.

Expert tip: A soil test tells you exactly what your soil needs. That way, you can use the right amount of fertiliser at the right time, helping your crops and protecting the environment.

Why are micronutrients important?

Soil tests don’t just check for NPK — they also measure micronutrients. These are nutrients plants need in small amounts, but they are just as important as the big ones. Without them, plants can’t grow properly, even if there is plenty of NPK.

Here are some important micronutrients for your crops:

Calcium (Ca) – helps build strong cell walls and prevents fruit problems.

• If missing: tomatoes and capsicum may get “blossom end rot” (black sunken spots on fruits), cabbage leaves may tip-burn.

Copper (Cu) – helps plants fight diseases and use other nutrients well.

• If missing: leaves may curl or wilt; maize and wheat may be more prone to fungal diseases.

Zinc (Zn) – important for seed germination, root growth, and healthy leaves.

• If missing: maize leaves may have yellow or white stripes, and plants stay short.

Manganese (Mn) – helps in photosynthesis and enzyme activity.

• If missing: leaves may have yellow patches between veins, especially in beans or legumes.

Iron (Fe) – needed for making chlorophyll (the green in leaves).

• If missing: young leaves turn yellow while the veins remain green — common in sukuma wiki and citrus.

Why should you care?

Think of micronutrients like vitamins for people — you don’t need much, but without them, you can’t stay healthy. Some Kenyan soils, especially sandy areas or land farmed for many years without compost or manure, may be poor in certain micronutrients.

Even someone with one acre can benefit from soil testing; it’s not just for big commercial farms. Our experience working with farmers has shown us that crucial best practices are frequently unknown, particularly to small-scale farmers. Many of them spend money on chemical fertilisers they don’t really need, which damages the soil and the environment. We can connect small-scale farmers with experts and access to compost, helping them save money, increase productivity, and preserve the land for future generations

Expert tip: An agronomist can look at your soil test and tell you if you need to add a special fertiliser, foliar spray, lime, or compost to replace missing micronutrients.

From Compost to Crops

In our previous article, we shared how compost can improve soil structure, boost nutrient levels, and encourage healthy plant growth. Compost is an excellent, natural way to correct some of the issues revealed in your soil test — whether it’s improving water retention in sandy soil, adding organic matter to clay soils, or providing slow-release nutrients for long-term fertility.

From results to action

Once your soil is tested, an expert agronomist can help you interpret the results. They’ll recommend the best crops for your soil type, the right amendments to apply, and strategies to maximise productivity — sustainably.

Healthy soil is the foundation of healthy crops. By testing before you plant, you’re not only improving your yields, you’re also protecting your land for the long term.