Why Fertilizer Timing Matters as Much as What Farmers Apply

For many Kenyan farmers, fertilizer is one of the largest investments made before a crop reaches the market.

Yet putting more nutrients into the soil does not necessarily translate into higher yields if those nutrients are applied at the wrong time, in the wrong quantities or without considering the condition of the soil.

The issue came into focus at the Agitech Grand Expo in Mwea, where agricultural input suppliers and crop specialists discussed some of the challenges facing farmers as they seek to improve yields while keeping production costs under control.

Speaking to AgriMachinery Africa at the event, Grace Njambi, Technical Sales Representative at Unifert Kenya, highlighted what she described as a common mistake among farmers: applying several fertilizer products at once in the belief that the crop will utilise all the nutrients throughout its growing cycle.

“There is a reason why most farmers end up losing a lot of money with fertilizers. It’s because they want to mix all the fertilizers and apply them all at once, whereas the crop only needs specific nutrients at specific stages,” Njambi explained.

Matching Nutrients to Crop Growth Stages

Crop nutrient requirements change as plants move from establishment to vegetative growth and eventually into reproductive and yield-forming stages.

According to Njambi, phosphorus is particularly important during the early stages because of its role in root development and crop establishment. As the plant moves into vigorous vegetative growth, nitrogen becomes increasingly important for supporting leaf and plant development.

During reproductive and fruiting stages, crops require a more balanced supply of nutrients, including nitrogen, phosphorus and potassium. The timing of these applications therefore becomes an important part of ensuring that nutrients are available when crop demand is increasing.

Njambi said applying large quantities of different nutrients at planting can result in inefficient use of some of those inputs.

“The crop will not take the nitrogen and potassium that the farmer incorporated into the soil at planting. By the time the plant reaches the fruiting stage, it shows deficiencies because the nitrogen that was applied earlier has been swept away by rain or leached down through the soil,” she said.

For farmers, the consequence can be another round of spending when nutrient deficiencies appear later in the season. What initially looks like a fertilizer investment can therefore become a cycle of additional applications if nutrient management is not matched to crop development.

The Economics of Better Fertilizer Management

Fertilizer efficiency is becoming increasingly important as farmers manage rising production costs.

The objective is not necessarily to apply more fertilizer, but to ensure that the nutrients being purchased are available to the crop when they can contribute most effectively to growth and yield formation.

This makes crop nutrition an economic issue as much as an agronomic one. A farmer may invest heavily in fertilizer at the beginning of a season, but if nutrients are lost or become unavailable before the crop reaches a critical growth stage, the return on that investment can be reduced.

For commercial producers, this calculation extends across the entire production system, including seed, labour, machinery, irrigation, crop protection and harvesting. Improving nutrient-use efficiency can therefore become part of a broader effort to control the cost of producing each tonne of crop.

Mwea’s Potassium Challenge

The issue is particularly relevant in Mwea, one of Kenya’s most important rice-growing regions, where intensive cultivation creates a continuing need for effective soil nutrient management.

According to Njambi, potassium deficiency is among the major nutrient challenges she encounters among farmers in the region.

“One of the major element deficiencies farmers in Mwea are facing is potassium,” she said.

Potassium supports several important plant functions, including water regulation, plant strength and stress tolerance.

Adequate potassium nutrition is also important as crops move towards yield formation.

Njambi said Unifert supplies Muriate of Potash (MOP), containing approximately 60–62% potassium oxide, as one of the fertilizer options available to farmers seeking to address potassium requirements.

However, the wider issue extends beyond a single nutrient. Farmers need to understand the specific requirements of their crops and soils rather than assuming that the same fertilizer programme will produce the same results across different fields.

Looking Beyond Nitrogen, Phosphorus and Potassium

Fertilizer programmes have traditionally focused heavily on the three primary nutrients — nitrogen, phosphorus and potassium.

But crop nutrition extends beyond NPK.

Njambi pointed to zinc and magnesium among the other nutrients that farmers need to consider when assessing crop performance.

Deficiencies in secondary and micronutrients may receive less attention than nitrogen or phosphorus, but they can nevertheless affect crop development.

The issue becomes particularly relevant under intensive cultivation, where nutrients are continuously removed from fields through harvested crops.

A planting fertilizer that provides the major nutrients may not necessarily address every nutrient requirement of a particular crop or soil.

This has contributed to growing interest in blended fertilizers that combine major nutrients with secondary and micronutrients.

Njambi said Unifert’s Uni Planting is one example, combining NPK with trace elements to support crop establishment.

Why Soil Analysis Matters

The discussion in Mwea also highlights a fundamental principle of modern crop nutrition: fertilizer programmes should be based on the needs of the crop and the condition of the soil.

Two farms growing the same crop can have very different nutrient requirements because of differences in soil type, previous cropping history, irrigation, rainfall, organic matter and nutrient removal.

This makes soil testing an important tool for determining what nutrients are already available and where deficiencies may exist.

Instead of simply asking which fertilizer is best, farmers can increasingly ask a more useful question: what does my soil need, and when does my crop need it?

That shift can help farmers move away from blanket applications and towards nutrient-management programmes that respond to actual field conditions.

From Fertilizer Application to Precision Crop Nutrition

Precision agriculture is often associated with GPS-guided machinery, drones, sensors and digital farm-management systems.

But precision can also begin with something much more fundamental: applying the right nutrient at the right time and in the right quantity.

For farmers, this can mean dividing fertilizer applications according to crop growth stages rather than attempting to supply the entire nutrient requirement in a single operation.

It can also mean identifying soil deficiencies and selecting fertilizer products accordingly, rather than relying on a standard programme season after season.

The approach is particularly relevant as farmers seek to increase production without allowing input costs to rise at the same pace.

Getting More From Every Hectare

Kenya’s farmers are under pressure to produce more from existing agricultural land while managing fertilizer costs, changing weather conditions and increasing demand for food.

Better crop nutrition will not solve all of these challenges. But ensuring that fertilizer investments translate into effective nutrient availability is an important part of improving farm productivity.

The discussion at Agitech in Mwea points towards a broader shift in thinking: fertilizer should not simply be viewed as an input applied to the field, but as part of a crop-management strategy that follows the plant through its different stages of development.

For farmers, that means paying closer attention to soil conditions, crop growth stages and nutrient requirements rather than relying solely on blanket fertilizer applications.

Ultimately, the objective is not simply to put more fertilizer into the soil.

It is to make every kilogram of fertilizer work harder for the farmer.

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• Kenya Withdraws 77 Pesticides from Market in Major Agricultural Reform

Martin Blessing

Martin is a writer at Agrimachinery Africa specializing in agricultural machinery, mechanization trends, and farm technology across Africa. His work focuses on tractors, harvesting equipment, irrigation systems, and emerging innovations helping farmers improve productivity and efficiency. Through in-depth industry coverage, he highlights technologies shaping the future of modern agriculture.