Agronomist's notebook: To reap long from the soil, work with it

Saturday December 15 2018

A researcher collects samples of soil from a farm, for testing.

A researcher collects samples of soil from a farm, for testing. Most of soil pollutants originate from human activities such as unsustainable farming practices, industrial effluents and mining, among others. FILE PHOTO | NMG  

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Soil is the basis of farming, yet a number of farmers, both who keep livestock and grow crops, do not take good care of it.

The importance of soil cannot be understated as it feeds plants, which subsequently feed animals and human beings.

Most farmers neglect soil mostly because it does not indicate stress directly unlike animals and plants that show physical symptoms.

The World Soil Day was marked on December 5 and the main aim of the celebrations was to raise awareness on the importance of stopping soil pollution.

The pollution is a worldwide problem that degrades the resource, the food we eat, the water we drink and the air we breathe.

Most of the soil pollutants originate from human activities such as unsustainable farming practices, industrial effluents and mining, among others.

In the agricultural sector, heavy use of chemicals such as pesticides have resulted in the presence of organic pollutants.

In my daily routine as an agronomist, I encounter farmers misusing chemicals in many ways. A good number use wrong chemical to control a specific pest and diseases and others improperly dispose empty containers.

Majority of the farmers do not have a soak pit where all the chemical residues should drain into, which means the spillovers drain into the soil. Excessive use of fertilisers also results in soil pollution.

Use of contaminated water for irrigation further plays a significant role in polluting the soil.

Soil rich in nutrients is fertile, and supports the plants to take nutrients out of it. To replace the nutrients, however, fertilisation is critical.

But most farmers excessively use inorganic fertilisers resulting to soil acidification or alkalinity due to a decrease in organic matter in the soil.

To have healthy soils, farmers should avoid the excessive use of chemicals by practising integrated pest and disease management, which is a combination of cultural, mechanical, biological or chemical methods.


This, therefore, means that chemicals should always be the last option. It's ideal also for the farmer to observe the pre-harvest interval (PHI) of the chemicals to avoid the excessive use of it.

PHI is the time that must lapse after spraying the chemical and before the produce is harvested. Each active ingredient in a chemical has its own PHI.

Spraying another chemical before this period has elapsed results to toxicity in the soil due to the over use of chemicals and mixing different active ingredients at the same time.

While using chemicals, ensure that they are registered with the regulatory bodies such as Pest Control Products Board because poor quality or fake chemicals affect the soil more.

The farmer should also read the chemical label, including the environmental hazard section, carefully. This helps to create awareness on the effect of the chemical you are using.

Chemical bottles should be properly disposed of by ensuring they are all perforated to avoid their reuse.

Also, the mixing point should have a soak pit and running water to ensure that the chemicals are well-diluted hence harmless to the soil and any spillovers don’t end up in the soil.

The use of organic fertiliser plays a significant role in preventing the excessive use of chemicals, which leads to soil pollution.

Farmers should, therefore, embrace conservation agriculture to minimise the disruption of the soil structure, its components and biodiversity. This will help to maintain minerals and moisture within the soil and stop erosion.

Conservation agriculture is achieved by practising minimum tillage, intercropping where different crop species are grown simultaneously, crop rotation and keeping the soil covered as much as possible.

In conclusion, for you to reap big from the soil and for long, work with it and not against it.


Your questions

I’m writing in regard to a bulb onion story that you featured in this section. I have a parcel of land in Kipsitet, Kericho and I have always wanted to grow bulb onions.

Your article encouraged me more. I’m not quite sure about the season, but is it fine if I do before end of the year?

Dekoech Ibrah

Before venturing into onion farming, you need to plan and consider the following factors:
• Variety
• Market demand and preferences.
• Weather condition due to climatic changes.
• Capital.
It is also important to do a soil test before planting to determine the nutritional status and the requirements.


I am interested in growing onions in Gem, Siaya County. Please advise on the following: varieties, rainfall availability, market and cost of production.


Onion size and market depends with your target consumer. Market women mostly prefer the small to medium sized bulbs while restaurants and hotels go for big bulb onions.

There are no specific varieties of onions adaptable for a particular region however management practices determine the yields to be obtained.

Most of the varieties will take 3-4 months after transplanting. If the rainfall is reliable, you can do adequate planning and plant when there is rain. The cost of irrigation is quite high compared to the reliance on rain.