Excess fertiliser application may cut by half farmer's crop harvest

Adding more commercial and organic fertiliser may cut by half the season harvest due to accumulation of ‘unnecessary’ nutrients in the soil that lead to poor performance of crops.

Crop Nutrition Lab Agronomist Karanja Kiiru said excess nutrients lead to blockage of absorption of other essential elements besides encouraging pest attack.

“It is false to think that the more the fertiliser applied, the more the yields. Excess application of farm yard manure for instance leads to accumulation of nitrogen, which suppresses other crucial elements from being accessed by crops for example molybdenum,” he said.

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The agronomist said farmers must regularly test soils to know the composition of nutrients. This will dictate the elements one will require to add or the crop to grow the following season to “flash out the imbalance”.

Excess elements like nitrogen from farm manure encourage pest attacks to crops.

“Farmers stand to save about 40 per cent of the total production cost by only testing the soil. They will not buy fertilisers supplying elements, which are already in excess. Besides, the cost of dealing with pests and related diseases will not be incurred,” Kiiru said.

READ ALSO: Mobile soil testing kits salvage Western Kenya soils

Half harvests

Patrick Njenga, a Kiambu County farmer harvested 22 110kg bags of Irish potatoes from a three quarter acre after the first season.

The second season, the yield dropped to 21 110kg even after adding three tonnes of animal manure as well as 150kg commercial fertiliser. He repeated the same in the third season and the harvest dwindled further instead of going up. The quality of the tubers was also dismal. 

Kiiru carried out soil testing for Njenga and in consultation with a crop pathologist, they found that fusarium wilt was setting in because of the repeated use of the same planting materials.

Nitrogen was also in excess.

“He asked me to use clean planting materials as well as add gypsum (acid neutraliser) to the soil. I used one tonne of manure and 50 kg of commercial fertiliser in my third planting. The harvest rose from the 21, and 22 to 41 bags,” Njenga said.

READ ALSO: Farmers record doubled yields with nitrogen fixing fertilizer

Cost of analysis

Crop Nutrition Lab offers basic soil testing at a Sh2,500. Complete analysis costs Sh5,000.

Basic testing entails analysis of soil PH and the major elements such as potassium, sulphur, phosphorus, calcium, nitrogen as well as organic matter.

Complete test involves detailed analysis of the elements such as iron, manganese, boron, copper, zinc and their presence ratio. An example is the calcium-nitrogen ratio.

Based on the outcome, the farmer is advised on the steps to take to realise the desired results.

In the photo: Amiran Kenya Agronomist Wycliffe Obwoge examines farmyard manure at Karen, Nairobi on April 19, 2016. PHOTO BY LABAN ROBERT

Kiiru can be reached on +254737576066

Crop Nutrition Lab can be reached on +254720639933 or This email address is being protected from spambots. You need JavaScript enabled to view it.