Excess application of commercial and organic fertilizer is harmful to crops and can reduce the desired crop yield by half, experts say.
According to Crop Nutrition Lab Agronomist Karanja Kiiru, excess fertilizer supplies the soil with unnecessary nutrients that may block the absorption of key elements and encourage pest attacks.
“It is false to think that the more the fertilizer 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.
Molybdenum is one of the eight ‘minor’ elements essential for plant growth. It transforms nitrogen in plants into amino acids. In legumes, it enables nitrogen fixation, leading to greater yields, while in non-legume crops, it enables plants to use nitrates absorbed from the soil.
Without enough Molybdenum, plants cannot efficiently reduce nitrates to ammonium for incorporation into amino acids. Instead, nitrates accumulate in the leaves, causing the edges of the leaves to become scorched or burnt from the buildup of the unused nitrates.
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Kiiru adds that farmers should regularly test their soils to know the elements that are missing to fix them or the crop to be grown in the next season.
“Farmers stand to save about 40 percent of the total production cost by only testing the soil. They will not buy fertilizers supplying elements that are already in excess. Besides, the cost of dealing with pests and related diseases will not be incurred,” Kiiru added.
According to a report by AGRA-Alliance, acidity levels in most farms in Kenya are higher as a result of the continuous use of fertilizer.
Most Kenyan farmers use fertilizers without regard for soil type and status. While some are unaware of the importance of knowing the status of their soils, others lament the high cost of testing.
A sample of soil tests at the national laboratory goes for Sh1,500, but a farmer requires about three sample tests from different points of the farm.
