By Francis Ndungu
Joel Kibuthua will, this month, finish a short season where he has harvested 100 crates of tomatoes from ¼ acre, compared with 20 crates before, following a soil test that drove him to rapid soil surgery and an immediate transformation in his farm.
As one of 7,000 Nyeri farmers offered free soil training by the National Agricultural Value Chain Development Project (NAVCDP), Joel leapt on the idea and took a soil sample from his fields to the KALRO labs for testing.
“After 21 days, the lab test was out ready to be collected. The result showed my soil had a pH of 2.5, which is very acidic. Chemical residues were also part of the findings, which was said to interfere with the soil microorganisms, and fusarium wilt, a fungal disease, dominated my soil,” said Joel.
“After the soil testing was when I realised the reason why my tomatoes wilted prematurely. I was told the fusarium wilt was a soil-borne disease that attacked leguminous crops. The disease was a major threat to my crops since it caused wilting in my french beans causing losses. I was advised to do crop rotation with non leguminous crops so as to break their stages and treat organic manures before applying them to my crops to kill soil borne fungi and bacteria,” said Joel.
He also set about solving his soil acidity and the other problems revealed. He stopped using diammonium phosphate (DAP) fertiliser, which had contributed to the phosphorus buildup making his soil too acidic. Instead, he switched to NPK fertiliser and applied lime to neutralize the acidity. He also transitioned to organic pest control to eliminate the chemical residues that were harming his soil health.
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Said agronomist Alex Maine: “Different crops require different soil pH levels. For example, coffee thrives in acidic soils, while potatoes do better in neutral conditions.” Long-term use of the wrong fertilizers, excessive chemical application, and continuous planting of the same crops without rotation can disrupt soil balance, leading to poor yields.
In Nyeri, experts estimate that acidic soils with poor nutrients have reduced yields to one tenth of their healthy level, which is what prompted the soil training drive by NAVCDP. Its aim is to increase farmers’ output in the area by at least 70 percent.
The nutrient deficiencies it’s trying to address include nitrogen deficiency, which causes older leaves to turn yellow from the tip downward, and phosphorus deficiency, which results in purplish or reddish discoloration.
Potassium shortages also cause leaf signs, creating yellowing along leaf edges, while molybdenum deficiency leads to leaf curling.
All these deficiencies can be corrected by using organic animal manures and foliar fertilisers.
Joel used foliage fertilisers for the boran and zinc deficiencies that were found, and also introduced legume intercropping to help fix his phosphorus deficiency.
Yet, despite the radical change in yields when degraded soil is corrected, the adoption of soil testing remains low, said Alex.
“Some farmers dismiss it as expensive, while others struggle with the transition from subsistence to commercial farming. Many farmers don’t attend soil testing training sessions, citing other commitments. The involvement of county government agencies in decision-making also slows the process,” he said.
However, Joel reports that his own farm is now completely changed.
“I never knew crops could communicate. Now, I understand that discoloration and stunted growth are signs of soil imbalance. Since implementing the recommended changes, my farm has transformed, and I expect even better results in the coming seasons,” he said.