Charcoal and sawdust keep my crops healthy

The two greenhouses measuring 22 by 72 metres each on the outskirts of Nyeri Town are full of lush crops. On one side of the greenhouses are capsicum plants and on the other spinach.

Both crops are flourishing, making many visitors ask the owner of the farm, Grace Githaiga, about her secret.

The secret lies in strange quarters as we came to learn. Grace applies in her farms charcoal dust, sawdust, organic manure and fertiliser after every three planting seasons, an art of farming she says helps her to grow healthy vegetables and reduces costs by nearly half.

When Seeds of Gold met Grace recently, she had just arrived at her farm from a market in Nyeri where she had gone to supply vegetables to traders.

This was her third week of harvest. Grace walked to a tap outside one of the greenhouses, opened it and let water flow to the plants. She uses drip irrigation, which helps control the amount of water the crops get.

“I use sawdust to retain moisture in the soil and the charcoal dust to keep diseases and pests at bay. I mix the two with manure and apply on the farm a week before I plant,” says Grace, who learned the art from agricultural officers at Wambugu Agricultural Training Centre in Nyeri.

She then adds DAP fertiliser a week after planting. But the fertiliser is in much smaller quantities because of the manure use.

“This helps the crops, particularly, spinach to grow very first. I normally start harvesting in about a month.”

“Spinach grows fast because it absorbs plenty of water from the soil and there is enough circulation of air. Capsicum matures in about two to three months,” the farmer, who has erected her two greenhouses on part of her quarter acre, says.

Prof Mary Obukutsa, Head of Horticulture Department at the Jomo Kenyatta University of Agriculture and Technology, says charcoal has carbon that makes soil more fertile.

“There is scientific evidence that when charcoal is applied to soils, it significantly increases crop yields and improves soil fertility. Charcoal dust also helps in decreasing nutrient loss through leaching by percolating water,” she notes.

“The pores in charcoal provide a suitable habitat for many micro-organisms by protecting them from predation and drying.”

FINISHED COMPOST

The organisms are important in processing rich compost manure. According to the don, charcoal increases Cation Exchange Capacity, a factor that influences soil fertility by increasing the ability of the soil to retain nutrients so that they are not washed away by water.

Prof Obukutsa further observes that adding small amounts of sawdust to the soil increases organic matter and improves texture.

“Sawdust takes time to decompose, thus, it works well in moist, heavy soils like clay. Sawdust also acts as a bulking agent, allowing air into the soil. It takes approximately a year to transform raw sawdust into finished compost.”

She adds that sawdust, especially from hardwood trees like walnut, acts as a natural weed killer and keeps away pests because of its acidifying effect on the soil. It is also good choice for mulching. Mixing charcoal, sawdust and organic manure makes the three complement each other and optimise the benefits, according to the expert.

Charcoal will help to increase the pH, which is normally reduced by sawdust to levels that are optimal for nutrient availability.

“Mixing manure with sawdust reduces the effects of the latter on nitrogen depletion in the soil as it decomposes. To reduce these effects, it is recommended that you let the sawdust simmer in the compost pile for some time before using it in the garden,” she offers.

The three materials further improve soil structure and aeration leading to increased nutrient uptake and good root development.

Grace started her agribusiness in 2011 after investing Sh640,000, part of which was her savings while her husband provided the rest. She was working as a secretary at Pamki Coffee Farm (previously Kyanyange Coffee Farm) in Nyeri before she resigned go into farming.

The method of farming has helped her cut costs. 

“I do not spend a lot of water to irrigate my farm since the charcoal dust and sawdust help to retain moisture in the soil. Before I started this method of farming, I would spend up to Sh6,000 per month on water. I now spend Sh2,500 on water bills and Sh3,500 to buy fertiliser, manure, sawdust. I rarely spray the crops with pesticides because they are not attacked.”

She gets the charcoal dust from dealers in Nyeri Town, which she mixes with manure and saw dust in the ratio of 1:1:1. She measures the ingredients in a 20-litre bucket.

For her two greenhouses, the farmer uses about five 90kg bags of each of three materials.

“But I also apply inorganic fertiliser to enhance growth of the crops since it helps to increase nutrients in the soil that manure does not have.”

She harvests 70 to 80kg of capsicum and 60 to 75kg of spinach twice a week. She sells a kilo of capsicum for Sh40 at wholesale price, while a kilo of spinach at Sh50. This brings her earnings to about Sh50,000, much more than what she used to earn when she was employed.

Grace practises crop rotation, where she replaces capsicum or spinach with tomatoes. Last season, she planted tomatoes and was harvesting five to seven crates of tomatoes per week.