Farmers can easily tell the type of soils in their farms by simply observing the type of weeds that grow in it.
This is a cost -free and accurate method of soil sampling that can save farmers from hefty laboratory test costs, while still allowing them to determine the kinds of crops to grow.
According to several studies conducted by reputable farming agencies including the Garderner and ICRAF, weeds indicate the acidity or alkalinity of soils hence making it easier for a farmer to identify the kinds of crops that can be grown on them. Weeds can also give a hint on soil fertility, soil drainage and moisture levels in the soils.
A study conducted by Diana Barker, a soil sampling expert and published in the Gardener, shows that most prevalent types of weeds that grow in an area for a long time, tell the soil composition with an accuracy of 8 out of 10. The study, for instance, reveals that the Dandelion and Common Mullein weeds both indicate an acidic soil, but Common Mullein can also mean a low fertility soil. So, if you see the weed growing alone, it could mean a number of things, but when it grows along dandelions, this is a likely indication of an acidic soil.
The researcher also advices farmers to pay attention to the health of the weed while studying their soils. For example, a healthy stand of clover weed can be an indication of nitrogen deficiency in soil, while the same weed will grow in soil that had sufficient nitrogen, but will appear much less vigorous. The study, however, explains that some weeds like Purple Nettle and Shepherd’s purse can grow in most soil types and so are not reliable indicators.
Soils with a PH value of below 7 are deemed acidic. According to the study, weeds like Eastern Bracken, English Daisy, Ox-eye Daisy, Hawk Weed, Pineapple Weed, Wild Strawberries, Mayweed, Dandelion, Knapweeds, Pinks, plantains and Wild Radish are an indication of acidic soils. This means that if a farmer spots any of these weeds he can plant crops that do well in acidic soils including blueberries, endive, hydrangeas, rhododendrons, rhubarb, potatoes, shallots, sweet potatoes, and watermelons. In case the soils have high acid levels, the researcher recommends the addition of wood ash.
Those with a PH value above the neutral 7 are alkaline in nature hence support crops like beets, lettuce, muskmelons, onions, and spinach. The kinds of common weeds likely to grow in alkaline soils, according to the study, include Black Henbane, Nodding Thistle, Goosefoot, Wild Carrot, Field Peppergrass, White Mustard, Bladder Campion and Bellflower. To lower high alkalinity in soils, the expert explains that Sulfur can be added to the soils.
Fertile soils according to the research have a PH value ranging from 6.2 to 7. This, therefore, means that when weeds like Burdock, Butter Print, Fat Hen, Pokeweed, Pigweed, Queen Anne's Lace (Daucus carota) and Chickweed (Stellaria media) are spotted on a farm, soils there are fertile and a good for growing maize, lettuce, melons, peppers, squash, and tomatoes. Consequently, when weeds like Dog fennel, Biennial Wormwood, Broom sedge, Wild Radish, Sheep Sorrel and Yellow Toadflax grow in an area, this can can be an indication of poor or depleted soil. Beans, beets, carrots, legumes, parsnips, peas, radishes, sage, and thyme have tendency to tolerate poor soil conditions.
Weeds like Ox-Eye, Docks, , Goldenrods, Groundnut, Poison Hemlock, Horsetail, Jewelweed, Joe-pye weed, Lady’s thumb, Marsh Mallow, May apple, Meadow pink ,Meadow Sweet, Mosses,Stinging Nettles,Pennsylvania smartweed, Ragwort, Tansy, Sheep sorrel, Silvery cinquefoil, Sweet flag and Tall buttercup grow in wet soils while Arrow-leafed Wild, Field Bindweed, White Cockle, Cornflower, Dog Fennel, Goldenrods, Maltese Thistle, Sandbur, Small Nettle, and Yellow Toadflax grow in sand soils.
The observation of weeds as means to determine soil type is good news to millions of farmers across the world who cannot afford the high costs attached to professional soil sampling. It is expected to go a long way helping farmers identify suitable crops to grow in their farms especially at a time when a lack of key farming knowledge is blamed for poor produce, especially by small holder farmers who make up to 70 per cent of farmers in the world, according to a 2013 FAO report.