Based on an interview of Dr. Sahota by Peter Reschke; published in Ontario Farmer, February 19, 2013, Production Section, Page: B3.
When U.S. corn growing champion David Hula mentioned during a recent speech at a DuPont Pioneer high yield awards dinner in Stratford that he routinely includes sulphur, zinc and boron in his starter it was just what Dr. Tarlok Singh Sahota wanted to hear. The research manager at the Thunder Bay Research Station has been seeing the benefits of micronutrient applications in his plots for some time. Based on his observations, boron is becoming more deficient in soils, especially where more potassium and nitrogen fertilizer is used. Asked for his experience with crop response to boron, Sahota says producers should include boron in their soil test and, if the test is lower than one ppm, apply the micronutrient. “We have been doing this at Thunder Bay for years now and found beneficial results both on-station and on farms.”
Sahota says growers need to look beyond N, P and K when planning their fertility program. Canola growers are recognizing the importance of having sulphur in their program and boron may be the next nutrient to require attention. He says corn producers should focus on sulphur, zinc and boron.
While he admits that boron soil tests aren’t always reliable, Sahota says shortages will show up in the crop. For example, in alfalfa the top internodes will become shorter and the top leaves may become rusty in appearance. Those symptoms may not be apparent in corn but the crop may still suffer from so-called ‘hidden hunger’. While such crops may not show deficiency symptoms, there will be a yield impact, he says. In a dry year unfilled cob tops could point towards boron deficiency, he says. Tissue tests will tell the story but, at that time, it’s too late to make corrections. Sahota says having less than 20 ppm of boron in the upper third of the alfalfa plant at harvest or if the leaf opposite to the corn ear at silking has less than two ppm of boron, the crops would be considered deficient.
Sahota says boron availability is restricted in dry weather. If the soil has sufficient boron, a rain will fix the situation. “For example, an alfalfa crop with shorter internodes will outgrow that stage after a good rain; the new internodes will be of normal length though the older shorter internodes will remain short.” But if the rain is particularly heavy, boron may also leach from the soil, especially in sandy soils. Those soils are more likely to show deficiencies, he says. Most of the boron in soils is bound by the organic matter and released as that organic matter decomposes. Soils with between one and five ppm boron are considered adequate in boron, he says.
Sahota’s recommendation for boron application is to add one kilogram of actual boron per hectare. “But we have applied higher amounts (up to 2.25 kg/ ha) advantageously.” While there is concern about boron toxicity, Sahota says he’s only seen that situation in textbooks. Still, he warns against over-application. In a low or deficient soil, one kilo per hectare may not be enough, he says.
Boron is also affected by soil pH, Sahota explains. It’s more available in acidic soils but that increased solubility also means it’s more likely to leach away in lower pH situations. “Liming of the acidic soils to improve soil pH could restrict boron availability,” he says. The most boron-responsive crops are alfalfa, sugarbeet, cauliflower and celery. Tomato, cabbage, carrots, clover, lettuce and radish would be in the medium category, while corn, cereals, pasture grasses, potato, soybean and blueberries are less responsive. But, if boron is low in the soil, even these crops will respond well to an application, he says.