Is boron deficiency a problem for crops in Minnesota?

Signs of boron toxicity in soybeans. Boron toxicity can also be an issue, so be cautious if you're considering applying boron fertilizer. (Image credit: Dan Kaiser/University of Minnesota Extension)

By: Dan Kaiser, Extension soil fertility specialist

Boron (B) is a micronutrient needed in small quantities by crops. Since the need for the nutrient is low, there have not been recommendations for boron fertilizer application in most crops across Minnesota. Based on tissue sampling results, some say boron fertilizer is needed to maximize yields for some crops. However, the data indicating what a good versus a bad plant tissue concentration is across most of the Corn Belt is lacking as boron deficiencies are not widespread. Without a deficiency, it is very difficult to generate sufficiency levels in plant tissue samples.

Alfalfa

Boron deficiency for alfalfa has previously been identified in Minnesota. Alfalfa is much more sensitive to boron deficiencies than other crops. However, it is unlikely that your alfalfa is deficient in boron unless it is grown on sandy soil, organic matter concentrations are low, and the soil is dry.

Corn

A three-year study funded by the Agricultural Fertilizer Research and Education Council (AFREC) that ended in 2018 studied the impact of boron on corn. Nine irrigated and nine non-irrigated locations were established over three growing seasons. Boron was broadcast at 3 lbs per acre at all locations. Average corn grain yield was the same for strips with or without boron applied. Corn leaf samples were collected at all locations and boron tissue concentration as low as 4 ppm without an increase in yield. Based on the data collected, we could not establish a lower limit to a tissue boron concentration sufficiency range. It was clear though that the need for boron is not as widespread as has been reported in recent years. 

The data shown in the above chart come from 9 irrigated and 9 non-irrigated locations from 2016-2018. The data show leaf boron (B) concentration at the V10 corn growth stage and grain yield adjusted to 15.5% moisture.

Sugarbeet

Research was conducted on sugarbeet and results were similar to corn, with one exception. Sugarbeet tonnage decreased at a few of the locations with increased boron application rate. All sites were located on higher clay, higher organic matter soils which we suspected would not require additional boron. I have been sent pictures of potential sugarbeet boron deficiency in the past few years but most of those came from sandier soils in dry areas of the state. While it is possible for boron to increase yield, the decision to apply should be made on a site-by-site basis. In conversations with crop consultants across the state, some have been applying boron on sandy soils with what they think are positive results.

Soybean and dry bean

Soybean and dry beans are highly sensitive to boron toxicity so boron fertilizer application should be avoided. Multiple soybean research trials were conducted in Minnesota and we found that yield was not increased in most sites, while yield was actually decreased in a few sites. I have also encountered boron toxicity symptoms in dry bean following a foliar application of boron fertilizer. Reports of low boron in soybean or dry bean plants from tissue samples on sandy soils have come up in years past. There is not enough evidence to support application of boron for soybeans or dry beans and plant tissue tests are not a reliable indicator of a true deficiency in boron for these crops.

Boron toxicity

Outside of sandy soils, boron is not likely to be deficient and need fertilizer applied. Be careful if you are thinking about applying boron as some crops are highly sensitive to boron toxicity. Too much boron fertilizer can reduce yields in soybean and dry beans. Knowing the risks and rewards for application is important to ensure boron fertilizer application benefits you.

Learn more about boron for Minnesota soils at z.umn.edu/boron

Information for this post was provided through research funded by:

• Minnesota’s Agricultural Fertilizer and Education Council (AFREC)
• The Sugarbeet Research and Education Board of Minnesota and North Dakota 
• The Minnesota Soybean Research and Promotion Council 

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This article was first published in August 2020.