Nitrogen Fertilization
Dry beans are relatively poor N-fixers, producing less than 45% of their N requirement. Nitrogen uptake rates in dry beans range from 3.9-4.7 lbs N/cwt of seed, meaning a 2000 lbs/ac dry bean crop would require 78-90 lbs N/ac. This nitrogen may come from a combination of residual soil N, biological N fixation and N fertilizer.
As fertilizer nitrogen rate applied increases, nodulation decreases since plants become ‘lazy’ and rely on soil nitrogen alone. In 4 out of 6 on-farm trials, good to excellent nodulation was found to occur when N rates applied were below 70 lbs N/ac. In small-plot trials, nodulation has generally been less than with on-farm trials.
On-farm trial yield responses to different nitrogen rates have been inconsistent. At four trials, there was no yield response to different N rates and at two trials there were opposite responses. At one, the highest rate of N (140 lbs N/ac applied) reduced yield, while at another, the highest rate of N applied (70 lbs N/ac) increased yield. In the first scenario, yield was reduced due to prolonged vegetative growth and delayed maturity. The second scenario occurred in a drought year, where the contribution of mineralized-N was expected to have played less of a role, meaning the crop relied more heavily on applied fertilizer-N.
In small-plot trials at Carman and Portage (2017-2019), yield was increased with the highest rate of N fertilizer (140 lbs N/ac applied). When considering the return on investment, it was statistically the same for all rates of N application, meaning the economic optimum rate was to not apply any N fertilizer at all.
In more recent small-plot trials at Brandon, Melita and Carberry (2021-2022) on narrow-row black and pinto beans, there was no response to different N fertilizer rates at 9 out of 10 site-years. Black bean yield tended to increase with increasing N rates, but only significantly when compared to uninoculated beans at Melita in 2022. At Melita in 2022, black and pinto bean nodulation and yield (+390 lbs/ac) were improved with inoculant.
- Full Research Report: Nitrogen and Phosphorus Management for Black and Pinto Beans in Southwestern Manitoba (2021-2022) →
- Optimizing Nitrogen Rates for Pinto and Navy Beans (Small-plot Trials at Carman, Portage 2017- 2019) →
- On-Farm Evaluation of Nitrogen Rates in Dry Beans (2019 – 2023) →
Inoculant Evaluation
In 2023, four on-Farm Trials tested two liquid inoculant products in dry edible beans. Nodulation was assessed at flowering (R2) and no differences in nodulation numbers were found between uninoculated dry beans and those inoculated with either product. Total number of nodules per plant ranged from none present in trials where nitrogen was applied to 29/plant on average.
Small-plot research has also investigated dry bean inoculants at Carman and Melita from 2019-2021. Of product options available, N Charge improved yield and nodulation at Melita in 2020 and 2021.
Build a Bean Nitrogen Budget to Inform Your N Management Decisions:
- Set your yield goal (e.g., 2000 lbs)
- Calculate nitrogen uptake (multiply yield goal by 4.5 lbs/cwt = 90 lbs N)
- Account for soil residual N (0-24″) (e.g., soil N = 40 lbs N)
- Do you check nodulation in dry beans? (If no, skip to #6 and adopt as part of your scouting routine in 2023)
- Were your previous dry bean crops nodulated? (If yes, give a 40% N credit for biological N fixation by multiplying N uptake in #2 by 0.40 = 36 lbs N)
- Is your soil pH greater than 6.0? (If no, nodulation and N fixation capacity may be reduced and you should not rely on an N credit from #5)
- From N uptake (#2), subtract residual soil N (#3) and N credit (#5). This is your remaining N requirement (e.g., 90 – 40 – 36 = 14 lbs N/ac)
- If <20 lbs N/ac, N may be supplied through mineralization and deep N
- If >20 lbs N/ac, apply as fertilizer N