Nutrient Uptake and Removal
Source: John Heard 2008
Dry beans are poor N-fixers, on average fixing less than 50% of their nitrogen (N) requirement. Inoculants for dry beans are currently being researched in Manitoba. To date, they have not been widely commercially available or effective. As a result, dry beans are typically managed like a non-legume crop.
The majority of dry bean farmers (95%) apply supplemental N at an average rate of 60 to 70 lbs N/ac. Roughly 4.5 lbs of N are required per cwt – from a combination of residual soil N, biological N fixation or fertilizer. For a 2000 lb/ac dry bean yield this would mean the crop needs about 90 lbs N/ac.
Since 2017, nitrogen rates and inoculant products haven been researched by Kristen P. MacMillan at the Applied Pulse and Soybean Research Lab at the University of Manitoba and through MPSG’s On-Farm Network. Results from this research will be used to revisit soil fertility recommendations for dry beans in Manitoba.
Testing rates of 0 to 140 lbs N/ac applied, yield was only increased at the highest rate of nitrogen. Statistically, maximum dry bean yield was achieved at the lowest rate of N applied at 35 lbs N/ac. At the On-Farm Network trial sites, yield has not been increased by any nitrogen rate tested so far. Nodulation ratings at the on-farm sites (non-inoculated) have averaged 3.4 in 2020 and 1.6 in 2019 (on a 0-4 scale), indicating decent nodulation from pre-existing rhizobia in the soil.
These results will be further refined over the year. For now, here are the emerging N fertility guidelines:
- No supplemental N, no inoculation
- Expect 86-93% of maximum yield
- Economic optimum across 5 site-years
- Supplemental N at 35 lbs N/ac or ~70 lbs total N including soil residual
- If skipping N fertilizer is too risky
- Reach maximum yield without reducing nodulation
- As product availability and testing increases
- Inoculation and supplemental N?
- Needs research first
The maximum safe rate of seed-placed phosphorus (P) is 10 lbs P2O5/ac in narrow rows (<15”) and 0 in wide rows.
Dry beans don’t always respond to P fertilization. Research from NDSU (2009 – 2017) has found, on average, that P fertilization (in-furrow 10-34-0-0) increased yield by 310 lbs/ac (11% increase) compared to the untreated check. There was no difference between in-furrow vs. banded application, while broadcasted and midrow banded applications did not increase yield from the untreated check. Yield was similar between low (2.5 to 3 gpa) and high (5 to 6 gpa) rates of in-furrow-applied 10-34-0-0. The higher rate of fertilizer reduced plant population.
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