# NUTRIENT USE IN HIGH-YIELDING SNAP BEAN

2018

- Dept. of Soil Science, Univ. of Wisconsin-Madison

###### Project Media

Previous research (Wang et al., 2015) on snap bean response to N provided

interesting results, but it is unclear if the results are applicable to all fields. This

previous research was conducted in Plover, WI with high yielding DelMonte varieties.

Results suggested that 100 lb-N/ac was the optimal N rate (20 lb-N/ac in starter and 80

lb-N/ac in-season) when yields are greater than 9 ton/ac. However, typical yields for

snap bean are in the 4-5 ton/ac range (personal communication with processing crop

agronomists), which may not require 100 lb-N/ac (current UW recommendations are 60

lb-N/ac for yields up to 6.5 ton/ac). In addition, the previous research also indicated that

for non-nodulating varieties (i.e. varieties that do not allow root infection of rhizobium,

and thus do not directly obtain N fixed from the atmosphere), had an N utilization

efficiency of 68% when 100 lb-N/ac was applied. For nodulating varieties (in this case

the high-yielding Del Monte varieties) additional analysis using 15N stable isotope

concentrations was necessary to determine the true removal efficiency as it is unknown

how the addition of N fertilizer will inhibit the amount of N that is fixed. Preliminary

analyses of these results indicate that the 100 lb-N/ac rate completely inhibits N fixation

in snap beans. Now, it may seem counter-intuitive, but this is actually beneficial for

water quality. It means that the applied N is replacing the N fixed by the atmosphere

and is actually well-utilized in the system. If applying N fertilizer did not completely

inhibit N fixation, then much of the N that was applied would not be used and thus

leached to groundwater. However, 100% inhibition of N fixation occurred at the 100 lb-

N/ac rate, with lower N rates inhibiting a small percentage of N fixation. Now, if more

commonly used varieties require less N inputs (in the 50 to 80 lb-N/ac range) it is

important to know what the true N use efficiency is as less N on lower yielding varieties

may be less efficient than more N on higher yielding varieties. With all of the issues

concerning nitrate concentrations in the Central Sands, we know little about the actual

fate of N (or at least the utilization of applied N) in snap bean production systems.