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Nine-row air drill planting dry beans.

Dry Beans

Nitrogen Budget

(Reviewed 12/08, updated 12/08)

In this Guideline:


It is critical to determine the correct rate for nitrogen fertilizer application. Grain legumes are very efficient at using available soil N and often adjust their symbiotic N fixation to the amount available in the soil. As a result, excess nitrogen in the soil can severely reduce a stand by inhibiting root nodule formation, over-stimulating vine growth and leading to delay in plant maturity and late-season decline, as well as providing favorable conditions for insects, molds, and bacterial diseases.

The rate of nitrogen that needs to be applied is based on residual soil nitrogen levels, the nitrogen fixation characteristic of the bean type, and soil type (fixation is limited in heavy clay soils). Some varieties, such as those of blackeyes, may not need additional nitrogen. The following table lists the nitrogen fixation rates of various dry bean varieties:

Nitrogen fixation rates characteristic of well-nodulated bean types

Bean Type Rate (lb nitrogen/acre/season)
vine limas (baby/large) 80–100
blackeyes (cowpeas) 80–120
vine common 70
bush lima (large) 60
bush common 20–40
California early light red kidney 20
full-season kidney 40

PREPLANT APPLICATION
During final bed preparation, apply 20 to 40 lb nitrogen/acre, depending on the type of incorporation (into beds or sidedressing: 20 lb/acre; over entire field: 40 lb/acre). Use planter attachments to place nitrogen 4 to 6 inches below the surface of the soil and 4 to 6 inches beside the seed. Some blackeye growers apply up to 50 lb/acre of nitrogen to CB46, a relatively compact variety, to increase early crop growth and to allow it to compete more vigorously with weeds.

INOCULATING SEED WITH NITROGEN-FIXING BACTERIA
Optimal yield requires a proper balance between nitrogen applications and fixation through seed inoculation:

  • Inoculate seed with Rhizobium bacteria before planting, or apply inoculant to seed row while planting.
  • Wait 30 to 40 days for bacteria to infect seedling roots and develop nodules.

APPLICATIONS DURING CROP GROWTH
If the soil sample demonstrated the need for nitrogen in excess of the crops fixation capacity, then sidedress the root zone, 30 to 40 days after planting inoculated seed. Use ammonium nitrogen or insoluble nitrogen.Soluble nitrogen, in the form of UN32, is used by some growers in May or early June, and in winter for garbanzo beans.

To determine the amount of nitrogen fertilizer needed:

  • Sample the soil for residual nitrate level.
  • Identify the pounds of nitrogen your bean variety fixes/acre/season.
  • Calculate the difference between available soil nitrogen levels and what your variety will fix to get the application rate.
  • If you have heavy clay soil, check with your farm advisor.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Dry Beans
UC ANR Publication 3446
General Information
W. M. Canevari, UC Cooperative Extension, San Joaquin County
C. A. Frate, UC Cooperative Extension, Tulare County
L. D. Godfrey, Entomology, UC Davis
P. B. Goodell, UC IPM Program, Kearney Agricultural Research Center, Parlier
R. F. Long, UC Cooperative Extension, Yolo County
C. J. Mickler, UC Cooperative Extension, Stanislaus County
S. C. Mueller, UC Cooperative Extension, Fresno County
J. L. Schmierer, UC Cooperative Extension Colusa County
S. R. Temple, Plant Sciences,UC Davis

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