Inoculation and Fertility

Soybeans must be inoculated with Bradyrhizobium japonicum, because this type of bacteria is not indigenous to Western Canadian soils. Ensure proper procedures for inoculation are followed according to manufacturer guidelines. There are liquid, peat, and granular types to choose from.

Delivery of granular inoculants to the seed row requires granular attachments for air seeders and row-crop seeders.

After one or two well-nodulated soybean crops, the rhizobia population in a field may be adequate for subsequent crops. However, it is recommended that inoculation continue each time soybean is sown to ensure efficient nodulation and nitrogen fixation. Soybeans are prone to iron chlorosis, which causes interveinal yellowing of the leaves, particularly when grown on saturated soils or soils high in carbonate levels or with salinity problems.

Soil test fields and choose fields that are low in nitrogen to plant soybeans. This will allow you to take advantage of the significant nitrogen fixing capability of soybean. However, field cropping history is important, especially for possible herbicide carryover residues. Follow re-cropping intervals on the herbicide labels because soybeans are sensitive to soil residues of several herbicides. Soil testing identifies nutrient deficiencies and provides the levels of nutrients needed for optimum yield.

Nitrogen (N): Examine the plants for adequate nodulation approximately three to four weeks following emergence. Active nitrogen fixation usually occurs one to two weeks later. If insufficient nodulation is evident, the grower may apply up to 50 lbs/acre N as broadcast.
Phosphate (P2O5): Phosphate is best applied as a sideband application at 30 to 40 lbs, P2O5/acre or using soil test recommendations. Applications with the seed must not exceed 20 lbs./acre. These rates are recommended for narrow row spacing with good moisture conditions. In wide row crop planting, the fertilizer is best side banded.
Potassium (K2O): Potassium deficiencies may be found on light textured soils. Potassium can be side banded with the phosphate.
Sulphur (S): If sulphur is required, ammonium sulphate can be side banded with the phosphate.  If using liquid, a blend of liquid phosphate and sulphur can be side banded based on soil test recommendations.  

Information adapted from the Saskatchewan Ministry of Agriculture.

Nodulation and Nitrogen Fixation Field Assessment Guide