Practice Abstract 47 - Protein content of soybeans - Wageningen University & Research

Short title (native language): 
Protein content of soybeans - Wageningen University & Research

Short summary for practitioners (native language): 
It is unclear why soybean protein content varies widely from year to year and from location to location. The range can be from 35% to over 42%. A literature study reveals the influential factors.
About 50% -75% of soya bean nitrogen requirement comes from N-fixation via root nodules, the rest from the soil.
A successful inoculation with Rhizobium bacteria is essential for achieving a high yield and protein content. The number and position of the nodules on the root system appears to be important. Side root and deeper root nodules may be essential for optimal N-fixation. Inoculating the soil rather than the seed, or in addition to the seed, seems to increase the N-fixation considerably. Spraying Rhizobium before flowering can also have a positive effect on the number and location of the nodules.
In high yielding crops N deficiency can occur during pod filling, N-fertilizer application in that crop stage may have a profitable effect on both yield and protein content.
During seed filling, the activity of the root nodules decreases and nitrogen is redistributed from the leaves and pods to the seed. Varieties with a higher protein content, appear to be able to continue with the N fixation until the R6 stage, fixing more nitrogen in a later crop stage to increase the protein content.
The protein content of soy is determined by the variety, cultivation method, growing conditions, and the root nodules. The interaction between all these factors and yield, makes it a very complex process. Farmers can’t control the protein content of their soy but can influence it by variety choice, and possibly an additional soil inoculation, and by a small N-application during pod filling stage. chris.devisser@wur.nl