Most soybeans are treated prior to planting because of the return on investment it provides. Using a high-quality seed inoculant such as Preside introduces millions of new live rhizobial bacteria to boost soil populations and resulting soy crop yield.
The growth of rhizobial inoculants
High soybean market prices are driving interest in rhizobial inoculants. With just a modest increase in yield required to offset the cost of inoculants, the additional expenditure makes economic sense. As seed and input prices are also high, also growers use such products to protect their investment.
Inoculants work by boosting rhizobia populations. Rhizobia are the group of soil bacteria that infect the roots of legumes to form root nodules. The bacteria take nitrogen from the air and supply it to the legumes. Soybeans use a lot of nitrogen per bushel. Almost all of the nitrogen stored by the bacteria is transferred to the legume. In this symbiotic biological relationship, the plant supplies the bacteria with habitat, nutrients and energy.
Which rhizobial inoculant to use?
Which rhizobial inoculants to choose and how they should be used depends on individual farm management practices and consideration of past disease and insect history. Soil environments change annually and within each year with different strains of bacteria doing well in lower pH levels and others in higher ones. Seed inoculants with mixed strains of rhizobia such as Preside Ultra can be particularly effective.
When to inoculate
Farmers have noted since ancient times that legumes act as ‘soil improvers. They noted that cereal crops were healthier and higher yielding when planted in soil that had been used to grow legumes previously.
Most experts agree that soybeans should be inoculated annually. There is a common belief that maintaining soy in a crop rotation system or planting soy every year will maintain sufficient rhizobia for continued effective growth.
However, over time rhizobia that is native to the soil becomes less effective at nodulation. Even fields with a recent history of soy will benefit from the introduction of new and stronger strains of rhizobia. Fields that have had a legume in several years will have significantly diminished levels of rhizobia.
Weather also plays a large part in soybean growth. Significant rainfall leading to standing water will reduce rhizobia populations. Likewise, long periods of dry weather can impact rhizobia numbers.
Inoculation is just one tool for effective soybean management but is one that has been increasingly utilised over the last 10 years or so. It is a particularly cost-effective one in increasing soy yields. Soy producers are now pushing yields further and inoculation is particularly important in years when conditions mean that growth is relatively poor and even in times when seed quality has been impacted negatively.