Soybean yield is often limited by soilborne pathogens or diseases. The average for soybean yield in the U.S. is 43.9 bushels per acre or only about 27% of the known yield potential (160 bushels per acre) for the crop.
The difference between harvested yield and potential yield is lost to a number of environmental stresses such as heat and drought as well as a complex of poorly understood soilborne pathogens. These pathogens invade plant roots causing tissue decay, a reduction in the number of root tips, a decrease in nodule size and loss of root function, says David Wright, director of contract research for the Iowa Soybean Association.
Major yield losses are found in areas where soils have high clay content or remain saturated for long periods of time. The key to improving soybean yield is to improve root health.
Key to improving soybean yield is to improve root health
One aspect of improving root health is increasing the number of roots, says Wright. Water and nutrients are absorbed into the root just behind the root tip, so increasing the number of roots means more water and nutrients can be absorbed. Healthy roots trigger faster plant growth and seed development when environmental conditions are not growth limiting.
In addition to anchoring the plant, the soybean root is responsible for absorbing large amounts of water and nutrients and then transporting them to the stem and leaves. When roots are damaged, the plant's ability to obtain water and nutrients is greatly reduced. Preventing damage to the root removes the stress and helps avoid unnecessary yield loss.
Diagnose the most important bean seedling disease problems
The most important disease pathogens associated with seedling root health include the soybean cyst nematode, Pythium species, Phytophthora sojae, Rhizoctonia solani, and Fusarium species. Iowa State University researchers found that each of these pathogens can impair root health alone, and also in combination with each other.
Pythium species cause seed decay, pre-emergence damping off and early post-emergence seedling death, says Wright. Seed infected with Pythium species may decay before the seed germinates, and as the seed decays it becomes soft and rotted. Phytophthora sojae also causes a soft, wet rotting of seed or seedling tissue similar to that of Pythium species. Infected seedlings may die prior to emerging from the soil or shortly thereafter.
Symptoms of Rhizoctonia solani infection generally show up on seedlings as dry, dark reddish-brown lesions just above the soil line. "Seedling loss from Rhizoctonia seedling blight is less common that from Pythium seed decay and Phytophthora root rot but when Rhizoctonia is present, the soybean stand loss can be severe," he adds.