New research reveals that soil pH is a useful guide for farmers and agronomists to detect and manage soybean cyst nematode  (SCN). The investigation uncovered a relationship between high soil pH, which is already outside the ideal growing conditions for soybean, and high SCN populations.
Scientists from Iowa State University  and University of Wisconsin-Madison  reported their findings in the July-August 2010 Crop Science , published by the Crop Science Society of America . Conducted on sites in both Iowa and Wisconsin, the study confirmed the relationship between high soil pH and SCN, which results in a lower yield.
Soybean cyst nematode is the single most damaging pathogen of soybean in the U.S., as well as in most of the other top soybean -producing countries of the world. Infestations may go unnoticed for years due to the lack of above-ground symptoms, leading to producers to unknowingly suffer yield declines. This makes calculating economics losses difficult, but yearly losses have been estimated at about $1.5 billion in the U.S. alone.
Rotating nematode-resistant soybean varieties with non-host crops is currently the best management practice. Knowing when it is necessary to begin managing for nematode cyst is crucial for maintaining yield. Planting resistant soybean in an infested field can result in an average improved yield of 10%.
The results of the study showed the size of nematode populations increased with higher soil pH, and while all soybean varieties suffered yield declines, nematode-resistant varieties declined the least. The researchers suggest that the impact of nematode population densities on soybean yield are related to soil pH, though the exact process through which this occurs remains unclear.
“Our data indicate that soil pH can be used as a guide to researchers, agronomists and farmers attempting to account for natural variability of [SCN] population densities without prior knowledge of the nematode’s distribution in a field,” states lead-author Palle Pedersen. “Based on our results, agronomists and farmers would be well-served to assay areas of high pH in fields to determine the presence or absence of [nematodes]. Soybean breeders should take soil pH into account when establishing nurseries for their breeding program.”
The researchers also noted it was unusual for an obligate parasite, like SCN, to live in an environment not ideally suited to its host. Soybean typically requires a lower soil pH, and yet the highest nematode populations where found in areas well above the optimum range for soybean growth.
The study was funded by the soybean checkoff  through the Iowa Soybean Association , Wisconsin Soybean Marketing Board  and the North Central Soybean Research Program .
The full article is available for no charge for 30 days following the date of this summary. View the abstract at http://crop.scijournals.org/cgi/content/abstract/50/4/1458 .