| Department of Agronomy Newsletter | Winter 1999 |
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Development of indicators of soil health in agricultural systems Fertilizers have helped to eliminate nutrient deficiencies as factors limiting crop growth, and modern field machinery provides many options for tillage and soil management. The biological dimension of cropped soils may be the next frontier for integrated crop management to enhance resource sustainability and the success of farmers. We need to learn more about the possibilities presented by better understanding the relationships between soil and crop management, the life of the soil, and sustainable crop production for Pennsylvania. Soil quality represents the life of the soil. Dr. Les Lanyon, professor of soil fertility, Dr. Laurie Drinkwater, adjunct assistant professor and director of U.S. programs at Rodale Institute, and Dr. Jon Chorover, assistant professor of environmental soil chemistry, are leading research teams that are exploring the impact of soil and crop management on the microbiological activity in Pennsylvania soils. Their goal is to develop simple tests or management guidelines that allow producers to better understand the condition of life in their farms' soils and to monitor trends in soil quality indicators over time. This can help in identifying practices that improve soil quality and long-term sustainability. As part of a USDA Sustainable Agriculture Special Research Grant, Lanyon and Drinkwater have collected soil samples from the long-term Hunter Rotation Experiment at the R.E. Larson Agricultural Research Center in Rock Springs and from the Farming Systems Trail at the Rodale Research Farm in Kutztown, PA. |
Battling soybean white mold In 1996, a wet, cool summer contributed to a statewide soybean white mold outbreak in Pennsylvania that caused a yield loss estimated at 10-20 percent. Dr. Barbara W. Pennypacker, associate professor of agronomy and senior research associate, is working diligently on methods to control white mold of soybeans, which is caused by the fungus Sclerotinia sclerotiorum. In the past several decades, soybeans have become increasingly important to Pennsylvania agriculture. In 1997, soybeans were the fourth most important crop in the state with 365,000 acres harvested at a value of $97 million. Back in 1970, only 3000 acres of soybeans were planted in the Commonwealth. Recently, however, several farmers with river-valley fields told Pennypacker they may have to stop growing this valuable crop unless recommendations can be made on how to control white mold. Cool temperatures, abundant rainfall, and frequent, lingering fogs provide the ideal conditions for spore production and infection of soybeans. Fields bordering creeks and rivers often have chronic problems with soybean white mold because morning and evening mists provide the moisture the fungus requires to produce spores and infect plants. The fungal spores are wind blown and when they land on soybean flowers, they begin to grow, rapidly infecting the main stem and girdling it. Sclerotia, the black, resting bodies of the fungus, form on and in the soybean stem and eventually fall to the ground. Sclerotia can remain viable in the soil for up to seven years. They become active when weather conditions are favorable and produce tiny, orange-tan mushrooms. |
The mushrooms produce the spores that infect soybean plants. Pennypacker's research has important implications for Pennsylvania soybean producers. Her 1998 field work showed that there are measures that growers with chronic white mold problems can take that appear to minimize the impact of the disease on yield and reduce the white mold threat to future crops. Last summer's field research on agronomic control measures looked at the effect of row spacing on white mold severity. The experiment tested 14", 21", and 28" row widths. As the row width increases the number of plants per acre decreases, which, in the absence of white mold, reduces yield potential. However, a moderate amount of white mold was present and , contrary to predictions, yield increased as row width increased. Soybeans in 14" rows yielded 42 bushels per acre whereas those in 21" and 28" rows produced 49 and 48 bu/acre, respectively. Efforts to increase soybean yield potential by growing the crop in narrow rows may contribute to the growing incidence of white mold. 
Dr. Barbara Pennypacker
evaluates a soybean field infected with white mold.
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