Long-Term Agroecological Research at the USDA-ARS Farming Systems Project, Beltsville, Maryland.

The USDA-ARS Farming Systems Project, part of the Lower Chesapeake Bay Long-Term Agroecological Research site, evaluates the sustainability of two conventional and three organic grain cropping systems that mimic typical farms in the Mid-Atlantic region. Conventional systems are 3-year crop rotations using either no-tillage or chisel plowing as primary tillage. Organic systems are 2-, 3-, or 6-year crop rotations.  Results after 20 years show that inter-annual yield variability is greater than yield differences among management systems in a given year.  For example, corn yield is strongly positively related to the amount of rainfall received while corn is pollinating or is in the grain filling stage, i.e. 6-10 weeks after planting.  Results also show multiple tradeoffs in system performance. For example, while corn and soybean yields are generally greater in conventional than organic systems, economic returns are greater in organic systems due to organic price premiums. While soil C and potentially mineralizable nitrogen are greater in the organic than the conventional systems, nitrous oxide emissions in the 2- and 3-year organic rotations are double those in the 6-year rotation and the two conventional systems.  However, global warming potential—due to the dominant role of soil C—is lower in the 3-year organic rotation than in the two conventional systems.  Finally, results show that the longest rotation among organic systems, which includes a perennial forage, improves corn yield by 30%, reduces economic risk 7-fold, lowers weed pressure 68%, reduces dependence on animal manure and associated P loading by 33%, and reduces soil erosion 62% compared to the shortest organic rotation. On-going and future research focuses on better understanding factors controlling yield variability (plant available soil moisture and nitrogen, weed competition, soil quality, crop varieties and interactions among factors), and soil microbial community and nitrogen dynamics.