Maintaining soil organic carbon (SOC) in frequently tilled, intensive organic vegetable production systems is a challenge that is not well understood. Compost and cover crops are often used to add organic matter to the soil in these systems. Compost contributes relatively stabilized carbon (C) while cover crops provide readily degradable (labile) organic matter. Our objectives were to quantify C inputs, and to assess the effects of urban yard-waste compost, winter cover crop frequency and cover crop type on SOC and labile C stocks during eight years of intensive, organic production that usually included two vegetable crops per year in a long-term systems study in Salinas, California. Total C inputs from pelleted fertilizer, compost, vegetable transplant potting mix, vegetable residue and cover crops, including estimates of below ground inputs, ranged from 40 to 108 Mg ha-1 in the five systems evaluated. Following a rapid decline in SOC stocks in year 1, compost had the largest effect on SOC stocks increasing mean SOC over years 2 to 8 by an average of 9.4 Mg ha-1 , while increased cover crop frequency (annual vs. quadrennial) led to an additional 3.4 Mg ha-1 increase. In contrast, cover cropping frequency had the largest effect on permanganate oxidizable labile C (POX-C), increasing POX-C by 26% after 8 years. Labile POX-C was well correlated with microbial biomass C and nitrogen. Compost had the greatest effect on total SOC stocks, while increasing cover crop frequency altered the composition of SOC by increasing the proportion of labile C. These results suggest that frequent winter cover cropping has a greater potential than compost to increase nutrient availability and vegetable yields in high-input, tillage intensive vegetable systems.

Core Ideas Premium prices resulted in greater organic system returns despite lower yields. Perennial forage in extended rotation improves organic system economic performance. Perennial forage stabilizes returns, reducing economic risk. ABSTRACT Increased demand for organic grain in the United States is resulting in increased production. However, no economic analysis in the United States accounts for post 2005 increases in commodity prices, fuel, and fertilizer costs. This analysis includes costs, yields, and net returns from the five cropping systems at the USDA‐ARS Farming Systems Project in Beltsville, MD, between 2006 and 2014. Costs for organic corn (Zea mays L.)–soybean (Glycine max (L.) Merr.) (Org2) and corn–soybean–wheat (Triticum aestivum L.) (Org3) rotations and a 3‐yr conventional Chisel Till grain rotation were similar, but expenses in an organic 6‐yr (Org6) corn–soybean–wheat–alfalfa (Medicago sativa L.) rotation were higher due to the cost of managing an alfalfa crop. The conventional no‐till grain rotation production costs were lowest. Tillage was a major contributor to total cost in the four tilled systems. Mean returns from Org6 (US$858) were similar to those from No‐till ($702) while returns for Org2 and Org3 ($585 and $589) were similar to those for Chisel Till ($502). Among organic systems economic risk was inversely proportional to crop rotation length. The shorter organic rotations were more sensitive to changes in organic price premiums relative to Org6. At Org2 and Org3 breakeven price premiums the Org6 mean return would only be reduced by 32 and 37%, respectively, remaining similar to Chisel Till. For Org6 risk was much lower than the other organic and the conventional systems, demonstrating that long, diverse rotations reduce overall risk, even in comparison to a conventional No‐till system.

Untreated biological soil amendments of animal origin (BSAAO), such as manure, are commonly used to fertilize soils for growing fruit and vegetable crops and can contain enteric bacterial foodborne pathogens. Little is known about the comparative longitudinal survival of pathogens in agricultural fields containing different types of BSAAO, and field data may be useful to determine intervals between manure application and harvest of produce intended for human consumption to minimize foodborne illness. This study generated 324 survival profiles from 12 different field trials at three different sites (UMES, PA, and BARC) in the Mid-Atlantic United States from 2011 to 2015 of inoculated nonpathogenic Escherichia coli (gEc) and attenuated O157 E. coli (attO157) in soils which were unamended (UN) or amended with untreated poultry litter (PL), horse manure (HM), or dairy manure solids (DMS) or liquids (DML). Site, season, inoculum level (low/high), amendment type, management (organic/conventional), and depth (surface/tilled) all significantly (P < 0.0001) influenced survival duration (dpi100mort). Spatiotemporal factors (site, year, and season) in which the field trial was conducted influenced survival durations of gEc and attO157 to a greater extent than weather effects (average daily temperature and rainfall). Initial soil moisture content was the individual factor that accounted for the greatest percentage of variability in survival duration. PL supported greater survival durations of gEc and attO157, followed by HM, UN, and DMS in amended soils. The majority of survival profiles for gEc and attO157 which survived for more than 90 days came from a specific year (i.e., 2013). The effect of management and depth on dpi100mort were dependent on the amendment type evaluated. IMPORTANCE Current language in the Food Safety Modernization Act Produce Safety Rule states no objection to a 90- or 120-day interval between application of untreated BSAAO and harvest of crops to minimize transfer of pathogens to produce intended for human consumption with the intent to limit potential cases of foodborne illness. This regional multiple season, multiple location field trial determined survival durations of Escherichia coli in soils amended with manure to determine whether this interval is appropriate. Spatiotemporal factors influence survival durations of E. coli more than amendment type, total amount of E. coli present, organic or conventional soil management, and depth of manure application. Overall, these data show poultry litter may support extended survival of E. coli compared to horse manure or dairy manure, but spatiotemporal factors like site and season may have more influence than manure type in supporting survival of E. coli beyond 90 days in amended soils in the Mid-Atlantic United States.