BackgroundSale of organic foods is one of the fastest growing market segments within the global food industry. People often buy organic food because they believe organic farms produce more nutritious and better tasting food from healthier soils. Here we tested if there are significant differences in fruit and soil quality from 13 pairs of commercial organic and conventional strawberry agroecosystems in California.Methodology/Principal FindingsAt multiple sampling times for two years, we evaluated three varieties of strawberries for mineral elements, shelf life, phytochemical composition, and organoleptic properties. We also analyzed traditional soil properties and soil DNA using microarray technology. We found that the organic farms had strawberries with longer shelf life, greater dry matter, and higher antioxidant activity and concentrations of ascorbic acid and phenolic compounds, but lower concentrations of phosphorus and potassium. In one variety, sensory panels judged organic strawberries to be sweeter and have better flavor, overall acceptance, and appearance than their conventional counterparts. We also found the organically farmed soils to have more total carbon and nitrogen, greater microbial biomass and activity, and higher concentrations of micronutrients. Organically farmed soils also exhibited greater numbers of endemic genes and greater functional gene abundance and diversity for several biogeochemical processes, such as nitrogen fixation and pesticide degradation.Conclusions/SignificanceOur findings show that the organic strawberry farms produced higher quality fruit and that their higher quality soils may have greater microbial functional capability and resilience to stress. These findings justify additional investigations aimed at detecting and quantifying such effects and their interactions.

In the majority of agricultural soils, ammonium (NH +) is rapidly converted to nitrate (NO 3-) in the biological ammonia and nitrite oxidation processes known as nitrification. The often rate-limiting step of ammonia oxidation to nitrite is mediated by ammonia oxidizing bacteria (AOB) and ammonia oxidizing archaea (AOA). The response of AOA and AOB communities to organic and conventional nitrogen (N) fertilizers, and their relative contributions to the nitrification process were examined for an agricultural silage corn system using a randomized block design with 4 N treatments: control (no additional N), ammonium sulfate (AS) fertilizer at 100 and 200 kg N ha-1 , and steer-waste compost (200 kg total N ha-1) over four seasons. DNA was extracted from the soil, and real-time PCR and 454-pyrosequencing were used to evaluate the quantity and diversity of the amoA gene which encodes subunit A of ammonia monooxygenase. Soil pH, nitrate pools, and nitrification potentials were influenced by ammonium and organic fertilizers after the first fertilization, while changes in AOB abundance and community structure were not apparent until after the second fertilization or later. The abundance of AOA was always greater than AOB but was unaffected by N treatments. In contrast, AOB abundance and community structure were changed significantly by ammonium fertilizers. Specific inhibitors of nitrification were used to evaluate the relative contribution of AOA and AOB to nitrification. We found that AOB dominantly contributed to potential nitrification activity determined at 1 mM ammonium in soil slurries and nitrification potential activity was higher in soils treated with ammonium fertilizers relative to control soils. However, AOA dominated gross nitrification activity in moist soils. Our result suggests that AOB activity and community are more responsive to ammonium fertilizers than AOA but that in situ nitrification rate is controlled by ammonium availability in this agricultural soil. Understanding this response of AOA and AOB to N fertilizers may contribute to improving strategies for the management of nitrate production in agricultural soils.

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Relationships between soil microbial diversity and soil function are the subject of much debate. Process-level analyses have shown that microbial function varies with soil type and responds to soil management. However, such measurements cannot determine the role of community structure and diversity in soil function. The goal of this study was to investigate the role of gene frequency and diversity, measured by microarray analysis, on soil processes. The study was conducted in an agro-ecosystem characterized by contrasting management practices and soil types. Eight pairs of adjacent commercial organic and conventional strawberry fields were matched for soil type, strawberry variety, and all other environmental conditions. Soil physical, chemical and biological analyses were conducted including functional gene microarrays (FGA). Soil physical and chemical characteristics were primarily determined by soil textural type (coarse vs fine-textured), but biological and FGA measures were more influenced by management (organic vs conventional). Organically managed soils consistently showed greater functional activity as well as FGA signal intensity (SI) and diversity. Overall FGA SI and diversity were correlated to total soil microbial biomass. Functional gene group SI and/or diversity were correlated to related soil chemical and biological measures such as microbial biomass, cellulose, dehydrogenase, ammonium and sulfur. Management was the dominant determinant of soil biology as measured by microbial gene frequency and diversity, which paralleled measured microbial processes.

Significant bectarage of certified organic dryland wheat (Triticum aestivum L.) is planted in tbe western United States. Yields are severely constrained by lack of precipitation, so many dryland organic wbeat farmers do not grow cover crops or apply fertilizer due to the inability to recoup application costs in tbe short term. Composts have a strong carryover effect, however, and the long-term benefits of infrequent applications to soil quality, yield, and economics on dryland wbeat-fallow systems bave not been evaluated. Soils were sampled in 2008 and 2010 from the site of a previous compost response trial located on a commercial dryland wbeat farm in Snowville, UT. Dairy manure compost was applied in 1994 at the rate of 50 Mg dry matter ha"' in a randomized complete block design with tbree replicates. Sixteen years later, soils from compost-amended plots contained 1.6-fold higher total organic C (1.43% vs. 0.89%, p < 0.002), higher microbial biomass, debydrogenase, acid and alkaline pbosphatase activity and higher plant available P, K, and Zn relative to amended controls in the top 5 cm. The 5-to 10-cm layer contained 1.6-fold higher total organic C, higher plant available P and K and higher debydrogenase, acid and alkaline phospbatase activity in 2010. Tbe 2-yr average yield increased from 0.5 Mg ba"' in the control plots to 1.0 Mg ha"' in the amended plots (p = 0.004). Wben compared with tbe yield gain of 2.3 Mg ha"^ measured in 1995 to 1997, the estimated balf-life of the compost effect was 6 yr. Despite the long-term benefits measured in tbis study, the viability of using compost in dryland wbeat production will depend on tbe availability and proximity of growers to sources of compost.