Interactions of VAM fungi, pesticides and crops

V esicular arbuscular mycorrhizal fungi (V AM) are beneficial root symbionts of most crops, including corn and soybeans. These fungi colonize plant roots, facilitating nutrient ex­ change between the plant and the fungus. The plant supplies carbon for fungal growth; in turn, the VAM enhances uptake of relatively immobile nutrients such as phosphorus (P). The network of external fungal filaments, or hyphae (see photos below), extends outside the root up to several centimeters in the soil, allowing the fungus access to soil P otherwise unavailable to the plant

Theme Overview: Agriculture and Water Quality in the Cornbelt: Overview of Issues and Approaches

Resource /Energy Economics and Policy, Q25,

Coupling Manure Injection with Cover Crops to Enhance Nutrient Cycling

Large-scale hog (Sus scroja) production is a major agricultural enterprise in the Midwest. Large numbers of confined hogs produce about 50 million tons per year of swine manure in Iowa alone. Rapid expansion of concentrated animal feeding operations (CAFOs) has resulted in increased concentrations of manure nutrients in surface waters which contribute about 15% of the total nitrate load in the Mississippi River Basin. Producers are being encouraged to develop manure management practices that fulfill crop production requirements, while minimizing the potential for environmental pollution. The most commonly used manure management practice in the Midwest involves fall application to land where corn (Zea mays L.) will be grown in the subsequent growing season. Fall planted annual cover crops can capture manure nutrients and immobilize them in plant biomass, subsequently reducing the potential for nutrient loss through run-off or leaching. Decomposition of cover crop residue the following spring may help synchronize manure N availability and corn N uptake, improving nutrient-use efficiency within the crop rotation

Environmental Benefits and Management of Small Grain Cover Crops in Corn-Soybean Rotations

These slides offer research results on cover crops

Estimating Atrazine Leaching in the Midwest

Data from seven Management Systems Evaluation Areas (MSEM) were used to test the sensitivity of a leaching model, PRZM-2, to a variety of hydrologic settings common in the Midwest. Atrazine leaching was simulated because the use of atrazine was prevalent in the MSEA studies and it frequently occurs in the region\u27s groundwater. Results of long-term simulations using regional and generalized input parameters produced ranks of leaching potential similar to those based on measurements. Short-term simulations used site-specific soil and chemical coefficients

A Tale of Three Watersheds: Nonpoint Source Pollution and Conservation Practices across Iowa

Resource /Energy Economics and Policy, Q25,

Evaluation of the impact of tillage/cropping systems on soil microflora and week seedbank predation

Soil erosion and pesticide use are critical issues in sustainable agriculture. With a view to decreasing the amount of pesticides used for weed control, researchers assessed the impact of tillage, cropping systems and weed management regimes on seasonal and long-term weed and weed seedbank population dynamics, especially in Conservation Reserve Program land being returned to production

Impact of temperature and hydraulic retention time on pathogen and nutrient removal in woodchip bioreactors

Woodchip denitrification bioreactors are an important edge-of-field practice for treating agricultural drainage; however, their ability to filter microbial pollutants has primarily been explored in the context of wastewater treatment. Upflow column reactors were constructed and tested for E. coli, Salmonella, NO3-N, and dissolved reactive phosphorus (DRP) at hydraulic retention times (HRTs) of 12 and 24 h and at controlled temperatures of 10 and 21.5 °C. Influent solution was spiked to 30 mg L−1 NO3-N, 2–8 × 105 E. coli and Salmonella, and 0.1 mg L−1 DRP. Microbial removal was consistently observed with removal ranging from 75 to 78% reduction at 10 °C and 90–96% at 21.5 °C. The concentration reduction ranged from 2.75 to 9.03 × 104 for both organisms. HRT had less impact on microbial removal than temperature and thus further investigation of removal under lower HRTs is warranted. Nitrate concentrations averaged 96% reduction (with load removal of 14.6 g N m−3 d−1) from 21.5 °C columns at 24 HRT and 29% reduction (with load removal of 8.8 g N m−3 d−1) from 10 °C columns at 12 HRT. DRP removal was likely temporary due to microbial uptake. While potential for removal of E. coli and Salmonella by woodchip bioreactors is demonstrated, system design will need to be considered. High concentrations of these microbial contaminants are likely to occur during peak flows, when bypass flow may be occurring. The results of this study show that woodchip bioreactors operated for nitrate removal have a secondary benefit through the removal of enteric bacteria