Michel A. Cavigelli

Challenges and opportunities for mitigating nitrous oxide emissions from fertilized cropping systems

Nitrous oxide (N2O) is often the largest single component of the greenhouse-gas budget of individual cropping systems, as well as for the US agricultural sector as a whole. Here, we highlight the factors that make mitigating N2O emissions from fertilized agroecosystems such a difficult challenge, and discuss how these factors limit the effectiveness of existing practices and therefore require new technologies and fresh ideas. Modification of the rate, source, placement, and/or timing of nitrogen fertilizer application has in some cases been an effective way to reduce N2O emissions. However, the efficacy of existing approaches to reducing N2O emissions while maintaining crop yields across locations and growing seasons is uncertain because of the interaction of multiple factors that regulate several different N2O-producing processes in soil. Although these processes have been well studied, our understanding of key aspects and our ability to manage them to mitigate N2O emissions remain limited.

Corn-yield estimation through assimilation of remotely sensed data into the CSM-CERES-Maize model

One of the applications of crop simulation models is to estimate crop yield during the current growing season. Several studies have tried to integrate crop simulation models with remotely sensed data through data‐assimilation methods. This approach has the advantage of allowing reinitialization of model parameters with remotely sensed observations to improve model performance. In this study, the Cropping System Model‐CERES‐Maize was integrated with the Moderate Resolution Imaging Spectroradiometer (MODIS) leaf area index (LAI) products for estimating corn yield in the state of Indiana, USA. This procedure, inversion of crop simulation model, facilitates several different user input modes and outputs a series of agronomic and biophysical parameters, including crop yield. The estimated corn yield in 2000 compared reasonably well with the US Department of Agriculture National Agricultural Statistics Service statistics for most counties. Using the seasonal LAI in the optimization procedure produced the best results compared with only the green‐up LAIs or the highest LAI values. Planting, emergence and maturation dates, and N fertilizer application rates were also estimated at a regional level. Further studies will include investigating model uncertainties and using other MODIS products, such as the enhanced vegetation index.

Mineralizable carbon, nitrogen, and water-extractable phosphorus release from stockpiled and composted manure and manure-amended soils

Much of land-applied manure is surface-broadcast or incorporated to a shallow depth of fields under crop Dissolved N and P transfer to runoff water may increase with residue and conservation tillage management because of surface applications and shallow soil incorporation of animal manure. Information is needed regarding water-extractable nutrient release the need to conserve stored soil water for crop producduring manure decomposition to quantify that potential transfer to tion (Unger and Parker, 1976; Dao and Nguyen, 1989; runoff in permanent pastures and conservation tillage systems. ReDao, 1993; Schwartz et al., 2002). Incorporating manure lease of net mineralizable C (MIN_C), net mineralizable N (MIN_N), using inversion or disk tillage may improve the effiand dissolved reactive P (DRP) was determined in stockpiled and ciency of manure nutrient utilization by crops, but intencomposted cattle (Bos taurus) manure and manure-amended soils at sive tillage often eliminates the benefits associated with 4, 20, and 35 C for 322 d at about 60% water-filled pore space. Flushes conservation tillage practices such as reduced soil water of CO2–C exceeding 100 mg kg 1 d 1, inorganic N, and DRP were evaporation, erosion and runoff control, and soil C storreleased rapidly from both manures when incubated alone or as soil age (Jones et al., 1985; Gilley et al., 1997; Dao, 1993, amendments. Dissolved P release varied inversely with sorption ca1998; Allmaras et al., 2000). Large quantities of stockpacity and degree of P saturation in an Aridic Paleustalf and Torrertic Paleustoll. Net mineralizable C, MIN_N, and DRP flux densities were piled cattle and poultry manure or manure mixed with lognormally distributed during the 322-d incubation. Results from the bedding materials are also applied to Conservation Relognormal modeling approach suggest that incubations needed to be serve Program grasslands and pastures (Marshall et al., performed only for as long as needed to attain the 50% maximal flux 2001). As a result, manure particulates remain on the density beyond the maximum to predict MIN_C, MIN_N, and DRP soil surface, causing elevated flow-weighted NH4–N and release flux density distributions. Significant nonlinear relationships DRP concentrations in runoff after manure applications exist between ln(cumulative CO2–C) and inorganic N or DRP and (Pierson et al., 2001). Water-extractable manure nutrihave an inflexion point between 14 and 20 d. The nonlinearity of the ents may directly discharge to surface waters or build C-to-N and C-to-DRP relationships indicates multiple substrate pools up at the soil surface and increase the potential for N and supports the use of lognormal distributions to describe MIN_C, and P losses and contamination of surface and ground MIN_N, and DRP release from manures and manure-amended soils and to shorten laborious incubations. water via surface and subsurface transport mechanisms (Liebhardt et al., 1979; Sharpley et al., 1993; James et al., 1996; Jansen et al., 2000; Zhang et al., 2002). Information regarding decomposition and particulate L production in the United States increasnutrient mineralization in manures at the soil surface is ingly occurs in confined animal feeding operations needed. Insights into the decomposition process may (CAFOs). Large numbers of animals are gathered in a be gained from the knowledge of transformations that relatively small land area where huge quantities of nutrioccur during the composting of animal manure to which ents in feeds are imported to support the operations of no additional materials (i.e., crop residues, wood chips, dairies and poultry (Gallus gallus domesticus), swine saw dust, etc.) have been added. The N fraction has been (Sus scrofa domesticus), and beef cattle production facilextensively studied to predict the N-supplying capacity ities (CAST, 1996). Large-scale CAFOs faced with inof composts (Gale and Gilmour, 1986; Hadas and Portcreasing pollution potential are managing manure as a noy, 1994; Thomsen and Olesen, 2000). Manure and waste product (Natl. Res. Counc., 1993; CAST, 1996). manure compost MIN_N is associated with proteins and This results in intensive land applications of manure in is thus strongly correlated with N released by digestion the immediate vicinity of the feedlots because of the with pepsin (Castellanos and Pratt, 1981). Composihigh cost of transporting manure for distances greater tional differences, primarily in total C and N between than about 30 km. Such management practices have manures and composts, result in significant differences resulted in nutrient-loaded soils in agricultural fields in manure and compost MIN_N. A linear relationship near CAFOs (Zhang et al., 2002). was observed between MIN_N and MIN-C as percentAnimal manure has long been used as an organic age of added total N and C during the first 4 wk of source of plant nutrients and organic matter to improve incubation of 10 manures and composts added to a Typic the physical and fertility conditions of agricultural lands. Abbreviations: CAFO, confined animal feeding operation; CM, comT.H. Dao, USDA-ARS, AMBL, BARC-East, Beltsville, MD 20705posted manure; DRP, dissolved reactive phosphorus; flux densitymax, 2350; and M.A. Cavigelli, USDA-ARS, SASL, 10300 Baltimore Ave., maximal flux density; MIN_C, net carbon mineralized; MIN_N, net Beltsville, MD 20705-2350. Received 14 June 2002. *Corresponding nitrogen mineralized; PDF, probability density function; S-1, first firstauthor (thdao@anri.barc.usda.gov). order reaction; S-2, second first-order reaction; SM, stockpiled manure; WFPS, water-filled pore space. Published in Agron. J. 95:405–413 (2003).

US agricultural nitrous oxide emissions: context, status, and trends

The use of commercial nitrogen (N) fertilizers has led to enormous increases in US agricultural productivity. However, N losses from agricultural systems have resulted in numerous deleterious environmental impacts, including a continuing increase in atmospheric nitrous oxide (N2O), a greenhouse gas (GHG) and an important catalyst of stratospheric ozone depletion. Although associated with about 7% of total US GHG emissions, agricultural systems account for 75% of total US N2O emissions. Increased productivity in the crop and livestock sectors during the past 30 to 70 years has resulted in decreased N2O emissions per unit of production, but N2O emissions from US agriculture continue to increase at a rate of approximately 0.46 teragrams of carbon dioxide equivalents per year (2002–2009). This rate is lower than that during the late 20th century. Improvements in agricultural productivity alone may be insufficient to lead to reduced emissions; implementing strategies specifically targeted at reducing N2O emiss...

Suitability of composts as potting media for production of organic vegetable transplants.

Composts, used alone or in mixtures with other materials, can serve as horticultural potting media in organic production systems. In this study, we evaluated the suitability of two locally available composts as media for lettuce and tatsoi produced organically in an unheated greenhouse. One of the composts was produced from food residuals with landscape wastes as a bulking agent, while the other was generated from used horse bedding. Although the two materials had relatively similar total N contents, C:N ratios, and bulk densities, they performed very differently as potting media. Net N mineralization, measured in laboratory incubations, was high in the compost derived from food residuals, but the horse-bedding compost showed net N immobilization, perhaps due to high salinity. Crop production in the food residuals compost was statistically similar to a control treatment consisting of a commercial peat-based potting medium with synthetic fertilizer. Crop growth in the medium consisting of horse-bedding compost, used at 100% or in a 50%/50% mixture with a commercial substrate of bark, peat, and sand, was unacceptable for commercial production. Although the cost per flat of the food residuals compost was slightly higher than that of the commercial peat-based medium, for organic production this additional cost may be insignificant since there are limited potting media options, and price premiums are typically available.

Community composition and population genetics of insect pathogenic fungi in the genus Metarhizium from soils of a long-term agricultural research system

Fungi in the genus Metarhizium are insect pathogens able to function in other niches, including soil and plant rhizosphere habitats. In agroecosystems, cropping and tillage practices influence soil fungal communities with unknown effects on the distribution of Metarhizium, whose presence can reduce populations of crop pests. We report results from a selective media survey of Metarhizium in soils sampled from a long-term experimental farming project in the mid-Atlantic region. Field plots under soybean cultivation produced higher numbers of Metarhizium colony-forming units (cfu) than corn or alfalfa. Plots managed organically and via chisel-till harboured higher numbers of Metarhizium cfu than no-till plots. Sequence typing of Metarhizium isolates revealed four species, with M. robertsii and M. brunneum predominating. The M. brunneum population was essentially fixed for a single clone as determined by multilocus microsatellite genotyping. In contrast, M. robertsii was found to contain significant diversity, with the majority of isolates distributed between two principal clades. Evidence for recombination was observed only in the most abundant clade. These findings illuminate multiple levels of Metarhizium diversity that can be used to inform strategies by which soil Metarhizium populations may be manipulated to exert downward pressure on pest insects and promote plant health.

Subplots facilitate assessment of corn yield losses from weed competition in a long-term systems experiment

Weeds can limit crop yield, particularly in organic systems where herbicide technologies are unavailable. Weedy and weed-free subplots were established within the full plots of a long-term Farming Systems Project at Beltsville, Maryland, USA, to determine the effect of weed competition on corn yields in six of the first ten years of an experiment designed to compare conventional and organic cropping systems. Weed abundance was determined in two ways, by sampling above-ground biomass and by estimating percent of soil area covered by weeds. Percent weed cover was shown to be linearly related to weed biomass but was more comprehensive than biomass sampling for determining the overall weed abundance in the larger full plots. The relationship between corn yield and weed cover estimates in subplots was used to estimate corn yield losses to weed competition and weed-free yield in the full plots. Weed competition reduced corn grain yield in all years in subplots, however, the degree of yield reduction ranged from 4 to 76%. This considerable variability was explained by rainfall whereby the highest yield loss occurred in years with below-average rainfall and the lowest yield loss occurred in years with above-average rainfall. Estimation of full-plot corn yield loss to weed competition demonstrated that yield differences between the conventional and organic systems were explained not only by weed competition but also by nitrogen availability. Results suggested that, in years with above-average rainfall, nitrogen availability was more limiting to organic corn yield than weed competition, but that, in years with below-average rainfall, weed competition was more limiting than nitrogen availability.

Soil microbial community characteristics along an elevation gradient in the Laguna Mountains of Southern California

We sampled soil at four sites in the Laguna Mountains in the western Sonoran Desert to test the effects of site and sample location (between or beneath plants) on fatty acid methyl ester (FAME) and carbon substrate ulilization (Biolog) profiles. The four sites differed in elevation, soil type, plant community composition, and plant percent cover. Soil pH decreased and plant density increased with elevation. Fertile islands, defined as areas beneath plants with greater soil resources than bare areas, are present at all sites, but are most pronounced at lower elevations. Consistent with this pattern, fertile islands had the greatest influence on FAME and Biolog profiles at lower elevations. Based on the use of FAME biomarker and principal components analyses, we found that soil microbial communities between plants at the lowest elevation had proportionally more Gram-negative bacteria than all other soils. At the higher elevation sites there were few differences in FAME profiles of soils sampled between vs. beneath plants. Differences in FAME profiles under plants among the four sites were small, suggesting that the plant influence per se is more important than plant type in controlling FAME profiles. Since microbial biomass carbon was correlated with FAME number ðr ¼ 0:85; P , 0:0001Þ and with FAME named ðr ¼ 0:88; P , 0:0001Þ and total areas ðr ¼ 0:84; P , 0:0001Þ; we standardized the FAME data to ensure that differences in FAME profiles among samples were not the result of differences in microbial biomass. Differences in microbial substrate utilization profiles among sampling locations were greatest between samples taken under vs. between plants at the two lower elevation sites. Microbial substrate utilization profiles, therefore, also seem to be influenced more by the presence of plants than by specific plant type. Published by Elsevier Science Ltd.

Weed Seed Persistence and Microbial Abundance in Long-Term Organic and Conventional Cropping Systems

Weed seed persistence in soil can be influenced by many factors, including crop management. This research was conducted to determine whether organic management systems with higher organic amendments and soil microbial biomass could reduce weed seed persistence compared with conventional management systems. Seeds of smooth pigweed and common lambsquarters were buried in mesh bags in organic and conventional systems of two long-term experiments, the Farming Systems Project at the Beltsville Agricultural Research Center, Maryland, and the Farming Systems Trial at the Rodale Institute, Pennsylvania. Seed viability was determined after retrieval at half-year intervals for 2 yr. Total soil microbial biomass, as measured by phospholipid fatty acid (PLFA) content, was higher in organic systems than in conventional systems at both locations. Over all systems, locations, and experiments, viable seed half-life was relatively consistent with a mean of 1.3 and 1.1 yr and a standard deviation of 0.5 and 0.3 for smooth pigweed and common lambsquarters, respectively. Differences between systems were small and relatively inconsistent. Half-life of smooth pigweed seeds was shorter in the organic than in the conventional system in two of four location-experiments. Half-life of common lambsquarters was shorter in the organic than in the conventional system in one of four location-experiments, but longer in the organic than in the conventional system in two of four location-experiments. There were few correlations between PLFA biomarkers and seed half-lives in three of four location-experiments; however, there were negative correlations up to −0.64 for common lambsquarters and −0.55 for smooth pigweed in the second Rodale experiment. The lack of consistent system effects on seed persistence and the lack of consistent associations between soil microbial biomass and weed seed persistence suggest that soil microorganisms do not have a dominating role in seed mortality. More precise research targeted to identifying specific microbial functions causing seed mortality will be needed to provide a clearer picture of the role of soil microbes in weed seed persistence. Nomenclature: Common lambsquarters, Chenopodium album L. CHEAL; smooth pigweed, Amaranthus hybridus L. AMACH

Ground Beetle (Coleoptera: Carabidae) Assemblages in Organic, No-Till, and Chisel-Till Cropping Systems in Maryland

Abstract Ground beetle assemblages were compared in organic, no-till, and chisel-till cropping systems of the USDA Farming Systems Project in Maryland. The cropping systems consisted of 3-yr rotations of corn (Zea mays L.), soybean (Glycine max L. Merr.), and wheat (Triticum aestivum L.) that were planted to corn and soybean during the 2 yr of field sampling (2001–2002). Each year, ground beetles were sampled using pitfall traps during three 9- to 14-d periods corresponding to spring, summer, and fall. A total of 2,313 specimens, representing 31 species, were collected over the 2 yr of sampling. The eight most common species represented 87% of the total specimens collected and included Scarites quadriceps Chaudoir, Elaphropus anceps (LeConte), Bembidion rapidum (LeConte), Harpalus pensylvanicus (DeGeer), Poecilus chalcites (Say), Clivina impressefrons LeConte, Agonum punctiforme (Say), and Amara aenea (DeGeer). Canonical variates analysis based on the 10 most abundant species showed that the carabid assemblages in the three cropping systems were distinguishable from each other. The organic system was found to be more different from the no-till and chisel-till systems than these two systems were from each other. In 2002, ground beetle relative abundance, measured species richness, and species diversity were greater in the organic than in the chisel-till system. Similar trends were found in 2001, but no significant differences were found in these measurements. Relatively few differences were found between the no-till and chisel-till systems. The estimated species richness of ground beetles based on several common estimators did not show differences among the three cropping systems. The potential use of ground beetles as ecological indicators is discussed.