R. Howard Skinner

High Biomass Removal Limits Carbon Sequestration Potential of Mature Temperate Pastures

Decades of plowing have depleted organic C stocks in many agricultural soils. Conversion of plowed fields to pasture has the potential to reverse this process, recapturing organic matter that was lost under more intensive cropping systems. Temperate pastures in the northeast USA are highly productive and could act as significant C sinks. However, such pastures have relatively high biomass removal as hay or through consumption by grazing animals. In addition, the ability to sequester C decreases over time as previously depleted stocks are replenished and the soil returns to equilibrium conditions. The objective of this research was to use eddy covariance systems to quantify CO(2) fluxes over two fields in central Pennsylvania that had been managed as pastures for at least 35 yr. Net ecosystem exchange measurements averaged over 8 site-years suggested that the pastures were acting as small net C sinks of 19 g C m(-2) yr(-1) (positive values indicate uptake). However, when biomass removal and manure deposition were included to calculate net biome productivity, the pastures were a net source of -81 g C m(-2) yr(-1) (negative values indicate loss to the atmosphere). Manure generated from the hay that was consumed off site averaged 18 g C m(-2) yr(-1). Returning that manure to the pastures would have only partially replenished the lost C, and the pastures would have remained net C sources. Heavy use of the biomass produced on these mature pastures prevented them from acting as C sinks.

Nitrogen uptake and partitioning under alternate- and every-furrow irrigation

Alternate-furrow irrigation, combined with fertilizer placement in the non-irrigated furrow, has the potential to reduce fertilizer leaching in irrigated corn (Zea mays L.). The potential also exists, however, for reduced N uptake under alternate-furrow irrigation. This study examined the effects of fertilizer placement and irrigation treatment on N uptake, roota→shoot→root circulation, and partitioning between reproductive and vegetative tissues. Rainfall was above average in both years of the study, especially during May and June, so that root growth beneath the non-irrigated furrow was equal to root production beneath the irrigated furrow. Under those conditions, soil NO3 concentration in the fertilized furrow during late-vegetative and reproductive growth was greater in the alternate-furrow compared with the every-furrow treatment, resulting in increased fertilizer N uptake during reproductive growth and increased N partitioning to reproductive tissues under alternate-furrow irrigation. About 80% of the fertilizer N found in roots had first been translocated to the shoot and then returned via the phloem to the root system. Nitrogen cycling from root to shoot to root was not affected by irrigation treatment. Alternate-furrow irrigation successfully increased N uptake and reduced the potential for NO3leaching when environmental conditions allowed adequate root development in the non-irrigated furrow, and when the growing season was long enough to allow the crop to reach physiological maturity.

Root distribution following spatial separation of water and nitrogen supply in furrow irrigated corn

Proper management of water and fertilizer placement in irrigated corn (Zea mays L.) has the potential to reduce nitrate leaching into the groundwater. Potential management practices tested in a two year field experiment included row or furrow fertilizer placement combined with every or alternate furrow irrigation. To understand how fertilizer availability to plants could be affected by these management practices, root growth and distribution in a Ulm clay loam soil were examined. Spring rains were greater than normal in both years providing adequate moisture for early root growth in both irrigated and non-irrigated furrows. As the non-irrigated furrow began to dry, root biomass increased as much as 126% compared with the irrigated furrow. The greatest increase was at lower depths, however, where moisture was still plentiful. When early season moisture was available, roots proliferated throughout the soil profile and quickly became available to take up fertilizer N in both irrigated and non-irrigated furrows. Root growth responded positively to fertilizer placement in the furrow in 1996 but not in 1995. Excessive N leaching in 1995 may have limited the response to fertilizer N.

Grazing Can Reduce the Environmental Impact of Dairy Production Systems

Incorporating managed rotational grazing into a dairy farm can result in an array of environmental consequences. A comprehensive assessment of the environmental impacts of four management scenarios was conducted by simulating a 250-acre dairy farm typical of Pennsylvania with: (i) a confinement fed herd producing 22,000 lbs of milk per cow per year; (ii) a confinement fed herd producing 18,500 lbs; (iii) a confinement fed herd with summer grazing producing 18,500 lbs; and (iv) a seasonal herd maintained outdoors producing 13,000 lbs. Converting 75 acres of cropland to perennial grassland reduced erosion 24% and sediment-bound and soluble P runoff by 23 and 11%, respectively. Conversion to all perennial grassland reduced erosion 87% with sediment-bound and soluble P losses reduced 80 and 23%. Ammonia volatilization was reduced about 30% through grazing, but nitrate leaching loss increased up to 65%. Grazing systems reduced the net greenhouse gas emission by 8 to 14% and the C footprint by 9 to 20%. Including C sequestration further reduced the C footprint of an all grassland farm up to 80% during the transition from cropland. The environmental benefits of grass-based dairy production should be used to encourage greater adoption of managed rotational grazing in regions where this technology is well adapted.

Biochar amendment of soil improves resilience to climate change.

Because of climate change, insufficient soil moisture may increasingly limit crop productivity in certain regions of the world. This may be particularly consequential for biofuel crops, many of which will likely be grown in drought‐prone soils to avoid competition with food crops. Biochar is the byproduct of a biofuel production method called pyrolysis. If pyrolysis becomes more common as some scientists predict, biochar will become more widely available. We asked, therefore, whether the addition of biochar to soils could significantly increase the availability of water to a crop. Biochar made from switchgrass (Panicum virgatum L.) shoots was added at the rate of 1% of dry weight to four soils of varying texture, and available water contents were calculated as the difference between field capacity and permanent wilting point water contents. Biochar addition significantly increased the available water contents of the soils by both increasing the amount of water held at field capacity and allowing plants to draw the soil to a lower water content before wilting. Among the four soils tested, biochar amendment resulted in an additional 0.8–2.7 d of transpiration, which could increase productivity in drought‐prone regions or reduce the frequency of irrigation. Biochar amendment of soils may thus be a viable means of mitigating some of the predicted decrease in water availability accompanying climate change that could limit the future productivity of biofuel crops.

Micrometeorological Methods for Assessing Greenhouse Gas Flux

Micrometeorological methods for measuring CO 2 and N 2 O provide an opportunity for large-scale, long-term monitoring of greenhouse gas flux without the limitations imposed by chamber methods. Flux gradient and eddy covariance methods have been used for several decades to monitor greenhouse gases and large international networks now exist to coordinate efforts to understand environmental and management effects on CO 2 flux. Less information is available on N 2 O flux and an expanded effort to provide year-round assessment of this important greenhouse gas is needed. This chapter provides an overview of common micrometeorological methods used for flux measurements, discusses benefits and shortcomings of these methods, outlines corrections and adjustments to the raw data that are needed to obtain meaningful measurements and fill gaps in the data, and provides examples of unique insights into mechanisms that control greenhouse gas fluxes that can be obtained through micrometeorological methods.

Environmental Impacts of Switchgrass Management for Bioenergy Production

In this chapter, we review major environmental impacts of growing switchgrass as a bioenergy crop, including effects on carbon sequestration, greenhouse gas emissions, soil erosion, nutrient leaching, and runoff. Information from life cycle analyses, including the effects of indirect land use change (iLUC), is examined to quantify the full impact of migration to bioenergy cropping systems on both managed and natural ecosystems. Information on the environmental impacts of switchgrass cultivation is scarce and there exists a critical need for additional research. What limited information there is suggests that switchgrass provides multiple environmental benefits compared to annual crop cultivation. However, benefits generally appear to be similar to other perennial crops.

Nutritive value of Virginia wildrye, a cool-season grass native to the northeast USA

blue wildrye (E. glaucus Buckley), and Dahurian wildrye (E. dahuricus Turcz ex Greiseb) the most noteworthy Interest in native plant species for conservation and production of the Elymus wildryes as forages and briefly mentioned has increased because of new federal policies. We evaluated accessions of the native cool-season grass Virginia wildrye (Elymus virginicus Virginia wildrye for revegetating prairie (Asay and JenL.) from the northeastern USA for nutritive value and its association sen, 1996). Closely related, both Virginia wildrye and with plant morphological traits. Thirteen accessions, one cultivar Canada wildrye are highly self-fertile allotetraploids (Omaha), and one commercial ecotype of Elymus were transplanted (2n 28) with the SSHH genome constitution (Asay into single-row field plots in late summer of 2000 at Beltsville, MD, and Jensen, 1996). Very little breeding has been done Rock Springs, PA, and Big Flats, NY. Two orchardgrass (Dactylis in either species. In an evaluation of 30 grass species in glomerata L.) cultivars were included. Primary growth was harvested Saskatchewan, Canada, Virginia wildrye was considered in April (Beltsville) or May (Rock Springs and Big Flats) of 2001 and a promising forage grass, but lack of winter hardiness 2002 and analyzed for neutral detergent fiber (NDF), crude protein limited its persistence (Lawrence, 1978). Hereafter in (CP), and digestible NDF (dNDF). Nutritive value measures were this paper, the terms “Elymus” and “wildrye” will refer related to plant morphological attributes [leaf width, length, area, and leaf-to-stem mass ratio (LSR)]. Virginia wildrye accessions difto E. virginicus. fered (P 0.01) in nutritive value and often had lower NDF and Genetic variation for nutritive value occurs within higher CP and dNDF than the commercial ecotype, Omaha cultivar, many species of cool-season introduced grasses (Casler and orchardgrass. The LSR accounted for most of the variation in et al., 1996). Sometimes the variation in nutritive value nutritive value. Orchardgrass was more mature at harvest than Elymus results simply from differences in maturity or plant morentries and thus lower in nutritive value. Neutral detergent fiber was phology. For example, the LSR of grasses typically denegatively correlated with LSR (r 0.26 to 0.74, P 0.05), clines with maturity and is accompanied by a decrease whereas CP and dNDF were positively correlated (r 0.36 to 0.80 in nutritive value (Nelson and Moser, 1994). Nutritive for CP and 0.44 to 0.74 for dNDF, P 0.05). Neutral detergent fiber value of grasses, however, can be improved by changing was also positively correlated (r 0.27 to 0.86, P 0.05) with leaf the cell wall composition without affecting plant matulength. Virginia wildrye is comparable to other cool-season grasses in nutritive value. rity or gross morphology [e.g., in smooth bromegrass (Bromus inermis Leyss); Casler and Carpenter, 1989]. Plant morphology can influence other traits related to livestock performance. For example, leaf width in tall M forage grasses grown in the northeastern fescue was negatively related to leaf tensile strength USA are introduced species such as orchardgrass, and, hence, positively related to preference by grazing bluegrass (Poa spp.), or tall fescue (Festuca arundinacea cattle (MacAdam and Mayland, 2003). Schreb.). Native warm-season perennials, such as switchGreater interest in the use of native grass species in grass (Panicum virgatum L.) and big bluestem (Androconservation and other plantings has created a need for pogon gerardii Vitman), account for most of the native more information on the suitability of locally adapted grasses used in forage systems. Few, if any, native coolnative species for the northeastern USA. We could not season grasses have been evaluated as potential forage find any information on the nutritive value of Elymus species in the northeastern USA. New federal policies as a forage grass in the northeastern USA. Previously, related to invasive species, conservation plantings, and we reported on the productivity, morphology, and perfarm programs have created greater interest in native sistence of several Elymus accessions at three locations plants for conservation and production during recent in the northeastern USA (Sanderson et al., 2004). Our years (Richards et al., 1998; Federal Register, 1999). objective in this study was to evaluate the same northVirginia wildrye, a perennial cool-season grass native eastern accessions of Virginia wildrye for nutritive value. to the northeastern USA, grows along streams, forest margins, and in other moist areas (Pohl, 1947; HitchMATERIALS AND METHODS cock, 1971). It is recommended as a component in some conservation plantings for revegetation. Asay and JenThe experiment was conducted at the USDA-NRCS Plant sen (1996) considered Canada wildrye (E. canadensis L.), Materials Center in Big Flats, NY (42 N, 76 54 W, elevation 290 m), the Russell E. Larson Agricultural Research Center at Rock Springs, PA (40 48 N, 77 52 W, elevation 365 m), Matt A. Sanderson and R. Howard Skinner, USDA-ARS Pasture and the USDA-NRCS National Plant Materials Center in Systems and Watershed Management Research Unit, Bldg 3702, CurBeltsville, MD (39 02 N, 76 56 W, elevation 36 m) during 2000 tin Road, University Park, PA 16802-3702; Jennifer Kujawski, USDAto 2002. Soil types were Unadilla silt loam (coarse-silty, mixed, NRCS National Plant Materials Center, Beltsville, MD 20705; Martin van der Grinten, USDA-NRCS Plant Materials Center, Big Flats, NY active, mesic Typic Dystrudepts) at Big Flats, Hagerstown silt 14830. Received 5 December 2003. *Corresponding author (mas44@ psu.edu). Abbreviations: ADF, acid detergent fiber; CP, crude protein; dNDF, digestible neutral detergent fiber; IVTD, in vitro true digestibility; Published in Crop Sci. 44:1385–1390 (2004).  Crop Science Society of America LSR, leaf-to-stem mass ratio; NDF, neutral detergent fiber; SLA, specific leaf area. 677 S. Segoe Rd., Madison, WI 53711 USA

Planting Native Species to Control Site Reinfestation by Japanese Knotweed (Fallopia japonica)

Japanese knotweed (Fallopia japonica) is a highly invasive species that has become a serious problem in riparian zones and along road and railroad right-of-ways in North America and Europe. Once established, it forms solid colonies choking out other herbaceous vegetation, displacing native species, negatively affecting wildlife, and altering hydrological processes. We evaluated the ability of 6 native species mixtures to prevent recolonization by Japanese knotweed at a site receiving either 1 or 2 yr of glyphosate applications and mowing to suppress existing Japanese knotweed stands. One year of spraying and mowing was not sufficient to adequately suppress Japanese knotweed. By 37 months after sowing, only the multi-species riparian buffer mixture (RBM) had plant cover >20%, whereas cover for all other mixtures was <10%. Japanese knotweed had successfully reinvaded all plots with percent cover ranging from 72–96%. Two years of spraying and mowing reduced Japanese knotweed percent cover to an average of 12% (range 7–18%) during the first 2 yr after sowing and to 28–43% by 37 months. Only 2 species mixtures adequately established when sown following 2 yr of Japanese knotweed suppression, the RBM and a mixture of Virginia wildrye (Elymus virginicus) and prairie cordgrass (Spartina pectinata). Percent cover for both mixtures was >80% at 25 months after sowing and ≥50% after 37 months. Two years of Japanese knotweed suppression was necessary before native species mixtures could successfully compete against invasive recolonization.

Implications of Observed and Simulated Soil Carbon Sequestration for Management Options in Corn-based Rotations

Managing cropping systems to sequester soil organic C (SOC) improves soil health and resilience to changing climate. Perennial crops, no-till planting, manure, and cover crops can add SOC; however, their impacts have not been well documented in the northeastern United States. Our objectives were (i) to monitor SOC from a bioenergy cropping study in Pennsylvania that included a corn ( L.)-soybean [ (L.) Merr.]-alfalfa ( L.) rotation, switchgrass ( L.), and reed canarygrass ( L.); (ii) to use the CQESTR model to predict SOC sequestration in the bioenergy crops (with and without projected climate change); and (iii) to use CQESTR to simulate influence of tillage, manure, cover cropping, and corn stover removal in typical dairy forage (silage corn-alfalfa) or grain corn-soybean rotations. Over 8 yr, measured SOC increased 0.4, 1.1, and 0.8 Mg C ha yr in the bioenergy rotation, reed canarygrass, and switchgrass, respectively. Simulated and measured data were significantly correlated ( < 0.001) at all depths. Predicted sequestration (8-14 Mg C ha over 40 yr) in dairy forage rotations was much larger than with corn-soybean rotations (-4.0-0.6 Mg C ha over 40 yr), due to multiple years of perennial alfalfa. No-till increased sequestration in the simulated dairy forage rotation and prevented a net loss of C in corn-soybean rotations. Simulations indicated limited impact of cover crops and manure on long-term SOC sequestration. The low solids content of liquid dairy manure is the likely reason for the less-than-expected impact of manure. Overall, simulations suggest that inclusion of alfalfa provides the greatest potential for SOC sequestration with a typical Pennsylvania crop rotation.