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.

Effects of dietary protein concentration on ammonia volatilization, nitrate leaching, and plant nitrogen uptake from dairy manure applied to lysimeters.

This lysimeter experiment was designed to investigate the effects of dietary crude protein (CP) concentration on nitrate-N (NO-N) and ammonia (NH) losses from dairy manure applied to soil and manure N used for plant growth. Lactating dairy cows were fed diets with 16.7% CP (HighCP) or 14.8% CP (LowCP) content. Feces and urine were labeled with N by ruminal pulse-doses of NHCl. Unlabeled and N-labeled feces and urine were used to produce manure for a study with 21 lysimeters in a greenhouse. Manure application rate was 277 kg N ha. Ammonia emissions were measured at 3, 8, 23, 28, 54, and 100 h after manure application. Manure was incorporated into the soil, and a leaching event was simulated. Spring barley was planted (387 plants per m) 7 d after the leaching event and harvested at senescence. Ammonia emission rates and the contribution of urinary N to NO-N were on average about 100% greater for HighCP vs. LowCP manures. With both LowCP and HighCP manures, a greater proportion of urinary vs. fecal N was recovered in leachate NO-N. There was no difference in whole-crop barley N yields between LowCP and HighCP manures, but barley kernel N yield tended to be greater ( = 0.09) for lysimeters treated with HighCP manures. Using a unique labeling approach, this lysimeter experiment demonstrated that when applied at equal soil N application rates, manure from cows fed the HighCP diet resulted in markedly greater NH emissions and urinary N losses with leachate NO-N than manure from cows fed the LowCP diet.

The LTAR Common Experiment at Upper Chesapeake Bay: Integrated.

Corn (Zea mays) crops harvested as grain in autumn do not provide opportunity for cover crop establishment, which may be remedied by interseeding cover crops into growing corn. Grazing cover crops after corn grain harvest could provide added revenues and increase nutrient cycling in the system while providing additional ecosystem services. However, tradeoffs between cash crop productivity and cover crop inclusion, and use as grazed forage, are not fully understood. This 4-year Long-Term Agroecosystem Research Integrated Common Experiment project evaluated the effect of interseeding cereal rye (Secale cereale) into corn for grazing after corn grain harvest on corn grain yield and late-season grazing. Cereal rye was interseeded into corn in early June. After corn grain harvest, six paddocks at each location were randomly allotted to grazed (GRAZ) or not grazed (NG). The GRAZ paddocks were grazed with beef cattle in late autumn and again in early spring if regrowth allowed. Paddocks were flown with an unmanned aerial system (UAS) to characterize spatial forage yield and quality. Cereal rye provided an additional 20-30 grazing days in the autumn for 24 beef cows on 4.8 ha. Early spring growth shows potential to provide even greater forage yields than autumn, but growth is less dependable. Corn grain yields did not decrease except in 2019 (dry year) when yields were 40% lower. There were no significant differences in soil health indicators between GRAZ and NG paddocks. The UAS shows promise as a tool for monitoring forage yield and quality and optimizing grazing management.

The LTAR Cropland Common Experiment in the Upper Chesapeake Bay.

Dairy production is a key agricultural enterprise in the Upper Chesapeake Bay (UCB) basin, where phosphorous (P) and nitrogen (N) loading contribute to eutrophication. Import of forages and grains and application of mineral fertilizers contribute to nutrient imbalances in the basin. The UCB Long-Term Agroecosystem Research Cropland Common Experiment aims to evaluate diverse crop rotations that minimize the need for imported feed, maximize year-round living cover, and reduce nutrient losses. UCB's plot-scale experiment was established in 2018, incorporating an ongoing cropping system study that was established by the Pennsylvania State University in 2010. An alternative dairy cropping rotation (including silage and grain corn [Zea mayes L.], alfalfa [Medicago sativa L.]/orchardgrass [Dactylis glomerata L.] mix, winter rye silage [Secale cereale L.], and sorghum-sudangrass [Sorghum × drummondii (Steud.) Millsp. & Chas]) that employed manure injection, integrated pest management, and less frequent manure application was compared to a prevailing, conventionally managed silage corn-alfalfa rotation with higher manure application rates. A field-scale experiment was established in 2019 to monitor alternative production practices (manure injection and avoidance of neonicotinoid seed treatment) and prevailing practices in three fields on a commercial dairy farm. Findings suggest that crop rotation diversification, manure injection, and integrated pest management have the potential to increase the economic and environmental sustainability of dairy cropping systems, but long-term evaluation is needed for confirmation.

Low-disturbance manure incorporation effects on ammonia and nitrate loss.

Low-disturbance manure application methods can provide the benefits of manure incorporation, including reducing ammonia (NH3) emissions, in production systems where tillage is not possible. However, incorporation can exacerbate nitrate (NO3⁻) leaching. We sought to assess the trade-offs in NH3 and NO3⁻ losses caused by alternative manure application methods. Dairy slurry (2006-2007) and liquid swine manure (2008-2009) were applied to no-till corn by (i) shallow (<10 cm) disk injection, (ii) surface banding with soil aeration, (iii) broadcasting, and (iv) broadcasting with tillage incorporation. Ammonia emissions were monitored for 72 h after application using ventilated chambers and passive diffusion samplers, and NO3⁻ leaching to 80 cm was monitored with buried column lysimeters. The greatest NH3 emissions occurred with broadcasting (35-63 kg NH3-N ha⁻), and the lowest emissions were from unamended soil (<1 kg NH-N ha⁻¹). Injection decreased NH-N emissions by 91 to 99% compared with broadcasting and resulted in lower emissions than tillage incorporation 1 h after broadcasting. Ammonia-nitrogen emissions from banding manure with aeration were inconsistent between years, averaging 0 to 71% that of broadcasting. Annual NO3⁻ leaching losses were small (<25 kg NO3-N ha⁻¹) and similar between treatments, except for the first winter when NO3⁻ leaching was fivefold greater with injection. Because NO3⁻ leaching with injection was substantially lower over subsequent seasons, we hypothesize that the elevated losses during the first winter were through preferential flow paths inadvertently created during lysimeter installation. Overall, shallow disk injection yielded the lowest NH3 emissions without consistently increasing NO3⁻ leaching, whereas manure banding with soil aeration conserved inconsistent amounts of N.

Envisioning the manureshed: Toward comprehensive integration of modern crop and animal production.

The specialization and intensification of agriculture have produced incredible gains in productivity, quality, and availability of agricultural commodities but have resulted in the separation of crop and animal production. A by-product of this separation has been the accumulation of manure regions where animal production is concentrated. Enter the "manureshed," an organizing framework for integrating animal and crop production where budgeting of manure nutrients is used to strategically guide their recycling and reuse in agricultural production systems where manure resources are of highest value. To move beyond regional nutrient balance analyses into the transformational realm required to mitigate "wicked" manure problems, manureshed management requires recognition of the challenges to systematically reorganizing resource flows. In better integrating crop and livestock systems, manureshed management must account for the unique nature of managing manure nutrients within individual livestock industries, anticipate trade-offs in substituting manure for commercial fertilizer, promote technologies to refine manure, and engage extensive social networks across scales that range from the farmgate to nation and beyond.

Manuresheds offer a system-level strategy for recovering manure's fertilizer value. Manuresheds address nutrient imbalances and environmental and socioeconomic outcomes. Manuresheds scale from single operations to a "mega-manureshed" transecting the southeastern United States. Manureshed management supports the strategic alignment of technologies, markets, and networks.

Challenges and opportunities for manureshed management across U.S. dairy systems: Case studies from four regions.

The manureshed represents cropland needed to safely assimilate manure nutrients from an animal feeding operation. Dairy manuresheds can be contained on-farm but may need to involve additional farms that can assimilate excess nutrients. We present case studies reviewing challenges and opportunities to manureshed management in four major dairy-producing states using available information on local manuresheds. Additionally, geographic information system software was used with data from regulated Minnesota dairies to assess cropland assimilative capacities and transport needs surrounding large dairies. Manureshed requirements vary across regions, but increased import of feed and soil phosphorus accumulation constrain on-farm manure utilization across the United States. In Minnesota, a growing proportion of Jersey cattle and differences in continuous corn (Zea mays L.) vs. corn-alfafa (Medicago sativa L.) rotations contribute to the amount of land needed to absorb dairy manure nutrients. Farm-gate budgets reveal that N-based manuresheds can be contained within Idaho dairies, but P-based manuresheds extend beyond the farm. In New Mexico, relocation of surplus manure nutrients off the farm is common via informal networks, but incentives to strengthen these networks could ensure sustainable manureshed management. Evaluation of manureshed requirements in Pennsylvania is often complicated by the need for additional nutrient management planning and greater understanding of nutrient balances on the preponderance of small dairies. Nutrient imbalances with highly concentrated dairy production often lead to the need for manure transport off-farm. However, advances in herd and cropland management offer opportunities to improve on-farm nutrient efficiencies, and emerging networks and technologies promise to facilitate manure export when needed.

Subsurface application of manures slurries for conservation tillage and pasture soils and their impact on the nitrogen balance.

Injection of cattle and swine slurries can provide soil incorporation in no-till and perennial forage production. Injection is expected to substantially reduce N loss due to ammonia (NH3) volatilization, but a portion of that N conservation may be offset by greater denitrification and leaching losses. This paper reviews our current knowledge of the impacts of subsurface application of cattle and swine slurries on the N balance and outlines areas where a greater understanding is needed. Several publications have shown that liquid manure injection using disk openers, chisels, or tines can be expected to Sreduce NH, emissions by at least 40%, and often by 90% or more, relative to broadcast application. However, the limited number of studies that have also measured denitrification losses have shown that increased denitrification with subsurface application can offset as much as half of the N conserved by reducing NH3 emissions. Because the greenhouse gas nitrous oxide (N2O) is one product of denitrification, the possible increases in N2O emission with injection require further consideration. Subsurface manure application generally does not appear to increase leaching potential when manure is applied at recommended rates. Plant utilization of conserved N was shown in only a portion of the published studies, indicating that further work is needed to better synchronize manure N availability and crop uptake. At this time in the United States, the economic and environmental benefits from reducing losses of N as NH3 are expected to outweigh potential liability from increases in denitrification with subsurface manure application. To fully evaluate the trade-offs among manure application methods, a detailed environmental and agricultural economic assessment is needed to estimate the true costs of potential increases in NO2O emissions with manure injection.

Manure application technology in reduced tillage and forage systems: a review.

Managing manure in reduced tillage and forage systems presents challenges, as incorporation by tillage is not compatible. Surface-applied manure that is not quickly incorporated into soil provides inefficient delivery of manure nutrients to crops due to environmental losses through ammonia (NH3) volatilization and nutrient losses in runoff, and serves as a major source of nuisance odors. An array of technologies now exist to facilitate the incorporation of liquid manures into soil with restricted or minor soil disturbance, some of which are new: shallow disk injection; chisel injection; aeration infiltration; pressure injection. Surface banding of manure inforages decreases NH3 emissions relative to surface broadcasting, as the canopy can decrease wind speed over the manure, but greater reductions can be achieved with manure injection. Soilaeration is intended to hasten manure infiltration, but its benefits are not consistent and may be related to factors such as soildrainage characteristics. Work remains to be done on refining its method of use and timing relative to manure application, which may improve its effectiveness. Placing manure under the soil surface efficiency by injection offers much promise to improve N use efficiency through less NH3 volatilization, reduced odors and decreased nutrient losses in runoff, relative to surface application. We identified significant gaps in our knowledge as manyof these technologies are relatively new, and this should help target future research efforts including environmental, agronomic, and economic assessments.

Role of rainfall intensity and hydrology in nutrient transport via surface runoff.

Loss of soil nutrients in runoff accelerates eutrophication of surface waters. This study evaluated P and N in surface runoff in relation to rainfall intensity and hydrology for two soils along a single hillslope. Experiments were initiated on 1- by 2-m plots at foot-slope (6%) and mid-slope (30%) positions within an alfalfa (Medicago sativa L.)-orchardgrass (Dactylis glomerata L.) field. Rain simulations (2.9 and 7.0 cm h(-1)) were conducted under wet (spring) and dry (late-summer) conditions. Elevated, antecedent soil moisture at the foot-slope during the spring resulted in less rain required to generate runoff and greater runoff volumes, compared with runoff from the well-drained mid-slope in spring and at both landscape positions in late summer. Phosphorus in runoff was primarily in dissolved reactive form (DRP averaged 71% of total P), with DRP concentrations from the two soils corresponding with soil test P levels. Nitrogen in runoff was mainly nitrate (NO3-N averaged 77% of total N). Site hydrology, not chemistry, was primarily responsible for variations in mass N and P losses with landscape position. Larger runoff volumes from the foot-slope produced higher losses of total P (0.08 kg ha(-1)) and N (1.35 kg ha(-1)) than did runoff from the mid-slope (0.05 total P kg ha(-1); 0.48 kg N ha(-1)), particularly under wet, spring-time conditions. Nutrient losses were significantly greater under the high intensity rainfall due to larger runoff volumes. Results affirm the critical source area concept for both N and P: both nutrient availability and hydrology in combination control nutrient loss.

Measurement of greenhouse gas flux from agricultural soils using static chambers.

Measurement of greenhouse gas (GHG) fluxes between the soil and the atmosphere, in both managed and unmanaged ecosystems, is critical to understanding the biogeochemical drivers of climate change and to the development and evaluation of GHG mitigation strategies based on modulation of landscape management practices. The static chamber-based method described here is based on trapping gases emitted from the soil surface within a chamber and collecting samples from the chamber headspace at regular intervals for analysis by gas chromatography. Change in gas concentration over time is used to calculate flux. This method can be utilized to measure landscape-based flux of carbon dioxide, nitrous oxide, and methane, and to estimate differences between treatments or explore system dynamics over seasons or years. Infrastructure requirements are modest, but a comprehensive experimental design is essential. This method is easily deployed in the field, conforms to established guidelines, and produces data suitable to large-scale GHG emissions studies.