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Sustainable intensification is an emerging model for agriculture designed to reconcile accelerating global demand for agricultural products with long-term environmental stewardship. Defined here as increasing agricultural production while maintaining or improving environmental quality, sustainable intensification hinges upon decision-making by agricultural producers, consumers, and policy-makers. The Long-Term Agroecosystem Research (LTAR) network was established to inform these decisions. Here we introduce the LTAR Common Experiment, through which scientists and partnering producers in US croplands, rangelands, and pasturelands are conducting 21 independent but coordinated experiments. Each local effort compares the outcomes of a predominant, conventional production system in the region ('business as usual') with a system hypothesized to advance sustainable intensification ('aspirational'). Following the logic of a conceptual model of interactions between agriculture, economics, society, and the environment, we identified commonalities among the 21 experiments in terms of (a) concerns about business-as-usual production, (b) 'aspirational outcomes' motivating research into alternatives, (c) strategies for achieving the outcomes, (d) practices that support the strategies, and (e) relationships between practice outreach and adoption. Network-wide, concerns about business as usual include the costs of inputs, opportunities lost to uniform management approaches, and vulnerability to accelerating environmental changes. Motivated by environmental, economic, and societal outcomes, scientists and partnering producers are investigating 15 practices in aspirational treatments to sustainably intensify agriculture, from crop diversification to ecological restoration. Collectively, the aspirational treatments reveal four general strategies for sustainable intensification: (1) reducing reliance on inputs through ecological intensification, (2) diversifying management to match land and economic potential, (3) building adaptive capacity to accelerating environmental changes, and (4) managing agricultural landscapes for multiple ecosystem services. Key to understanding the potential of these practices and strategies are informational, economic, and social factors-and trade-offs among them-that limit their adoption. LTAR is evaluating several actions for overcoming these barriers, including finding financial mechanisms to make aspirational production systems more profitable, resolving uncertainties about trade-offs, and building collaborative capacity among agricultural producers, stakeholders, and scientists from a broad range of disciplines.

Core Ideas Soil management affects carbon and water dynamics. Net ecosystem production was higher in reduced till systems. Ecosystem respiration was higher in tillage systems. Residue management most likely to affect net ecosystem production and ecosystem respiration. Corn [Zea mays L.] and soybean [Glycine max (L.) Merr.] are important US crops, and soil management typically comprises tillage activities, yet improvements in management practices may have substantial impact on C and water dynamics. This study's aim was to determine management impact on C and water fluxes. Four eddy covariance stations monitored evapotranspiration (ET) and net ecosystem production (NEP) in 2016–2017 in two corn–soybean–rotation systems—a conventional and a transitional system to reduced till with cover crop (i.e., aspirational). Net biome production (NBP), gross primary production (GPP), ecosystem respiration (RE), and inherent water use efficiency (IWUE*) were calculated. Aspirational site NEP was higher than the conventional site with 565 vs. 421 g C m−2 in corn, and 108 vs. −64 g C m−2 in soybean. The aspirational RE was lower than under conventional management for both corn and soybean. Aspirational corn GPP was lower than conventional with 1285 and 1405 g C m−2, and no difference in soybean with 750 and 742 g C m−2. Linear regression (p < 0.05) showed higher NEP regression slopes in spring in the conventional compared with the aspirational system, with −0.016 and −0.004 in soybean, and −0.012 and −0.005 in corn. The soybean‐years were a C source in both management systems. Although annual ET was similar among crops and management with 589 to 610 mm, the growing season IWUE* was higher under conventional management. Reduced tillage substantially improved C dynamics in corn and soybean, whereas ET was less affected.

Vegetative buffers have been shown to reduce nutrient loss associated with the transport of detached soil particles and may through plant uptake offer a means to capture dissolved nutrients moving to surface waters through the soil solution. The objective of this 4-year study was to evaluate changes in the biomass and P content of the roots and shoots of plants growing in a multi-species versus a single species riparian buffer as an index of P capture potential. Periodic harvests of above ground vegetation were combined with root cores to estimate the total standing biomass and the pool of P in plant tissue in three vegetative cover types dominated by either switchgrass (Panicum virgatum L.), an alfalfa (Medicago sativa L.)-smooth bromegrass (Bromis inermis Leyss) mix, or a fast growing superior cottonwood (Populus deltoids Bartr., clone 42-7). An existing stand of smooth brome served as the single species control. Standing biomass increased in all three cover types during the 4 years of study, with the greatest increases observed in the cottonwood (2345 g m-²) and switchgrass (1818 g m-²). Biomass production in the smooth brome control did not change during the study period. Based on the 4th-year samples, standing pools of P closely paralleled total plant biomass and root surface area with cottonwood accumulating the greatest amount of P at 19.4 g m-² compared to 4.3 g m-² for the smooth brome control. Estimates of potential P export via biomass harvest from a mixed buffer over a 4-year interval were 101 kg ha-¹ compared to 62 kg ha-¹ for the smooth brome control; a 63% increase in export capacity due largely to the inclusion of cottonwood. Addition of a fast growing woody species combined with periodic biomass harvests has the potential to reduce P movement to surface waters.

A significant portion of the NO3 from agricultural fields that contaminates surface waters in the Midwest Corn Belt is transported to streams or rivers by subsurface drainage systems or “tiles.” Previous research has shown that N fertilizer management alone is not sufficient for reducing NO3 concentrations in subsurface drainage to acceptable levels; therefore, additional approaches need to be devised. We compared two cropping system modifications for NO3 concentration and load in subsurface drainage water for a no‐till corn (Zea mays L.)‐soybean (Glycine max [L.] Merr.) management system. In one treatment, eastern gamagrass (Tripsacum dactyloides L.) was grown in permanent 3.05‐m‐wide strips above the tiles. For the second treatment, a rye (Secale cereale L.) winter cover crop was seeded over the entire plot area each year near harvest and chemically killed before planting the following spring. Twelve 30.5 × 42.7‐m subsurface‐drained field plots were established in 1999 with an automated system for measuring tile flow and collecting flow‐weighted samples. Both treatments and a control were initiated in 2000 and replicated four times. Full establishment of both treatments did not occur until fall 2001 because of dry conditions. Treatment comparisons were conducted from 2002 through 2005. The rye cover crop treatment significantly reduced subsurface drainage water flow‐weighted NO3 concentrations and NO3 loads in all 4 yr. The rye cover crop treatment did not significantly reduce cumulative annual drainage. Averaged over 4 yr, the rye cover crop reduced flow‐weighted NO3 concentrations by 59% and loads by 61%. The gamagrass strips did not significantly reduce cumulative drainage, the average annual flow‐weighted NO3 concentrations, or cumulative NO3 loads averaged over the 4 yr. Rye winter cover crops grown after corn and soybean have the potential to reduce the NO3 concentrations and loads delivered to surface waters by subsurface drainage systems.

Watershed contamination from antibiotics is becoming a critical issue because of increased numbers of confined animal-feeding operations and the use of antibiotics in animal production. To understand the fate of tylosin in manure before it is land-applied, degradation in manure lagoon slurries at 22°C was studied. Tylosin disappearance followed a biphasic pattern, where rapid initial loss was followed by a slow removal phase. The 90% disappearance times for tylosin, relomycin (tylosin D), and desmycosin (tylosin B) in anaerobically incubated slurries were 30 to 130 hours. Aerating the slurries reduced the 90% disappearance times to between 12 and 26 hours. Biodegradation and abiotic degradation occur, but strong sorption to slurry solids was probably the primary mechanism of tylosin disappearance. Dihydrodesmycosin and an unknown degradate with molecular mass of m/z 934.5 were detected. Residual tylosin remained in slurry after eight months of incubation, indicating that degradation in lagoons is incomplete and that residues will enter agricultural fields.

Soil properties and water contents (theta) vary spatially, but management effects on spatial patterns are poorly understood. This study's objective was to compare surface-soil properties and theta in two small watersheds (30-43 ha) in Iowa's loess hills. Both watersheds were in continuous corn (Zea mays L.) from 1972 through 1995, one (CW1) under conventional tillage and the other (RW3) under ridge tillage. In 1996, CW1 was converted to no-till. Surface-soil (0-0.2 m) samples were collected along hillslope transects during 2002 and 2003, including four dates with water-content measurements by gravimetry in both watersheds. Soil bulk density (rho(b)), organic carbon (OC), and texture were determined, along with terrain attributes (elevation, slope, surface curvature, contributing area, and wetness index). After accounting for landscape-position effects, RW3 had more OC (2.1 versus 1.7%) and smaller rho(b) (1.16 versus 1.25 Mg m(-3)) than CW1 (P < 0.001). Larger theta values occurred in RW3 (P < 0.002) when theta was >33%. Landscape position and terrain attributes better explained variation in theta in RW3 than CW1. Also, OC was correlated with theta in RW3, but not in CW1. Soil textures were similar (within 2%,) but finer in CW1 (P < 0.05). Pedotransfer functions confirmed that differences in soil properties between watersheds resulted in greater theta in RW3 than CW1, particularly at low soil-water potential, and that more distinct patterns of theta should occur in RW3. Results indicate long-term conventional tillage in CW1 affected soil properties and water-holding characteristics in ways that decreased water retention and muted spatial patterns of theta.

Riparian buffers prevent sediment and phosphorus (P) from reaching streams but their accumulation in buffers is seldom measured. This study's objectives were to determine accumulations of sediment and phosphorus in a multi-species riparian buffer and characterize spatial-temporal patterns of phosphorus in soil water and groundwater. The buffer was planted in 2000, below a steep-sloping field in row-crop production under no-tillage management in Iowa's Loess Hills. Topographic surveys were conducted in 2002, after the buffer was fully established, and again in 2005. Mapped differences in elevation showed sediment accretion was associated with concentrated flow pathways and lateral flow along the buffer-crop margin. About 32% of the buffer's outer switchgrass ( Panicum virgatum L.) zone had sediment accumulations exceeding 4 cm (1.6 in), which totaled 14.5 Mg ha −1 (over three years) contributing area, or 4.8 Mg ha −1 yr −1 (2.1 t ac −1 yr −1 ). Among five soil plots, total phosphorus in accreted sediment varied from 7 to 55 g m −2 (0.02 to 0.18 oz ft −2 ) totaling 9.6 kg P ha −1 (8.5 lb P ac −1 ) contributing area. Phosphorus concentrations in soil water were greatest beneath the switchgrass, compared to the crop and the buffer's inner vegetation zones ( p < 0.05). Concentrations in soil water and groundwater were also greater where sediment accumulated, presumably due to increased infiltration of runoff. Sediment and phosphorus trapping occurred despite no-tillage management on the contributing hillslope and relatively dry conditions during the study. This emphasizes the importance of installing multiple, complementary conservation practices in sensitive environments. Considering seasonal risks of runoff when selecting buffer species and anticipated runoff patterns when designing buffer areas could reduce subsurface phosphorus losses through riparian areas.

Runoff losses of nitrogen (N) and phosphorus (P) from field applied manure can contribute to surface water pollution. Grass hedges may reduce runoff losses of nutrients and sediment. The objective of this study was to evaluate the effects of narrow switchgrass (Panicum virgatum L.) hedges (−0.75 m wide) on the transport of P and N from a field receiving beef cattle feedlot manure under tilled and no-till conditions. This study was conducted on a steep (12 % average slope) Monona silt loam (fine-silty, mixed, superactive, mesic Typic Hapludolls) soil near Treynor, Iowa. The experiment was a split-plot with no-till and disked systems as main plots and subplots of manure, fertilizer, and check with or without a grass hedge. A rainfall simulator was used and runoff was collected from both the initial and the following wet simulations. Only 38% of the no-till plots and 63% of disked plots had any runoff during the initial 6.4 cm hr −1 water application. A single narrow grass hedge reduced runoff concentrations of dissolved P (DP) by 47%, bioavailable P (BAP) by 48%, particulate P (PP) by 38%, total P (TP) by 40%, and NH 4 -N by 60% during the wet simulation on the no-till plots receiving manure, compared with similar plots with no hedges. The corresponding reductions in concentrations as a result of a grass hedge for DP, BAP, PP, TP, and NH 4 -N on the disked plots were 21, 29, 43, 38, and 52%, respectively. Runoff NH 4 -N concentration from fertilizer applied to the disked plots was reduced by 61%, NO 3 -N by 21%, and total N (TN) by 27% during the wet simulation when grass hedges were used. Grass hedges also reduced total quantities of DP, BAP, TP, and NH 4 -N during the wet simulation. The TP loss was 3.3% of applied P fertilizer and was 0.3% of applied manure P. Narrow grass hedges were effective in reducing P and N losses in runoff from both manure and fertilizer application.

A watershed's water quality is influenced by contaminant‐transport pathways unique to each landscape. Accurate information on contaminant‐pathways could provide a basis for mitigation through well‐targeted approaches. This study determined dynamics of nitrate‐N, total P, Escherichia coli, and sediment during a runoff event in Tipton Creek, Iowa. The watershed, under crop and livestock production, has extensive tile drainage discharging through an alluvial valley. A September 2006 storm yielded 5.9 mm of discharge during the ensuing 7 d, which was monitored at the outlet (19,850 ha), two tile‐drainage outfalls (total 1856 ha), and a runoff flume (11 ha) within the sloped valley. Hydrograph separations indicated 13% of tile discharge was from surface intakes. Tile and outlet nitrate‐N loads were similar, verifying subsurface tiles dominate nitrate delivery. On a unit‐area basis, tile total P and E. coli loads, respectively, were about half and 30% of the outlet's; their rapid, synchronous timing showed surface intakes are an important pathway for both contaminants. Flume results indicated field runoff was a significant source of total P and E. coli loads, but not the dominant one. At the outlet, sediment, P, and E. coli were reasonably synchronous. Radionuclide activities of 7Be and 210Pb in suspended sediments showed sheet‐and‐rill erosion sourced only 22% of sediment contributions; therefore, channel sources dominated and were an important source of P and E. coli The contaminants followed unique pathways, necessitating separate mitigation strategies. To comprehensively address water quality, erosion‐control and nitrogen‐management practices currently encouraged could be complemented by buffering surface intakes and stabilizing stream banks.

This rainfall simulation study provided information on the effects of 0.72 m (2.4 ft) wide switchgrass hedges located at the bottom of plots on runoff and soil loss under both no-till and tilled conditions. The study area, which had slopes ranging from 8 to 16%, had produced corn for 33 years and the grass hedges had been established for six years. Simulated rainfall [64 mm hr −1 (2.5 in hr- 1 )I was applied for two hours to plots (3.7 m (12 ft) wide by 10.7 m (35.1 ft) long/with corn residue and to plots where corn residue was removed. The narrow grass hedges substantially reduced runoff and soil loss. Under no-till conditions, the plots with corn residue and pass hedges averaged 52% less runoff and 53% less soil loss tban similar plots without grass hakes. Under tilled conditions, the plots with corn residue and grass hedges averaged 22% less runoff and 57% Less soil loss than comparable plots without grass hedges. The plots with corn residue removed but with grass hedges present averaged 41 % less runoff and 63% less soil loss than similar plots without grass hedges. Narrow grass hedges are an effective conservation measure, especially when used in conjunction with such conservation practices as no-till or reduced-till firming systems.