Matthew D. Ruark

Dissolved organic carbon losses from tile drained agroecosystems.

Artificial subsurface drainage is commonly used in midwestern agriculture and drainage losses of dissolved organic carbon (DOC) from such systems are an under-quantified portion of the terrestrial carbon (C) cycle. The objectives of this study were to determine the effect of common agricultural management practices on DOC losses from subsurface tile drains and to assess patterns of loss as a function of year, time of year, and drainflow. Daily drainflow was collected across six water years (1999-2004) from a restored prairie grass system and cropping systems which include continuous corn (Zea mays L.) and corn-soybean [Glycine max (L.) Merr.] rotations fertilized with urea-ammonium-nitrate (UAN) or swine (Sus scrofa) manure lagoon effluent. The DOC concentrations in tile drainflow were low, typically <2 mg L(-1). Yearly DOC losses, which ranged from 1.78 to 8.61 kg ha(-1), were not affected by management practices and were small compared to organic C inputs. Spring application of lagoon effluent increased yearly flow-weighted (FW)-DOC concentrations relative to other cropping systems in three of the years and increased monthly FW-DOC concentrations when drainflow occurred within 1 mo of application. Drainflow was significantly and positively correlated with DOC loss. Drainflow also affected DOC concentrations as greater 6-yr cumulative drainflow was associated with lower 6-yr FW-DOC concentrations and greater daily drainflow was associated with higher daily DOC concentrations. Our results indicate that lagoon effluent application and fertilizer N rates do not affect long-term losses of DOC from tile drains and that drainflow is the main driver of DOC losses.

Nitrate, phosphate, and ammonium loads at subsurface drains: agroecosystems and nitrogen management.

Artificial subsurface drainage in cropland creates pathways for nutrient movement into surface water; quantification of the relative impacts of common and theoretically improved management systems on these nutrient losses remains incomplete. This study was conducted to assess diverse management effects on long-term patterns (1998-2006) of NO, NH, and PO loads (). We monitored water flow and nutrient concentrations at subsurface drains in lysimeter plots planted to continuous corn ( L.) (CC), both phases of corn-soybean [ (L.) Merr.] rotations (corn, CS; soybean, SC), and restored prairie grass (PG). Corn plots were fertilized with preplant or sidedress urea-NHNO (UAN) or liquid swine manure injected in the fall (FM) or spring (SM). Restored PG reduced NO eightfold compared with fields receiving UAN (2.5 vs. 19.9 kg N ha yr; < 0.001), yet varying UAN application rates and timings did not affect NO across all CCUANs and CSUANs. The NO from CCFM (33.3 kg N ha yr) were substantially higher than for all other cropped fields including CCSM (average 19.8 kg N ha yr, < 0.001). With respect to NH and PO, only manured soils recorded high but episodic losses in certain years. Compared with the average of all other treatments, CCSM increased NH in the spring of 1999 (217 vs. 680 g N ha yr), while CCFM raised PO in the winter of 2005 (23 vs. 441 g P ha yr). Our results demonstrate that fall manuring increased nutrient losses in subsurface-drained cropland, and hence this practice should be redesigned for improvement or discouraged.

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.

Seasonal losses of dissolved organic carbon and total dissolved solids from rice production systems in northern California.

Water quality concerns have arisen related to rice (Oryza sativa L.) field drain water, which has the potential to contribute large amounts of dissolved organic carbon (DOC) and total dissolved solids (TDS) to the Sacramento River. Field-scale losses of DOC or TDS have yet to be quantified. The objectives of this study were to evaluate the seasonal concentrations of DOC and TDS in rice field drain water and irrigation canals, quantify seasonal fluxes and flow-weighted (FW) concentrations of DOC and TDS, and determine the main drivers of DOC and TDS fluxes. Two rice fields with different straw management practices (incorporation vs. burning) were monitored at each of four locations in the Sacramento Valley. Fluxes of DOC ranged from 3.7 to 34.6 kg ha(-1) during the growing season (GS) and from 0 to 202 kg ha(-1) during the winter season (WS). Straw management had a significant interaction effect with season, as the greatest DOC concentrations were observed during winter flooding of straw incorporated fields. Fluxes and concentrations of TDS were not significantly affected by either straw management or season. Total seasonal water flux accounted for 90 and 88% of the variability in DOC flux during the GS and WS, respectively. Peak DOC concentrations occurred at the onset of drainflow; therefore, changes in irrigation management may reduce peak DOC concentrations and thereby DOC losses. However, the timing of peak DOC concentrations from rice fields suggest that rice field drainage water is not the cause of peak DOC concentrations in the Sacramento River.

Environmental concerns of phosphorus management in potato production.

Phosphorus (P) losses from agricultural systems are a cause of degraded surface water quality of lakes and streams. In freshwater systems, P is often the most limiting nutrient for algae growth and an increase in P additions to these systems can cause a shift in ecology. These shifts can result in a degradation of the water resource as habitat or for recreation. In an effort to combat the negative effects of agriculture management practices on surface water quality, federal and state regulations require some level of assessment to guide P applications. Areas with large amounts of potato production are of particular concern with respect to P loss since potatoes are a high P demanding crop and are inefficient users of applied P. In many cases, soils in potato production are managed with a higher soil test P concentration compared to other crops and P applications for optimum production exceed P removal. When potato production fields are maintained at high soil test P levels, this may increase the risk of P loss in runoff. However, based on soils and landscape positions where potatoes are grown, there may be little risk of transport. While there appears to be little risk of P loss on low-sloping, sandy soils, output from the Wisconsin Phosphorus Index suggests that more steeply sloping fields can pose some risk, especially when soil test P concentrations exist at above optimum levels. At high soil test P levels, no P may be required for optimum yield in rotated crops, but production practices of these crops may need to be altered to reduce P losses. Furrow-irrigated and tile-drained fields may also pose risks of P loss to the environment. While the P demands of potato are greater than those for most crops, it is likely that most of this P will not be exported via surface runoff. Careful management considerations must be made when producing potatoes on high sloping soils, especially those close to surface water bodies. Future considerations of P management and water quality will focus on assessing leaching risk of P and this contribution to surface waters.ResumenLas pérdidas de fósforo (P) de sistemas agrícolas son una causa de degradación en la calidad del agua superficial de lagos y corrientes. En los sistemas de agua dulce, el P es a menudo el nutriente más limitante para el crecimiento de algas y un aumento en la adición de P a estos sistemas puede causar un cambio en la ecología. Estos cambios pueden resultar en degradación del recurso hídrico como hábitat o para recreación. En un esfuerzo para combatir los efectos negativos de prácticas de manejo en agricultura en la calidad del agua superficial, las regulaciones federales y estatales requieren algún nivel de análisis para guiar las aplicaciones de P. Las áreas con grandes cantidades de producción de papa son de preocupación particular con respecto a pérdida de P, ya que las papas son un cultivo de alta demanda de P y usan ineficientemente el P aplicado. En muchos casos, los suelos en la producción de papa se manejan con una concentración más alta de P en suelos probados en comparación con otros cultivos, y las aplicaciones de P para producción óptima exceden a su remoción. Cuando los campos de producción de papa se mantienen a altos niveles de P en el suelo, esto pudiera aumentar el riesgo de pérdida de P por lixiviación. No obstante, con base en los suelos y posiciones en el paisaje donde se cultivan las papas, pudiera haber poco riesgo de transporte. Mientras que aparentemente pudiera haber poco riesgo en pérdida de P en suelos arenosos, de laderas suaves, la información del Índice de Fósforo de Wisconsin sugiere que campos con mayor inclinación pudieran representar algún riesgo, especialmente cuando las concentraciones probadas de P existen por encima de los niveles óptimos. A altos niveles de P, pudiera no requerirse para rendimiento óptimo en cultivos en rotación, pero las prácticas de producción de estos cultivos pudieran necesitar alteración para reducir pérdidas de P. Campos de riego por surcos y con drenaje con losas pudieran también representar riesgos de pérdida de P al ambiente. Mientras que las demandas de P en papa son mayores que las de la mayoría de los cultivos, es probable que la mayor parte de este P no se exportará por vía de lixiviación superficial. Deben de hacerse consideraciones cuidadosas de manejo al producir papas en suelos de grandes inclinaciones, especialmente aquellos cercanos a los cuerpos de agua superficial. Futuras consideraciones en el manejo de P y calidad del agua se enfocarán en el análisis de riesgo de lixiviación de P y su contribución a aguas superficiales.

Potato Response to Nitrogen Form and Nitrification Inhibitors

Several previous experiments where nitrification inhibitors have been used with potato have resulted in yield and/or tuber quality reductions, especially when used in combination with all-ammonium fertilizer N sources. This experiment examined the effectiveness of inhibitors over a 3-year period when used with several N sources with varying ammonium-N contents, all applied at emergence on an irrigated loamy sand in central Wisconsin. In 3 of 6 site-years, use of an inhibitor increased total tuber yield with one or more of the N sources. Inhibitor use also sometimes increased tuber N accumulation and apparent recovery of applied fertilizer N. However, in 4 of 6 site-years, inclusion of an inhibitor with all-ammonium fertilizer N decreased harvested U.S. No. 1 tubers. This decrease was primarily due to an increased proportion of off-shape cull tubers, likely in response to the aversion of potato to ammonium nutrition. While use of inhibitors may have some application for potato production on irrigated sandy soils, it is clear that when they are used, the N fertilizer should be a mixed ammonium/nitrate fertilizer source.ResumenVarios experimentos previos en los que inhibidores de nitrificación se han usado en papa, han resultado en reducción de rendimiento y/o calidad de tubérculo, especialmente cuando se han empleado en combinación con fuentes de fertilizantes de puro amonio. En este experimento se examinó la efectividad de inhibidores en un período de tres años cuando se usaron con varias fuentes de N de diferentes contenidos de N-amoniacal, todo aplicado a la emergencia en un suelo franco-arenoso de riego en la región central de Wisconsin. En 3 de 6 sitios-años, el uso de un inhibidor aumentó el rendimiento total de tubérculo con una o más de las fuentes de N. El uso del inhibidor también algunas veces aumentó la acumulación del N del tubérculo y la aparente recuperación del N del fertilizante aplicado. No obstante, en 4 de los 6 sitios-años, la incorporación de un inhibidor con un fertilizante de puro amonio disminuyó la cosecha de tubérculos U.S. No. 1. Esta disminución se debió primeramente a un aumento en la proporción de tubérculos deformados eliminados, posiblemente en respuesta a la aversión de la papa a la nutrición amoniacal. Mientras que el uso de inhibidores pudiera tener alguna aplicación para la producción de papa en suelos arenosos de riego, está claro que cuando se usen, el fertilizante nitrogenado deberá ser de una mezcla de fuentes amonio/nitrato.

Does Plant Biomass Manipulation in Static Chambers Affect Nitrous Oxide Emissions from Soils

One of the most widespread approaches for measurement of greenhouse gas emissions from soils involves the use of static chambers. This method is relatively inexpensive, is easily replicated, and is ideally suited to plot-based experimental systems. Among its limitations is the loss of detection sensitivity with increasing chamber height, which creates challenges for deployment in systems including tall vegetation. It is not always possible to avoid inclusion of plants within chambers or to extend chamber height to fully accommodate plant growth. Thus, in many systems, such as perennial forages and biomass crops, plants growing within static chambers must either be trimmed or folded during lid closure. Currently, data on how different types of biomass manipulation affect measured results is limited. Here, we compare the effects of cutting vs. folding of biomass on nitrous oxide measurements in switchgrass ( L.) and alfalfa ( L.) systems. We report only limited evidence of treatment effects during discrete sampling events and little basis for concern that effects may intensify over time as biomass manipulation is repeatedly imposed. However, nonsignificant treatment effects that were consistently present amounted to significant overall trends in three out of the four systems studied. Such minor disparities in flux could amount to considerable quantities over time, suggesting that caution should be exercised when comparing cumulative emission values from studies using different biomass manipulation strategies.

Surface-Applied Calcium Phosphate Stimulates Weed Emergence in Flooded Rice

Abstract Weeds are the major biotic constraint to rice production. Field observations have suggested that certain fertilizer regimes could enhance infestations of particular weed species emerging with rice. The study objective was to determine the effect of surface-applied calcium phosphate on weed growth in flooded California rice systems. In field and pot studies, triple superphosphate (TSP) applied to the soil surface increased weed emergence. Surface-applied TSP increased the number of sedge and broadleaf weeds, including smallflower umbrella sedge, blue-flowered ducksalad, redstem, ricefield bulrush, waterhyssop, and California arrowhead. A laboratory study measured germination of smallflower umbrella sedge and ricefield bulrush in response to the application of phosphorus (P) and calcium (Ca), which comprise 20 and 15% of TSP, respectively. Calcium stimulated smallflower umbrella sedge germination and had no effect on ricefield bulrush germination. Phosphorus did not stimulate either smallflower umbrella sedge or ricefield bulrush germination. Results indicate that surface applications of calcium phosphate increase the growth of certain weed species and that Ca may stimulate germination of smallflower umbrella sedge. By incorporating preplant applications of calcium phosphate into the soil profile, growers can reduce weed pressure from certain species. Alternatively, surface applications of calcium phosphate may be useful to stimulate weed emergence in stale-seedbed management. Nomenclature: Blue-flowered ducksalad, Heteranthera rotundifolia (Kunth) Griseb.; California arrowhead, Sagittaria montevidensis Cham. & Schlecht.; redstem, Ammannia coccinea Rottb.; ricefield bulrush, Schoenoplectus mucronatus (L.) Palla; waterhyssop, Bacopa spp. L.; smallflower umbrella sedge, Cyperus difformis L.; rice, Oryza sativa L.

Nutrients and sediments in surface runoff water from direct-seeded rice fields: implications for nutrient budgets and water quality.

Nutrient losses from rice fields can have economic and environmental consequences. Little is known about nutrient losses in surface runoff waters from direct-seeded rice systems, which are common in the United States and increasingly more so in Asia. The objectives of this research were to quantify nutrient losses from California rice fields in surface runoff waters and to determine when and under what conditions losses are greatest. Research was conducted in 10 rice fields varying in residue (burned or incorporated) and water management over a 2-yr period. Concentrations of NH-N and NO-N in runoff water across sites, seasons, and management practices averaged <0.1 mg N L. Runoff water PO-P concentration averaged 0.14 mg L and was not affected by season or straw management practices. However, P fluxes were higher in the winter when rice straw was burned (2.59 kg ha) as opposed to incorporated (0.44 kg ha). Average seasonal runoff water K concentrations did not vary with season and straw management, although they were highest at the onset of the winter season. Average total suspended solids (TSS) concentrations did not vary by season but were highest during the winter in the straw-incorporated fields (46 mg L). Rice fields were sinks for K (4.9 kg K ha) during the growing season. Fields were not significant sources of nutrients or TSS during the growing season; however, during the winter fallow they could be sources of NH-N, P, K, and TSS, especially as water fluxes from fields increased.

An at-grade stabilization structure impact on runoff and suspended sediment

In recent years, agricultural runoff has received more attention as a major contributor to surface water pollution. This is especially true for the unglaciated area of Wisconsin, given this areas steep topography, which makes it highly susceptible to runoff and soil loss. We evaluated the ability of an at-grade stabilization structure (AGSS), designed as a conservation practice to reduce the amount of overland runoff and suspended sediment transported to the surface waters of an agricultural watershed. Eight years of storm and baseflow data collected by the US Geological Survey–Wisconsin Water Science Center on a farm in west central Wisconsin were analyzed for changes in precipitation, storm runoff volume, and suspended sediment concentration before and after installation of an AGSS. The agricultural research site was designed as a paired watershed study in which monitoring stations were installed on the perennial streams draining both control and treatment watersheds. Linear mixed effects model analyses were conducted to determine if any statistically significant changes occurred in the water quality parameters before and after the AGSS was installed. Results indicated no significant changes (p = 0.51) in average event precipitation and runoff volumes before and after installation of the AGSS in either the treatment (NW) or control (SW) watersheds. However, the AGSS did significantly reduce the average suspended sediment concentration in the event runoff water (p = 0.02) in the NW from 972 to 263 mg L–1. In addition, particle size analyses, using light diffraction techniques, were conducted on soil samples taken from within the AGSS and adjacent valley and ridge top to determine if suspended sediments were being retained within the structure. Statistical analysis revealed a significantly (p < 0.001) larger proportion of clay inside the AGSS (37%) than outside (30%). These results indicate that the AGSS was successful in reducing the amount of suspended sediment transported to nearby surface waters. The cost of an AGSS can range from US