Sylvie M. Brouder

Greenhouse gas fluxes in an eastern corn belt soil: weather, nitrogen source, and rotation.

Relative contributions of diverse, managed ecosystems to greenhouse gases are not completely documented. This study was conducted to estimate soil surface fluxes of carbon dioxide (CO(2)), methane (CH(4)), and nitrous oxide (N(2)O) as affected by management practices and weather. Gas fluxes were measured by vented, static chambers in Drummer and Raub soil series during two growing seasons. Treatments evaluated were corn cropped continuously (CC) or in rotation with soybean (CS) and fertilized with in-season urea-ammonium nitrate (UAN) or liquid swine manure applied in the spring (SM) or fall (FM). Soybean (SC) rotated with CS and restored prairie grass (PG) were also included. The CO(2) fluxes correlated (P <or= 0.001) with soil temperature (rho: 0.74) and accumulated rainfall 120 h before sampling (rho: 0.53); N(2)O fluxes correlated with soil temperature (rho: 0.34). Seasonal CO(2)-C emissions were not different across treatments (4.4 Mg ha(-1) yr(-1)) but differed between years. Manured soils were net seasonal CH(4)-C emitters (0.159-0.329 kg ha(-1) yr(-1)), whereas CSUAN and CCUAN exhibited CH(4)-C uptake (-0.128 and -0.177 kg ha(-1) yr(-1), respectively). Treatments significantly influenced seasonal N(2)O-N emissions (P < 0.001) and ranged from <1.0 kg ha(-)(1) yr(-1) in PG and SC to between 3 and 5 kg ha(-1) yr(-1) in CCFM and CSUAN and >8 kg ha(-1) yr(-1) in CCSM; differences were driven by pulse emissions after N fertilization in concurrence with major rainfall events. These results suggest fall manure application, corn-soybean rotation, and restoration of prairies may diminish N(2)O emissions and hence contribute to global warming mitigation.

Impact of climate change on crop nutrient and water use efficiencies

Implicit in discussions of plant nutrition and climate change is the assumption that we know what to do relative to nutrient management here and now but that these strategies might not apply in a changed climate. We review existing knowledge on interactive influences of atmospheric carbon dioxide concentration, temperature and soil moisture on plant growth, development and yield as well as on plant water use efficiency (WUE) and physiological and uptake efficiencies of soil-immobile nutrients. Elevated atmospheric CO(2) will increase leaf and canopy photosynthesis, especially in C3 plants, with minor changes in dark respiration. Additional CO(2) will increase biomass without marked alteration in dry matter partitioning, reduce transpiration of most plants and improve WUE. However, spatiotemporal variation in these attributes will impact agronomic performance and crop water use in a site-specific manner. Nutrient acquisition is closely associated with overall biomass and strongly influenced by root surface area. When climate change alters soil factors to restrict root growth, nutrient stress will occur. Plant size may also change but nutrient concentration will remain relatively unchanged; therefore, nutrient removal will scale with growth. Changes in regional nutrient requirements will be most remarkable where we alter cropping systems to accommodate shifts in ecozones or alter farming systems to capture new uses from existing systems. For regions and systems where we currently do an adequate job managing nutrients, we stand a good chance of continued optimization under a changed climate. If we can and should do better, climate change will not help us.

Root development of two cotton cultivars in relation to potassium uptake and plant growth in a vermiculitic soil

Abstract Cotton ( Gossypium hirsutum L.) cultivars exhibit marked differences in yield on vermiculitic soils where late-season K deficiency causes yield reductions. A two-year field study was conducted to determine whether differences in root growth contribute to the differing sensitivity to late-season K deficiency of two cultivars. Cultivar ‘Acala GC510’ accumulated 41% more dry-matter, 37% more K, and proeuced 22% (1986) to 28% (1987) more seed cotton than the sensitive cultivar ‘Acala SJ-2’. Levels of extractable K were greatest in the surface 0–0.30 m, decreasing sharply below this depth. Root-length and surface-area density of both cultivars were greatest in the 0.10–0.20-m soil layer but least in the surface 0–0.10 m. Fluctuations in soil matric potential were greatest in the 0.10-m topsoil layer, which limited root extension in this zone. The K-efficient cultivar had a larger mean root diameter and an increased rate of root extension after peak bloom that resulted in 58% more total root surface area by mid-August. Differences in root surface area at 0.10–0.30-m depth were positively correlated with cultivar differences in K uptake, and root development in this subsurface layer appears to be critical for adequate K acquisition by cotton in soil with low subsoil K supply. Root surface area of both cultivars at 0.15–0.30 m was negatively correlated with soil bulk density, but root surface area of the more K-efficient cultivar was consistently greater across the range of measured bulk density. The results demonstrate significant genotypic differences in K uptake and sensitivity to late-season season K deficiency that were associated with differences in the determinacy of root growth after peak bloom and/or in root-growth response to soil bulk density.

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.

Perennial rhizomatous grasses as bioenergy feedstock in SWAT: parameter development and model improvement

The Soil and Water Assessment Tool (SWAT) is increasingly used to quantify hydrologic and water quality impacts of bioenergy production, but crop‐growth parameters for candidate perennial rhizomatous grasses (PRG) Miscanthus × giganteus and upland ecotypes of Panicum virgatum (switchgrass) are limited by the availability of field data. Crop‐growth parameter ranges and suggested values were developed in this study using agronomic and weather data collected at the Purdue University Water Quality Field Station in northwestern Indiana. During the process of parameterization, the comparison of measured data with conceptual representation of PRG growth in the model led to three changes in the SWAT 2009 code: the harvest algorithm was modified to maintain belowground biomass over winter, plant respiration was extended via modified‐DLAI to better reflect maturity and leaf senescence, and nutrient uptake algorithms were revised to respond to temperature, water, and nutrient stress. Parameter values and changes to the model resulted in simulated biomass yield and leaf area index consistent with reported values for the region. Code changes in the SWAT model improved nutrient storage during dormancy period and nitrogen and phosphorus uptake by both switchgrass and Miscanthus.

Watershed-scale impacts of bioenergy crops on hydrology and water quality using improved SWAT model.

Cellulosic bioenergy feedstock such as perennial grasses and crop residues are expected to play a significant role in meeting US biofuel production targets. We used an improved version of the Soil and Water Assessment Tool (SWAT) to forecast impacts on watershed hydrology and water quality by implementing an array of plausible land‐use changes associated with commercial bioenergy crop production for two watersheds in the Midwest USA. Watershed‐scale impacts were estimated for 13 bioenergy crop production scenarios, including: production of Miscanthus × giganteus and upland Shawnee switchgrass on highly erodible landscape positions, agricultural marginal land areas and pastures, removal of corn stover and combinations of these options. Water quality, measured as erosion and sediment loading, was forecasted to improve compared to baseline when perennial grasses were used for bioenergy production, but not with stover removal scenarios. Erosion reduction with perennial energy crop production scenarios ranged between 0.2% and 59%. Stream flow at the watershed outlet was reduced between 0 and 8% across these bioenergy crop production scenarios compared to baseline across the study watersheds. Results indicate that bioenergy production scenarios that incorporate perennial grasses reduced the nonpoint source pollutant load at the watershed outlet compared to the baseline conditions (0–20% for nitrate‐nitrogen and 3–56% for mineral phosphorus); however, the reduction rates were specific to site characteristics and management practices.

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.

Cotton root and shoot response to localized supply of nitrate, phosphate and potassium: Split-pot studies with nutrient solution and vermiculitic soil

Vertical stratification of plant-available K in vermiculitic soil profiles contributes to a late-season K deficiency that limits cotton (Gossypium hirsutum L.) yields on affected soils. Split-root solution culture and split-pot soil experiments were conducted to determine whether root distribution and cultivar differences in root extension in these stratified profiles result from a compensatory response to localized enrichment with NO3-N, PO4-P, and/or K in the root zone. Compensatory root growth was greatest in response to localized NO3-N enrichment. For two cultivars examined in solution culture, 74% of new root development occurred in the half-pot providing 90% of the total NO3-N supply. Only 60% of cultivar root development occurred in the half-pot providing 90% of the PO4-P. No compensatory root growth was observed in response to localized K enrichment. In the split-pot system, the proportion of total root surface area developing in a half-pot was highly correlated with localized soil NO3-N levels (r2=0.81), while increased K availability in one half of the root zone did not affect root distribution. Mean soil NO3-N supply to the whole root system determined shoot N accumulation (r2=0.97). Shoot K accumulation was not related to soil K availability but was strongly correlated with mean root surface area density (r2=0.86). Cultivar ‘Acala GC510’, known to be less sensitive to K deficiency than ‘Acala SJ-2’, had significantly larger root diameter in all nutrient-supply environments. Under conditions of K stress, ‘Acala GC510’ had increased root branching and allocated greater dry matter to roots relative to shoots than ‘Acala SJ-2’. The results demonstrate that K acquisition by cotton is strongly influenced by the quantity and distribution of NO3-N in the root zone through its effects on root proliferation, and that distinct cultivar differences associated with crop performance on low K soils can be detected in short-term, solution culture growth systems.

Evaluation of simulated strategies for reducing nitrate-nitrogen losses through subsurface drainage systems.

The nitrates (NO(3)-N) lost through subsurface drainage in the Midwest often exceed concentrations that cause deleterious effects on the receiving streams and lead to hypoxic conditions in the northern Gulf of Mexico. The use of drainage and water quality models along with observed data analysis may provide new insight into the water and nutrient balance in drained agricultural lands and enable evaluation of appropriate measures for reducing NO(3)-N losses. DRAINMOD-NII, a carbon (C) and nitrogen (N) simulation model, was field tested for the high organic matter Drummer soil in Indiana and used to predict the effects of fertilizer application rate and drainage water management (DWM) on NO-N losses through subsurface drainage. The model was calibrated and validated for continuous corn (Zea mays L.) (CC) and corn-soybean [Glycine max (L.) Merr.] (CS) rotation treatments separately using 7 yr of drain flow and NO(3)-N concentration data. Among the treatments, the Nash-Sutcliffe efficiency of the monthly NO(3)-N loss predictions ranged from 0.30 to 0.86, and the percent error varied from -19 to 9%. The medians of the observed and predicted monthly NO(3)-N losses were not significantly different. When the fertilizer application rate was reduced ~20%, the predicted NO(3)-N losses in drain flow from the CC treatments was reduced 17% (95% confidence interval [CI], 11-25), while losses from the CS treatment were reduced by 10% (95% CI, 1-15). With DWM, the predicted average annual drain flow was reduced by about 56% (95% CI, 49-67), while the average annual NO(3)-N losses through drain flow were reduced by about 46% (95% CI, 32-57) for both tested crop rotations. However, the simulated NO(3)-N losses in surface runoff increased by about 3 to 4 kg ha(-1) with DWM. For the simulated conditions at the study site, implementing DWM along with reduced fertilizer application rates would be the best strategy to achieve the highest NO(3)-N loss reductions to surface water. The suggested best strategies would reduce the NO(3)-N losses to surface water by 38% (95% CI, 29-46) for the CC treatments and by 32% (95% CI, 23-40) for the CS treatments.

Feasibility of On-the-go Mapping of Soil Nitrate and Potassium Using Ion-Selective Electrodes

A prototype of an automated soil sampling system for on-the-go measurement of soil pH has been developed and evaluated (Papers No. 98-3094, 99-1100 & 01-1045). It was shown that automated mapping of soil pH using ion-selective electrodes (ISE) on naturally moist soil is an effective alternative to conventional manual grid mapping. In this work the feasibility of applying a similar technique to map potassium and nitrate-nitrogen content was tested. It was found that polymer membrane K+ and NO3 - ion-selective electrodes can be used to predict other analytical measurement methods (atomic absorption spectroscopy and cadmium reduction) commonly used in soil laboratories. Significant correlations (R2 = 0.56 - 0.94) were observed while using both direct and soil solution measurements. Obtained results represent snapshots of real-time availability of K+ and NO3 - ions in soil solution, which could be used as indirect indicators for adjusting variable application rates of potassium or nitrogen fertilizers in combination with other layers of spatial data.