Nitrous oxide emissions from soybean in response to drained and undrained soils and previous corn nitrogen management.

While corn (Zea mays L.)-soybean (Glycine max. Merr. L) is a predominant rotation system in the US Midwest the residual effect of nitrogen (N) fertilization to corn on the following year's soybean and N2O emissions under different soil drainage conditions has not been studied. Our objective was to quantify agronomic parameters and season-long N2O emissions from soybean as affected by N management (0-N and optimum N rate of 135 kg N ha-1 as single or split application) during the previous corn crop under drained and undrained systems. Urea was applied to corn, and residual N effects were measured on soybean the following year in a poorly drained soil with and without subsurface tile drainage. Drainage reduced N2O emissions in one of three growing seasons but had no effect on soybean yield or N removal in grain. Nitrogen management in the previous corn crop had no effect on soybean grain yield, N removal, or N2O emissions during the soybean phase. Even though soybean symbiotically fixes N and removes more N in grain than corn, N2O emissions were more than two times greater during the corn phase (mean = 1.83 kg N ha-1) due to N fertilization than during the soybean phase (mean = 0.80 kg N ha-1). Also, N2O emissions in the corn years were increased possibly due to decomposition of the previous year's soybean crop residue compared to corn residue decomposition in the soybean years. Tile drainage, especially where wet soil conditions are prevalent, is a viable option to mitigate agricultural N2O emissions.

Microplot Design and Plant and Soil Sample Preparation for 15Nitrogen Analysis.

Many nitrogen fertilizer studies evaluate the overall effect of a treatment on end-of-season measurements such as grain yield or cumulative N losses. A stable isotope approach is necessary to follow and quantify the fate of fertilizer derived N (FDN) through the soil-crop system. The purpose of this paper is to describe a small-plot research design utilizing non-confined 15N enriched microplots for multiple soil and plant sampling events over two growing seasons and provide sample collection, handling, and processing protocols for total 15N analysis. The methods were demonstrated using a replicated study from south-central Minnesota planted to corn (Zea mays L.). Each treatment consisted of six corn rows (76 cm row-spacing) 15.2 m long with a microplot (2.4 m by 3.8 m) embedded at one end. Fertilizer-grade urea was applied at 135 kg N∙ha-1 at planting, while the microplot received urea enriched to 5 atom % 15N. Soil and plant samples were taken several times throughout the growing season, taking care to minimize cross-contamination by using separate tools and physically separating unenriched and enriched samples during all procedures. Soil and plant samples were dried, ground to pass through a 2 mm screen, and then ground to a flour-like consistency using a roller jar mill. Tracer studies require additional planning, sample processing time and manual labor, and incur higher costs for 15N enriched materials and sample analysis than traditional N studies. However, using the mass balance approach, tracer studies with multiple in-season sampling events allow the researcher to estimate FDN distribution through the soil-crop system and estimate unaccounted-for FDN from the system.

Nitrate Loss in Subsurface Drainage from a Corn-Soybean Rotation as Affected by Nitrogen Rate and Nitrapyrin.

Successful N management practices for the US Midwest must optimize crop production and minimize NO-N losses from subsurface tile drainage. The objective of this study was to measure the effects of N rate, N application timing, and nitrapyrin [2-chloro-6-(trichlormethyl) pyridine] on corn ( L.) production and NO-N in tile drainage water in a corn-soybean [ (L.) Merr.] rotation in Minnesota. Anhydrous ammonia was applied at 90 and 179 kg ha with nitrapyrin in the fall and at 134 kg ha with and without nitrapyrin in fall and spring. However, drainage water monitoring was only conducted on fall treatments. Over a 5-yr period, 71% of drainage occurred in April through June and <1% occurred from November through March due to frozen soil. Averaged across N treatments and crops, annual drainage ranged from 69 to 380 mm among years. From 2001 through 2003, NO-N concentrations averaged 13.8, 15.6, and 20.0 mg L in corn and 7.3, 8.2, and 12.6 mg L in soybean when 90, 134, and 179 kg N ha was fall applied with nitrapyrin to corn, respectively. Corn grain yields were greater with spring-applied N at 134 kg ha (11.3 Mg ha) than with fall-applied N at 134 and 179 kg ha with nitrapyrin (10.5 and 10.8 Mg ha, respectively), and nitrapyrin did not affect corn production or water quality. Fall application of N is common on cold soils in Minnesota. These data showed that fall application required a greater rate of N to optimize yield than spring and that greater fall rate often increased NO-N concentration and load in tile drainage water.

Tillage and Fertilizer Management Effects on Phosphorus Runoff from Minimal Slope Fields.

Phosphorus fertilization can increase P losses in surface runoff, but limited information is available for fields with <2% slopes in the US Midwest. Our objectives were to determine the effects of tillage-fertilizer placement (no-till-broadcast, strip till-broadcast; or strip till-deep placement, -15-cm subsurface band) and fertilizer rate applied in the fall (0, 52, or 90 kg PO ha yr) on runoff P concentrations and loads in fields with <2% slopes near Pesotum, IL, during fall and spring simulation runoff events, and to measure corn ( L.) and soybean [ (L.) Merr.] grain yield. Across four simulated runoff events, deep placement reduced dissolved reactive P (DRP) loads by 69 to 72% compared with the broadcast treatments. A tillage-fertilizer placement × P rate interaction showed that DRP and total P (TP) concentrations remained low when P was deep placed, regardless of P rate, whereas concentrations increased with increasing P rate for the broadcast treatments, but no differences existed for bioavailable P (BAP) (α = 0.05). At one site, rainfall simulation in the spring versus fall increased runoff volumes but sharply decreased BAP concentrations. During fall runoff simulations, deep placement reduced TP loads, and greater TP loads occurred with the 90- than the 52-kg PO ha yr rate. Similarly, when P was broadcast in the fall, DRP and TP concentrations were greater than deep-placed P, but no treatment differences occurred in the spring. Deep banding P and K did not reduce crop yield but reduced runoff losses of P from flat fields compared with broadcast P applications, particularly at high rates of P application.

Corn Nitrogen Management Influences Nitrous Oxide Emissions in Drained and Undrained Soils.

To date, no studies have evaluated nitrous oxide (NO) emissions of a single versus a split-nitrogen (N) fertilizer application under different soil drainage conditions for corn ( L.). The objective of this study was to quantify season-long cumulative NO emissions, N use efficiency, and soil N dynamics when corn received a recommended N rate as single or split-N application in Minnesota soils with and without tile drainage over two growing seasons. Preplant urea was broadcast incorporated, and in-season split-N was broadcast as urea plus urease inhibitor. Tile drainage reduced NO emissions during periods of excess moisture but did not affect grain yield or other agronomic parameters. Conversely, when precipitation was adequate and well distributed, tile drainage did not affect NO emissions, but it did enhance grain yield. Averaged across years, the undrained soil emitted 1.8 times more NO than the drained soil (2.36 vs. 1.29 kg N ha). Compared with the Zero-N control, the Single Preplant and Split N applications emitted 2.1 and 1.6 times more NO, produced 1.4 and 1.3 times greater grain yield, and resulted in 1.5 and 1.4 times more residual soil total inorganic N, respectively. Per unit of grain yield, the Split application emitted similar amounts of NO as the Zero-N control. Averaged across years and drainage, the Split application emitted 26% less NO than the Single Preplant application (1.84 vs. 2.48 kg N ha; < 0.001) with no grain yield differences. These results highlight that soil drainage can reduce NO emissions and that a split N application may be a feasible way to achieve NO reduction while enhancing grain yield.

Nitrogen Management for Corn and Groundwater Quality in Upper Midwest Irrigated Sands.

Groundwater contamination from NO-N leaching in corn ( L.) production with coarse-textured soils poses an environmental concern. Our objectives were to evaluate NO-N leaching in continuous corn (CC), corn after soybean ( L.) (CSb), and soybean after corn (SbC) in irrigated sandy soils in Minnesota related to (i) N rate using best management practices of split-N application, (ii) a split-N application and single preplant applications of enhanced-efficiency fertilizers (EEF), and (iii) residual N treatment in SbC. Urea (0-315 kg N ha in 45-kg increments) was broadcast as a split application (half at preplant and half at the V4 development stage) and polymer-coated urea (ESN), ESN/urea, and SuperU at preplant at a rate of 180 kg N ha on an Arvilla sandy loam soil. In May and June, 75% of the total drainage and 73% of the total NO-N leached occurred. At the economic optimum N rate (EONR), season-long NO-N leaching rates were 86 and 106 kg NO-N ha for CC and CSb, respectively. In CC, reducing the EONR by 20% reduced grain yield by 4% and NO-N leached by 9%, and a 25% reduction in EONR resulted in an additional 2% reduction for both, whereas no significant reductions occurred for CSb. Similar NO-N leaching occurred with EEFs and the split-N application. After 4 yr of no N application, we measured 9 to 20 mg NO-N L and leaching of 21 to 51 kg NO-N ha, highlighting the difficulty of meeting drinking water quality standards in corn cropping systems.

Nitrous oxide emissions from anhydrous ammonia, urea, and polymer-coated urea in illinois cornfields.

The use of alternative N sources relative to conventional ones could mitigate soil-surface NO emissions. Our objective was to evaluate the effect of anhydrous ammonia (AA), urea, and polymer-coated urea (ESN) on NO emissions for continuous corn ( L.) production. Corn received 110 kg N ha in 2009 and 180 kg N ha in 2010 and 2011. Soil NO fluxes were measured one to three times per week early in the growing season and less frequently later, using vented non-steady state closed chambers and a gas chromatograph. Regardless of N source, NO emissions were largest immediately after substantial (>20 mm) rains, dropping to background levels thereafter. Averaged across N sources, 2.85% of the applied N was lost as NO. Emission differences for treatments only occurred in 2010, the year with maximum NO production. In the 2010 growing season, cumulative emissions (in kg NO-N ha) were lowest for the check (2.21), followed by ESN (9.77), and ESN was lower than urea (14.07) and AA (16.89). Emissions in 2010 based on unit of corn yield produced followed a similar pattern, and NO emissions calculated as percent of applied N showed that AA losses were 1.9 times greater than ESN. Across years, relative to AA, ESN reduced NO emissions, emissions per unit of corn yield, and emissions per unit of N applied, whereas urea produced intermediate values. The study indicates that, under high N loss potential (wet and warm conditions), ESN could reduce NO emissions more that urea and AA.

Soil carbon stocks and carbon sequestration rates in seminatural grassland in Aso region, Kumamoto, Southern Japan.

Global soil carbon (C) stocks account for approximately three times that found in the atmosphere. In the Aso mountain region of Southern Japan, seminatural grasslands have been maintained by annual harvests and/or burning for more than 1000 years. Quantification of soil C stocks and C sequestration rates in Aso mountain ecosystem is needed to make well-informed, land-use decisions to maximize C sinks while minimizing C emissions. Soil cores were collected from six sites within 200 km(2) (767-937 m asl.) from the surface down to the k-Ah layer established 7300 years ago by a volcanic eruption. The biological sources of the C stored in the Aso mountain ecosystem were investigated by combining C content at a number of sampling depths with age (using (14) C dating) and δ(13) C isotopic fractionation. Quantification of plant phytoliths at several depths was used to make basic reconstructions of past vegetation and was linked with C-sequestration rates. The mean total C stock of all six sites was 232 Mg C ha(-1) (28-417 Mg C ha(-1) ), which equates to a soil C sequestration rate of 32 kg C ha(-1)  yr(-1) over 7300 years. Mean soil C sequestration rates over 34, 50 and 100 years were estimated by an equation regressing soil C sequestration rate against soil C accumulation interval, which was modeled to be 618, 483 and 332 kg C ha(-1)  yr(-1) , respectively. Such data allows for a deeper understanding in how much C could be sequestered in Miscanthus grasslands at different time scales. In Aso, tribe Andropogoneae (especially Miscanthus and Schizoachyrium genera) and tribe Paniceae contributed between 64% and 100% of soil C based on δ(13) C abundance. We conclude that the seminatural, C4 -dominated grassland system serves as an important C sink, and worthy of future conservation.