**3. Research involving controlled subsurface irrigation and drainage at the David M. Barton Agriculture Research Center**

This portion of the research project is a long-term assessment of controlled subsurface irrigation/drainage technologies with associated denitrification bioreactors. Tile drainage water chemistry and nitrate-ammonium concentrations available in soil from 2010 to 2013 are documented [47, 48]. These 4 years of investigation reveal soil nitrate concentrations generally showed an increase immediately after soil nitrogen fertilization practices and were sufficiently abundant to promote their transport from the soil resource to the tile drain effluent waters. The tile drainage chemistry data indicated (i) appreciable transport of nitrate-N in tile drain effluent waters (mean of 32 mg NO3-N/L in 2008, mean of 80 mg NO3-N/L in 2009, mean of 10 mg NO3-N/L in 2010, and mean of 15 mg NO3-N/L in 2012); (ii) denitrification soil pathways partially reduced a portion of the soil nitrate-N when the controlled drainage system establishes winter/early spring anoxic soil conditions, and (iii) the best strategy for reducing nitrate-N concentrations in tile drain effluent waters was adjusting: (i) N fertilization rates and (ii) the timing of their application.

Tile drainage from the 2014 soybean system illustrated pH levels near pH 6.5 ± 0.5 across all of the sampling sites for the duration of drainage. Greater nitrate sampling was performed in 2014 than 2013 because of the longer drainage interval; however, tile drainage effluent nitrate-N concentrations averaged from less than 10 mg NO3-N/L for many of the sampling sites/times to more than 80 mg NO3-N on at least four occasions (**Figure 2**). Ammonium concentrations in the tile drain effluents ranged from 0.25 mg NH4-N/L to near 5 mg NH4- N/L. The presence of appreciable nitrate and ammonium concentrations was reflective of a large nitrate pool remaining from the previous corn production and to a smaller extent soil organic matter mineralization. Phosphorus concentrations ranged from 0.1 to 3 mg P/L, thus phosphorus concentrations represent an environmental impact given they frequently exceed 0.2 mg PO4-P/L. Sulfate-S concentrations ranged from 2.5 to 5.5 mg SO4-S/L; however, these SO4-S concentrations were not considered an environmental hazard.

**Figure 2.** Drainage water nitrate-N concentrations from stop-log boxes in 2014.

Soil nitrate concentrations have been periodically monitored to estimate the soil nitrate pool for plant uptake and leaching potentials. The soil nitrate concentrations typically have fluctuated based on (i) the corn-soybean rotation stage, (ii) nitrogen (urea) fertilization rates and timing, (iii) soil denitrification (either intentionally establishing perched water tables by restricting drainage during the noncropping season and cropping season rainfall patterns), (iv) crop uptake (corn-soybean rotation and off-season cover crop establishment), and (v) soil mineralization and residue decomposition. Soil sampling established that nitrate-N concentrations were (i) greater after urea application for corn and (ii) dependent on rainfall patterns. Approximately 10–50% of the nitrate pool migrated from the upper 15 cm to the 15–30 cm layer within 1 month of application, with smaller portions of the nitrate pool ultimately percolating to deeper soil layers. As an example, 2013 (corn portion of the rotation) witnessed an April planting with urea (292 lbs/ac or 328 kg/ha) application just prior to 15 May 2013. On 15 May 2013, the majority of the urea was converted to ammonium with a portion of the ammonium converting to nitrate via nitrification reactions. On 7 June, the majority of the nitrogen application was nitrate, with a portion of the nitrate leaching into the 15–30, 30–45, and 45– 60 cm deep soil layers (**Table 1**). Soil nitrate concentrations postcorn harvest (data not shown) and 24 March 2014 soil nitrate concentrations were comparatively smaller. A substantial portion of the field nitrogen pool was documented to be associated with grain and residue production (approximately 60%) and the remainder associated with the soil nitrate pool and lost from the soil system because of tile drainage effluents or soil denitrification reactions.

Edge of Field Technology to Eliminate Nutrient Transport from Croplands: Specific Focus... http://dx.doi.org/10.5772/64602 11


Multiple replications.

0.2 mg PO4-P/L. Sulfate-S concentrations ranged from 2.5 to 5.5 mg SO4-S/L; however, these

Soil nitrate concentrations have been periodically monitored to estimate the soil nitrate pool for plant uptake and leaching potentials. The soil nitrate concentrations typically have fluctuated based on (i) the corn-soybean rotation stage, (ii) nitrogen (urea) fertilization rates and timing, (iii) soil denitrification (either intentionally establishing perched water tables by restricting drainage during the noncropping season and cropping season rainfall patterns), (iv) crop uptake (corn-soybean rotation and off-season cover crop establishment), and (v) soil mineralization and residue decomposition. Soil sampling established that nitrate-N concentrations were (i) greater after urea application for corn and (ii) dependent on rainfall patterns. Approximately 10–50% of the nitrate pool migrated from the upper 15 cm to the 15–30 cm layer within 1 month of application, with smaller portions of the nitrate pool ultimately percolating to deeper soil layers. As an example, 2013 (corn portion of the rotation) witnessed an April planting with urea (292 lbs/ac or 328 kg/ha) application just prior to 15 May 2013. On 15 May 2013, the majority of the urea was converted to ammonium with a portion of the ammonium converting to nitrate via nitrification reactions. On 7 June, the majority of the nitrogen application was nitrate, with a portion of the nitrate leaching into the 15–30, 30–45, and 45– 60 cm deep soil layers (**Table 1**). Soil nitrate concentrations postcorn harvest (data not shown) and 24 March 2014 soil nitrate concentrations were comparatively smaller. A substantial portion of the field nitrogen pool was documented to be associated with grain and residue production (approximately 60%) and the remainder associated with the soil nitrate pool and lost from the soil system because of tile drainage effluents or soil denitrification reactions.

SO4-S concentrations were not considered an environmental hazard.

10 Soil Contamination - Current Consequences and Further Solutions

**Figure 2.** Drainage water nitrate-N concentrations from stop-log boxes in 2014.

**Table 1.** Soil nitrate and ammonium concentrations.

**Figure 3.** Concentrations of nitrogen, potassium, and phosphorus in 2014 corn by plant organs (Error bars are the standard deviations of three replicates.).

The associated corn biomass (**Figure 3**) demonstrates that nitrogen is primarily associated with grain (65%) and is thus removed from the soil landscape by harvest. Similarly, potassium (27% associated with grain) and phosphorus (74% associated with grain) demonstrate different harvest removals.
