Submitted to: Environmental Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/18/2003
Publication Date: 1/23/2004
Citation: GOLLANY, H.T., MOLINA, J.E., CLAPP, C.E., ALLMARAS, R.R., LAYESE, M.F., BAKER, J.M., CHENG, H.H. NITROGEN LEACHING AND DENITRIFICATION IN CONTINUOUS CORN AS RELATED TO RESIDUE MANAGEMENT AND NITROGEN FERTILIZATION. ENVIRONMENTAL MANAGEMENT. 2004. Interpretive Summary: Crop production systems that optimize yield, improve soil and water quality, and reduce greenhouse gases are desirable. Two environmental concerns for applied nitrogen (N) fertilizers are: nitrate leaching (a major cause of groundwater contamination), and production of nitrous oxide (greenhouse gas emission that cause global warming). A long-term continuous corn study was begun in 1980 on a silt loam soil at the University of Minnesota Research Center, Rosemount, MN. Two fertilizer treatments, low N (18 lb N/acre) and high N (180 lb N/acre) application rates, and two types of residue management (residue harvested, and residue returned) were established in the spring of 1980, and continued until 1992. Our objectives were to: 1) measure the effects of N application rate on N losses due to leaching or emission of nitrous oxide; 2) examine the impact of residue on N transformation and losses; and 3) verify the capability of a computer program (NCSWAP/NCSOIL model) to simulate the dynamics of N in the soil-plant system. The model accurately predicted N in the plant and soil organic matter (SOM) at 0- to 15-cm and 15- to 30-cm depths for both fertilizer rates and residue managements. The predicted denitrification (conversion of nitrogen to nitrous oxide form) losses were 39, 46, and 51 lb/acre/year for low N fertilizer rates, and 40, 64, and 77 lb/acre/year for high N fertilizer rates, when the residue was returned at 0, 4000 (66%), 6000(100%) lb/acre rates, respectively. The corresponding predicted N loss due to nitrate leaching were 31, 29, and 28 lb/acre/year for low N fertilizer rates, and 86, 76, and 73 lb/acre/year for high N fertilizer rates, when the residue was returned at 0, 4000, 6000 lb/acre rates, respectively. During a 30-yr simulation, the predicted N loss shows more nitrate leaching past the 3 feet depth for residue harvested than residue returned plots. Less N leaching and denitrification predicted by the model for the low N than high N application rates. This study suggests that better synchronization of N release from the residue and addition of N fertilizer with plant-N uptake would minimize leaching and denitrification. Maintaining crop production levels while reducing greenhouse gases requires strategic residue and nitrogen (N) fertilizer management.
Technical Abstract: Abstract Maintaining crop production levels with reductions in terrestrial greenhouse gases requires strategic residue and N fertilizer management. Our objectives were to: 1) quantify the effect of nitrogen (N) application rate on N losses; 2) examine the role of residue returned on N transformation and losses; and 3) verify the capability of the NCSWAP/NCSOIL model to simulate the dynamics of N and 15N in the soil-plant system. Data obtained from a long-term continuous corn study on a silt loam soil (fine-silt over sandy or sandy-skeletal, mixed, mesic Typic Hapludoll), including rotary tillage plots with two N levels (20 and 200 kg N ha^-1), with two types of residue management (residue harvested, and residue returned) was used to calibrate the model. The model accurately predicted ^15N in the plant and soil organic matter (SOM) at the 0- to 15-cm and 15- to 30-cm depths for both fertilizer rates and residue managements. For the same amount of ^15N added (8 kg ^5N ha^-1), concentrations of ^15N in the corn and SOM were higher for the 20 than the 200 kg N ha^-1 treatments. Greater dilution of the 15N with non-tracer fertilizer added at the higher fertilizer rate was responsible for differences in 15N concentrations in the plant. The predicted cumulative N loss during a 30-yr simulation indicates more nitrate (NO_3^-) leaching past the 1 m-depth for residue harvested than residue returned plots, while higher denitrification rates were predicted for the residue returned than residue harvested. The simulated cumulative effects of N rates and residue returned on denitrification over a 30 years predicted an increased cumulative N losses from 1333, and 1320 kg N ha^-1 to 2574, and 1705 kg ha^-1 for the high and low N application rates, respectively. This study suggests that better synchronization of N release from the residue and addition of N fertilizer with plant-N uptake would minimize leaching and denitrification.