Minimizing Nitrogen Losses in a Corn–Soybean-Wheat Rotation using Best Management Practices Susantha Jayasundara, Gary Parkin, Claudia Wagner-Riddle, Peter von Bertoldi and Jon Warland Department of Land Resource Science, University of Guelph, Guelph, Ontario, N1G 2W1, Canada CONCLUSION • BM decreased NO 3 -N leaching and N 2 O-N emissions by 50% and 40%, respectively over a 4-year period when compared with conventional practices. • This reduction was due to optimizing inorganic N inputs by the use of soil NO 3 test and synchronizing N application to plant uptake (by side dressing) leading to increased N uptake efficiency ( 15 N data). • Zero tillage and cover cropping lead to less soil freezing due to increased snow cover resulting in lower N 2 O emissions during the spring thaw. • Grain yields were either not significantly different or higher in the BM compared with the conventional practices. ACKNOWLEDGMENTS Funding for this research was provided by the Canadian Foundation for Climate and Atmospheric Sciences, Agriculture and Agri-Food Canada/CCFIA, BIOCAP, and Ontario Ministry of Agriculture and Food (OMAF). RESULTS BACKGROUND  With conventional crop production practices N sources are not used efficiently.  Low N use efficiency in cropping systems has been linked to negative effects on the environment due to accumulation of reactive N forms in soils, ground and surface waters, and in the atmosphere.  Best management practices (BMP) that involve conservation tillage and improved N management methods are proposed as mitigation solutions for NO 3 leaching and N 2 O emissions but few studies have quantified both aspects at once. OBJECTIVE  To quantify the combined effect of multiple BMPs on productivity, NO 3 leaching, and N 2 O emissions in a corn-soybean-winter wheat rotation compared with conventional management practices. METHODS Site: Elora Research Station, University of Guelph, Ontario, Canada. Soil: Guelph Silt Loam (Typic Hapludalf). Management Systems: 1. Conventional system (CONV): Tillage: fall moldboard followed by spring disking. Fertilizer N: according to general recommendations (OMAF, 2002). For Corn - 150 kg N ha -1 as urea broadcasted at planting . For Wheat - 90 kg N ha -1 as urea broadcasted in early spring. 2. Best Management System (BM) Zero-tillage. Fertilizer N: for corn based on spring soil NO 3 test and applied as UAN 28% side-dressed at 6-leaf stage . For Wheat: 60 kg N ha -1 as urea (allowing 30 kg ha -1 N credit from preceding soybean). Use of over-winter cover crops when possible. (red clover under-seeded to winter wheat). Each system was imposed on 1.5 ha side by side plots and replicated twice. NO 3 leaching: determined using ceramic cup samplers and water balance approach. N 2 O emissions: determined using micrometeorological Flux-Gradient Method. 2001 Soybean 2000/2003 Corn 2002 Winter wheat Mineral N in 0-30 cm soil depth MJ J A SO ND J FMAMJ J ASOND J FMA M J J A SO ND J FMA MJ J ASOND J FMA 0 0.5 1 1.5 2 N 2 O f l u x (k g N 2 O-N ha - 1 month - 1 ) Conventional Best Management corn soy wheat clover corn 2000 2001 2002 2003 Monthly N 2 O fluxes N fert Spring thaw CONV BM 0 4 8 12 Ni t r ou s O x i de Em i ss i ons ( kg N/ ha) Growing season Inter-Grow.season Corn’00 Soybean’01 Wheat’02 Corn’03 Cumulative N 2 O emissions Plot 2 (BM) Plot 3 (BM) Plot 1 (CONV) Plot 4 (CONV) Instrument trailer 0 40 80 120 160 200 May-00 Sep-00 Jan-01 May-01 Sep-01 Jan-02 May-02 Sep-02 Jan-03 May-03 Sep-03 Jan-04 May-04 Month-Year kg N ha -1 CONV BM Corn Soybean Winter wheat Red clover (in BM) Corn NO 3 -N in Soil Solution at 80 cm depth 0 5 10 15 20 25 30 35 40 45 May-00 Sep-00 Jan-01 May-01 Sep-01 Jan-02 May-02 Sep-02 Jan-03 May-03 Sep-03 Jan-04 May-04 Month-Year NO 3 -N concentration (mg L -1 ) CONV BM Corn Soybean Winter wheat Red clover (in BM) Corn 0 10 20 30 40 50 60 70 80 May-00 Sep-00 Jan-01 May-01 Sep-01 Jan-02 May-02 Sep-02 Jan-03 May-03 Sep-03 Jan-04 May-04 Month - Year Monthly Drainage (mm) CONV BM Monthly Drainage 0 1 2 3 4 5 6 7 8 9 10 2000 2001 2002 2003 Grain (Mg ha -1 ) Conv BM 4.3 3.9 2.4 3.5 6.8 7.6 8.9 8.4 NS P<0.0001 NS NS Corn Corn Soybean Winter wheat Year Period Drainage (mm) NO 3 -N leached (kg ha -1 ) Conv BM Conv BM P value 2000 GS a ------------------- not measured ------------------ IG 171 159 57.9 27.8 0.004 2001 GS 31 41 8.4 6.1 0.114 IG 164 157 17.9 9.7 <0.0001 2002 GS 44 23 2.6 0.7 0.002 IG 154 112 8.5 3.4 0.001 2003 GS 16 29 2.1 1.9 0.665 IG b 105 114 15.2 6.3 0.0004 Cumulative 685 635 112.6 55.9 a GS = growing season, IG = inter-growing season. b Values for 2003 inter-growing season include Nov and Dec months only. Cumulative drainage and NO 3 -N leaching Grain yield