Nitrogen Dynamics in Soils from the Red River Valley of the North

The objectives of this study were to evaluate the effects of (i) N management on crop yield, N availability, and N losses from a silty clay having subsurface drainage, (ii) soil moisture and nitrification inhibitor nitrapyrin [2-chloro-6-trichloro methyl pyridine, NP] on N2O emissions, and (iii) urea N-additives on NH3 volatilization and N2O emission losses from two contrasting soil textures (silty clay and sandy loam). The mean yields for corn (Zea mays L.), wheat (Triticum aestivum L.), sugarbeet (Beta vulgaris L.), and soybean (Glycine max L.) were 7.4, 0.9, 47.0, and 2.6 Mg ha-1 in 2012, and were 8.3, 4.1, 38.3, and 3.0 Mg ha-1 in 2013, respectively, across N and drainage treatments. Applying recommended N-rate along with NP increased N availability to crops, particularly under the subsurface drained condition. Application of extra N-rate than recommended only increased N losses associated with N2O and NH3 emissions. In the laboratory, N2O emissions from urea applied at 250 kg N ha-1 to silty clay soil were 0.14, 0.96, and 4.00% of applied-N at 30, 60, and 80% WHC, respectively. At WHC ? 60%, NP reduced N2O emissions by 2.6 to 4.8 fold compared to urea alone. Ammonia volatilization was higher from sandy loam (0.7 to 4.3% of applied-N) than from silty clay (0.1 to 0.4% of applied-N). In sandy loam, applying urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) and polymer coated urea (PCU) reduced NH3 losses by 32.3% and 84.2%, respectively, compared to untreated-urea. In silty clay, NBPT reduced NH3 volatilization by 71.4% relative to untreated-urea. N2O emissions did not differ between soils, and were between 3.7 to 7.4% of applied-N. In sandy loam, NP, SuperU (urea containing NBPT and nitrification inhibitor dicyandiamide), and PCU reduced N2O emissions by 23.5%, 43.8%, and 51.1%, respectively, compared to urea alone. Within the scope of two years of the field study, subsurface drainage and N management influenced soil N availability more than crop yield, emphasizing the need for long term research on subsurface drainage effect on crop yield. Soil moisture, texture and N management exert strong influence on NH3 volatilization and N2O emission