Materials and Methods

1. Ammonia Volatilization Following Banding of Urea to Seven Agricultural SoilsP. Rochette, M. Chantigny, D.A. Angers, J.D. MacDonald, L. Lamontagne,N. Bertrand and F. Boiffard. Soils and Crops Research Center, Québec City, QC, Canada. Results and Discussion Table 2. Cumulative volatilization Soil Cumulative NH3 losses (% of N applied) S1 17.3 S2 11.6 S3 10.5 S4 1.4 S5 0.3 S6 0.2 S7 0.0 • Total NH3 volatilization: • varied between 1 and 18% of applied urea-N, • were greatest on S1 followed by S2 and S3, • were ≈ 0 for S5, S6 and S7 and very small on S4. Introduction • Urea accounts for 40% of global nitrogen fertilizers sales. • Surface application of urea to agricultural soils can result in high NH3 volatilization losses (Sommer et al., 2004). • Soil incorporation of broadcasted urea reduces volatilization. • Incorporation in bands is not as efficient because of a large localized pH increase in the urea band (Rochette et al., 2009a). • NH3 volatilization from urea incorporated in bands may be influenced by soil properties. Introduction Volatilization Relationships between cumulative NH3-N losses and selected soil properties. y = 4960 e-0.17x ; r2 = 0.99 y = 44421 e-0.24x ; r2 = 0.87 y = e0.01x ; r2 = 0.28 • Volatilization: • was very low in 4 out of 7 soils, • began 3 to 4 days after urea application, • increased rapidly followed by a gradual decline, • was greater in soils with lower clay content. Objective Assess the propensity of soils with contrasting characteristics to emit NH3 from urea incorporated in bands. Cumulative NH3 losses (mg N m -2) y = -1801x + 4041; r2 = 0.81 y = 1285 - 2444; r2 = 0.99 Materials and Methods • Strongly to moderately acid agricultural soils (7) with contrasting clay content were selected in the Quebec City region (Table 1). • Surface 10 cm of each soil was sampled in October 2008. • Soils were sieved to ≤ 2 mm and moistened to -200 kPa. • Soils were packed to 1.00 g cm-3 in stainless steel cylinders (I.D.: 20 cm; H : 12 cm) (Fig. 1) and incubated for 28 d using a dynamic chamber at 20°C (Rochette et al., 2009b). Soil pH • Cumulative volatilization losses: • were highly correlated with soil clay content, CEC and buffer capacity, • NH3 volatilization losses were negligible for soils with: • Clay content above 20%, • CEC above 20 meq/100 g, • Buffer capacity above 1.8. Soil pH increased by 1.9 to 3.2 units in response to hydrolysis of urea. Conclusions Fig. 1. Soil incubation dynamic systems. “Soil solution” NH4-N (CaCl2 0.005M) • Significant losses of NH3 can occur when urea is incorporated in bands. • Magnitude of losses differs among soils. • The impact of incorporating urea on NH3 volatilization in bands is strongly influenced by soil properties, and decreases with increasing clay content, CEC and buffer capacity. • Volatilization is more closely related to soluble than with total soil NH4-N. • We conclude that : • 1) volatilization is lower in soils with a greater NH4 adsorption, • 2) the increased volatilization observed under field conditions on the S4 soil by Rochette et al. (2009a) cannot be generalized. • Soil pH, NH4+-N and NO3--N content were monitored in the urea band in containers (0.8 m x 0.4 m x 0.1 m) (Fig. 2). Fig. 2. Soil containers used for soil sampling and analysis. “Total” NH4-N (KCl 2M) Table 1. Selected properties of the seven soils at initiation of experiment. References • Total NH4-N in the urea band increased similarly in all soils. • Soil solution NH4-N in the urea band increased more in soils with lower clay content. Sommer, S.G., J.K. Schjørring, and O.T. Denmead. 2004. Ammonia emission from mineral fertilizers and fertilized crops. Adv. Agron. 82: 557-622. Rochette, P., D.A. Angers, M.H. Chantigny, N. Bertrand, M.-O. Gasser and J.D. MacDonald. 2009a. Banding of urea increased ammonia volatilization in a dry acidic soil. J. Environ. Qual., 38:1383-1390. Rochette, P., D.A. Angers, M.H. Chantigny, J.D. MacDonald, N. Bissonnette, and N. Bertrand, N. 2009b. Ammonia volatilization following surface application of urea to no-till and conventionally tilled soils: a laboratory comparison. Soil Till. Res. 103:310-315.