Nitrate Loss in Subsurface Drainage as Affected by Nitrogen Fertilizer Rate
2001
Jaynes, D.B. | Colvin, T.S. | Karlen, D.L. | Cambardella, C.A. | Meek, D.W.
The relationships between N fertilizer rate, yield, and NO₃ leaching need to be quantified to develop soil and crop management practices that are economically and environmentally sustainable. From 1996 through 1999, we measured yield and NO₃ loss from a subsurface drained field in central Iowa at three N fertilizer rates: a low (L) rate of 67 kg ha⁻¹ in 1996 and 57 kg ha⁻¹ in 1998, a medium (M) rate of 135 kg ha⁻¹ in 1996 and 114 kg ha⁻¹ in 1998, and a high (H) rate of 202 kg ha⁻¹ in 1996 and 172 kg ha⁻¹ in 1998. Corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] were grown in rotation with N fertilizer applied in the spring to corn only. For the L treatment, NO₃ concentrations in the drainage water exceeded the 10 mg N L⁻¹ maximum contaminant level (MCL) established by the USEPA for drinking water only during the years that corn was grown. For the M and H treatments, NO₃ concentrations exceeded the MCL in all years, regardless of crop grown. For all years, the NO₃ mass loss in tile drainage water from the H treatment (48 kg N ha⁻¹) was significantly greater than the mass losses from the M (35 kg N ha⁻¹) and L (29 kg N ha⁻¹) treatments, which were not significantly different. The economically optimum N fertilizer rate for corn was between 67 and 135 kg ha⁻¹ in 1996 and 114 and 172 kg ha⁻¹ in 1998, but the net N mass balance indicated that N was being mined from the soil at these N fertilizer levels and that the system would not be sustainable.
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