Residual Soil Nitrate after Potato Harvest
2003
Bélanger, Gilles | Ziadi, Noura | Walsh, John R. | Richards, John E. | Milburn, Paul H.
Nitrogen loss by leaching is a major problem, particularly with crops requiring large amounts of N fertilizer. We evaluated the effect of N fertilization and irrigation on residual soil nitrate following potato (Solanum tuberosum L.) harvests in the upper St-John River valley of New Brunswick, Canada. Soil nitrate contents were measured to a 0.90-m depth in three treatments of N fertilization (0, 100, and 250 kg N ha⁻¹) at two on-farm sites in 1995, and in four treatments of N fertilization (0, 50, 100, and 250 kg N ha⁻¹) at four sites for each of two years (1996 and 1997) with and without supplemental irrigation. Residual soil NO₃–N content increased from 33 kg NO₃–N ha⁻¹ in the unfertilized check plots to 160 kg NO₃–N ha⁻¹ when 250 kg N ha⁻¹ was applied. Across N treatments, residual soil NO₃–N contents ranged from 30 to 105 kg NO₃–N ha⁻¹ with irrigation and from 30 to 202 kg NO₃–N ha⁻¹ without irrigation. Residual soil NO₃–N content within the surface 0.30 m was related (R ² = 0.94) to the NO₃–N content to a 0.90-m depth. Estimates of residual soil NO₃–N content at the economically optimum nitrogen fertilizer application (Nₒₚ) ranged from 46 to 99 kg NO₃–N ha⁻¹ under irrigated conditions and from 62 to 260 kg NO₃–N ha⁻¹ under nonirrigated conditions, and were lower than the soil NO₃–N content measured with 250 kg N ha⁻¹ We conclude that residual soil NO₃–N after harvest can be maintained at a reasonable level (<70 kg NO₃–N ha⁻¹) when N fertilization is based on the economically optimum N application.
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