Yield and nitrogen uptake of monocropped maize from a long-term tillage experiment on a poorly drained soil

Abstract

Little information is available on the long-term impact of tillage systems on grain yield and nitrogen (N) uptake of maize (Zea mays L.) in the upper Midwest region of the USA. An 11 year (1982–1992) study comparing the effects of continuous autumn moldboard plowing (CT) vs. no-tillage (NT) on yield and N removal of monocropped maize was conducted on a poorly drained, well-tiled Webster clay loam soil in southern Minnesota, USA. Maize was fertilized each spring with ammonium nitrate (NH₄NO₃) at the rate of 200 kg N ha⁻¹. Lower soil temperatures and an apparent increase in surface soil density associated with NT resulted in delayed silking by about 6 days and 25 g kg⁻¹ wetter maize grain at harvest compared with CT during the 11 year period. Grain yield and N removal in the grain were consistently greater for CT than for NT owing to a combination of immobilization of surface applied N, lower spring soil temperatures, and surface soil consolidation limiting the root growth of plants leading to less N uptake with NT. Maize grain yield averaged 8.64 Mg ha⁻¹ with CT and 7.33 Mg ha⁻¹ with NT during the 11 year period. In the last 4 years of the study maize grain yield with CT averaged 2.46 Mg ha⁻¹ (40%) more than with NT. Soil samples collected to a 22.5 cm depth in 1987 after 6 years of continuous tillage indicated significant reduction in pH in the top 2.5 cm of NT soil owing to nitrification of NH₄⁺ in the surface-applied fertilizer N and mineralization of plant residue. Significant accumulation of P in the surface soil (top 2.5 cm) also occurred in the NT soil, owing to deposition of P by residue on the soil surface. Plowing the established NT plots after 11 years resulted in a trend towards increased yield and N uptake compared with CT plots in the residual year (1993). Results from this long-term study indicate that CT is superior to NT for maize production on these poorly drained soils, especially when stress conditions of excess rainfall and/or growing season temperature extremes occur.