Effect of soil disturbance on N availability across a variable landscape in southern Ontario

Abstract

Although the effect of soil disturbance on N mineralization has been studied under field conditions, the spatial variation of this effect at the landscape scale has not been investigated. The objective of this study was to determine the spatial variation of the effect of tillage on plant N availability across a variable landscape in southern Ontario and to identify the causal factors. A field experiment was conducted from 1998 to 2001 using two spring tillage operations (no-tillage (NT) and conventional tillage (CT)) prior to planting corn ( Zea mays L.) on a field, which was planted to barley ( Hordeum vulgare L.) in the preceding season. Tillage treatments were implemented at five positions in the landscape. The corn plants received either 0 or 140 kg N ha −1. Plant N availability was approximated by adding the amount of soil mineral N present in the 0–30 cm depth and N contained in the aerial phytomass in the zero N treatment. The plant available N (PAN) content was significantly higher in the CT treatment than that in the NT treatment during the first 2 months after the tillage operation, with differences ranging from 2.1 to 6.5 mg N kg −1. This effect did not vary with soil properties. In a supplementary laboratory incubation study, which simulated the field tillage operation under controlled conditions, the PAN did not increase in the disturbed soils at any point during the 90-day incubation period. It was hypothesized that the change in the soil physical environment (e.g., soil temperature) could have had a greater influence on the observed differences in the field experiment than the availability of physically protected organic matter in this long-term cultivated field.