Method and timing of grassland renovation affects herbage yield, nitrate leaching, and nitrous oxide emission in intensively managed grasslands

Abstract

Managed grasslands are occasionally ploughed up and reseeded in order to maintain or increase the sward productivity. It has been reported that this renovation of grassland is associated with a flush of soil organic nitrogen (N) mineralization and with a temporary increase in soil mineral N contents. Here, we report on the effects of method and time of grassland renovation on herbage yield, nitrate (NO 3 -) leaching and nitrous oxide (N 2 O) emission. Field experiments were carried out at three sites (two sandy soils and a clay soil) in the Netherlands for three years. Renovation of grassland increased the percentage of Perennial ryegrass from 48-70% up to more than 90%. However, averaged over three years, dry matter yields were higher for the reference (not reseeded) swards (on average 13.6 Mg ha -1 for the highest N application rate) than for the renovated grasslands (12.2-13.1 Mg ha -1 dry matter). Grassland renovation in April did not increase N leaching in comparison to the reference. However, renovation in September increased the risk of leaching, because mineral N contents in the 0-90 cm were in November on average 46-77 kg N ha -1 higher than in the reference. Contents of dissolved organic N (DON) in the soil were not affected by renovation. Renovation increased N 2 O emissions by a factor of 1.8-3.0 relative to the reference grassland. Emissions of N 2 O were on average higher after renovation in April (8.2 kg N 2 O-N ha -1 ) than in September (5.8 kg N 2 O-N ha -1 ). Renovation without ploughing (i.e. only chemically destruction of the sward) resulted in a lower percentage of perennial ryegrass (60-84%) than with ploughing ([90%). Moreover, N 2 O emissions were higher after renovation without ploughing than with ploughing. Clearly, farmers need better recommendations and tools for determining when grassland renovation has beneficial agronomic effects. Losses of N via leaching and N 2 O emission after renovation can probably not be avoided, but renovation in spring in stead of autumn in combination with ploughing and proper timing of fertilizer application can minimize N losses.

The effect of renovation of long-term temperate grassland on N2O emissions and N leaching from contrasting soils

“…In Ireland however, grasslands are reseeded on average every 30 years (Humphreys & Casey, 2002) with a substantial associated risk of losing large amounts of accumulated soil organic matter (SOM) (Velthof et al, 2010). The common practice is ploughing followed by fertilisation, both of which can lead to substantial losses of reactive nitrogen (N).…”

“…The common practice is ploughing followed by fertilisation, both of which can lead to substantial losses of reactive nitrogen (N). These losses occur due to both the incorporation of plants residues and the disruption of soil aggregates which exposes protected SOM to decomposition (Velthof et al 2010). Losses of reactive N include nitrous oxide (N2O) and leached nitrogen principally in nitrate (NO3-N) form, and dissolved organic nitrogen (DON) (Velthof et al 2010).…”

“…These losses occur due to both the incorporation of plants residues and the disruption of soil aggregates which exposes protected SOM to decomposition (Velthof et al 2010). Losses of reactive N include nitrous oxide (N2O) and leached nitrogen principally in nitrate (NO3-N) form, and dissolved organic nitrogen (DON) (Velthof et al 2010). Nitrogen losses due to denitrification as either N2 or N2O predominantly occur on heavier soils, due to lower soil redox potentials, while leaching can play a more significant role in losses following ploughing and fertilisation in light structured, well drained soils (Sogbedji et al, 2000;Dennis et al, 2012).…”

“…Studies of Velthof et al (2010) and Necpalova et al (2013) focused on various aspects of this issue with Velthof et al (2010) particularly focussing on the impact of timing of ploughing and variable fertilisation rates, while Necpalova et al (2013) assessed full system N loss.…”

“…However, both studies exhibited experimental weaknesses such as using soil samples as indicator of leaching instead of direct measurements (Velthof et al, 2010) or using only one soil type and delaying the start of measurements until a few months after reseeding (Necpalova et al, 2013).…”