Abstract
Agricultural soils are at risk of nitrogen (N) leaching especially during the fallow period in autumn and winter.
Cover crops are grown to capture soil mineral N that otherwise would leach to the groundwater. They can serve
as green manure providing mineral N to the cash crop in spring. We investigated whether mixing species of cover
crops can enhance N capture and therefore reduce N leaching more effectively than pure stands in autumn
without increasing the risk of N leaching in spring. We hypothesised that mixed species with complementary
traits will capture more N and accumulate more biomass. It was also expected that residues from cover crops with
higher biomass and lower C:N ratio would mineralise faster and subsequently increase N leaching in spring. In a
4-year field experiment, cover crops were grown between August and February in a rotation with different cash
crops. We used eight cover crop treatments, including three pure stands: radish (Raphanus sativus), vetch (Vicia
sativa) and oats (Avena strigosa), all possible 2- and 3-species mixtures and a fallow (no cover crop). Treatment
effects on leaching losses were estimated by analysing N concentrations in samples of leached pore water below
the rooting zone and by modelling the volume of water leached per plot. Most N leaching occurred in autumn
and winter while the amount of N leached in spring was negligible due to the lower precipitation. N leaching in
autumn correlated negatively with cover crop biomass, N uptake and root length density. Radish and oats were
the most productive species and dominated mixtures. Compared to the fallow, radish and mixtures that con-
tained radish reduced N leaching by 49–73% and were characterized by quick soil cover, high N uptake and low
to moderate C:N ratio. Subsequently, residues from radish and mixtures containing radish mineralized quickly,
resulting in an increase in soil mineral N in spring by 70–110% as compared to fallow. This mineral N did not
leach in spring and was available to the subsequent cash crop. This study demonstrates the importance of species
selection in cover crop mixtures and recommends the use of radish-based mixtures if the purpose is to reduce N
leaching in autumn and provide mineral N in spring.
Cover crops are grown to capture soil mineral N that otherwise would leach to the groundwater. They can serve
as green manure providing mineral N to the cash crop in spring. We investigated whether mixing species of cover
crops can enhance N capture and therefore reduce N leaching more effectively than pure stands in autumn
without increasing the risk of N leaching in spring. We hypothesised that mixed species with complementary
traits will capture more N and accumulate more biomass. It was also expected that residues from cover crops with
higher biomass and lower C:N ratio would mineralise faster and subsequently increase N leaching in spring. In a
4-year field experiment, cover crops were grown between August and February in a rotation with different cash
crops. We used eight cover crop treatments, including three pure stands: radish (Raphanus sativus), vetch (Vicia
sativa) and oats (Avena strigosa), all possible 2- and 3-species mixtures and a fallow (no cover crop). Treatment
effects on leaching losses were estimated by analysing N concentrations in samples of leached pore water below
the rooting zone and by modelling the volume of water leached per plot. Most N leaching occurred in autumn
and winter while the amount of N leached in spring was negligible due to the lower precipitation. N leaching in
autumn correlated negatively with cover crop biomass, N uptake and root length density. Radish and oats were
the most productive species and dominated mixtures. Compared to the fallow, radish and mixtures that con-
tained radish reduced N leaching by 49–73% and were characterized by quick soil cover, high N uptake and low
to moderate C:N ratio. Subsequently, residues from radish and mixtures containing radish mineralized quickly,
resulting in an increase in soil mineral N in spring by 70–110% as compared to fallow. This mineral N did not
leach in spring and was available to the subsequent cash crop. This study demonstrates the importance of species
selection in cover crop mixtures and recommends the use of radish-based mixtures if the purpose is to reduce N
leaching in autumn and provide mineral N in spring.
| Original language | English |
|---|---|
| Article number | 108803 |
| Number of pages | 12 |
| Journal | Field Crops Research |
| Volume | 292 |
| DOIs | |
| Publication status | Published - 2023 |