Reducing Nitrogen Loss from Tillage Ground - Catch Crop Update from the Agricultural Catchments Programme
All farming sectors have to reduce nitrogen (N) loss, in order to restore all water bodies to a good status by 2027. On free draining, nitrate leaching prone sites, research has shown that overwinter green cover can substantially reduce nitrate leaching to ground water from fallow crop land. The Agricultural Catchments Programme has been monitoring a tillage dominant river catchment in Castledockrell, Wexford since 2008 and has been focusing on winter green cover research. Ireland’s 5th Nitrates Action Programme (NAP), requires in all circumstances that 75-80% of harvested crops be shallow cultivated or sown with a crop within 14 days of harvest. The earlier the green cover is established, the more N it can capture.
In 2021, four on-farm sown catch crops were selected with a range of sowing dates for sampling. Table 1 details the sowing dates and preceding agronomic detail. All crops were rape/leafy turnip.
Table 1. Sowing date and agronomic detail of catch crops selected for crop sampling 2021.
| Date of Sowing | Crop Following | Sowing Method | Added Nutrients | Seeding Rate |
|---|---|---|---|---|
| 10th August | Spring Barley | Disc Tilled with Spinner on Back | Pig Slurry <1000g/acre | 8kg/ha |
| 20th August | Winter Barley | Spirit One Pass Drill | 1 bag of 18-6-12 | 8kg/ha |
| 4th September | Spring Barley | Disc Tilled with Spinner on Back | 0 | 8kg/ha |
| 10th September | Spring Barley | Direct Drill | 0 | 8kg/ha |
Crop samples were taken for dry matter yield determination (Figure 1). The August sown crops yielded much more than the September sown crops through the sampling period.
Figure 1. The effect of sowing date on yield (kg DM/Ha) of catch crops at six dates in autumn 2021.
As a follow on, this year a study is under way comparing the effect of 4 cover crop treatments on nitrate leaching, crop yield, crop N and soil fertility.
- Natural cover regeneration;
- Shallow cultivation and natural regeneration;
- Shallow cultivation with leafy turnip & forage rape;
- Shallow cultivation with phacelia & vetch.
As part of the NAP, farmers must leave 20-25% of their stubble ground uncultivated for overwintering birds. This year we have begun sampling seed, an important food source for birds, in uncultivated, shallow cultivated and sown catch crop ground on farms to track seed food source for wild birds over the winter period.
To compliment this work, a knowledge transfer campaign on catch crops is under way with a field scale demonstration site to be the focal point for tillage discussion groups this winter. The site will demonstrate the effect of sowing date (19th August/ 2nd Sept), post sowing rolling (with or without), and mixture type (1. Leafy turnip & forage rape; 2. Raddish, mustard, vetch, clover, forage rape, phacelia and linseed; 3. Phacelia, vetch & clover).