Nitrogen: Don’t exceed limits on cereal crops

As farmers get nitrogen out on cereal crops, it is important to make sure that nutrient limits are not exceeded.

Some farmers may try to compensate for nitrogen that may have been lost from the soil over the winter. But the limits outlined below cannot be exceeded.

Nitrogen is applied according to the ‘nitrogen index’. Index 1 refers to soil which has been in continuous cereals for five years or more or soil that was in maize in the previous year. Index 2 refers to land which was in oilseed rape, peas, beans, potatoes, beet, kale or mangles in the previous year.

Depending on the number of years the land has been out of grass, it will fall into index 1, 2, 3 or 4.

The amount of nitrogen (kg/ha) permitted in each index and for each cereal crop is detailed in the table below.

Data source: Department of Agriculture

Winter barley

Winter barley crops in index 1 may receive up to 180kg/ha of nitrogen (N). This figure decreases with index. Soils in index 4 may receive 80kg/ha.

Where proof of yields higher than 8.5t/ha (at 20% moisture content) have been achieved in the past three years, an additional 20kg/ha of N may be applied for each additional tonne above the reference yield.

Winter wheat

Winter wheat crops in index 1 may receive 210kg/ha of N. Winter wheat being grown on an index 4 soil, for example after grass, can receive 80kg/ha.

Where proof of yields above 9t/ha (at 20% moisture content) are available in the past three years, an extra 20kg/ha of N may be applied for each tonne over this yield.

Winter oats

Winter oats can receive 145kg/ha on index 1 soils. On index 4 soils, winter oats can receive 45kg/ha of N.

The reference yield for winter oats is 7.5t/ha (at 20% moisture content). For each additional tonne achieved above this yield, an extra 20kg/ha may be applied.