Strategic use of spring fertiliser in grassland

The AHDB Nutrient Management Guide provides evidence-based recommendations to help you judge how much nitrogen to apply to grass. This article provides top information and tips for fertilising grassland this spring.

Spring grass is a highly valuable component of livestock's diet, especially for grazing animals. It is extremely digestible and high in crude protein, and why it is regarded as the highest-quality feed on the farm in spring.

The main objectives of spring grazing management are to increase the proportion of grazed grass in the diet. Early spring grazing will also help increase grass quality in future grazing rotations. Therefore, grass should be utilised as much as possible in the animal’s diet.

During the early grazing season (February or March), a balance must be found between feeding the animal adequately, sustaining high animal performance, and conditioning the sward for the late spring/summer grazing season.

The level of fertilisation required by grassland depends on:

• Soil nitrogen supply (SNS) status
• The growth potential of the land, termed the ‘Grass Growth Class’
• The level of production of the system

The crop nutrient recommendations found in RB209 Section 3 Grass and forage crops are based on the requirement of the crop, which is adjusted for nitrogen available from the soil (SNS).

Nitrogen fertiliser, organic manure use and management history in the last 1–3 years are also considered when determining the SNS status of each field.

Balancing these elements means that the nitrogen applied to grass can be tailored to make the most efficient use of the SNS to achieve the desired level of production.

Soil nitrogen supply (SNS) status

Determining the soil nitrogen supply status of grassland, from Section 3 (Table 3.6, page 13) of The Nutrient Management Guide (RB209).

The Grass Growth Class (GGC) describes the ability of a site to respond to nitrogen depending on soil type and rainfall.

The better the GGC, the greater the efficiency of nitrogen use and the greater the dry matter yield response.

Indicative grass dry matter yield by Grass Growth Class (GGC)

Indicative grass dry matter yield by Grass Growth Class (GGC) chart from Section 3 (Figure 3.1, page 14) of The Nutrient Management Guide (RB209).

Determining Grass Growth Class (GGC)

Determining Grass Growth Class, from Section 3 (Table 3.1, page 14) of The Nutrient Management Guide (RB209).

• Measure soil temperature to identify when the plant is actively growing so that nitrogen fertiliser can be applied to promote growth

Grass growth starts when the soil at a depth of 10 cm reaches 5°C for five consecutive days. White clover and other legumes begin to grow at 8°C. Grass in compacted and wet soils will start growing later because the high moisture content makes the soil colder.

• Lack of soil nitrogen supply can limit spring grass growth. However, keep in mind that the incorrect application of early nitrogen is wasteful, costly and increases the risk of point and diffuse pollution
• Always check the weather forecast before making slurry or fertiliser nitrogen applications – do not spread slurry or fertiliser if rain or very cold weather is forecast
• Check the soil trafficability to determine what capacity the soil can support moving vehicles before spreading to avoid damage to the soil
• Measure farm cover and use grass growth predictions from GrassCheck GB to inform decision-making around slurry and nitrogen fertiliser application
• Target the areas of the farm most likely to respond to early application of nitrogen, such as perennial ryegrass, free draining paddocks, drier paddocks, or recently reseeded fields
• Paddocks or fields that have heavy covers of grass built up on them (10 cm+) from the previous autumn and over the winter should be grazed before applying N
• Paddocks with little or no grass covers should receive cattle slurry first and N later. These will be the last to be grazed in the first rotation