Nutrient use efficiency - Agri environmental update

Nutrient use efficiency can vary widely across soil types and the level of production across farms. Being aware of what’s required to improve nutrient efficiencies can decrease losses to waterways, reduce greenhouse gas and air emissions while also increasing production and profitability in a sustainable manner at farm level.

At farm level it’s vital that soil health and nutrient use efficiency is managed to optimise grass quantity and quality for our grass-based milk production system. The following steps should be considered when looking to improve nutrient efficiencies on farm

• Carry out soil tests
• Correct soil pH
• Target index of 3 for both Phosphorus and Potassium
• Recycling of slurry and farmyard manures
• Balancing nutrients with compound fertiliser

Nitrogen use efficiency

Nitrogen Use Efficiency is a relatively new term that is being discussed more regularly. NUE calculates all nitrogen (N) inputs on the farm vs the outputs. It’s important to understand where the N sources are on farm. Typically, they come from chemical fertiliser, purchased feeds (concentrates and forage), slurry (imported). Chemical fertiliser is likely the biggest source, however it is important to remember the lesser sources such as feed conversion in cattle and excreting nitrogen. It is equally important to understand the outputs for N on your farm. These typically happen through milk sales, livestock and forage sales and exported slurry. Nitrogen use efficiency across Ireland is typically 25%. By improving this figure, we also have the ability to reduce losses to our groundwaters.

Steps in increase N efficiency

• Ensure that other elements of soil fertility are optimised. Utilisation of N will be reduced if P or K levels or pH are too low.
• Increased use of clover in swards reduces the amount of N fertiliser used.
• Match N application to grass growth and stocking rate
• Managing grazing effectively, focusing on high levels of grass production and utilisation, leads to increase milk output per unit of N applied
• Applying Urea early in the year when conditions are appropriate reduces the GHG emissions associated with fertiliser manufacture and cost

White Clover

The use of white clover can increase the tonnes of dry matter grown, because it is a higher quality feed it will increase animal performance and it will also reduce dependence on chemical nitrogen which will increase nitrogen use efficiency. White clover has rhizobia bacteria in its roots that fix nitrogen from the air and it can supply between 50-200kg N/ha per year.

Include Sulphur

Sulphur (S) is a very important nutrient for grassland and it is closely associated with nitrogen uptake and efficiency. Sulphur and nitrogen works closely together as grass grows, S is required to convert N to plant dry matter. Sandy, lighter soils with low organic matter tend to be more prone to S deficiency. For grazing a ratio of 12:1 for N and S is recommended and for silage crops 20kg/ha is recommended.

Improving NUE has many opportunities not only to improve water quality by reducing nitrogen leaching, but also by reducing costs and increasing profitability at farm level.

Recently Glanbia Ireland launched its “GAIN Momentum” programme. Great Grass, one of the pillars within the programme, focuses on soils and grassland management. The programme aims to maximise grassland production in a sustainable manner. Maximising spring grass growth is one of the central parts of the programme. Two of the key area’s that contribute to this in early spring are:

• Early Nitrogen – spring grass is the cheapest form of livestock feed in a dairy herd, each extra day at grass delivers €2.70/day/cow extra income. One of the key drivers of spring grass growth is the use of Nitrogen, apply approximately 32 units/acre for the month of March depending on soil type
• Early “P” – Phosphorus plays a very important role in the plant as it contributes to energy provision, root development and root stimulation. As a nutrient, it is very immobile in the soil and when we look at its functions we must remember that low soil temperatures inhibit its availability and therefore spring is the optimum time for application