In this installment of the Soil Fertility Series in conjunction with Grassland Agro, the focus is on nitrogen (N) and the factors to consider to try and improve efficiency and reduce N losses.

We will also meet with the farm manager of the Salesian Agricultural College in Palleskenry, Co. Limerick, and see how the farm has progressed through the spring and how it is adapting to the challenges facing farming in relation to reducing our greenhouse gas (GHG) emissions.

Meeting maximum potential

N plays a critical role in achieving maximum grass growth potential. The main yield components of grass are the number of leaves and dry matter content.

Higher yields come from optimising tiller numbers, maintaining a green leaf canopy and achieving a high dry matter content.

A balanced fertiliser programme including all essential elements such as N, phosphorus (P), potassium (K), sulphur (S) and calcium (Ca) is vital to achieving productivity in Irish grassland production.

A background to the Salesian Agricultural College

The college was founded in 1919 by the Salesians of Don Bosco, the college remains under the auspices of the Salesians of Don Bosco Ireland and works in partnership with Teagasc, while commercial farm enterprises support some of the teaching and training activities of the college.

The farm runs a herd of 400 spring-calving dairy cows and a herd of 30 spring-calving suckler cows. 60 beef calves are reared from the dairy herd and there is also a mid-season lambing flock of 65 ewes.

All enterprises operate to a high level of technical efficiency. The current EBI of the dairy herd is €171 and the replacement index of the suckler herd is €175, placing both herds in the top 2% of herds nationally.

Stocking rate

The overall farm stocking rate is 2.20 LU/ha (190kg of organic N/ha) and the farm operates under a nitrates derogation. To sustain this stocking rate and run largely grass-based production systems, soil fertility, reseeding and grassland measuring are three key ingredients, all of which need to work in tandem.

Grass Growth in Pallaskenry

The table below shows details of grass growth at the college over the past few years.

*To April 10, 2020

Grazing 2020

Grazing started this year on January 28. According to the college it never had spring-calving cows grazing in January before. The farm had an opening average farm cover (AFC) – on January 15 – of 883kg DM/ha and on January 31 had climbed to an AFC of 955kg DM/ha.

The closing cover on December 5 last was 705kg DM/ha, giving a daily growth rate of just over 4kg DM/ha/day in December and January.

The dairy herd is now in its second round of grazing and grass measuring is carried out every four days.

The college is on track with its fertiliser programme to ensure maximum grass growth for the farm. This is thanks to a structured approach by using a farm specific fertiliser plan, based on soil fertility and stocking intensity.

The role of Nitrogen

N is the crucial nutrient for influencing grassland yield. Requirements for K, phosphate, S, Ca, and magnesium (Mg) are related to the amount of applied N.

There is a large demand for these nutrients during early spring growth and to avoid limiting yield it is critical that enough quantities of nutrients are available to the plant for uptake when required.

Nitrogen is the key to achieving high dry matter yields and is often strategically used to increase production as it is needed. The key to achieving high yields is to apply the correct amount of nitrogen, from the right source at the right time.

Essentially N is the fuel that drives grass growth. However, like most fuel the efficiency is driven by the capacity of the engine. The ability of N to drive growth and improve efficiency is dictated by the capacity of the plant, the time of year and pathways to losses.

Nitrogen for grazing

N is a critical nutrient to drive grass yield, but also quality – namely protein. The average response to 1kg of N in early spring N is now approximately 10kg DM of grass. N plays a fundamental role in grass recovery after grazing, which is important coming into the second round of grazing.

By early April, farmers should have approximately 100 units of N/ac applied to achieve maximum growth rates and sustain high stocking rates.

The target should be to apply 40 units of N/ac in the month of April. The weather in April can vary and prove very dry and harsh and this can lead to potential N loss through volatilisation, especially from urea.

One way of minimising this is to apply protected urea. Protected urea and phased release N products work to reduce N losses because they bind closely to soil particles and are less likely to be lost to the waterway in comparison to CAN.

Throughout the main grazing season, N will prove critical to maintain growth and quality and to achieve this we should target an application of 1 unit of N/ac/day on the grazing rotation and this should be balanced with S, as previously discussed in our series at a ratio of 1 unit S : 10-12 units N.


Nitrogen for Silage

The importance of high-quality silage has never been more evident than this spring with the delayed turnout of cattle to grass due to the awful weather conditions.

Farmers need to put a focus on quality silage, rather than producing a higher quantity of lower value feed. Silage ground needs to be closed by the middle of April and cut by mid to late May to ensure quality.

Each week delayed in cutting silage after heading-out date will decrease dry matter digestibility (DMD) by seven units and further delay second cuts by a subsequent two weeks.

What level of nitrogen do I need for first-cut silage?

Target the use of 80-100 units/ac for permanent pasture and 90-110 units/ac for reseeds. Generally, allow 2 units/day from application date to cutting date. For quality silage, harvest the crop in late May. Grass will shoot out between May 20 and May 25.

Reseeding

Reseeding is critical to optimising the return on fertiliser inputs and the college aims to reseed 10-15% of the farm annually.

Over 50% of grass has been reseeded in the past four years. This year the plan is to start reseeding from mid-April as the college has had difficulties getting herbicide applied and grazing completed when reseeding in August.

Grass seed varieties are chosen based on the Pasture Profit Index (PPI), with clover included. Abergain and Aberchoice have been the mixture of choice for the past three years.

No ploughing takes place on the farm and all fields are disced followed by one run of a power harrow with an air-seeder. The field is then rolled. Fertiliser applied post sowing normally consists of Nutristart NPK supplied by Grassland Agro at 175kg/ac (3.5 bags/ac).

Going forward the college intends to use Alzon NEO N (46% N). This protects the N from varying weather conditions to maximise nitrogen use efficiency (NUE) and support maximum growth rates while limiting excess nitrate levels in the grass.

The application of Alzon follows an application of Nutrigrass P which includes N, P, S & Na. This product contains a phased release N and a plant biostimulant to maximise N conversion to protein for the N applied in the product and conventional N applications thereafter.

Nutrigrass P also contains Grassland Agro’s revolutionary protected P, namely Top Phos.

Fertiliser Plan Salesian Ag College

A fertiliser plan was prepared for the college by Dr. PJ O’Connor of Grassland Agro. The farm was soil sampled in January 2018 – one sample per paddock. It will be sampled again in the autumn of 2020.

The fertiliser programme commenced last December with the application of muriate of potash. The first applications of 2020 went on from January 18 to January 20. Protected urea (Alzon Neo) was applied at 23 units/ac to two-thirds of the grazing/silage area.

One-third of the farm where grass covers were at 800kg DM/ha or less received slurry at 3,000 gallons/ac. This was applied using an umbilical cord with a dribble bar.

This is the fourth year using the umbilical system with a dribble bar in the college and the benefits of reducing traffic on farm roadways, through gaps and in fields, has had environmental benefits.

The second application of fertiliser was 25kg/ac of Alzon Neo across the entire farm, while the third application at the beginning of April was Nutrigrass P on the grazing area. Silage ground has received slurry + urea + Sulfammo N30 enhanced N fertiliser.

What is Protected Urea and how does it work?

Protected urea is treated with an active ingredient called a urease inhibitor. The urease inhibitor can be coated onto the outside of the fertiliser granule (Eco Coat) or incorporated into the urea granule melt during manufacture (Alzon).

Going one step further to protect N losses, Alzon contains a nitrification inhibitor to protect N losses to the waterways.

How do urease and nitrification inhibitors work and what role do they play in stopping N loss?

A urease enzyme is responsible for the conversion of urea to ammonium. During this conversion ammonia gas can be lost from untreated urea.

A urease inhibitor blocks the active site of the urease enzyme and reduces the rate of urea converting to ammonium, in turn reducing ammonia loss. Urease inhibitors are present both in Eco Coat and Alzon based products.

A nitrification inhibitor, which is unique to ALZON NEO-N, reduces the rate of conversion of ammonium to nitrate and stabilises the rate of N available to the plant. This further improves the efficiency of the ALZON products over the standard protected urea products.

Back to the farm and preparations are underway for the breeding season. Catch up with news from the college on its social media platforms.