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Maximise the potential of grass

March 18, 2021

Fertile soils coupled with good grassland and grazing management are key to profitable milk production. With a continuing financial squeeze on dairy farm margins, this will become even more important as grass is the cheapest feed farmers can offer cows according to CAFRE Dairying Adviser, Conail Keown. Improving soil fertility should be a priority on dairy farms to increase grass production and offset more expensive purchased feed. This article outlines key steps to managing and improving soil fertility, and looks at why planning spring turnout on farms can benefit a dairy business.

Starting point: ‘monitoring and measuring’

Approximately 90% of grassland soils throughout Ireland do not have adequate levels of either lime, phosphorus, or potassium. A shortage in one or more of these nutrients will reduce the grass produced on that land. A simple soil test costing around £10 is the starting point to establish the current nutrient status of soils on the farm.

A recent Business Development Group meeting highlighted the importance of sampling the whole farm, not only a few paddocks regularly. Sampling the whole farm allows you to generate and build a true picture of the farm soil fertility status, and using this information in a nutrient management plan throughout the season allows the correction of any deficiency.

Target the soil index for optimal grass production

The target for soil phosphorous (P) and potassium (K) is index 2+. Replacing nutrients removed by grazing or harvesting grass to maintain an index of 2+ will ensure optimum growing conditions for the grass plant. Soils at index 1 and 2 for P and K have a lower nutrient supply and therefore require additional nutrients every year to reach soil index 2+. Research conducted by AFBI and other research centres has shown that soils at index 2+ for P and K can produce an extra 1.5t /ha of grass dry matter over soils with index 1 for these nutrients. This is equivalent to 15% more grass production on many farms across the country, which can represent a significant saving in concentrate costs on farms if this grass is utilised correctly.

Soil AcidityNitrogenPhosphatePotash% fertiliser wasted
Extremely acid pH 4-530%23%33%71.34%
Very strong acid pH 5.053%24%52%53.67%
Strongly acidic pH 5.577%48%77%32.69%
Medium acid pH 6.089%52%100%19.67%
Neutral pH 7.0100%100%100%0%
The effect of soil pH on fertiliser utilisation efficiency
Soil structure and pH

Conail advises that soil structure is critical. You are looking for a nice aerobic soil made up of appropriate proportions of minerals, organic matter, water and air.

The pH level has a significant impact on other nutrients as highlighted in the table above, the optimum grassland being 6.5.  Anything less than a pH of 6 is considered acidic which will reduce the soils’ ability to release nutrients and reduce response to chemical and organic fertiliser. From the table above, a soil with pH 5.5 will be underutilising nutrients applied by a significant 32%. A soil analysis report will provide recommendations for lime for each sample tested, lime should be applied based on this information to achieve the best results.

Maximise the use of slurry where possible

Organic manures are a valuable source of Nitrogen (N), P and K, and can effectively replace chemical fertiliser. With chemical fertiliser prices currently high, targeting slurry spreading in the early spring is a cost effective way of replenishing soil nutrient levels.

13.5m3 (3000gal) of dairy cow slurry contains the same amount of available N as 50kg of 27% CAN. This gives the potential for significant financial saving in purchased chemical fertiliser.

Why is early grazing just so important on dairy farms?

Conail states that getting cows out to grass in early spring has a number of benefits, the obvious benefit comes with reduced feed costs for the herd. Other benefits include the preparation of the grazing block for the season ahead by stimulating growth, increased herd performance with a higher quality diet, reduced supplements, and reduced workload.

Recent grass analysis highlighted the quality of grass available in early spring (table below). Dairy farms can capitalise on this quality feed which can be as much as 1.5tDM/ha before grass growth really starts in early April, but only if the correct autumn closing procedures on the grazing block have been followed.

   UnitGrass Sample 1  date 15/2/21         
Cover 3200kgDm/ha
Grass Sample 2  date 1/3/21
Cover 2800kgDm/ha
Dry Matter%18.622.5
Grass analysis report 2021
Key steps required to improve spring grazing
  1. Develop a spring grazing plan for the farm to allocate grass based on key dates and targets. Allow the first rotation to extend from Mid-February to early April when grass growth or supply will meet the herd demand. See table below for an active grazing plan generated for 180 cow autumn calving herd using Agrinet grazing management software. The wet start to February has delayed grazing on this farm.
WeekHa/DayTarget Ha Grazed
by week end
Target %Actual Ha Grazed
by week end
15/02 – 21/020.533.716.41.81
22/02 – 28/020.597.8413.53.22
01/03 – 07/030.6712.5321.66.84
08/03 – 14/030.7717.9230.9 
15/03 – 21/030.9124.2941.9 
22/03 – 28/031.1132.0655.3 
29/03 – 04/041.4242.0072.4 
05/04 – 11/041.9855.8696.3 
2021 Actual grazing plan for 180 cow herd on 60ha grazing block
  • Achieve target post-grazing height of 4cm to enable plants to capture sunlight energy.
  • Spring nitrogen is essential to boost growth on the grazing block. Expect an average grass growth response of 10kg DM per 1kg N applied per ha in spring.
  • Ensure good infrastructure on farm to allow access to grass, the aim is to minimise ground damage, and protect regrowth during spring grazing.
  • Use good grazing management principles like back fencing grazed areas, on/off grazing in wet conditions, only 12 hour allocations during first rotation, and stick to the planned areas and targets in the grazing plan.