Building up soil fertility has been identified within the Dairylink Ireland programme as a means of improving the economic and environmental sustainability of participating farms.

Phase two participant John Oliver has recently carried out a review of soil fertility on his farm to develop a more efficient nutrient management programme.

All phase two farmers sampled soil on their farms in late 2018 to assess initial levels of soil fertility in terms of pH, phosphorus (P) and potassium (K). This exercise was then repeated the following winter in January 2020.

Achieving an optimal soil pH (6.0 to 6.5) is critical for ensuring the efficient uptake of nitrogen (N), P and K for grass growth.

John began a liming programme as soon as ground conditions allowed last spring.

In 2018, John Oliver discovered that around 50% of the area sampled had a soil pH of less than 5.8 (Table 1) and some fields had a soil pH as low as 5.3.

He quickly began a liming programme where fields with a low soil pH received up to 6.2t/ha of lime (2.5t/ac). The impact of this strategy can be seen already, as the latest results showed that less than 2% of the area sampled had a soil pH below 5.8 (Table 1).

The plan is to continue applying lime to fields with a low pH, which will include some additional land that John has recently started farming. He is also considering applying smaller amounts of lime (0.4t/ha or 1t/acre) to areas with a soil pH of 6.1 to 6.2 in an effort to bring those areas closer to pH 6.5.

Soil P and K

As highlighted three weeks ago when discussing Stephen Wallace’s farm (see www.ifj.ie/wallacesoils), soil P and K is important for developing root growth and minimising the impact of external stress on the grass plant.

Typical targets under the Northern Ireland soil index system for soil P on intensively managed grassland are around 2+, while the optimal index for soil K is around 2- to 2+

A review of the latest soil analysis reports revealed some interesting findings. For example, the distribution of soil P around John’s farm does not appear to have varied greatly from 2018 to 2020, with perhaps a slight increase in the proportion of land sampled with a P index less than 2- (Table 2).

When we looked at the distribution of soil K, we found that the proportion of land sampled with soil K index of 2- or less is increasing (Table 3). The reasons for this are not entirely clear. However, it is interesting to note that 57 % of fields sampled with lower K indices were being cut for silage. This is now being taken on board and incorporated into the nutrient management plan for the farm.

Preparing a nutrient management plan

A nutrient management plan was prepared by entering soil analysis results, anticipated crops to be grown and details of any planned organic manure applications into the DAERA online nutrient calculator program.

This program can be used by anyone who is registered for DAERA online services.

The results of this operation have allowed John to formulate a plan which he is incorporating into his first round of fertiliser applications. This in turn should allow him to improve soil P on fields which were identified as having a P deficit, while not oversupplying P and causing a negative impact on the environment.

Targets

Additional K is also being targeted for fields allocated for silage. The strategy varies according to whether grass is being produced for grazing or silage and will be implemented as soon as ground and weather conditions permit.

The plan for first-round fertiliser on the Oliver farm includes:

  • Grazing – fields with a soil P index of 2- or less will receive 125kg to 185kg/ ha (1 to 1.5 bags/ac) of a compound fertiliser, likely 20:10:10, followed by 125kg/ha (1 bag/ac) of straight N (23% N). All other fields will receive the same amount of N applied as straight N.
  • Silage – all areas for first-cut silage will receive around 33m3/ha (3,000 gallons/ac) of slurry applied using low-emission slurry spreading techniques, followed by around 340kg/ha (2.8 bags/acre) of a zero P fertiliser (23:0:10) in an effort to improve K reserves in these areas.
  • Key points

  • Take soil samples from areas which have not received any nutrient applications as soon as possible.
  • Use the DAERA online calculator to develop your own nutrient management plan.
  • Check the weather forecast and ground conditions before applying any nutrients.
  • Utilise slurry and farmyard manure, and then top up additional nutrient requirements with chemical fertilisers.
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