National Soil Analysis Programme 2019

Nitrates, Biodiversity and Engineering Division

Department of Agriculture, Food and the Marine

Clare Casey, Assistant Agricultural Inspector, Nitrates, Biodiversity and Engineering Division

(October, 2020)

Contents

1.0 Introduction ...................................................................................................................................... 1

2.0 Presentation of soil test results ........................................................................................................ 2

2.1 The soil index system ..................................................................................................................... 2

2.2 Assumptions used when compiling data ....................................................................................... 3

3.0 National Soil Fertility Results and Statistics for 2019 ....................................................................... 3

4.0 Overall Findings ................................................................................................................................. 5

4.1 Soil pH ........................................................................................................................................... 5

4.2 Soil P levels .................................................................................................................................... 5

4.3 Soil K levels .................................................................................................................................... 6

4.4 Overall soil fertility ........................................................................................................................ 6

5.0 Conclusions ....................................................................................................................................... 8

References ............................................................................................................................................ 10

1

1.0 Introduction

Since 2017 DAFM has completed an annual National Soil Survey based on soil test results

released from both the private laboratories and Teagasc laboratories that analyse soil samples for

Irish farmers. The purpose of the survey is to provide an overview of soil fertility over time. In

2017 the Feedingstuffs, Fertilisers, Grain and Poultry Division had responsibility for the survey of

2016 results. Since 2018, the Nitrates, Biodiversity and Engineering division of DAFM has been

responsible for collecting the data and analysing the soil results for soil samples. Participation in

the programme is on a voluntary basis. Table 1 below shows the numbers of participating private

laboratories on an annual basis and the respective total sample results available for analysis..

Table 1 Annual sample results available

Year No. of Participating Private Labs

1

Total samples (Private and Teagasc)

2016 8 203,000

2017 6 153,984

2018 8 167,832

2019 7 109,365 1 n=-8, number of private laboratories invited to participate since 2016. Teagasc has participated annually.

The available information on soil samples varies somewhat between laboratories. While some

datasets included soil type and county, the majority returned data for Phosphorus (P), Potassium

(K) and pH therefore the survey includes only these parameters. Summary statistics for the

number of samples with good overall fertility are also presented in terms of environmental and

agronomic optimum ranges of these parameters.

Soil analysis was conducted separately for Teagasc samples and private laboratory samples and

then these were combined for the overall fertility analysis.

The co-operation of the private laboratories in providing the 2019 data is greatly appreciated by

DAFM.

2

2.0 Presentation of soil test results

2.1 The soil index system

The results from the laboratory analysis of soil samples are translated into soil test index ranges

for practicality and usability in terms of providing advice to farmers. A description of the soil test

index system is shown in Table 2.1 (Wall and Plunkett, 2016).

Table 2.1 Soil Index system

Soil Index Index description Response to fertilisers

1 Very low Definite

2 Low Likely

3 Medium Unlikely/tenuous

4 Sufficient/excess None

The soil P index depends on the level of available P in soil and this is determined by measuring

the quantity of P that is extracted by Morgan’s solution. The ranges for P index 1 - 4 are shown

below in Table 2 (Wall and Plunkett, 2016).

Table 2.2 Soil P index ranges for grassland and other crops

Soil Index Grassland (mg/l) Other crops (mg/l)

1 0.0 - 3.0 0.0 - 3.0

2 3.1 - 5.0 3.1 - 6.0

3 5.1 - 8.0 6.1 - 10.0

4 Above 8.0 Above 10.0

The soil K index depends on the available level of K in the soil which is determined by measuring

the quantity of K that is extracted by Morgan’s solution. The ranges for K index 1 – 4 are shown

below in Table 2.3 (Wall and Plunkett, 2016).

Table 2.3 Soil K index ranges for grassland and other crops

Soil Index Grassland (mg/l) Other crops (mg/l)

1 0 – 50 0 - 50

2 51 – 100 51 - 100

3 101 – 150 101 - 150

4 Above 150 Above 150

3

2.2 Assumptions used when compiling data

All labs submitted at least pH, P and K data for all soil samples analysed. Associated meta-data for

these soil samples such as county, soil type, farming system etc. was either limited or non-

existent for the majority of these data sets. Therefore it was necessary to make some

assumptions to enable full analysis of these data which are as follows:

1. All soil test results are assumed to be from mineral soil types. In reality a smaller proportion

of these soil samples tested are from organic or peaty soils (i.e. soils ≤20% SOM), however, as

these cannot be identified, all data were assumed to be and analysed as if they were mineral

soil types (e.g. optimum pH for mineral soils ≥6.3 vs 5.5 for organic soils).

2. All soil results are assumed to be from grassland soils. In reality a smaller proportion of these

samples are from tillage fields. As the soil index ranges for P are different for grassland versus

tillage soils knowledge of the origin of the samples would allow a more accurate

characterisation and analysis of these data.

3.0 National Soil Fertility Results and Statistics for 2019

Soil fertility results are presented for all soil sample data submitted to DAFM for 2019. Table 3.1

shows the breakdown of sample numbers for each parameter. There is a 35% reduction in

available data for 2019 when compared to 2018.

Table 3.1 Number of soil samples analysed for each parameter

Parameter Total samples Teagasc samples

Private Labs

samples

pH 109,365 30,396 78,869

P 109,282 30,465 78,817

K 109,290 30,465 78,825

Table 3.2 shows the soil pH, P and K ranges respectively, number of samples and percentage of

total soil samples within each index range for all soil samples analysed in 2019.

4

Table 3.1 Soil pH, P and K ranges for all samples combined

pH

Soil pH Total Samples % per range Teagasc samples

Private

samples

<5.5 9,345 9 1,455 7,890

5.5 - 5.9 22,971 21 6,429 16,542

6.0 - 6.2 20,399 19 6,126 14,273

6.3 - 6.5 21,140 19 6,052 15,088

6.6 - 6.9 20,061 18 5,967 14,094

≥7 15,349 14 4,467 10,882

109,265 100 30,496 78,869

Phosphorus

Potassium

Morgan’s K

(mg/l) Index

Total

Samples

% per

index

Teagasc

samples

Private

samples

0 – 50 1 14,841 14 2,898 11,943

51 – 100 2 36,937 34 9,612 27,325

101 – 150 3 27,564 25 8,213 19,351

> 150 4 29,948 27 9,742 20,206

109,290 100 30,645 78,825

Morgan’s P

(mg/l) Index

Total

Samples

% per

index

Teagasc

samples

Private

samples

0.0 - 3.0 1 20,593 19 7,577 13,016

3.1 - 5.0 2 25,066 23 7,635 17,431

5.1 - 8.0 3 26,729 24 7,081 19,648

>8 4 36,894 34 8,172 28,722

109,282 100 30,465 78,817

5

4.0 Overall Findings

The results presented for 2019 are from different soils and different fields and so a like for like

comparison between previous years and 2019 is not possible. Therefore, comparison of results

between years is not directly meaningful as sample sites are not correlated. However, it is

possible to conclude on national trends.

4.1 Soil pH

The soil pH levels from all soil samples 2019 showed that 51% of the samples were optimal (pH ≥

6.3) (Figure 1). This proportion of samples in this sub-optimal range was similar across all

laboratories. This is indicative of a possible improvement in soil pH since whereby data in 2017

and 2018 indicated that only 41% and 47% of samples were at optimal pH, respectively.

Figure 1 Comparison of all 2019 data for pH results

4.2 Soil P levels

In 2019 42% of the soils were at index 1 and 2 meaning very low to low soil P levels (Figure 2).

This compares to 58% and 50% at index 1 and 2 in 2017 and 2018, respectively. There was little

change in soils at the optimal index 3, with 24% of soils in 2019 compared to 21% and 23% for

2017 and 2018 respectively. There was an increase in proportion of soils in index 4, to 34% in

2019 from 28% in 2018 (36% of private laboratory samples and 27% of Teagasc samples were at

Index 4).

A soil P index of 3 is considered optimal as index 1 and 2 soils result in poor grass and crop

productivity and also reduced nitrogen use efficiency whereas index 4 soils increase the risk of P

losses to waters.

9

21 19 19 18 14 13

22 17 17 18

12

0

10

20

30

<5.5 5.5-5.9 6.0-6.2 6.3-6.5 6.6-6.9 ≥7

%

pH

2019

2018

6

Figure 2. Comparison of all 2019 data for P indices

4.3 Soil K levels

The results for 2019 indicate that 42% of soil samples were at a K index 1 and 2 compared to

55% and 50% in 2017 and 2018, respectively. There has been little change in the proportion of

soils at the optimal level of index 3 being 25% in 2019 (24% and 26% in 2017 and 2018,

respectively) and 2017 respectively. There a slight increasing trend in the proportion of soils at

index 4 continued, increasing from 24% to 26% in 2017 and 2018, respectively, to 27 % in 2019.

It is important to aim for a K index of 3 and reduce the number of 1, 2 and 4 soils to achieve

optimum fertility.

Figure 3 Comparison of all 2019 data for soil K Indices

4.4 Overall soil fertility

The assessment of 2019 samples indicates that only 23% of soils sampled had agronomic

optimum soil fertility levels, pH ≥ 6.3, and P & K ≥ index 3. However, this is greater than 19% and

14% that was determined for 2018 and 2017 respectively. In 2019, 77% soil samples had soil

fertility status which was deficient in at least one parameter – pH, P and / or K (Figure 4). Poor

soil fertility has a major impact on grassland and cropland productivity. For the purposes of these

soil samples, they are all assumed to be grassland and the associated optimum agronomic

fertility.

19 23 24

34

25 25 23 28

0

20

40

0-3.0 3.1-5.0 5.1-8.0 >8 %

mg P/L

2019

2018

14

34

25 27

14

36

26 24

0

20

40

0-50 51-100 101-150 >150

%

mg K/L

2019

2018

7

Figure 4 Percentage of total soil samples tested in 2019 with pH, P and K levels capable of meeting crops production targets for high yield crops.

As there are both agronomic and environmental targets for agricultural soils in Ireland, soil test P

levels must be considered when assessing these goals. Soil test P is used to assess the risk of P

loss to waters and P index 4 soils are considered highest risk for P loss to water quality through

surface runoff or leaching pathways. In considering the environmental effects, thereby excluding

index 4 soils, optimal soil fertility for environmental and agronomic targets was assessed. Only

13% 5.83% of the soils meet both agronomic and environmental targets. This is slightly better

than the figures of 6 and 5 for 2018 and 2017 respectively. The relative increase in soils at index 4

means that some of the agronomic gains are at the expense of similar environmental gains.

Figure 5 Percentage of total soil samples tested in 2019 with optimal agronomic and environmental levels for P, K and pH.

23%

77%

Soil fertility meeting agronomic targets

Deficient soil fertility

pH ≥ 6.3, P and K ≥ Index 3

13%

87%

Soil fertility meeting agronomic and environmental targets

Deficient soil fertility

pH ≥ 6.3, P Index 3 and K ≥ Index 3

8

5.0 Conclusions

1. The analysis of the 109,265 soil analysis results from 7 of the 8 private laboratories and the

Teagasc laboratories give a picture of the soil fertility status in the year 2019. Information on soil

type and farm type from all the laboratories was not available. This is of significance in making an

overall assessment of soil fertility levels; it would be highly beneficial if such information could be

made available in the future. It would also be beneficial to have farm stocking rate and county.

2. Low soil pH has been shown to be a major issue in Irish soils. A total of 51% of soils in 2019

were sub optimal for pH. As a result, nutrients in the soils are not being made available to the

plants and cannot be used efficiently. In 2017 and 2018 totals of 59% and 53% of soils were sub-

optimal for pH respectively. While there is no direct linkage between fields sampled in 2018 and

those in 2019 it is clear that nationally low soil pH continues to be a major issue. Liming can raise

soil pH to optimal levels, however, lime use has decreased in Ireland significantly (see Figure 6).

Lime sales in 2019 increased to 1,028,696t compared to 737,118t in 2017. This may have been

due to the prevailing conditions during and after the unseasonably hot and dry summer, as this

figure had dropped again in 2019 to 762,865t. Since 2020 a liming programme is required on

farms with a Nitrates Derogation. It is important that outside of this requirement that liming is

encouraged as a means to optimise pH on farms to increase nutrient use efficiency.

Figure 6 Lime sales figures from 1970 - 2019

0

500,000

1,000,000

1,500,000

2,000,000

2,500,000

19

81

1

98

2

19

83

1

98

4

19

85

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6

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87

1

98

8

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89

1

99

0

19

91

1

99

2

19

93

1

99

4

19

95

1

99

6

19

97

1

99

8

19

99

2

00

0

20

01

2

00

2

20

03

2

00

4

20

05

2

00

6

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07

2

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2

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13

2

01

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15

2

01

6

20

17

2

01

8

20

19

Lime sales (1981-2019)

9

3. Low P and K soil levels are impacting on production and sustainability. The 4th Nitrates

Action Programme for 2019 -2021 (S.I. 605 of 2017) contains an important measure to address

the low P level in grassland with the enhanced P build-up programme. However, excessive build

up of P in soils appears to be an increasing problem, see point 4. below.

4. The results indicate a high percentage of soils at Phosphorus index 4 in 2019. With 34% of

our soils at Index 4, there are implications for water quality, nutrient management and increased

farm costs.

5. While there has been an improvement in the agronomic fertility this appears to be related to

an increase in the relative amount of soils at the environmentally sensitive P Index of 4. Nutrient

management planning must continue to be a priority objective.

10

References

Wall, D.P., Plunkett, M., 2016. Major and micro nutrient advice for productive agricultural crops,

4th edition, Teagasc Johnstown Castle, Wexford.

SI 605 of 2017. Statutory Instruments European Union (Good Agricultural Practice for protection

of waters) Regulations 2017.