A. What is it?

B. Why is it important?

C. How is it done?

In OutNutrients Nutrients

Getting the balance right!

Nutrients In

Nutrients Out

Why manage nutrients?

1. Potential to reduce fertiliser costs

2. Protect the environment

3. Meet Nitrates Directive requirements

4. Efficiently meet crop nutrient

requirements

Soil testing and analysis

Nutrient requirements for crop

Calculate what to put in / on the soil for crop

Green waste or mushroom compost ◦ free or cost of delivery/spreading

Savings◦ Slurry – saving up to £95/ha◦ FYM – saving up to £309/ha◦ Dependant on the nutrient requirement

Essentially, adding organic materials reduces the amount of chemical fertiliser required

Chemical fertiliser is expensive!

Remember...◦ nutrients in result in nutrients out

Excessive fertiliser, slurry, manure can result in:◦ Leaching◦ Soil particle loss◦ Nutrient runoff causing enrichment or

eutrophication Biggest trheat to NI waterways

◦ Waste of money

Nutrients N and P can become pollutants if over applied

Nitrated Directive sets out rules/regs for arable and grassland crops

Need to follow guidance on soil analysis

See pages 68 & 69 of the NAP Booklet

Crop requirement for phosphate

See page 72 Nitrates Guidance Booklet

Remember main crop nutrients:

N = Nitrogen P = Phosphorus K = Potassium

Also Sulphur, Magnesium and Calcium◦ These do not appear directly on fertiliser but are

often incorporated

Law of limiting factors

Liebigs Barrell

Water represents crop If even one nutrient

(major or minor) isbelow crop requirement,the crop will not performto full potential

Step 1 - Soil analysisStep 2 - What does the soil analysis mean?Step 3 - Estimate Nitrogen requirementsStep 4 - What nutrients does the crop

require?Step 5 - How many nutrients can be

supplied by organic manures?Step 6 - Which chemical fertiliser can supply

the remaining nutrients required

What information is on soil analysis?

What key nutrient is missing?

Nitrogen is not included in soil analysis

Estimated after considering ◦ rainfall ◦ soil type ◦ previous cropping

Soil Nitrogen Supply (SNS) Index – the higher the index, the lower the requirement

RB209

Rainfall in Northern Ireland is classed as ◦ Moderate/Medium (600-700mm annual rainfall

or 150-250mm excess winter rainfall)◦ OR◦ High (over 700mm annual rainfall or over 250mm

excess winter rainfall)

Depending on moderate or high rainfall, SNS index will vary slightly.

Soil type affects HOW nutrients are retained

Light and/or shallow soils have POOR retention (leaching)

Medium, deep clay or deep silt soils have MODERATE – GOOD retention

Soils with over 10% organic matter can retain TOO MUCH, meaning nutrients may not be available to the plant (lock-up)

MostNI

Soils

Low and medium N vegetables are crops such as carrots, onions, radish, swedes or turnips where the amount of crop residue is relatively small.

Crop requirement depends on:•Crop type•What’s already in the soil

The higher the soil nutrient reserves (Soil Index), the lower the need for additional nutrients

RB 209

Index for Phosphorus (2)

Index for Potassium (1)

SNS, P, K Index

0 1 2 3 4 5 6

Kg/ha

Turnips, Parsnips

Nitrogen (N) –all soil types

170 130 100 70 20 0 0

Phosphate (P5O2) 200 150 100 50 0 0 0

Potash (K2O) 300 250 200 (2-)150 (2+)

0 0 0 0

We know from high rainfall that N needs index 1

We know from soil analysis that P needs index 2 and K needs index 1

SNS, P, K Index

0 1 2 3 4 5 6

Kg/ha

Turnips, Parsnips

Nitrogen (N) –all soil types

170 130 100 70 20 0 0

Phosphate (P5O2) 200 150 100 50 0 0 0

Potash (K2O) 300 250 200 (2-)150 (2+)

0 0 0 0

What is the requirement?N = index 1 =P = index 2 =K= index 1 =

130 kg/ha100 kg/ha250 kg/ha

Soil◦ Soil analysis - index shows the recommended

amount of P and K to add to soil◦ SNS index gives recommended amount of N to add

Manure / green waste / slurry◦ Adds both nutrients and organic matter to help

with soil structure

Chemical fertiliser◦ Adds the remaining nutrients necessary to meet

crop requirements

RB209 gives nutrient availability for a range of manures, slurries and organic matter:

Organic Matter type

Nutrient content(kg/t)

N P K

Farm Yard Manure

1.8 3.5 7.2

Green Waste

<0.2 3.0 5.5

Assume you have 10 ton green waste compost to apply over 2 acres (i.e. 5 ton/acre)

To find the volume applied of a particular organic material:

Ton/acre applied x 2.471 = volume applied t/ha

5 ton/acre x 2.471 = 12.355 t/ha

Volume applied =12.355 t/ha

To find the nutrient content of a particular organic material:

Kg/t Nutrient applied x volume applied t/ha = nutrient content

N = 0.2 x 12.355 P = 3.0 x 12.355 K = 5.5 x 12.355

Organic Matter type

Nutrient content(kg/t)

N P K

Green Waste <0.2 3.0 5.5

Volume applied

=12.355 t/ha

To find the nutrient content of a particular organic material:

Kg/t Nutrient applied x volume applied t/ha = nutrient content

N = 0.2 x 12.355 P = 3.0 x 12.355 K = 5.5 x 12.355

Organic Matter type

Nutrient content(kg/t)

N P K

Green Waste <0.2 3.0 5.5

=2.471 kg/ha

=37.065 kg/ha

=67.95 kg/ha

You now know: Nutrient requirement for

crop from the soil analysis

Nutrient content of adding an organic matter (example)

Now you need to add chemical fertiliser to make up the balance

N P K

130 100 250

2.5 37 68

127.5 63 182

N Nitrogen

P Phosphorus

K Potassium

S Sulphur

………NO3 Nitrate

………P2O5 Phosphate

………K2O Potash

………S04 Sulphate

Nutrients needed by crops for growth

Chemical Fertiliser

20 12 25

% Nitrogen(N)

% Potash(K20)

% Phosphate(P205)

Step 6

1 50kg bag/acre = 125kg/ha

We need ◦ 127.5kg/ha N, 63kg/ha P, 182 kg/ha K

1 50kg bag/acre = 125kg/ha

Need to find out what 20-12-25 fertiliser really offers in order to find out the balance.

Calculate the amount of N, P & K supplied when applying 10 bags of 20-12-25 per hectare. ◦ One bag of fertiliser = 50kg

A) number of bags/ha x 50kg = applicationrate

A) 10 bags/ha x 50kg = 500 kg/haapplication rate

Remember application rate = 500kg/ha

B) % nutrient x application rate kg/ha = nutrient applied100 (kg/ha)

N = 20 x 500kg/ha = 100

P = 12 x 500kg/ha =100

K = 25 x 500kg/ha =100

Remember application rate = 500kg/ha

B) % nutrient x application rate kg/ha = nutrient applied100 (kg/ha)

N = 20 x 500kg/ha = 100

P = 12 x 500kg/ha =100

K = 25 x 500kg/ha =100

100 kg/ha Nitrogen

60 kg/ha Phosphorus

125 kg/ha Potassium

(1)

N

Kg/ha

(2)

P2O5

(1)

K20

A

Crop requirement

(Based on crop type & soil analysis)

130 100 250

B

Available nutrients green waste compost (5 ton/acre)

2.5 37 68

C

Available nutrients Chemical fertiliser 20-12-25 (10bags/ha)

100 60 125

What we know so far...

(1)

N

Kg/ha

(2)

P2O5

(1)

K20

A Crop requirement 130 100 250B Available nutrients green waste

compost 2.5 37 68

C Available nutrients Chemical fertiliser

100 60 125

D Total Inputs (B+C) 102.5 97 193

Balance left (A – D)(Nutrient still required)

What is the balance?

(1)

N

Kg/ha

(2)

P2O5

(1)

K20

A Crop requirement 130 100 250B Available nutrients green waste

compost 2.5 37 68

C Available nutrients Chemical fertiliser

100 60 125

D Total Inputs (B+C) 102.5 97 193

Balance left (A – D)(Nutrient still required)

27.5 3 57

What is the balance?

From the given inputs of◦ Existing soil nutrients◦ Added organic matter◦ Chemical fertiliser

Most of the nutritional needs are met

Remaining Balance

N P K

27.5 3 57

What happens with the remaining balance?

Fertiliser application may be split over 2 or more treatments (in seed bed, over crop, etc), allowing opportunity to...

Use straight fertiliser (just N or K) Could change an input (try calculation using

FYM or slurry)

Remaining Balance

N P K

27.5 3 57

Must not exceed ◦ Nitrogen requirement ◦ Phosphorus requirement

Can lead to pollution

Remaining Balance

N P K

27.5 3 57

1. N, P, K In = N, P, K Out2. Nutrient sources soil, manure/organic matter and

fertiliser3. Make best use of nutrient sources

Save money Protect the environment Meet Nitrates Directive Requirements

4. How? Soil sampling and analysis is the starting point Estimate crop needs Use manure/organic matter effectively Only use fertiliser to top-up any outstanding crop

needs5. Help

Crop Nutrient Recommendation Calculator Nitrates Guidance RB209 Codes of Good Agricultural Practice

Nutrient Calculation