Farm Business Update 2014 presentation of Johnny Johnston taken from the Aylsham Event.

1. Meetings for Natural England - January/February 2014

2. Fertile soil, crop production and the
environment
Johnny Johnston
Lawes Trust Senior Fellow
Rothamsted Research

3. Defining soil fertility
A fertile soil is one that
produces optimum yields in an
economically sustainable way for
the grower
has least adverse environmental
impact
among other attributes must contain
adequate plant nutrients

4. Plant-available nutrients in soil
Plants take up nutrients like nitrogen, phosphorus,
potassium, magnesium, sodium through the roots from
the soil solution when present in plant-available forms
and these can be supplied by fertilizers
BUT fertilizers are not an end in themselves but a
means to an end in achieving optimum yields by
supplementing the indigenous supply in the soil
So knowledge of the soil supply is critically important
Hence soil analysis is an important management tool
in decisions as to how much fertilizer/manure to apply

5. Need to think about fertilizers in two groups
Group 1 - nitrogen and sulphur fertilizers
Irrespective of the fertilizer type most of the nitrogen is
converted to nitrate and sulphur to sulphate, the forms in
which these two nutrients are taken up by the plant
any residue of nitrate and sulphate is not retained in soil
- nitrate may be converted to nitrous oxide, a greenhouse
gas or be leached out when water drains through the soil
- sulphate is leached out and takes calcium with it leading
to soil acidification
Both nitrogen and sulphur need to be applied annually

6. Need to think about fertilizers in two groups
Group 2 - phosphate, potash and magnesium fertilizers
Negligible amounts of these three fertilizers are likely to
be leached from soil
Part of any residue remains in soil – usually the topsoil –
in plant-available forms so an increasing and valuable
reserve accumulates and soil analysis can be used to
measure the amount
Deciding on the amount of each of these three fertilizers
to apply depends on the amount in the soil which can be
taken up by plant roots

7. Nitrogen use increased from the 1960s
Availability of nitrogen fertilizers –
ammonium nitrate was no longer
required for munitions
Introduction of cultivars able to
respond to extra nitrogen
Availability of agrochemicals to
control weeds, pests and diseases
Winter wheat yields on Broadbalk
Inefficient use of nitrogen has both
a cost to the farmer
and
can have an adverse environmental
impact

8. Crop % SOM Fertiliser N applied
N0 N1 N2 N3
Potatoes 4.32 24.2 38.4 44.0 44.0
tubers, t/ha 1.73 11.6 21.5 29.9 36.2
Sugar beet 4.32 27.4 43.5 48.6 49.6
roots, t/ha 1.73 15.8 27.0 39.0 45.6
Spring barley 4.32 4.18 5.40 5.16 5.08
grain, t/ha 1.73 1.85 3.74 4.83 4.92
N0, N1, N2, N3: 0, 72, 144, 218 kg N/ha for root crops
0, 48, 96, 144 kg N/ha for barley
Silty clay loam soil, Rothamsted
Effect of soil organic matter on N-use efficiency - 1

9. Crop % SOM Fertiliser N applied
N0 N1 N2 N3
Potatoes 3.51 27.1 40.6 50.7 59.0
tubers, t/ha 1.31 25.7 35.6 41.7 43.2
Spring barley 3.37 2.58 5.12 6.85 7.81
roots, t/ha 1.31 2.19 5.00 6.73 7.05
Winter wheat 3.37 4.81 7.21 8.09 8.08
grain, t/ha 1.31 3.54 7.32 8.05 7.82
Winter barley 3.37 3.57 5.92 7.00 7.98
grain , t/ha 1.31 3.05 6.01 7.32 7.83
N0, N1, N2, N3: 0, 100, 200, 300 kg N/ha for potatoes
0, 50, 100, 150 kg N/ha for cereals
Sandy loam soil, Woburn
Effect of soil organic matter on N-use efficiency - 2

10. Effect of soil organic matter on N-use efficiency - 3
Yields, t/ha, of barley. Hoosfield, Rothamsted.
Annual treatment since 1852; PK fertilisers ♦, 35 t/ha FYM ■.
(A) cv Julia, 1976-79
(B) cv Triumph, 1988-91
(C) cv Cooper, 1996-99.

11. Efficient use of N requires sufficient plant-available
potassium in soil
Importance of both nitrogen and potassium in crop nutrition
Achieving large yields of most arable crops requires the rapid expansion of
the leaf canopy in spring so that the plant can capture sunlight energy to
convert carbon dioxide to sugars and then to dry matter
Nitrogen is a major driver of leaf canopy expansion which it does by
increasing both the number of individual cells and the size of cells
Some 80-90% of the total cell volume is water and to maintain cell turgor
(rigidity) there must be osmotic solutes within the water and plants prefer K.
So more and bigger cells, more water and thus more K
Compared to crops poorly–supplied with N cereals with adequate N can contain 10-15
t/ha more water and sugar beet 30-35 t/ha more water

12. 30
35
40
45
50
55
0 50 100 150 200
Saxmundham - Sugar
beet –roots – t/ha
192 mg
Kex/kg
114 mg
Kex/kg
0
2
4
6
0 50 100 150
Hoosfield - Spring barley
- grain – t/ha
329 mg
Kex/kg
55 mg
Kex/kg
0
10
20
30
40
0 72 144 216
485 mg
Kex/kg
130 mg
Kex/kg
Potato tubers –
t/ha
Exchangeable K in soil and applied N interactions
N fertiliser, kg/ha

13. Immediately Readily available Less readily Much less readily
available P and extractable P available and available and
in soil solution extractable P extractable P
Pool 1 Pool 2 Pool 3 Pool 4
Olsen P as determined in most UK labs
Current concepts about plant-available, inorganic
phosphorus in soil
Grain yield:
with adequate P, 6.9 t/ha;
with too little P, 2.9 t/ha
Importance of adequate plant-available soil P
Phosphate ions taken up from soil solution,
i.e. from pool 1
600,000litres water in topsoil
with 0.31 mg P/L = 0.18kg P/ha
Yet maximum P required about 0.6 kg P/ha per
day - so P in pool 1 replenished 3-4 times per
day
Total P in annual crops 20-40 kg P/ha so there
must be enough plant-available P in pools 2
and 3
Current recommendation to maintain soil at
P Index 2

14. How much P should there be in the readily-available pool?
As nutrient supply increases, yield
increases rapidly then more slowly to
reach a maximum. The soil supply
that gives near maximum yield is the
critical level
Examples of critical Olsen P for arable crops.
Although yield varied according to weather and
nitrogen supply, the critical value changed little

15. Efficient use of nitrogen depends on adequate plant-
available soil P

16. Annual variation in winter wheat yield and critical P
Fitted plateau yields of winter wheat and the critical Olsen P associated with 98% of that yield. Saxmundham: 1st wheats,
squares; 2nd wheats, triangles; 3rd/4th wheats, diamonds. Exhaustion Land: continuous wheat, circles. Filled symbols denote
crops receiving sufficient N to achieve maximum yield; open symbols denote crops receiving insufficient N.
Red symbols,
recent data from
HGCA experiments

17. A risk assessment approach to plant-available P levels
in soil
Number (and percent) of soils in different critical Olsen P groups in relation to soil type
Soil type and crop Range of Olsen P, mg/kg
6-15 16-25 26-35
Well-structured silty clay loam
Winter wheat 14 (88) 2 (12)
Spring barley 5 (83) 1 (17)
Poorly-structured sandy clay loam
Winter wheat 20 (46) 17 (40) 6 (14)
Spring barley 9 (50) 5 (28) 4 (22)
Poorly-structured heavy silty clay loama
Spring barley 2 (25) 4 (50) 2 25)
a excluding the results from soils with 1.5% SOM

18. Yield at 95% Olsen P Variance
Soil maximum associated accounted for
organic C with 95% yield
% t/ha mg/kg %
Field experiment
Spring barley 1.40 5.00 16 83
grain, t/ha 0.87 4.45 45 46
Potatoes 1.40 44.7 17 89
tubers, t/ha 0.87 44.1 61 72
Sugar beet 1.40 6.58 18 87
sugar, t/ha 0.87 6.56 32 61
Pot experiment
Grass dry matter 1.40 6.46 23 96
g/pot 0.87 6.51 25 82
Effect of soil organic matter on plant-available P
Explaining annual variation in maximum yield and associated Olsen P
• Annual weather
rainfall and sunshine
• Soil conditions
seedbed, soil structure

19. Soil structure

20. Compaction effects on soil structural conditions

21. Effect of a plough pan on
the growth and distribution of
winter wheat roots in
(a) December,
(b) March and
(c) June.
Total root length per unit ground area for
panned (solid bars)
unpanned soil (open bars).
Effect of soil pan on root growth

22. WoburnRothamsted
Without deep loosening
Wye Double Digger
Depth - cm
Cone resistance - bars
Plough depth
Winged subsoiler
Effect of using the Wye Double Digger in 1977 and a winged
subsoiler in 1977 and 1979 on cone resistance in 1981

23. Importance of soil structure
Root tips cannot enter very small pores, for cereals they must exceed 0.05 mm
Even with good structure, roots of annual crops rarely explore more than 25% of the top
soil to take up nutrients
Roots need to grow freely and quickly (especially for spring sown-crops) to access the
nutrients they require to achieve optimum yields. This is especially so for P because the
phosphate ion, H2PO4
-, only moves about 0.13 mm per day, the root must get to the P not
P to the root!
Using nitrogen efficiently, possibly using less and ensuring more is in the crop, requires
adequate plant-available P and K in the soil. A cost benefit to the farmer and less nitrate to
be lost to the environment
Most P is transferred from soil to water in eroded soil. A good soil structure aids water
infiltration and minimises surface runoff
Developing and maintaining a good soil structure is not easy but has benefits to the farmer
and the environment

25. Soil sampling and minimum cultivation
Illustration of the % of extractable P found at different depths of a soil which had
received only surface cultivations for 10 years
0 10 20 30 40 50 60
7.5-10.0 cm
5.0-7.5 cm
2.5-5.0 cm
Samplingdepths
% of P in top 15 cm (6 in) of soil

26. Soil sampling after starting minimum cultivation and
following changes in soil P status over time
An illustration of the potential for a soil sample to show an over-high value when
taken to the standard depth in a field where minimum cultivation has been practiced
Ploughdepth
Normal
representative
soil sample
Ploughed soil
Ploughdepth
Normal
representative
soil sample
Ploughed soil Min-till soil
Soil surface
Normal soil sample depth
Skewed
soil sample in
min-till
Min-till soil
Soil surface
Normal soil sample depth
Skewed
soil sample in
min-till
Min-till soil sample depth
Representative
soil sample in
min-till
Min-till soil sample depth
Representative
soil sample in
min-till