Trial system design and
results to date
Catherine Keeling
Warwick Crop Centre
N analysis
Maize/Slurry
Maize
Potato
Slurry
Food
Food
(Separated)
(Separated)
(Whole)
(Whole)
(Whole)
(Separated)
mg/l
mg/l
mg/l
mg/l
mg/l
mg/l
Total N
3620
3801
2914
4287
5876
4257
Mineral N
1489
1606
1933
3605
3738
2547
Ammonium-N
Nitrate-N
1484
5
1602
5
1932
1
3603
2
3736
2
2543
4
Min. N excess
12 x
13 x
16 x
30 x
31 x
21 x
Mineral N
In raw state digestates have:
 Between 10 and 30 times too much min. N
Dilution required
 100% of min. N in the form of ammonium


Direct toxicity
Acidifcation of rootzone
Nitrate amendment recommended
Mineral N
Dilution
Digestates diluted to achieve 120mg/l total min. N
Nitrate amendment
The 120 mg/l min. N is comprised of:


60% ammonium-N (from digestate)
40% nitrate-N (from amendment)
Diluted digestates
Maize/Slurry
Maize
Potato
Slurry
Food
Food
Target
(Separated)
(Separated)
(Whole)
(Whole)
(Whole)
(Separated)
mg/l
mg/l
mg/l
mg/l
mg/l
mg/l
mg/l
Amendment
(as KNO3)
N
120-150
Req. dilution factor
71
(21x)
71
(23x)
71
(27x)
71
(51x)
71
(53x)
71
(36x)
+ 50
(as MKP)
P
K
Ca
Mg
Fe
Mn
Mo
40-55
250-300
100-120
25
1200-1700
500-800
20-50
Total solids (%)
EC (dS m-1)
1.5-1.8
11
175
52
12
8
150
43
9
4
179
29
6
4
72
33
8
4
43
29
6
3
41
33
6
1897
164
0
767
107
0
176
30
0
446
86
0
138
25
0
240
36
0
0.26
2.2
0.22
2.1
0.08
2.1
0.10
1.9
0.05
2.1
0.08
1.9
+ 45
+ 200
(as KNO3 & MKP)
+ 1200
+ 500
+ 40
Typical commercial system
1-1-3 Calcium Potassium
NPK nitrate
nitrate
Water
Concentrated stock
solutions injected
into the irrigation
system
Free-flowing
drip stakes
Pressure
compensated
emitters
Experimental system
Pump
•
•
•
•
•
Water
Digestate
Potassium nitrate
Monopotassium phosphate
Iron, Mn, Mo
Ring
main
lay-out
Feed solutions
pre-mixed in
tanks
Low pressure 2 l/h
drip stakes (no
pressure
compensation)
Free-flowing
emitters
Day 18 (12 March)
Digestate
Control
Leaf growth (Day 18)
(length of largest terminal leaflet)
Treatment
Mean (mm)
Food (whole)
100
Control
99
Maize (sep.)
98
Food (sep.)
97
Potato (whole)
97
Maize/Slurry (sep.)
95
Slurry (whole)
95
5%*
(s.e.)
a
(1.7)
a
(2.6)
a
(1.4)
a
(2.1)
a
(2.5)
a
(1.2)
a
(2.9)
*Mea ns fol l owed by di fferent l etters woul d i ndi ca te s i gni fi ca nt di fference a t the 5% l evel
(GenSta t: Anova a nd Tukey tes t)
Initiation of flowering
(Day 20, 14 March)
Treatment
Mean (per ba g)
Control
9
Potato (whole)
8
Food (whole)
8
Slurry (whole)
8
Food (sep.)
6
Maize/Slurry (sep.)
6
Maize (sep.)
6
5%*
(s.e.)
a
(2.0)
a
(1.3)
a
(1.7)
a
(0.6)
a
(0.7)
a
(2.0)
a
(1.5)
*Mea ns fol l owed by di fferent l etters woul d i ndi ca te s i gni fi ca nt di fference a t the 5% l evel
(GenSta t: Anova a nd Tukey tes t)
Sedimentation
Maize (sep.)
Potato (whole)
Day 52
Day 52: Calcium deficiency
Day 59
Maize/Slurry (separated)
Day 59
Maize (separated)
Day 59
Potato (whole)
Diluted digestates
Maize/Slurry
Maize
Potato
Slurry
Food
Food
Target
(Separated)
(Separated)
(Whole)
(Whole)
(Whole)
(Separated)
mg/l
mg/l
mg/l
mg/l
mg/l
mg/l
mg/l
Amendment
(as KNO3)
N
120-150
Req. dilution factor
71
(21x)
71
(23x)
71
(27x)
71
(51x)
71
(53x)
71
(36x)
+ 50
(as MKP)
P
K
Ca
Mg
Fe
Mn
Mo
40-55
250-300
100-120
25
1200-1700
500-800
20-50
Total solids (%)
EC (dS m-1)
1.5-1.8
11
175
52
12
8
150
43
9
4
179
29
6
4
72
33
8
4
43
29
6
3
41
33
6
1897
164
0
767
107
0
176
30
0
446
86
0
138
25
0
240
36
0
0.26
2.2
0.22
2.1
0.08
2.1
0.10
1.9
0.05
2.1
0.08
1.9
+ 45
+ 200
(as KNO3 & MKP)
+ 1200
+ 500
+ 40
pH
8.5
8.0
pH
7.5
7.0
6.5
6.0
5.5
Conventional
Digestates
pH
8.5
8.0
pH
7.5
7.0
Feed
6.5
Leachate
(high LF)
6.0
Leachate
(low LF)
5.5
Control
Food (s)
Food (w)
Slurry (w)
Potato (w) Maize/Slurry Maize (s)
(s)
Total fruit weight
(up to 17 May)
2500
mean g per bag (8 plants)
2000
1500
1000
500
0
Maize (s)
Maize/Slurry
(s)
Potato (w)
Control
Food (s)
Food (w)
Slurry (w)
Average fruit weight
(up to 17 May)
18
16
14
mean g per fruit
12
10
8
6
4
2
0
Maize (s)
Potato (w)
Maize/Slurry (s)
Slurry (w)
Food (s)
Control
Food (w)
Taste testing:
Aggregated scores for aroma, texture, juciness and flavour
5
4
Score
3
2
1
0
Control
Slurry (w)
Potato (w)
Food (s)
Food (w)
Maize/Slurry
(s)
Maize (s)
Conclusion
 Digestates can perform at least as well as
conventional feeds in strawberry production, with
respect to both yield and consumer acceptability
 Need to run system at a pH appropriate to the
individual digestate
 Need to understand the relationship between feed pH
and rootzone pH
Next steps…
 Test digestates using a conventional injection drip
irrigation system
 pH tailored to individual digestate
 Do the emitters block?
 Experiment with nutrient/nitrate amendment
Maize
(s)
Potato
(w)
Maize/
Slurry (s)
 Can the naturally high K, well buffered digestates be used
unammended?