AHDB CP107b Field Lab – impact of digestates on soil health 29 June 2017
Agenda 10.00 Arrival, tea and coffee 10.20 Welcome, brief introduction to the GREAT soils project and the Field Lab at Mid Coul 10.30 Preliminary results from soil health testing in field trial (impact of digestates on soil health, crop growth and yield) 10.50 Field walk to look at digestate trials 11.40 Digestates – characteristics of different types and their likely impact types on soil health and quality 12.00 How to maximise the financial value of digestates and minimise the risk of damage to soil health through inappropriate application strategies. 12.20 Compliance with the law and farm assurance scheme rules 12.30 Future topics for discussion at remaining meetings 12.45 Lunch 13.30 Finish
Project Partners Funder: AHDB horticulture Leader: Soil Association Ben Raskin, Liz Bowles, Simone Osborn Partners: The Organic Research Centre Anja Vieweger and Bruce Pearce Earthcare Technical Audrey Litterick and Martin Wood Duration: 1 April 2015 – 31 March 2018
Aims of the project The project is: • Evaluating soil assessment methods for growers • Improving growers’ confidence in ‘reading the signs’ • Offering the opportunity to practise assessment methods with colleagues and advisors • Developing methods and approaches for practical soil analysis and evaluation to enable confident choice of management options. • Engaging with, and disseminating methods and approaches to a wide range of levy payers, growers, advisors and other stakeholders
Aims of the project Benefits for growers: • Improved health assessment of their soils; • Ability to follow a more accurate and integrated strategy for soil management, specifically adapted to their own conditions; • Better-informed decisions when aiming to optimise inputs, increase soil fertility and increase soil organic matter. Where growers are able to optimise and maintain soil organic matter levels, the benefits can be financially and environmentally significant. Improved soil health management can increase yields and potentially reduce costs as the land will become more productive .
Aims of the project • What is available out there? Critical review and evaluation of existing methods and approaches for assessing, benchmarking and improving soil health. • What is actually useful in UK soils? Determine the usefulness, efficiency and practical applicability of the methods and approaches during initial consultation and project as a whole. • Comparison of most relevant approaches. Six sites/farms have been selected for field trials (one in Scotland) and comparisons of soil management and soil assessment tools are being made in two project years (2016/2017 and 2017/2018)
Moray coast veg growers Field Lab Aim: To determine whether the application of whole digestate made from farm-produced energy crops has an impact on the health of soils in Moray coast vegetable rotations.
Moray Coast veg growers “Field Lab” Progress and plans: • Grower has applied digestate in Autumn 2016 and Spring 2017 to two fields • Will make additional one or two applications (weather-dependent) to same two fields later in 2017. • Control strips (no digestate applied) are being left in each field for comparison. • Treated and untreated areas of soils in the fields have been assessed and sampled prior to the first digestate application and around 1 to 3 weeks after two of the subsequent digestate applications.
Assessment methods • Routine analysis (Soil pH, extractable P, K, Mg) • Soil structural evaluations • Earthworm counts • Soil respiration • Quadrat weed counts in treated areas • Germination tests (weeds germinating in samples of known volume of digestate spread onto sand or growing media) • Bait lamina sticks • Underpants tests (!) • Crop growth and quality assessments?
Moray Coast Field Lab
Moray Coast Field Lab
Soil nutrient status Table 2. M8 field soil analysis results Digestate? Parameter Unit No Yes What does this mean? pH 1 - 6.1 6.0 pH is slightly below the target of 6.5 for vegetable rotations. Organic matter % 4.2 3.7 Fairly typical SOM level for this soil type in this region. Would be benefit in increasing it. Extractable nutrients Well below target of “high” for P P (status) 3 mg/l 3.5 (L) 3.0 (L) ″ Below or well below target of “high” for K K (status) 3 57 (L) 85 (M-) ″ Mg (status) 3 140 (M-) 154 (M-) At target for Mg CO 2 evolution 5 mg/kg 40 62 Soil has variable, low microbial respiration Soil texture SL SL Sandy loam
Soil nutrient status Table 2. M10 field soil analysis results Digestate? Parameter Unit No Yes What does this mean? pH 1 - 6.4 6.5 pH is pretty much at target of 6.5 for vegetable rotations. Organic matter % 4.5 4.0 Fairly typical SOM level for this soil type in this region. Would be benefit in increasing it. Extractable nutrients Below target of “high” for P P (status) 3 mg/l 5.6 (M-) 7.8 (M-) ″ Below or well below target of “high” for K K (status) 3 89 (M-) 47 (L) ″ Mg (status) 3 141 (M-) 115 (M-) At target for Mg CO 2 evolution 5 mg/kg 98 40 Soil has variable microbial respiration Soil texture SL SL Sandy loam
Soil structure assessments (VESS, Ball et al., 2012) Table 2 Visual assessments of soil structure in the 2017 grass clover leys Sampling zone score Mean Field area 1 2 3 4 5 score What does this mean? M8 3 2 2 2 3 1.6 Structure typical of fields which are in intensive No digestate vegetable rotations. Could be better, though recent dry weather is probably making the structure seem worse than it is. M8 2 3 3 2 3 1.6 As above Digestate M10 2 2 3 3 3 1.8 As above No digestate M10 3 2 2 2 3 2.2 As above Digestate
Soil compaction probe readings Table 3 Compaction as measured by a Dickey John compaction probe (2017 grass crops) Probe reading Mean Field 1 2 3 4 5 score What does this mean? M8 280 300 280 310 290 292 Compaction present, soil very firm in No digestate places. Almost certainly less bad than it looks – readings probably high due to recent dry weather. M8 290 300 310 320 280 300 As above Digestate M10 310 300 290 290 320 302 As above No digestate M10 190 260 250 280 270 250 As above Digestate
Earthworm counts Table 4 Earthworm counts in the 2017 grass clover leys Total no. of worms found of following sizes Total no. of worms Mean Juvenile (cm) Adult (cm) count 1 2 3 4 per pit 0-3 3-7 7-10 >10 <7 7-12 >12 Field area M8 0 2 0 1 0.8 0 2 1 0 0 0 0 No digestate M8 0 3 1 0 0 0 1 2 1 0 0 0 Digestate M10 0 1 0 0 0.3 0 0 1 0 0 0 0 No digestate M10 0 0 0 1 0.3 0 1 0 0 0 0 0 Digestate
Soil respiration measurements 90 80 70 60 50 40 mg CO 2 /g 30 soil/day 20 10 0 M8 No M8 M10 No M10 Digestate Digestate Digestate Digestate
Moray Coast veg growers “Field Lab” Quadrat weed counts: • Six 1m 2 quadrats were thrown down at random across the treated area and no weeds were found in any quadrat (although there were some weeds in the fields) • There is no evidence that use of digestate is resulting in increased weed growth in the grass clover leys.
Moray Coast veg growers “Field Lab” Germination tests: • Digestate was applied to the surface of wooden trays (25 x 25 cm x 10 cm depth) at the equivalent of 20 t/ha (2 kg/m 2 or 500 g per tray). • The digestate was either mixed thoroughly into the soil (1 tray) or it was spread across the soil surface in lines 20 cm apart, as it would be when spread using a band spreader (1 tray). • An equivalent amount of available N, P and K were used in a 3 rd tray so that a fair comparison could be made with soil not treated with digestate. • 100 mustard seeds were sown in each tray and their germination and growth was measured after 3 weeks and 7 weeks. • Trays were left out of doors on the soil surface and were watered regularly or rain was allowed to fall on them naturally. • Over 90% of the mustard seeds germinated in all trays. • There was no obvious difference in germination or growth between digestate-treated trays and straight-fertiliser trays.
Moray Coast Field Lab • Nutrient additions: Crop-based liquid digestate contains significant quantities of nutrients, especially N and K, but also P, Mg and S. • Analysis to date has shown that this is true here, (though significant amounts of nutrients, particularly N and K are ending up in the fibre) Nutrient content (kg/fresh tonne) of Kerrowgair separated liquid digestate N Phosphate Potash SO 3 MgO 3.4 1.4 5.6 0.6 ?
Moray Coast Field Lab Nutrient additions (kg/ha) when Kerrowgair liquid digestate is applied at 10, 20, 40 and 60 t/ha (in total) Application N (Crop-available N Phosphate Potash SO 3 rate at 60%) 10 t/ha 33 (20) 14 56 6 20 t/ha 66 (40) 28 112 12 40 t/ha 132 (79) 56 224 24 60 t/ha 198 (119) 84 336 36
Future work Assessments: 1. Crop yield and/or quality 2. Bait lamina sticks and pants 3. Post-last digestate appln. a) Routine analysis and SOM b) Soil structure assessments c) Soil compaction probe d) Worm counts e) Soil respiration (Solvita test with plate reader)
Final grower meeting for Moray Coast Field Lab Due spring 2017 (pre 31 March 2018): preferred date? Topics: 1. Present and discuss results of Field Lab 2. Present and discuss results from other UK field trials and field labs 3. Other?
Moray Coast veg growers “Field Lab” Thankyou!
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