Soil remediation through organic matter Audrey Litterick Copyright Earthcare Technical
Summary Why do some soils need remediation? Organic matter the one size fits all solution for sick soils? Why SOM content must be viewed in context When and how to add more organic matter Successful remediation and maintenance of healthy soils: What to measure and when (baseline and ongoing) Development of long-term soil improvement strategy
Why we know we have a problem: Yields dropping Pest or disease problems increasing Increased need for more powerful machinery Lack of earthworms Soil investigations??
Sick soils
Why do some soils need remediation? overcultivation: too frequent too destructive (eg. root crops) use of inappropriate machinery cultivation in inappropriate soil conditions lack of organic matter returns monocultures over-use of biocides? chemical/biological contamination severe structural issues (eg following use a building platform)
Few farmers and growers do in-depth soil investigations... routine analysis (ph, P, K, Mg) precision sampling in-depth chemical testing? organic matter testing? earthworm counts X soil physical investigations (e.g. depth, texture, structure and compaction, drainage) X soil health (smell, biological activity) X
The soil health time-bomb... There is growing awareness that our reliance on synthetic fertilisers and pesticides and our lack of attention to soil biology is coming home to roost! Soils need a healthy biological component to function properly as media for plant growth and we have neglected that component. We need to define soil health, understand it better and develop practical, cost-effective strategies to build and enhance it on our farms and holdings.
As growers, we need soils to be: a physically stable and beneficial medium for healthy growth of plants (including crop plants) a source of air, water and nutrients for root uptake a medium for storage and movement of water free from inappropriate or high concentrations of chemical and biological contaminants a filter or buffer, transforming harmful materials and minimising their entry to drainage waters and food chains a reservoir of organic matter and a rich variety of life, making a contribution to C sequestration
Soils must be healthy in order to fulfil these needs, but... There is no universally agreed definition of soil health. Perhaps we could say that soil health in a farming context is: The capacity of a of soil to function within a managed farming system, to sustain profitable, good yields of healthy crops and maintain environmental quality
Some of us are expecting too much of our soils and have expected too much for too long.
What we need to do: We need to measure soil health because only then can we learn how best to manage it. But how? Many potential methods/combinations of methods... No agreement on what works best... Different methods/test suites best for individual farms... Made more difficult because of the above and: Farmers busy and are unsure of cost/benefit relationship Lack of practical soil specialists
Test methods relevant to soil health Soil organic matter Microbial respiration Microbial profiling (presence of functional groups) Earthworm counts Soil structure throughout soil profile (including presence of compaction) Soil texture Soil ph and extractable P, K and Mg Others (e.g. presence of specific contaminants, pests or diseases)
What to choose? All tests? expensive! may not be necessary Some tests but if so, which ones?
Test methods relevant to soil health Soil ph and extractable P, K and Mg Soil organic matter Soil texture Microbial respiration (topsoil) Hands-on examination of soil structure throughout profile (including presence of compaction) Earthworm counts Interpret above based on knowledge of cropping system, soil type, altitude, aspect, presence of other relevant features and ALL organic matter returns Others (eg. presence of specific contaminants, pests, diseases) Microbial profiling (presence of functional groups)
Organic matter the panacea to all soil health problems? No! Many soils DO need organic matter and could benefit greatly from having higher SOM levels. However, some soils have plenty and their soil health issues are due to other things: e.g. low ph, low fertility, nutrient imbalances, drainage issues,, presence of low levels of disease etc.) Think broadly and test accordingly!
Test methods relevant to soil health Soil ph and extractable P, K and Mg Soil texture Soil organic matter Microbial respiration (topsoil) Hands-on examination of soil structure throughout profile (including presence of compaction) Earthworm counts Interpret results based on knowledge of cropping system, soil type, altitude, aspect, presence of other relevant features and ALL organic matter returns
Options DIY soil pits and interpretation (use books or online guidance?) Practical soils expert Lab analysis chemical & physical testing widely available biological testing less so (e.g. NRM soil health test suite) Interpretation (may need expert help? Full specialist service?
Example scenario SOM level is found to be lower than ideal for the soil texture and cropping system in question BUT... careful investigation has also shown: drainage issue in one part of the field ph is too low Mg:Ca ratio is too high, there are soil structural issues Sort the drain, apply Ca lime at appropriate rate Apply organic matter and consider strategy to continue how and when to add more on regular basis.
More soil organic matter gives: Improved structure and workability Increased water holding capacity and infiltration Increased biological activity Improved retention and turnover of nutrients Greater resilience to dry weather conditions
Which organic material is best? There is no best! Use those that are local, cheap and contain appropriate nutrients in appropriate forms. Ensure chosen materials have no detrimental effect (e.g. on ph, soil PTE content etc.) Use those which suit the crop and/or rotation in terms of nutrient profile and availability. Ensure that relevant farm assurance and produce buyers allow use in the manner intended! - e.g. manures from intensive farming systems are banned in organic production systems and those from extensive conventional systems must be stacked or composted for minimum periods before use in organic systems
Organic matter what, when, how much? Bulky organic material % organic matter in fresh material Green and green/food compost 16-21% Mushroom compost 12-15% FYM (strawy cattle) 12-15% Broiler litter 20-32% Fibre digestate 22-26% Whole and liquid digestate 0.5-3% Paper crumble 10 15% Green manures small, variable Crop residues small, variable
CompUse/Slide20/2012_04_30 % Total organic matter 100 90 80 70 60 50 40 30 20 10 0 Compost supplies stable organic matter (Lignin as % of total organic matter) Livestock manures Compost Paper crumble Source: Defra SOIL-QC project
Don t forget... All bulky sources of organic matter are ALSO fertilisers with a range of chemical, physical and biological properties.
Using your organic materials to best effect Understand main properties of your bulky organic material: Organic matter content [ ] Fertiliser content (total & readily available nutrients) [ ] Neutralising value? [ ] Presence of any undesirable properties (e.g. High C:N, high Cu content, high salt levels) Apply at appropriate rate (within the law, to provide agricultural benefit and no harm to the environment or your crops) Calculate the cost [ ] v the money saved [ ]
Potential organic matter sources Green and green/food compost FYM (various types) Mushroom compost Fibre digestate Whole digestate Green manures Crop residues Paper crumble
Organic material Green and green/food compost Strawy cattle manure Broiler litter Mushroom compost Comments Great source of long-lasting organic matter, excellent source of P, K, Mg, S and trace elements, can have neutralising value. Ensure you have a good supplier. Very good source of organic matter, excellent source of P, K and S. Needs careful treatment and use in rotations inc. ready to eat crops. Contains a lot of organic matter, but must be applied at low rates due to the high fertiliser nutrient content, so not the quickest way to build soil organic matter. Very good source of organic matter, excellent source of P, K and S. usually a powerful liming agent. Again, needs careful treatment and use in rotations inc. ready to eat crops.
Organic material Fibre digestate Whole and liquid digestates Comments Very variable in terms of its organic matter content depending on feedstocks and process (testing essential). Usually an excellent source of P, K, Mg, S and trace elements; often has a neutralising value. Ensure you have a good supplier. Very variable in terms of its organic matter content but usually low because mostly water! (testing essential). These are primarily fertilisers, not good sources of organic matter.
Organic material Paper crumble Green manures Crop residues Comments A good source of organic matter but should be used with care due to typically high C:N ratio (and risk of N lock-up). Can be a good source of plant nutrients depending on type. Always a waste (WML Regs.) Organic matter input is low per crop but these do much more than simply add organic matter (break crop from cereals can knock back cereal pests/diseases, can mine nutrients from deep in soil profile, can improve soil structure and protect soil over winter etc). Organic matter input is low per crop but there is increasing evidence that small, regular additions of organic matter can be very beneficial to earthworm activity and soil health.
Conclusions: Organic matter additions are often the key to remediating damaged soils which are functioning below their potential. When this is the case, a wide range of options should be considered as to the best and most costeffective strategy for increasing SOM. composts and FYMs remain some of the best solutions but even regular small additions of crop residues and green manures can make a difference. Don t lose sight of possibility that SOM is not the main problem or might not be an issue at all!
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