Soil biology, organic matter, structure, functioning and crop yield Matthew Shepherd Soil Biodiversity Specialist Natural England

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1 Soil biology, organic matter, structure, functioning and crop yield Matthew Shepherd Soil Biodiversity Specialist Natural England Overview What do we want from soil? Living soils Keeping soils alive Crop yields Checking soil biological health

2 What do we want from our soil? Natural Soils the beginning...

3 ... And now Natural vs Cultivated Mineral Soils Natural Stable aggregates C in large aggregates less prone to breakown High total C storage Survives without artificial fertiliser thrifty nutrient cycling Higher water retention High biomass, and activity high diversity of communities and functional groups Mostly stay put! Agricultural Less stable aggregates Rapid breakdown of aggregate C Lowest C storage (esp arable) High demands for artificial fertiliser leaky system More droughty Low biomass, some functional groups missing, more homogeneous low biodiversity. Erosionhigh source of sediment

4 Natural vs Cultivated Soils Machado, Soil a hidden world!

5 Plants Energy supply litter and root turnover Root penetration and enmeshment Root exudates and microbial associations Bacteria

6 Plants and fungi Photo: Sara Wright. Earthworms

7 Earthworms Improve soil structure Release nutrients Most active spring and autumn Improve drainage Mix soil Spread mycorrhizal spores Lose C emit N 2 O Generate humus Support other wildlife And the rest...

8 What does soil life do? Gives soil structure Helps soil function

9 Soil structure The clumping together of soil particles and air and water spaces in between Made by gluing, painting, sewing, eating, moving Some glue chemical self mulching but most is biological - humus, GRSPs Indicated by aggregate stability, bulk density, strength. Visual assessment Soil structure Wright, S. F. et al. Changes in Aggregate Stability and Concentration of Glomalin during Tillage Management Transition Soil Sci. Soc. Am. J :

10 Soil Function Water infiltration Porosity and connectivity Worm channels Water storage and supply Good structure for better root penetration Humus to hold moisture Mycorrhiza Soil Function Nutrient cycling and storage Right time active spring and autumn Right place - N release in rhizosphere GHG flux better structure = less N 2 O Decomposition AND storage of C

11 What we do to them Low inputs of C to soil = no fuel to support soil life. Disturbance kills big ones, and causes loss of soil C Compaction less space to live and air to breathe! Erosion/building over total habitat loss! Soil life is tough! Keeping soil alive Soil life evolved alongside diverse natural plant communities Can we emulate these communities in our agricultural soils to improve function? Characterised by: higher soil organic matter Lack of regular disturbance Diverse plant communities

12 Soil organic matter Total Soil PLFA content nm g Soil organic matter and total soil PLFAs y = ln(x) R² = % Soil Organic Matter (Loss on Ignition) Source: Natural England, ECBN data, Soil organic matter Bulk density g/cm Grassland soil organic carbon and bulk density in England and Wales y = ln(x) R² = % organic carbon (Walkley-black) Source: ADAS, Defra project BD5001

13 Soil organic matter GB soil organic matter and soil moisture content y = ln(x) R² = % Soil water content % Soil Organic Matter Source: Countryside Survey, 2007 Soil organic matter Cation Exchange Capactity (meq 100g_1 Soil organic matter and cation exchange capacity 140 y = ln(x) R² = Big improvements in soil function due to small changes at low SOM % Soil organic matter (loss on ignition) Source: Countryside Survey, 2007

14 Soil organic matter Raise organic matter -put more in, or lose less Add more organic matter from elsewhere recent review* Impact is gradual needs repeated applications Can ~double microbial biomass, C storage Increases aggregate stability reduces bulk density Best impacts at highest rates Stabilised (composted) less N lockup -slow release of N fertiliser, little N leaching Compost increase crop yield 250% Not available to all Manures don t travel *Diacono & Montemurro, Agronomy for Sustainable Development April 2010, Volume 30, Issue 2, pp Soil organic matter Almost all C from plants - grow more plants! Increase production more N = more biomass but residues must be returned Leaching and waste

15 Keeping soil alive Cover Crops Put more plant C into soil Maintaining soil life over winter through exudates and links with microbes Other advantages include... Prevention of erosion and runoff Biofumigationon destruction Cabbage family aren t mycorrhizal... If N applied when cover decomposes, may increase leaching Keeping soil alive Munkholm and Hamsem (2012) Soil Use and Management, 28:4,

16 Cover crops 4.9 t C ha-1 stored = ~0.2% increase Mutegi (2013) Soil Use and Management, 28:4, Keeping soil organic matter Lose less SOM how? More compacted or waterlogged? Stop decomposition? Biochar? Less disturbance *Alvarez, Soil Use and Management 21

17 Keeping soil organic matter Min or no-till soils have more C/SOM in topsoils, larger aggregates containing more SOC and more N Overall typically 2.1 t C ha -1 more than cultivated systems* Stable systems 12 tonnes C ha -1 more* Better for earthworms more deep burrowing and surface-active, and fungi. *Alvarez, Soil Use and Management, 21 No Till Years of treatment *Alvarez, Soil Use and Management 21

18 Keeping soil alive Soil life evolved with diverse plant communities Diverse covers and crops may complement and facilitate as well as compete Rotations and timings Wheat, Oats and Peas different soil microbial communities associated with different plants Higher non-bacterial component under peas Keeping soil alive Multicropping several crops same place & time Ryegrass & clover to Agroforestry New review Ehrmann & Ritz

19 Multicropping Few impacts on total SOM except under trees Interactive effects between plants and soil life More earthworms under trees and legume intercrops Legume N transfer to other plants -litter, exudates and mycorrhizas most in undisturbed systems Ammonia oxidising or free N fixing bacteria in the rhizosphere Increased chance of mutually supportive mycorrhizal networks More diverse soil organisms for natural disease prevention Multicropping More N fixed by legumes when competition from cereals or in diverse grasslands Different root patterns and depths avoid competition or accessing different nutrient pools (P) Harder to spread disease physical separation Better weed suppression by allelopathyor competition

20 Crop Yields Soil life and SOM impact on structure, disease, pest control, moisture retention and nutrient capture and cycling SHOULD have crop benefits... SOM has definite benefits in drought-prone soils Some evidence from long-term Rothamstedexpts. when other production limits are reached... Otherwise evidence is slight and often masked by N effects Perceived benefits... Source of case Net annual financial benefit ( /ha) study Project number Arable Livestock Mixed All SP (10) 1 58(8) 60 * (18) SP (6) 98 (6) 103 (11) 96 * (23) Average 69 (16) 98 (6) 84 (19) 80 (41) Time to realise net financial benefits (years) Project number Arable Livestock Mixed All SP SP Average Table 1: Net annual financial benefits /ha from SOM management by farming system 1 Numbers in parenthesis show number of case studies in each category. * Statistically significant, ANOVA F = 5.381, P = Defra project: SP08014

21 How can you tell if it s working? Organic matter comparison between fields etc. Typical ranges Cranfield University: Defra SP0310 How can you tell if it s working? Bulk density and infiltration Soil Structure dig a pit! Worms Biological assessment not well benchmarked

22 Conclusions Soil structure and function is driven by soil life Soil life is fuelled by soil C If you want your soil to work properly, you ve got to feed it! Adding soil C can work often have to grow your own Cover crops can help Disturbing soils wastes this organic matter Benefits may be wider than crop yield Measure SOM, look for good soil structure and get to know your worms Thank you!