3 Organic Matter, Soil Structure and Crop Yield

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1 // Department of Geography and Environmental Science Structure of talk Organic Matter Soil Structure and Crop Yield Dr Tom Sizmur What is soil structure? Soil organic matter: Does size matter? Organic matter as food for soil organisms How does organic matter and soil organisms improve soil structure? How can we use organic matter to improve soil structure and crop yield? University of Reading 8 Can we recognise good soil structure? Does soil structure improve from left to right or from right to left? What is soil made of? Primary particles Secondary particles

2 // What is soil structure? Large pores Aggregates and clods Aggregates and clods Aggregates Natural Smaller Porous Rounded Clods Man-made Larger Non-porous Angular corners (after breaking) 7 8

3 // Good soil structure: Large pores and small aggregates Aggregate stability Plant roots need to push aggregates away from them as they grow. They need somewhere to push the soil that they displace Therefore, aggregates should be smaller than the diameter of the plant roots Lots of small (< cm diameter) aggregates are better than a few large aggregates/clods 9 Aggregate Stability You can monitor/measure soil structure Visual Evaluation of Soil Structure: Grassland Arable ( years) % SOC.% SOC Highfield Arable/Grass Rotation Experiment Rothamsted (Established 99) Soil Use and Management Volume 7, Issue, pages 9-, JUN DOI:./j x

4 // Soil Structure Summary Good soil structure is: Large Pores (macro-pores) Allow displacement by roots Lots of small aggregates Small enough to be moved by roots (< mm) Stable aggregates That do not disintegrate in water (slake) How much soil organic matter do you have? Turn to the person next to you:. Do they know the soil organic matter content of their soil?. If they do then how much do they have?. What does this number mean to you? How much OM becomes SOM? Organic matter feeds soil biology Organic Matter (e.g. FYM, crop residues) CO Soil biology Soil Organic Matter Modified from RothC: The Rothamsted Carbon Model Kevin Coleman and David Jenkinson 998 CO Soil biology Soil Organic Matter The vast majority of the organic matter added to soils is metabolised relatively quickly by soil organisms Some of these soil organisms improve the structure of the soil.

5 // Minimum tillage experiment Rotation: Spring Barley Winter Oilseed rape Winter Wheat Spring Barley Minimum tillage Farmyard manure and Compost at,. and. t C ha - Nitrogen rates (N to N) Minimum tillage experiment Earthworm biomass (g m - ) t C/Ha. t C/ha. t C/Ha N Compost N FYM N Compost N FYM Earthworm biomass significantly increased by N rate and OM rate 7 8 Earthworms are ecosystem engineers Earthworms Improve drainage Reduce soil erosion Promote root growth Accelerate nutrient cycling Long before [the plough] existed the land was in fact regularly ploughed and still continues to be thus ploughed by earthworms Aporrectodea caliginosa 9

6 // Earthworms reduce soil strength You can monitor earthworms Soil strength -cm (Kph) R² =.9 No Straw Straw at t ha- Straw at t ha- Straw at t ha- 8 Endogeicearthworm biomass (g m - ) Organic Matter Summary Impact of OM on crop yield: Organic matter feeds soil biology Manures increase earthworm populations Earthworms reduce soil strength You can monitor your earthworm population Applications (. t C ha - ) Farmyard Manure Compost Anaerobic Digestate Straw Five nitrogen rates (N-N) Rotations Wheat Barley Oats Wheat Barley OSR Wheat Barley

7 // Oilseed rape: Yield Oilseed rape: Oil content OSR yield (t/ha) at 9% dry matter 7 Unamended Anaerobic Digestate Compost Farmyard Manure Barley straw Nitrogen (kg/ha) % Oil at 9% Moisture content Nitrogen (kg/ha) Unamended Anaerobic Digestate Compost Farmyard Manure Barley straw Poly. (Unamended) Oilseed rape: Straw yield Barley: Yield OSR straw yield (t ha - ) DM.... Unamended Anaerobic Digestate Compost Farmyard Manure Barley straw Linear (Unamended) Linear (Anaerobic Digestate) Linear (Compost) Linear (Farmyard Manure) Linear (Barley straw) Barley grain yield (t/ha) at 8% DM 8 Unamended Anaerobic digestate Compost Farmyard Manure Straw Poly. (Unamended) Nitrogen (kg ha - ) Nitrogen (kg/ha) 7 8 7

8 // Barley straw yield (t ha - ) DM Barley: Straw yield Unamended Anaerobic Digestate Compost Farmyard Manure Barley straw Nitrogen (kg ha - ) Grain Yield (t ha - ) Grain Yield (t ha - ) Sandy soils: Woburn organic manuring experiment Nitrogen (kg ha - ) Data Fitted Nitrogen kg ha - t C/ha t C/ha Effect size -... Sugar Beet S. Barley Sugar Beet S. Barley Sugar Beet S. Barley Sugar beet S. Barley S. Barley F. Maize W. Rye S. Barley 9 Sandy soils: Woburn organic manuring experiment Effect size Barley Sugar Beet Wheat Yield per plant (g) Grains per plant How does OM improve yield? Pot experiment: Wheat OM application rate (gc/kg soil) OM application rate (gc/kg soil) Ears per plant Yield per ear (g).... OM application rate (gc/kg soil) OM application rate (gc/kg soil) 8

9 // How can we use OM to improve soil structure and crop yield? : Mixtures Return crop residues Apply manures Reduce tillage Use cover crops/green manures Earthworm biomass (g m - ) 8 8 Unidentified Epigeic Anecic Endogeic All plots received tcha - Straw Compost Comp+Straw FYM FYM+Straw AD AD+Straw The Future Effect of substrate diversity on biological diversity, ecosystem services and resilience Perturbation Can we make better use of crop residues Fully funded PhD studentship currently advertised Starting October Increased resilience Increased resistance 9

10 // Summary Good soil structure is Large pores Lots of small aggregates Stable aggregates Organic matter feeds soil biology Manures increase earthworm populations Earthworms reduce soil strength, promote root growth and increase crop yield You can monitor soil structure and earthworms Visual Evaluation of Soil Structure OPAL Earthworm survey guide 7