Caitlin Hurley incorporating chopped straw on the family farm at Jagoes Mills, Kinsale, Co Cork. Caitlin says this is of great long-term benefit, providing additional organic matter along with carbon storage in the soil, and also putting a proper value on straw.
Slurry spreading in Co Carlow. Photo: Roger Jones
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Caitlin Hurley incorporating chopped straw on the family farm at Jagoes Mills, Kinsale, Co Cork. Caitlin says this is of great long-term benefit, providing additional organic matter along with carbon storage in the soil, and also putting a proper value on straw.
Mark Plunkett
As we move into the main cereal harvest, the combine and weigh bridge will be the final measure of crop performance for 2021.
The dry June and hot July will have accelerated the grain filling period, especially for winter wheats and spring cereal crops.
Where crops followed a break crop such as beans or maize, or had received an application of organic manures, they seemed to be more resilient to the hot, dry conditions and were greener for longer. This resulted in a longer grain-filling period.
The indicators of climate change seem to be with us: frequent changes in our weather patterns with either prolonged cold spells in April, high rainfall amounts in May and very dry and hot conditions in June and July.
Building resilience into our cropping systems starts with our soils. Building soil carbon or organic matter will help soils be more resistant to the extremes of weather events, and increasing soil carbon storage is an important tool for countering climate change.
Organic matter is the glue that gives our soils structure and is important for soil life, nutrient and water supply during the growing season.
Keeping an actively growing crop in the soil such as a cover crop or natural regeneration during fallow periods, or the addition of organic matter like cattle/pig slurry or milk processing sludge increases soil function. This has both environmental and productivity benefits.
These management activities help protect our soils, add carbon to feed soil biology and improve soil structure.
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Cover crops
Establishing cover crops over the coming days offers many soil, crop and environmental benefits.
An important function of a cover crop is to take up any remaining nutrients during the fallow period, such as nitrogen that was not utilised by the previous crop, thus improving water quality.
For example establishing a green cover on over wintered stubbles can recover 20 to 60kgN/ha.
An actively growing cover crop will also capture carbon over the autumn-winter-spring period, plus an actively rooted crop will improve soil drainage and structure.
Early establishment of cover crops after harvest is required to realise their full benefits. For example a good cover crop can capture 1.0 to 1.5t carbon/ha over the winter.
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Organic manures
Applying organic manures offers large benefits to continuous tillage soils on many fronts, from feeding soil biology such as earthworms to improving soil structure.
The likes of FYM, cattle/pig slurry, mushroom compost and dairy sludges are valuable sources of organic matter, carbon, nitrogen, phosphorus, potassium and micro-nutrients.
For example an application of 15m³/ha (1,500gals/ac) of cattle slurry will supply 0.35t C/ha, or 10t/ha of FYM will supply 1.0t C/ha, while 10t/ha of mushroom compost will supply 1.3t C/ha.
Straw chopping
Incorporating chopped straw is another route to building soil carbon levels.
Straw mainly contains carbon and rapid incorporation will aid the breakdown by soil biology.
Straw will return significant quantities of carbon and major plant nutrients such as potassium and low levels of phosphorus.
For example, a winter wheat grain crop yielding 10t/ha where straw is chopped will return 2kg P/ha, 50kg K/ha and 2.4t C/ha.
The above three practices show how much carbon can be captured annually. However the soil will only retain 15-20pc as soil organic carbon.
Research from Teagasc at the Knockbeg site showed that after eight years of straw incorporation, the soil organic carbon levels increased from 1.63pc to 1.75pc in the top 15cm of soil.
For organic manures the speed of soil organic carbon changes will depend on the manure type; for example FYM will supply large amounts of carbon compared to pig slurry.
An application of 25m³/ha of pig slurry will increase soil organic carbon levels by 0.0001pc.
Building soil carbon levels is a very slow process but the addition of small amounts of carbon in the short to medium term will help improve soil health and productivity over time.
Mark Plunkett is a Teagasc soil and plant nutrition specialist based at Johnstown Castle, Co Wexford
