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Tillage Update 12th August 2021

Mark Plunkett, Soil & Plant Nutrition Specialist reports on tillage topics currently. Rainfall amounts over the last week to 10 days has eased soil moisture deficits (SMD’s) in the majority of the country but in parts of the south east there still is a 30 to 40 mm SMD still present.

Over the coming weeks and months there may be options to improve soil health on tillage farms from adding organic matter / carbon to improving soil structure.

In the Fields Crop Update

Cover Crops

Establishing cover crops over the coming days and weeks as cover crops 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 between 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 there full benefits. For example a good cover crop can capture between 1.0 to 1.5t carbon/ha over the winter period.

Organic Manures

Applying organic manures offer large benefits to continuous tillage soils on many fronts from feeding soil biology such as earthworms to improving soil structure.  Where sources of manures are available such as FYM, cattle / pig slurry, mushroom compost, dairy sludge’s etc... These are valuable sources of organic matter / carbon (C), N, P K and micro nutrients.  For example an application of 15m³/ha (1,500gals/ac) 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.  Incorporation of straw into the soil is very important as straw mainly contains carbon and rapid incorporation will aid the break down by soil biology. Straw will return significant quantities carbon and major plant nutrients such as potassium (K) and low levels of phosphorus (P).  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 to 20% as soil organic carbon.  Research from Teagasc at the Knockbeg site showed that after 8 years of straw incorporation the soil organic carbon levels increased from 1.63% to 1.75% in the top 15cm of soil. For organic manures the speed of soil organic carbon changes will very much depend on the manure type for example FYM will supply large amounts of carbon compared to pig slurry and again it will take annual applications to change levels over time. Building soil carbon levels is a very slow process but the addition of small amounts of carbon will help soil health and productivity over time.

Winter Oilseed Rape (WOSR)

Over the coming weeks crops of winter oilseed rape will be established. Check soil test results and aim for a soil pH 6.5, where lime is required apply before sowing and work well into the seed bed. Based on P & K soil test results apply recommended rates at sowing time to ensure rapid rooting and crop establishment. Table 1 below shows the recommended rates of P & K for WOSR crops.  Apply a fertiliser such as 0-10-20 or alternatively an organic fertiliser such as pig / cattle slurry, mushroom compost, dairy processing sludge etc. Organic fertilisers will supply carbon as well as the crops N, P & k requirements.

Oilseed rape has a great ability to take up N during crop establishment and early spring compared to cereal crops.  Where organic manures are available they can supply a proportion of the crops N requirements and reduce crop chemical N requirements in the spring of 2022. Ensure that liquid manures are well agitated / mixed and applied at a consistent rate evenly from start to finish. Table 2 below shows typical fertiliser values for a range of organic manures.

Soil Testing

Now is a great time to take fresh soil samples and take stock of soil fertility levels and plan nutrient programmes for the coming season.  August & September provides an ideal window of opportunity to apply ground limestone and correct soil pH.  Aim to maintain the agronomic optimum pH 6.5 to 6.8. 

Soil Structure Problems

The dry soil conditions and high soil moisture deficits (SMD’s) present the ideal window to carry out subsoiling where soil compaction is present.  Take out the spade and examine the top 25 to 50cm of soil to identify the presence of soil compaction.  This will ensure that the sub-soiler is operated at the correct depth to maximise soil cracking effect under the current dry soil conditions.  For further information on soil structure assessment / videos please check out Soil Quality

The Tillage Edge Podcast- Planting Cover crops

Cover crops can be useful for many different functions in a field but some farmers see them as an inconvenience both to plant and to manage before the next crop.  Dr. Richie Hackett a researcher in Teagasc, Oak Park, Carlow has been working with cover crops for over 10 years and joined the podcast to go through some of his findings especially the advantages of panting cover crops early. 

Richie explained cover crops are useful for mopping up nitrogen, growing organic matter, reducing soil erosion, helping soil structure and soil health and can supply nitrogen to the next corp.  Richie advocated planting early as trials show a 2t DM/ha reduction in crop grown for every three week delay in planting from late July.  Richie was surprised by the scale of the differences however commented that all crops were ploughed back in before the next cop without difficulty or the use of glyphosate.

Listen to Dr. Richie Hackett discussing cover crops in the podcast episode below

Richie has produced a video outlining the advantages of planting cover crops early. Watch it here below

Find out more information and advice from the Teagasc Crops team here. The Teagasc Crops Specialists issue an article on a topic of interest to tillage farmers every Thursday on Teagasc Daily