Tillage update - Chopped straw reducing crop establishment in min-tilled winter crops

Mark Plunkett, Soil & Plant Nutrition Specialist reports on winter crops and how they are developing in the southeast. On the shortest day of the year, he visited a number of crops in east Wicklow with Local Tillage advisor Martin Bourke to catch up on how winter crops have been developing.

Mark and Martin visited a number of min-tilled winter crops (wheat, rye & OSR) where the only difference was whether straw was baled or chopped at harvest time.

Winter Wheat

The first crop they visited was a crop of winter wheat sown on  4^th October after winter oilseed rape & straw chopped.  This crop was established with a min-till cultivation system.  The seedbed was firm, with a well-established even crop with good rooting and tillering.  Weed control was very good, as a pre-emergence herbicide had been applied. There was no signs of slug activity as the seedbed was nice and firm.

Winter Rye

The next crop we visited was a min-tilled crop of winter rye sown on 10^th October after a high yielding winter wheat crop with straw chopped & incorporated.  Crop establishment was variable across this field with very good plant stands to very low plant stands.  Upon investigation the poor establishment was associated within a 4.5 metre zone directly behind the combine and ~ 1.5 metre either side the crop had very good establishment (see figure 1).  The large volume of straw appears to have reduced crop establishment as shown in the picture below and indicates the importance of spreading straw evenly across the full width. This crop will need continued monitoring for pest activity over the coming weeks. Early action in the new year will be required to promote plant development.  

Figure 1: Effect of straw incorporation in a crop of winter rye

We visited another crop of winter wheat sown after a crop of spring oats where the straw had also been chopped and incorporated. This crop was sown on 30^th October and soil conditions were very good at time of sowing. Again this crop had an unevenness across the field but not as distinct as the winter rye. This may be due to the lower volume of straw. Again crop establishment within the 4 meter zone directly behind the combine header (7.5m) was not as good with the 1.5m zones either side with good plant establishment. See figure 2 showing the effect of chopped straw on crop establishment.  Again this crop will need to be assessed in January and tiller manipulation maybe required.

Figure 2: Effect of straw incorporation in a crop of winter wheat.

Winter Oilseed Rape (WOSR)

The next crop we visited was a crop of WOSR planted on 5^th  September.  This crop was min-till established and had very even crop development across the field.  The straw from the previous high yielding crop of winter wheat had been baled and removed.  This crop is typical of many OSR crops currently with a well-developed canopy.  These crops have a GAI of 2.0+ indicating that up to 100kgN/ha has been taken up to date.  Where these canopies can be maintained it will significantly reduce crop fertiliser N requirements in 2022.   

Figure 3: Min-tilled winter oilseed rape with a well developed canopy where straw was baled.

The next crop we visited was a crop of oilseed rape planted after a crop of winter wheat where the straw had been chopped. This crop was planted on the 28^th August also with a min-till cultivation system. The most notable factor in this field was the large variability in crop establishment across the field. The crop had very good to very low plant populations as shown in figure 4 below.  The poorer establishment was associated with the chopped straw.  Secondly, decomposing chopped straw requires an available N source for the soil bacteria to break down the straw. We estimated N uptakes in the good and poor areas of the crop (weighting leaf volume x est. plant N % x est. DM%). The good area est. N uptake was 51 kg N/ha compared to 14kg N/ha in the poor areas. This crop will need protection from pigeons over the next number of weeks to minimise grazing and to retain the developed crop canopy.    

Figure 4: The effect of chopped straw on establishment of winter oilseed rape

Chopping Straw

Chopping straw is a relatively new practice on Irish farms in 2021 and brings many benefits to tillage soils from improving soil structure to retaining more soil carbon but also potential pit falls.  The following are a number of factors to consider when integrating chopped straw into a tillage system:-

1. Ensure the straw chopper is set up and able to spread the straw evenly across the full spread width
2. High yield crops with large straw volumes here in Ireland can be difficult to spread
3. Incorporation of straw is very important but it will be difficult to redistribute the straw across the spread width
4. Aim to incorporate straw rapidly after harvest to promote straw breakdown
5. Consider leaving a higher stubble to ensure better re-distribution of straw across the spread width
6. Consider cultivator type / set up to get good mixing of soil and straw
7. Where possible ensure seedbeds are well consolidated to reduce possible pest activity after sowing

Tillage Edge Podcast

In this weeks edition Andy Mahon, an Irish man and farm manager of a large farm in the UK, discusses with Michael Hennessy how his season went from June to December this year.  

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.