July 13, 2016
Five-year black-grass management trial show valuable winter wheat performance gains without major rotational change
The right establishment strategy alone can make all the difference to winter wheat performance even with the most challenging grass weed populations, reveals the UK’s most comprehensive black-grass management trial programme.
Concluding last season, the establishment system study across 6 ha and a full five-year winter cropping rotation at Agrii’s Stow Longa black-grass technology centre near Huntingdon has enabled the crop performance and weed control success of more than 2000 separate cultivation and sowing date strategies to be compared. And, with a final year’s wheat yield difference of fully 7t/ha between the best and worst performing strategies in exactly the same field, the findings are truly spectacular.
“Our investigations across 16 ha of heavy ground with some of the most resistant black-grass in the country since 2000 have demonstrated advantages from a range of cultural controls,” explained Agrii head of agronomy, Colin Lloyd who has overseen the work from day one. “These include increasing seed rates, growing more competitive wheat varieties, spring cropping and, most recently, well-managed catch and cover crops.
“The establishment work we’ve run in conjunction with Lemken from 2010 to 2015 has shown how much growers can do to tackle the scourge of black-grass without the need for major rotational change.”
Amongst the wealth of findings to emerge from the five different cultivation regimes and two sowing dates examined by the Agrii team over the five-year wheat/rape/wheat/wheat/wheat rotation, two key ingredients for black-grass management success stand out – ploughing and delayed drilling.
“Our study shows that a plough used tactically can make all the difference,” Colin Lloyd stressed. “What’s more, its effects can be very long-lasting. For instance, ploughing instead of min-tilling in 2010 with identical establishment practice in the following four years led the black-grass population in our 2014/15 wheat crop to almost halve from 501 heads/m2 to 266/m2.
“Having said that, it’s important to appreciate that ploughing does most good where the weed seed has been concentrated near the surface by several years of shallow tillage. It has to give full inversion too, so the bulk of the seed is buried below the germination zone. And following it with another ploughing can undo all the good by bringing viable seed back to the surface.”
Regardless of cultivation regime, some of the most consistently marked differences in both black-grass control and crop performance at Stow Longa have come from delaying drilling by around a month – from late September to late October.
Drilling after the second week of October has delivered a yield advantage of more than 25% in every one of the four years of wheat in the rotation with an average annual increase of 41% for an extra income of over £360/ha/year.
This has come from levels of black-grass control of around 90% against little more than 60% for earlier drilling as later drilling invariably enables far more weed seed to germinate and be glyphosated-off ahead of sowing.
“Interestingly too, we’ve found later drilling can almost always do much to overcome problems created by inappropriate cultivation,” pointed out Colin Lloyd. “It has particular value where previous cultivation to different depths has left black-grass seed well distributed throughout the soil profile, making any rotational ploughing a less effective solution.
“Deliberately delaying drilling on heavy land certainly takes planning and skill. But providing you have sufficient flexibility and capacity to employ the most appropriate varieties and equipment for the season we’ve found its value significantly outweighs its risk. All the more so, if you build in the option of delaying your drilling until the spring should conditions get in the way of late autumn sowing.”
Parallel Stow Longa trials comparing spring with autumn drilling have been very encouraging in this respect. Solstice sown in late-September 2013 averaged just 4.8 t/ha with a black-grass population of 212 ears/m2 to deliver a margin over input costs of £389/ha. While drilling into decent conditions at the beginning of November gave 7.76 t/ha with 18 ears/m2 and a margin of £903/ha, Mulika drilled in the first week of the following April averaged 6.5 t/ha with no black-grass ears for a margin of £729/ha; a valuable option, indeed, in a season less favourable for later autumn drilling.
“The 95%-plus control levels needed to stop black-grass increasing in the rotation can still be achieved from the can in some places,” Colin Lloyd observed. “However, reliable control increasingly demands complex pre-em stacking, depends on sufficiently good seedbed and weather conditions for residual activity, and can cost the best part of £200/ha.
“So, it’s fantastic to see how valuable the right establishment strategies can be in helping to keep on top of seriously yield-limiting and costly black-grass problems. Alongside this, our research underlines there are no simple ‘beyond-the-can’ solutions here, though.
“As we’ve seen in more than 15 years of work at Stow Longa, success depends on stacking the most appropriate cultural and chemical controls for the particular farm circumstances and seasonal conditions. We are continuing to explore additional opportunities for doing this in our cover cropping research, in particular, and look forward to being able to provide increasingly effective practical solutions for growers in the years ahead.”