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Black-grass trial highlights value in shallow cultivations

New field trials are using rice grains to mimic black-grass seeds are said to have clearly demonstrated the implications of different cultivation techniques for integrated management of weed populations.



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At Syngenta’s black-grass focus site at Barton, near Cambridge, one key revelation has been the value of initial shallow stubble cultivations.

 

James Southgate, field technical manager responsible for the site, says: “There has been advice to leave black-grass seeds on the surface to germinate post-harvest, and only cultivate in dry conditions to bring up moisture. However, there has been ample surface moisture this season and yet a 5cm shallow Carrier cultivator pass produced a hugely advantageous weed seed chit.”

 

The trial showed the single pass system incorporated around half of the black-grass seed into the soil germination zone and left 50 per cent on the surface.

 

“That would indicate that, where time and conditions allow, a second shallow cultivation pass would almost certainly be beneficial to incorporate seed and trigger a second flush.

 

“It’s quick, relatively low cost and to remove such a significant proportion of black-grass seed return at the first step of an integrated crop management programme is a really positive start,” says Mr Southgate.

Plough pass

Plough pass

With the trial site’s field cultivations, the rice grain test demonstrated ploughing could effectively bury 98-99 per cent of black-grass seed deep enough to prevent germination.

 

“It also demonstrated the importance of setting up the plough correctly and the skills of the operator – particularly to ensure the skimmers are adjusted to turn the surface layer into the furrow bottom, before the furrow turns over to bury the seed,” Mr Southgate adds.

 

Using a one pass, min-till system to achieve a seedbed on the heavy ground site this season, the rice grains showed that black-grass seeds were being distributed extremely evenly throughout the 14cm of cultivated profile.

 

Mr Southgate says: “On easy soils, where you can achieve a fine level surface, black-grass may only be able to chit from 5cm or less – so two-thirds of seeds may be sufficiently buried with the min-till pass to prevent germination.

 

“But on a heavy soil with a cloddy surface, sufficient light may still be able to penetrate for black-grass to emerge from 8cm or more, which could result in up to 60 per cent of seeds establishing.”

 

Mr Southgate says this could mean close to 50 per cent more black-grass seedlings to tackle with subsequent control options.

Direct solutions

While direct drilling is said to allow for minimal black-grass seed movement, the rice trials showed that, even with an ultra-low disturbance drill, around 5 per cent of black-grass seed would drop down the slot with the cereal seed.

 

“Given the conditions the seed is being placed into, you could anticipate high levels of germination and emergence – with direct competition to the emerging crop. It’s certainly a very good result, but you would still be facing a large number of highly competitive plants needing further control,” says Mr Southgate.

Key findings

  • Post-harvest stubble cultivations are important to encourage black-grass to chit; there is perceived wisdom to leave seed on the surface, but even this year with ample soil moisture a 5cm shallow pass, or two, has been extremely beneficial

 

  • Min-till effectively mixes seed evenly through the cultivated zone, so, if soil conditions are good and a nice surface created, germination may only be from 5 cm or less (two-thirds of seed safely buried), but on heavy soils with deep fissures light will still penetrate to enable seed emergence from 8cm or more, equating to over 60 per cent of seed incorporated from the surface.

 

  • The indicator rice showed direct drilling can still result in 5 per cent of black-grass seed going down the slot with the seed, even on a minimal disturbance drill

 

  • Ploughing was extremely effective at burying indicator rice, but set-up of the skimmers to turn the surface under the furrow is crucial or significant amounts of seed will be left mixed in the soil at germination depth

Source: Syngenta

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