In most cases, the aim of cultivation is to prepare the seedbed and stimulate germination of black-grass which can be sprayed off before the crop is drilled. If this is the case the most important thing is to make sure that the cultivation pass is higher disturbance than drilling. If drilling is comparatively high disturbance, it is likely to kick more black-grass seed into life and make the job of pre-em and post-em herbicides much harder.
Deep cultivation is there to remove compaction. If soil structure is good down to depth then there is little need to cultivate deeper because all that is required is some tilth to sow into and a little disturbance to cause weed germination. Dig soil pits and use yield maps to identify any zones suffering from deep compaction and deal with these areas separately. Usually the areas most affected are headlands and hollows where water drains away last.
Targeted ploughing is a very valuable tool unless the farm is in a zero till system. Many farmers choose to use it as a ‘reset button’ when the weed burden is too high and bring clean soil to the surface and bury seed. Black-grass seeds must be within 5cm of the soil surface to germinate. Where seed return is high, ploughing will bury seeds to a depth in which they cannot grow, killing off around 80% of them year on year.
The principle is fine but ploughing must be done to a high standard to properly invert the soil otherwise some black-grass may remain near the surface and germinate. The other factor is making sure that the soil being brought up is clean of black-grass seed so check whether ploughing or deep non-inversion tillage has been used on the land in recent years. Fields that are ploughed too regularly will bring dormant buried black-grass seeds back to the soil surface, only worsening the problem so it is important to know the cultivation history of each field and stick to a strict regime. As a general rule, leave at least 4–5 years between ploughing any particular field.
When used as part of a wide rotation (4+ years), ploughing can see reductions in black-grass up 75-96% when used in a min-till system.
For subsequent pre-emergence herbicides to be effective, a good seedbed is important. Seedbeds should have a fine but firm tilth in order to get the most out of residual herbicides such as Liberator. A fine, even tilth will allow for a more even coverage of pre-ems, preventing pockets of untreated soil where black-grass can later emerge.
A seed bed that is dry with cloddy lumps can provide a haven for weeds seeds over winter where chemicals can’t reach them, putting a great deal of pressure on post-ems.
Most importantly a good seedbed will help the crop get up and away quickly so it can compete directly with weeds.
If delayed drilling cannot be achieved due to weather constraints or if soils are likely to be unfit to travel if postponed, rolling after drilling will encourage black-grass to germinate quickly when pre-ems are at their most effective. Cultivating the soil surface at a depth of no more than 5cm, the rake evenly distributes straw, shaking seed onto the floor and exposing it to daylight, resulting in germination. The roll ensures good soil-to-seed contact without impacting on the structure of the upper soil layer, so that even with heavy rain, the soil retains its drainage qualities.
Find out more about how crop rotations can improve soil health, limit herbicide resistance, help with time and cost management, and break the cycle of black-grass.
Read our top five tips to help eliminate black-grass using cultural controls