Mechanical and Manual Weed Control, sensitive and timely cultivations

0/1* Unlikely to apply to hill farms and upland farms. Likely to be common in associated lowland. Recommended – likely to occur for reasons outlined

*See Table 2 page 8

In terms of impact on biodiversity and particularly floral diversity, the inappropriate use of farm machinery can be detrimental not only for its effects on soil quality but also for its impact in areas such as peat-rich upland hills. The effects of the use of heavy machinery can be compared with heavy and sustained poaching causing loss of soil structure and compaction.

In conventional farming, pesticides are used to control weeds, pests and diseases. The use of weed wipers and all herbicides is prohibited by organic standards so organic farmers are more reliant upon good husbandry. Well timed cultivations, good grazing management and regular topping or use of a weed puller in an integrated programme are the basis for control of grassland weeds such as docks, thistles and rushes.

Timely cultivations and the appropriate timing of weeding operations, is crucial, equally so for topping perennial grassland weeds as for preparation of a seed bed for arable crops. One well-timed weeding will be better than several operations at the wrong time.

In arable crops on associated lowland there are a number of mechanical methods to control weeds e.g. steerage hoes, brush weeders, thermal weeders, comb-harrows, and powered and non-powered rotary cultivators. For many arable crops, the early stages of development (4-6 weeks) are particularly important; the first weeding operation of the year may be necessary across a whole field to provide a weed-free environment for planting or sowing, although subsequent operations can be confined to inter-row weeding, intra-row or patch weeding.

6.6.1 Biodiversity Impacts: Flora

Any weed control method directly affects floral biodiversity as species are removed to increase nutrient availability and space for crop plants. Removal of noxious and toxic species is likely to be done by hand and is therefore less damaging overall to flora. The practice of removal and suppression of weed flora in arable crops is, by its nature, a negative influence on floral diversity. It is an indiscriminate process and problematic, aggressive weed species being removed along with more benign and possibly rare ones. Cultivation combined with controlled grazing as weed control rarely allows the lifecycle of a flowering plant to be completed, and here the importance is revealed of marginal habitats such as hedgerows, buffer strips and field headlands, as refugia for arable flora species. The practice of spring cropping on organic farms and more varied rotations using grass leys increases crop structure provide opportunities for less robust species to establish themselves (Shepherd et al., 2003).

6.6.2 Biodiversity Impacts: Fauna

Manual weed control, although more time consuming and in some circumstances physically demanding, is likely to be much less disruptive than chemical controls.

The key to good farmland biodiversity lies in providing a diverse mosaic of habitats and timely sowing and harvests (Soil Association, 2002). The well documented decline in some farmland bird species such as skylark (Alauda arvensis) and lapwing (Vanellus vanellus) has largely been attributed to the widespread change from spring to autumn-sown crops. The latter, particularly winter wheat, are often too tall to allow nest building and easy movement of chicks (Soil Association, 2002). In uplands, the timing of spring cropping and silage/hay making as prescribed by Tir Gofal would meet organic standards, but would be limited by the physical constraints of growing cereal crops. The timing of cutting for silage is particularly crucial for ground nesting birds and small mammals such as brown hare (Lepus europaeus) which nest and rear their young in pasture.

Heavy machinery can have a devastating impact on biodiversity if used at sensitive times of fauna lifecycles. Use of machinery during nesting periods for ground nesting birds and mammals should be carefully monitored to ensure that eggs and young are not disturbed or destroyed (Dodds, Appleby & Campbell, 1996). Use of mechanical weed control and aeration methods, especially chain harrowing, may be problematic for ground-nesting birds if carried out after April (Soil Association, 2002).

6.6.3 Soil Quality Impacts

Soil is a fragile limited resource, easily destroyed and in need of protection from farming practices, erosion and pollution (MAFF, 1998; MAFF, 1999). The relationship between ‘the living soil’ and plants, animals and human health is central to organic farming; and the sensitive use of machinery is a fundamental practice. All field operations on an organic farm, including spreading of manures and slurries should only be carried out only when conditions are favourable. Maintenance of good soil structure relies on the correct type of cultivation using appropriate equipment and when the soil has the correct moisture content. This in turn will support a more diverse agricultural soil ecology.

A number of studies have examined the effect of organic farming practices on soil. Using a ‘Soil protection index’ of erosion risk a higher index was found on organic and integrated farms in 80% of cases, with a higher index for organic than integrated farms (Hausheer, 1988). Overall the studies suggest that there is likely to be a net positive impact on soil conservation from organic farming (O'Riordan, 2001) (Stolze et al., 2000)

6.6.4 Air Quality Impacts

Any type of cultivation has the capacity to release N in gaseous and soluble form. Arable cropping which is rarely carried out in upland and hill farming but is more common in the associated lowlands, or ploughing for re-seeding of pasture which is a limited practice in hills and uplands, may cause heavy losses of N through oxidation if carried out during times of heavy or prolonged rainfall.

6.6.5 Water Quality Impacts

Cultivations may cause N leaching and siltation, if carried out during or before periods of heavy rainfall (see also 6.1.5).

6.6.6 Resource Use Impacts

6.6.7 Agri-environment Scheme Requirements

There are many agri-environment requirements in place to prevent poorly timed cultivation impacting on biodiversity.

6.6.8 Standards Changes

Seeding times of upland plants are likely to be later in the year than lowland species and the later nesting and breeding times for upland species should be taken into account when carrying out field operations.

6.6.9 Further Research

This is an area that is relatively un-researched from the bio-diversity standpoint. Research is required to investigate different cutting/harvesting dates with respect to habitats and species and the ongoing impact of this in a rotational and upland situation.

6.6.10 Education & Dissemination

Mechanised weed control is a potential cause of disturbance if timed wrongly and can be the cause of death of birds and mammals (Soil Association, 2002).

Careful shallow ploughing in fields with an established seedbank will ensure that plant diversity will be protected and allowed to flourish during rotations and spread seed to other locations. (Soil Association, 2002).

Cultivations should be timed to avoid likely periods of heavy rainfall to minimise N leaching and oxidation and soil erosion.