18 August 1995

Erosion fears mean US aims to mulch soils

By Peter Hill

NEW tillage implements and drills are being used by US arable growers to meet stiff targets for crop residue incorporation. But unlike their UK counterparts who will be doing their utmost to bury or fully incorporate straw and stubble from this years harvest, farmers are having to keep plenty of material on the surface.

Fears of continuing soil erosion in many of the countrys main arable areas have prompted a US government-backed soil conservation programme which, this year, threatens farm support payment penalties for farmers who fail to achieve at least 30% soil surface coverage by crop residues.

The target is an average across the farm – not for individual fields – so ploughing can still be used for crops needing a clean, well-tilled seedbed, providing minimal incorporation in other fields compensates.

Mulch or minimum tillage, involving less soil working than conventional techniques, has become more widely used as a result of the programme. Surveys suggest it accounts for 60% of all conservation cultivation, with direct drilling now the fastest growing technique.

Equipment manufacturers have been quick to develop new combination tillage implements, as well as drills able to cope with firm soils and lots of surface trash. Case, which sells a range of field implements as well as tractors and combines, is looking at whether its drills and cultivators could sell in the UK.

A backbone chassis forming the frame of the Case 6800 Combo Mulch Ripper carries tandem discs at the front and deep soil ripping and heavy spring tines at the back. Disc penetration is helped by vertical hydraulic rams, while a choice of leg profiles and point shapes determines the sort of finish left behind the implement. A drawback for potential UK users is that none of the four sizes – from 3.5m to 5.8m – fold for transport.

The companys "Early Riser" drill has discs in pairs on a common hub but positioned so the leading edges are staggered. The design is claimed to form a clean V-shaped slot whereas non-staggered discs tend to form a W-shaped slot. That can lead to variation in seeding depth, Case claims, with some seed lying in the bottom sections of the slot, some sitting on the central peak.

Heavy coulter springs help the discs penetrate trashy, minimum cultivated surfaces, and tines can be carried on a drawbar-mounted toolbar.

The main task for growers is to work out how best to control residue incorporation by using different implements, changing the way existing implements are used, and by using fewer cultivation passes.

Reducing the forward speed, working depth and gang angle of disc cultivators, for example, can increase residue surface coverage from barely 20% to nearer 70%, according to US studies. Shallower working depths and narrower shanks can produce similar results with tine cultivators.