Thoughts About Tillage

Press, Volume CVI, Issue 31365, 10 May 1967, Page 33

Thoughts About Tillage

Tilling the soil has been an essential part of agriculture ever since primitive man first fashioned a crude grubber from a bent stick.

Until the early part of this century (and up to the present time in some of the more backward parts of the world), the development of tillage Implements has been bv a process of trial and error. This process has been influenced mainly by the soil conditions and farming practices in the locality where the implement was made, and by the characteristicxof the motive power available —men or draught animals! But the resultant infinite variety of, for example, ploughs and plough components (particularly shares and mouldboards) is quite incompatible with pre-sent-day practices of mass production and world-wide marketing of tillage equipment And since the early 19205, the widespread acceptance and relatively rapid development of tractors has meant that much more power and speed has become available for operating tillage implements. It has therefore become imperative to take a critical look at just how well (or how badly!) the “traditional” implements are suited to present-day tillage requirements. For some years now many individuals and organisations in several countries (among them the Tillage Research Committee of the World Ploughing Organisation) have been investigating the properties of soils, the performance and development of implements, the characteristics of the tilth resulting from their use, and the tilth requirements for healthy germination and development of seeds and plants. The plough has for so long been regarded as the most important single tillage implement in the agriculture of temperate regions that it might be regarded as heresy to suggest that it could ever lose this position! And yet, let’s face it, the combination of mouldboard plough and pneumatic-tyred farm tractor is an inefficient one for applying the power of a tractor engine to the task of starting to prepare a seedbed. Why is this? For a plough to do its job, it has to be pulled through the soil. The bigger the plough and the heavier the soil, the greater is the force required to pull the plough. And ail the pull which is needed has to be obtained from the tractor wheels (or tracks) gripping the soil. The greater the pull which is needed, the greater the weight which must be carried by the tractor wheels to get enough grip without too much slip. So, as tractors get more powerful and ploughs get bigger, the soil is subjected to greater compaction which, on heavier soils, can mean a slowingdown of soil moisture movement and some restriction of root growth. What can be done to get the best out of a newer and more powerful tractor without unduly increasing soil compaction? Rather than using it to pull a bigger plough at about the same speed as before, it could possibly be used to pull the same size of plough at a significantly higher speed. Admittedly, many ploughs in many soils would leave a rough finish If they were operated at more than four to five miles an hour, especi-

ally what ploughing old turf. This Is not altogether surprising as the plough’s shape wag' derived by trial and error over very many years to suit the slow speed of draught animals. Plough mouldboard shapes -which are better suited to the high speed of modern tractors are now being introduced by several manufacturers, and they will no doubt be further improved through studies now being made with the aid of high-speed modern computers! As might be expected,

this striving for higher speeds also has its drawbacks. For one thing, the faster a plough is travelling, the greater the damage it is likely to sustain if it is brought to a sudden halt by some buried obstruction. Consequently, several modern ploughs incorporate stump-jump release mountings between individual bodies and the main frame: so-called “bar-point” shares could also reduce the incidence of share breakage in very stony conditions. But the demand for greater speed is not by any means restricted to the ploughing operation—higher speeds are often required in subsequent field operations, and such speeds can be attained with less risk and greater comfort if the paddock surfaces are reasonably smooth. Reversible ploughs and land levellers can be very helpful in minimising surface roughness.

The force which is needed to pull a plough in heavy soils can be considerably reduced—by as much as 20 to 30 per cent according to some trials—by surfacing the mouldboard with one of the polyethylene family of plastics (similar to the coating on the housewife’s nonstick saucepan or frying pan). These also allow mouldboards to “scour” better in sticky soils, but are quickly damaged in stony land. But even though better shapes permit higher speeds and better materials demand lower pulls, ploughing still depends on traction and traction depends on tractor weight And from the soil’s point of view, this latter may often be excessive. Is It not possible, then, to apply the power of the tractor engine more directly to the job of tilling the soil? Of course it is, as anyone; who has used a rotary cultivator knows. Some trials in the United States showed that one pass with a rotary cultivator (at a fairly j “coarse” setting) produced; a tilth equivalent to that■ obtained by ploughing, tandem discing twice and harrowing once. While it has proved very satisfactory for some classes of work, the rotary cultivator as we know it today is not the answer to all major tillage problems. Some makers of this type of equipment have already introduced modified designs aimed at producing a rather coarser tilth: as a “bonus,” these modified designs require less power to drive them. Numerous other devices for applying mechanical power direct to tillage have been proposed or tried. Drawings in books and journals published in the latter half of last century

show many weird and wonderful mechanical diggers based on steam engines. In more recent times, various arrangements of horizontal screws, vertical “stirrers” and reciprocating tines or blades have been tried but none has gained widespread acceptance. It has been shown that if a certain amount of vibration is applied to the tip of a grubber tine, the force required to pull it through the soil can be significantly reduced, although the total power required to operate it (including power through the power take-off for vibration) remains about the same. Whether this vibration principle can be applied successfully to the plough is at present not known. Every cultivation operation costs money, so it is obviously very desirable to cut the number of operations to a minimum, and to ensure that the energy put Into those which are retained is used to the best advantage. Is it really necessary to cultivate an entire paddock just to provide a seedbed and favourable growing environment for a crop which is to grow in dis-

tinct rows with a substantial distance between them? Where row spacings are of the order of two to three feet—as with maize in the U.S.A.—so-called strip tillage has already been tried; overdrilling of pastures is no longer a novelty in New Zealand, and several experiments are under way to assess the acceptability of sowing cereal crops direct into uncultivated ground.

Will any of these “new”—in some cases it would be more correct to say “rediscovered”—ideas ever replace the plough or radically alter its design? Only time can tell and It will probably be many years before plough manufacturers need fear any substantial falling-off in the sales of their product Likewise will ploughmen continue for a long time to guide that time-honoured implement with the skill which is so strikingly demonstrated at local and national level, as well as at world ploughing contests.

The writer of the accompanying article it G. G. LINDSAY, senior lecturer in agricultural engineering at Lincoln College.