Although great labor savers, rotary tillers are not ideal. One objection to the type with sharp tines is that it produces too fine a soil particle. Excessive tilling with this type of equipment breaks down the structure of the soil and brings on heavy crusting. Many home gardeners are disappointed when they find that the loose, fluffy loam of spring has turned to a crusted solid mass by midsummer, into which water penetrates with difficulty. Another result of too-fine a particle is that more organic matter is needed to improve tilth following the use of a tiller. Apparently many of the organic particles get coated with clay so thoroughly they cannot act as soil conditioners. Most modern machines now have a cutting-knife tine, set at an angle, which does not churn the soil to a fine dust.
Another drawback of rotary tillers is their tendency to build up a tillage pan-a hard, water-tight layer just below the loosened soil. I have taken a spade and removed the loose layer of soil right after tilling and found beneath it a layer of packed soil almost too firm to show a heel print.
The tendency to crust and pack can be overcome by supplying the soil with extra organic matter or by using a mechanical soil conditioner such as leached steam cinders, vermiculite or Perlite. Sand is not a good material to use: its aggregate-in-concrete effect is accentuated when in contact with fine clay particles. I estimate that between 33 and SO per cent more organic material is needed in a soil when a rotary tiller is used than when the same soil is plowed or hand-dug. Of course, when this extra material is supplied, the result is a rich, deep, mellow loam in perfect tilth.
The problem of a tillage pan is not quite as easy to solve. The ideal answer is to trench the entire area before a tiller is used, after which a pan may not build up for many years. The compacting effect can be delayed somewhat by changing the depth to which the tines penetrate each time the soil is worked. In farm practice, chisel plows are used to drive a sharp narrow point through the tillage pan and
shatter it. To my knowledge, there is no available home garden version of the chisel plow. Some smart manufacturer of rotary tillers would do the gardening fraternity a favor if he would develop such a device that could be interchanged with the tines for use at least once a year. It would bring rotary tillage close to perfection.