By Eric Sideman, Ph.D.
The rototiller has gotten a bad rap in recent decades. Perhaps it deserves it, perhaps not; in any case it is important to avoid its misuse in order to preserve soil.
Temptation to use this power tool is worst in the early spring, when cabin fever or perhaps simply being anxious to get started on our beloved gardening has us rushing out to prepare the soil for planting. While the garden soil in April may look ready to work, usually it is too cool and wet for seeds to germinate. Most gardeners recognize this and hold off planting, but they cannot seem to hold back on the tiller – and with lots of time on hand, they till for hours, back and forth, back and forth, until the garden looks like a bed made under the guidance of a compulsive camp counselor rather than a well prepped seed bed.
Bud Wallace used to call this “recreational tillage.” Wallace was old when I met him – a retired University of Maine Extension agent who wanted to farm full time. He gave up the paycheck but never the chance to give advice on growing crops; and his favorite topic was soil.
When I was applying for my job at MOFGA many years ago, I went to Wallace’s farm to talk with him. Although not organic, he was very active in MOFGA. In fact, he was among the original MOFGAites. His love for gardening, not only for the crops but even more for soil husbandry, aligned with the bond between all those early MOFGA founders.
It was early spring at this time, and of course our conversation drifted away from what he thought I could do to get the MOFGA job and toward preparing the soil. We started talking about rototillers, and Wallace mentioned “recreational tillage,” and how so many folks cannot resist the temptation to “PULVERIZE THE SOIL.” He was shouting by then.
I address this topic now because I know when this edition of The MOF&G shows up, all of us will need all the help we can get to resist the temptation to spend hours and perhaps even weeks tilling. Pulverizing the soil is actually destroying the soil structure – and good soil structure is critical for good crop growth.
Soil structure refers to the arrangement of primary soil particles (sand, silt and/or clay) and organic matter into secondary aggregations. Each aggregation is a group of many hundreds of thousands of soil particles forming crumbs or clumps of various shapes and sizes. Sandy soils may have little or no aggregation, while loams (soils with a good balance of sand, silt and clay) and clays exhibit varying degrees due to natural processes.
Soil structure, i.e., soil particle aggregation, affects the ability of the soil to hold water, nutrients and, probably most importantly, to have space for air. A soil made of only small particles has only small pores and tends to become waterlogged. That is, all the spaces between the particles fill with water, leaving no room for air. In such a soil, plant roots suffocate, because few plant species can move oxygen from above- to below-ground parts.
On the other hand, a soil made of only large particles (e.g., sand) has only large pores and holds plenty of air, but because water drains so freely through this soil, soluble nutrients are easily leached (washed out). Cation exchange capacity (CEC – the ability of the soil to hold onto positively charged nutrients) also plays a role, but that is a topic for a different article. For now I just want to stress that a mixture of different pore sizes is best.
Several environmental factors promote aggregation, including freezing and thawing, wetting and drying, plant and animal activity, soil tillage and additions of organic matter. Adding organic matter itself does not improve soil structure; its subsequent decomposition does. During the decomposition process chemicals are released that act as glues cementing tiny soil particles together into aggregates. Fungi may initially enmesh soil particles, holding them together; and electrochemical properties (negative charges) of humus (decomposed organic matter) organize and stabilize soil aggregates. But aggregate stability seems to depend heavily on slime produced as microbes decompose fresh organic matter. In a heavy clay soil, improved structure will loosen soils, leading to better aeration and drainage, increased plant root penetration and more rapid solute (nutrient) diffusion. In sandy soils, improved structure will help bind soil particles together, reducing wind and water erosion and increasing nutrient and water-holding capacity.
Many agricultural practices degrade soil structure, so crop production subsequently declines. The most severe damage comes from working wet soils, which are easily compacted. Compaction destroys pores and breaks apart aggregates. Some compacted clay soils may be practically impervious to water. Even dry soil can be damaged by excess tilling.
The temptation to till in early spring is great, but use your pent up energy to resist that temptation. Remember, over-zealous tilling will pulverize your soil; in other words, it destroy valuable soil structure that you worked hard to create, through adding organic matter to your soil.
Eric is MOFGA’s organic crop specialist. You can reach him at 568-4142 or [email protected].