Building a healthy soil that can resist challenges

Tuesday, June 5, 2012

The health of your soil can affect the way it responds to too much water, dryness or heat

by KEITH REID

It's often said that weather is the biggest factor in setting the yield for a crop. This is true as far as it goes, but it ignores how much the health of the soil can affect the way the crop responds to the weather.

Crops growing on abused soil can grow well when conditions are ideal, but they start to suffer at the first sign of too much water, dryness or heat. Healthy soil, on the other hand, produces crops that continue to grow well despite these challenges, and will generate good yields in all but the worst weather. Incidentally, this will mean more bushels in the bin every year, but especially in the years when prices are high.

What can we do, then, to build a healthy soil?

Rooting around. Plant roots are the absolute best tool for improving soil health, particularly the roots of perennial forage crops. Large, deep tap roots break up compaction, and open up channels that allow air and water to penetrate the soil, as well as pathways for crop roots to follow.

Fine, fibrous roots form a lattice that binds the soil into aggregates that hang together in wet or dry conditions. These roots also leak sugars and amino acids into the soil to feed an abundance of micro-organisms next to the roots, which cycle nutrients and help glue the soil structure together. These processes take time, so the soil in an old pasture will have better tilth than that from a young hay field, which will be better than a field that has been in continuous annual crops.

Tillage can create a structure similar to that of a pasture, with luck and skill, but it will quickly break down with the first rainfall. The plow, the disk and the cultivator can break down aggregates, but they cannot build them up.

Retiring land from production for several years is probably not an option for most, but you can get some of the benefits by rotating between different crops. Crop roots will follow root channels from a different crop, but will avoid the old root channels from the same species and try to push through the tight soil between instead.

Adding wheat or another cereal into the rotation provides at least one year of fibrous roots to the soil to help stabilize soil structure. Adding a forage crop multiplies the benefit, so that a following corn crop can be virtually "drought-proof."  

Cover crops can also fill this role, although they are not around as long, so the impact is not as profound as from multi-year forage stands. Be sure to choose a cover crop that fits in with your crop rotation for maximum benefits.

With organic matter, more is better. Organic matter plays many roles in a healthy soil – a water-stable glue to hold soil aggregates together, a sponge to hold soil moisture, a reservoir for nutrients and a food source for the many soil organisms that drive nutrient cycles. Regular additions of fresh organic materials, like manure or crop residues, will keep these functions running optimally, but only if the losses of existing soil organic matter through erosion or excess tillage are minimized.

When in doubt, keep out! Even with a good rotation and ample organic matter, driving over the soil when it is too wet, or tilling the soil too often or too intensively, can compact the soil and destroy the network of medium to large pores that are so important to good soil health. Stay off the field if the ground is wet and keep tillage passes to a minimum to protect the soil structure you have worked so hard to create.

Is the chemistry right? In a way, making sure that you don't have severe nutrient deficiencies or soil acidity should be first on the list because it is easiest to fix, but I have chosen to put it last because it is so seldom a major issue on farms in Ontario. A soil test will tell you if the soil pH is too low, in which case an investment in lime will be necessary. Otherwise, the growth of the plants that can build a healthy soil will be reduced.

The same soil test will tell you where fertilizer or manure is needed to correct shortages of major nutrients. Plants that are not growing well because they are starved for nutrients will not generate the organic matter to help build a better soil. BF

Keith Reid is Manager (Eastern Canada). Soil Nutrient and GHG Management, Agriculture and Agri-Food Canada, Guelph