By Sjoerd Duiker, Soil Scientist
Record precipitation in South Carolina earlier this month is another reminder of the importance to protect our soils year-round. According to the Weather Channel, 5-day precipitation ranging from 17-23 inches shattered all records in this southern state. The NOAA weather site in North Charleston recorded 11.5 inches on Oct. 10, more than what was ever measured in one day at this site in its 77-year history. Reports from personal weather stations exceed these amounts.
To put things in perspective, average annual rainfall in most of South Carolina is between 55 and 60 inches. In Pennsylvania, we receive, on average, between 40 and 50 inches in a year (total of snow and rain).
The South Carolina records remind us that averages are of limited value when thinking about the weather. They also suggest that we need to prepare for more volatile precipitation in the eastern U.S., as predicted by many climatologists. These large precipitation events will cause most erosion and should be the focus of our attention instead of annual averages.
In one long-term study in eastern Ohio, 66% of erosion was caused by four precipitation events out of a total of 4,000 events over a 28-year period. These measurements were made in several watersheds. In one watershed, one rainstorm caused half of the erosion in this 28-year period. The events in South Carolina showed that record rainfall events can occur at practically any time of the year.
Normally, the rain is most “erosive” — most aggressive — in the July/August period, but here we are in October and that is when it happened. Think about your crop rotation and when your fields are unprotected and try to find ways to minimize those times.
One has to be ready for “the big one.” How can this be done? No one practice alone will suffice, but keeping soil covered with living vegetation and dead organic mulch, also called “soil armor” is among the more important ones, combined with zero soil disturbance.
At least 30% soil cover at all times is considered essential, but more is desirable. The cover can be living or dead, or ideally a combination of the two. The benefits of soil consolidation achieved with continuous no-tillage cannot be overlooked either, nor the value of having living roots in the soil to anchor it in place.
Having high soil armor can be achieved by using no-tillage, growing high-residue crops in the rotation, leaving the residue in the field, growing cover crops during fallow periods and spreading packed manure. Using diversity in your crop rotation is also very effective because it means not all your fields are exposed at the same time — for example, after you harvest corn silage.
High intensity, large rainfall events are likely to frequent Pennsylvania, just like they did South Carolina earlier this month. Hopefully we will not be hammered by catastrophic storms like them, but it is a reminder that we need keep our soils armored at all times of the year.