Two weather fronts, one from the East and one from the West, collided last Thursday May 15th, causing the atmosphere near the U.S. East coast to be squeezed like a sponge.
Concentrated flow can cause gully formation, even in no-tillage, calling for remedial practices such as grassed waterways
The system moved from South to North, dumping large amounts of precipitation on Pennsylvania, particularly in the center of the state. Reports came in of 3-7 inches of rain in parts of Union, Mifflin and Centre Counties, most of it falling on Thursday night into Friday during a 6 hour period.
The rain caused flash floods along rivers and streams, which often looked brown like chocolate from sediment lost from fields, construction sites, and stream banks. The rain was unusual, because normally we don’t get more than 3.5 inches in the entire month of May. The normal period of highly erosive rainfall is in July and August when crops protect the soil but this time the rain came just at the time of corn, soybean and hay crop establishment, when soil is most exposed.
You may have noticed that streams flowing through forests or grasslands typically flow clean, while those flowing through areas with bare soil are brown. This shows the need to keep soil covered throughout the year, and as much as possible with living vegetation. Crop residue or vegetative cover breaks the impact of raindrops on the soil, which cause soil aggregates to break down and fine soil to clog pore spaces. This process results in the formation of a seal which has dramatically reduced infiltration – and triggers the process of runoff. Residue or vegetative cover also helps reduce the velocity of runoff, giving the water more time to infiltrate in to the soil. The roots of living crops hold soil in place, protecting it from being moved by runoff.
While others may take their time to get serious about soil erosion, we in Pennsylvania do not have such a luxury – more than 60% of our cropland is highly erodible, and our soils are often shallow and contain many coarse fragments and rocks. When we lose topsoil we quickly notice it in reduced productivity. That is why practices such as no-tillage to maintain crop residue cover and cover crops to ensure living roots in the soil year-round are so important.
In some crop rotations it becomes difficult to establish vigorous cover crops after harvest and we see gully formation in areas of concentrated flow, even in no-tillage. While the disk may be used to smooth these gullies over we are still not addressing the root of the problem, which is the lack of something to hold that soil in place. If you see gully formation in no-tillage fields it may be necessary to establish a grassed waterway or dam runoff from upslope with a diversion. These practices still have their place, depending on your particular situation. This past week again shows us that we need to be constantly vigilant about soil erosion – otherwise that one event can just catch us unawares doing irreparable damage.
Source : psu.edu