what is gully cropping
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As farmers, nutrient management planners and soil conservationists, many of us deal with the estimated loss of soil from fields. We often use a very important tool called the Revised Universal Soil Loss Equation (commonly referred to as RUSLE2). If you have a nutrient management plan, you know about RUSLE2. This tool, however, only estimates soil loss in the form of sheet and/or rill erosion. This is the gradual and sometimes unnoticeable erosion that sheets off fields or that forms small, uniformly spaced and sized channels (less than 4 inches deep). With proper crop rotations, reduced tillage, good cover cropping, good organic matter and even proper manure applications, we can manage for this erosion fairly simply and inexpensively.
Gullies, on the other hand, are the “unaccounted for” erosion that can have a major impact on soil loss, soil health, water quality, and crop yields. Gullies are water formations with increased intensity to sheet and rill erosion, and can also exacerbate sheet/rill erosion. While we have all seen photos of giant gullies big enough to consume a tractor, those tend to be rare. However, the gullies in Vermont farm fields are no less impactful on our landscape. According to an older, but interesting analysis from USDA-NRCS in 1997, they estimated that (19 years ago), roughly 6.1 tons/acre of soil loss per year was attributed to gully erosion, making up roughly 58% of the total sediment lost through water erosion annually (the remaining 4.5 tons/acre/year was from sheet and rill erosion).
Types of Gullies
Ephemeral gullies recur in the same area each time they form, can be partially or totally erased or filled in with tillage, and frequently form in well-defined depressions or natural drainage in a field. As described by the USDA –NRCS (1997), “most ephemeral gullies occur on fields with highly erodible soils, little or no crop residue cover or where crop harvest disturbs the soil.” They are associated with water flow in areas where runoff is great, including snow-melt runoff like that experienced in the Northeast.
Ephemeral gully erosion on a moderately sloped Vergennes clay corn field in southern Chittenden County. The example pictured here equates to an estimated 9.9 tons of soil loss per year.+
True or ‘classic’ gullies are “channels too deep for normal tillage operations to erase.” (NRCS, 2015). They may get bigger in subsequent years, but can also stabilize and become more permanent drainage channels. They tend to start as ephemeral gullies that were left untreated. They can also start as a result of tillage, for example adjacent to a dead furrow. Or they may start at the edges of established grassed waterways or buffers that were inadequately sized or not maintained.
Classic gully erosion on a field on a Covington and Vergennes clay soil corn field. This gully has since been fixed with assistance from NRCS. This gully started upland as an ephemeral gully but progressed into a classic gully. Cover crop and no-till weren’t enough to stop the gully erosion once it began. In two years, it was responsible for an estimated 234 tons of soil loss (or roughly 117 tons per year). +
In this pictured example, a gully started upland as an ephemeral gully, but when it reached a dead furrow, this larger scale channel formed. You can see how quickly a gully like this can be an even more significant contributor of soil loss than typical sheet and rill erosion. Depending on how the field is managed a gully like this can account for two to four times the sheet and rill erosion from an entire 25-acre field. It’s hard to tell, but in the picture you can see the field had been cover cropped and no-till planted to corn, but it was too late to prevent the ultimate result. This gully has subsequently been repaired and now has a diversion at the upland slope to prevent its reoccurrence.
Management Implications
This type of significant erosion has many costs associated with it: water quality degradation, decreased yields, and the sometimes significant costs to repair (potentially tens of thousands of dollars). The cost of fixing and maintaining an area where a classic gully has formed can be drastically more expensive and time intensive than preventing them from forming. Once a gully begins forming, additional measures will need to be implemented. Continuing to till and level out an ephemeral gully every year only introduces more soil into the drainage area
Gullies, on the other hand, are the “unaccounted for” erosion that can have a major impact on soil loss, soil health, water quality, and crop yields. Gullies are water formations with increased intensity to sheet and rill erosion, and can also exacerbate sheet/rill erosion. While we have all seen photos of giant gullies big enough to consume a tractor, those tend to be rare. However, the gullies in Vermont farm fields are no less impactful on our landscape. According to an older, but interesting analysis from USDA-NRCS in 1997, they estimated that (19 years ago), roughly 6.1 tons/acre of soil loss per year was attributed to gully erosion, making up roughly 58% of the total sediment lost through water erosion annually (the remaining 4.5 tons/acre/year was from sheet and rill erosion).
Types of Gullies
Ephemeral gullies recur in the same area each time they form, can be partially or totally erased or filled in with tillage, and frequently form in well-defined depressions or natural drainage in a field. As described by the USDA –NRCS (1997), “most ephemeral gullies occur on fields with highly erodible soils, little or no crop residue cover or where crop harvest disturbs the soil.” They are associated with water flow in areas where runoff is great, including snow-melt runoff like that experienced in the Northeast.
Ephemeral gully erosion on a moderately sloped Vergennes clay corn field in southern Chittenden County. The example pictured here equates to an estimated 9.9 tons of soil loss per year.+
True or ‘classic’ gullies are “channels too deep for normal tillage operations to erase.” (NRCS, 2015). They may get bigger in subsequent years, but can also stabilize and become more permanent drainage channels. They tend to start as ephemeral gullies that were left untreated. They can also start as a result of tillage, for example adjacent to a dead furrow. Or they may start at the edges of established grassed waterways or buffers that were inadequately sized or not maintained.
Classic gully erosion on a field on a Covington and Vergennes clay soil corn field. This gully has since been fixed with assistance from NRCS. This gully started upland as an ephemeral gully but progressed into a classic gully. Cover crop and no-till weren’t enough to stop the gully erosion once it began. In two years, it was responsible for an estimated 234 tons of soil loss (or roughly 117 tons per year). +
In this pictured example, a gully started upland as an ephemeral gully, but when it reached a dead furrow, this larger scale channel formed. You can see how quickly a gully like this can be an even more significant contributor of soil loss than typical sheet and rill erosion. Depending on how the field is managed a gully like this can account for two to four times the sheet and rill erosion from an entire 25-acre field. It’s hard to tell, but in the picture you can see the field had been cover cropped and no-till planted to corn, but it was too late to prevent the ultimate result. This gully has subsequently been repaired and now has a diversion at the upland slope to prevent its reoccurrence.
Management Implications
This type of significant erosion has many costs associated with it: water quality degradation, decreased yields, and the sometimes significant costs to repair (potentially tens of thousands of dollars). The cost of fixing and maintaining an area where a classic gully has formed can be drastically more expensive and time intensive than preventing them from forming. Once a gully begins forming, additional measures will need to be implemented. Continuing to till and level out an ephemeral gully every year only introduces more soil into the drainage area
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