Soil Erosion & Vineyard Productivity Factors Influencing Erosion Rate Soil Conservation Practices Vineyard Floor Management for Soil Conservation Vineyard Establishment & Erosion Control More Information
Tim Martinson, Cornell University
Surface runoff and resulting soil erosion are the principal means by which fertilizers, sediment, and pesticide residues reach surface waters. Infiltration of ‘ponded’ runoff through permeable soils can move nitrogen and pesticide residues into ground water. Controlling water flow through and out of your vineyard will greatly reduce transport of contaminants off site, and will preserve your vineyard’s productivity. Three proven methods of reducing runoff and erosion are to
- divert excess water around your vineyard,
- slow runoff out of your vineyard, and
- provide ground covers that break the force of raindrops before they reach the soil.
Soil Erosion and Vineyard Productivity
Soil erosion involves movement of soil particles from one area to another. In arid areas, disturbed soil is often moved by wind. In areas with more rainfall, however, water movement is the prime force behind soil erosion. Soil engineers recognize two types of soil erosion:
- Gully erosion involves the mass movement of soil from an area of concentrated flow, often following heavy rainfall. Gullies expand rapidly and are highly visible.
- Sheet and rill erosion, as the name implies, involves more subtle loss of soil across an entire area. It is more constant, but harder to spot, since it involves movement of an imperceptibly small layer of soil.
Runoff and soil erosion impact surface water quality directly through deposition of sediments in waterways, streams, lakes and estuaries. It is also the principal means by which fertilizers and pesticides (particularly herbicides) applied to a vineyard move offsite, as they are often attached to soil particles. Soil erosion also limits the productivity of vineyards. For example, in almost any older vineyard in New York, one can find eroded knolls where subsoil layers are exposed, and swales or depressions with deep deposits of sediment. Much of this erosion can be traced to clean tillage and frequent disking practiced from the mid-1800s through the early 1980s. This soil movement complicates vineyard management and leads to more variability in vine size and performance. In flatter areas with permeable soils, runoff accumulates in low areas of vineyards, where it can slowly infiltrate into groundwater. For these reasons, soil conservation practices that control water movement both into and out of vineyards, and limit the force of rainfall hitting the soil, are the best means for maintaining sustainable production and avoiding off-site movement of pesticides and fertilizers.
Factors Influencing Rates of Erosion
Topography, soil characteristics, rainfall, and ground cover determine the annual rate of soil erosion. Soil conservation professionals use a tool called the Revised Universal Soil Loss Equation (RUSLE) to estimate annual rates of soil erosion on a particular site. This equation predicts an annual rate of soil loss (A) based on several factors that influence erosion. These factors are:
- Rainfall. The amount and intensity of rainfall in a given climate influence the amount of runoff and leaching.
- Soil type: Soils differ in their ‘erosivity’ or ‘erodibility’ based on composition, soil particle sizes, and reaction to freeze/thaw cycles.
- Slope length: The longer a slope, the more area it drains and the more water it carries.
- Slope steepness: Water runs faster and with more force down steeper slopes than down shallow slopes.
- Crop factor: The type and sequence of crops grown affect erosion. For example, continuous corn would be more prone to soil loss than corn planted in rotation with alfalfa and small grains. Perennial crops like grapes with less frequent tillage and soil disturbance would have a lower crop factor than annually seeded crops.
- Management factor: This factor is used to account for different management practices. For example, ‘no-till’ corn, where crop residues are left on the surface, would reduce erosion compared with corn grown with clean tillage. Similarly, a vineyard with row middles disked four times annually would be more prone to erosion than one with permanent cover or straw mulch in row middles.
Soil conservation professionals use RUSLE as a planning tool to determine how different management practices or structures would affect the annual soil loss. For example, installing diversions or terraces would reduce erosion by reducing the effective slope length. The general goal is to reduce the annual estimated soil erosion (A) to less than the annual replacement or soil formation rate, generally between 3 and 5 tons per acre per year. If that sounds like a lot, consider that an acre-foot of soil weighs about 2 million pounds, and that 5 T/acre/year would amount to a layer about 0.03 inches thick.
Soil Conservation Practices
Soil conservation practices prevent erosion and maintain clean water in three ways. First, diversion of water around vineyards keeps water clean, because it doesn’t wash over disturbed soil in the first place. Filtering of water through soil (drainage systems) and ground covers removes soil particles and other material suspended in water that passes through vineyards. Finally, ground covers provide a protective barrier that breaks the force of raindrops that could otherwise dislodge soil particles. Key soil conservation practices used in vineyards are:
Diversion Ditches. Diversion ditches are soil structures constructed at intervals across the slope. They collect water from slopes and divert it into natural drainage ways. They are seeded and gently graded, and slow the water down to reduce its erosive force. They can reduce the amount of water running through a vineyard by as much as 80%.
Water and Sediment Control Basins. Raising a berm across a gully with a subsurface outlet pipe that discharges at the base of the slope will collect runoff, and this will stop erosion by slowing down water and collecting the sediment.
Buffer Strips. All vineyards require headlands and grassed areas around their perimeters to allow machinery to turn around. These grassed areas also protect natural drainageways by filtering surface water that leaves vineyards before it gets to streams, drainageways and depressions. Generally, about 40 feet of headland around vineyards is adequate for a buffer strip.
Drainage Tile. Subsurface drainage tile, commonly used in vineyards with moderate to heavy-textured soils, also helps protect water quality in two ways. Drainage tile reduces surface runoff that would otherwise occur when soils become saturated with water. It also allows water to be filtered through the soil, which removes many contaminants that would be present in surface runoff.
Vineyard Layout. Planting vineyards so that the rows run across the slope rather than up and down the slope can reduce erosion by up to 50 per cent. In New York’s Finger Lakes Region, east and west-facing slopes predominate, so planting across the slope allows vineyard rows to be oriented north and south, which allows for maximum sunlight interception as well as soil conservation. In other areas, slope direction varies, and all other things being equal, vineyards should be planted across slopes (even if doing so results in east-west rows rather than north-south row orientation) to control erosion. Steep slopes (>15 to 20% slope) may need to be planted up and down hills to allow safe use of machinery, but such sites will be prone to more erosion as well.
Vineyard Floor Management for soil conservation
Changes in vineyard floor management practices have undoubtedly had the greatest positive effect on reducing soil erosion and improving water quality in New York vineyards. From the 1940s to the early 1980s, most growers practiced clean tillage between vineyard rows. This method of weed control, which involved up to four or five passes through a vineyard annually, left vineyards vulnerable to soil erosion during much of the growing season. Its use has left a lasting legacy of highly eroded land, some of which no longer supports profitable grape production.
Currently, many floor management options are available that reduce soil erosion while eliminating unwanted competition from weeds.
Permanent Sod. Current herbicides allow growers to maintain a 30-inch wide weed-free strip under the vines while leaving permanent sod in row middles. Recent research on highly vigorous wine grape vineyards (hybrids and V. vinifera) in the mid-Atlantic region suggests that under-the-row cover crops can also be useful in managing excess vigor.
Mulch. Straw mulch is commonly applied in row middles, especially in eroded sites with less vigorous vines. Although expensive to apply, it has many beneficial effects — it conserves soil moisture, increases availability of soil nutrients, provides a barrier to reduce the force of rain drops, and can directly increase yield by up to 20 per cent on some sites.
Seeded cover crops. No-till seeding of row middles is another practice used by some growers. Typically growers seed cereal rye in the fall, which germinates before winter. It then resumes growth in early spring, and is later mowed or killed with a contact herbicide. The decomposing straw left behind also has chemical substances that prevent new weeds from germinating and extends the ‘weed-free’ time. Reduction of tillage, while reducing soil erosion, also has the added benefit of allowing more timely operation of equipment after rainfall and reducing soil compaction from machinery.
Using cover crops and mulches to protect the soil surface has an enormous effect on annual rates of erosion. Mulches reduce the force of rainfall hitting the soil by 98 per cent, according to Jim Balyczek, Soil Conservation District Manager, Yates County, New York. Use of permanent cover crops in row middles on a 10 per cent slope with a 200 feet slope length reduced potential annual erosion from 5.1 T/acre under ‘clean tillage’ to 0.39 T/acre, in an example provided by Tibor Horvath, NYS Conservation Agronomist, USDA Natural Resources Conservation Service, New York.
The appropriate cover crop plants to seed will vary by region. Contact your local extension representative for recommendations on cover crop plants that may be suitable for your area or region.
Vineyard Establishment and Erosion Control
Vineyards may be especially vulnerable to soil erosion during establishment. Many non-bearing vineyards are maintained with clean tillage to help vines get off to a strong start without undue competition from weeds. Small vines don’t develop much of a canopy to intercept rainfall before it reaches bare soils. The best time to consider and install soil conservation structures is while you are planning and designing layout of the vineyard. So consider these steps when establishing a vineyard:
- Consult a soil conservation professional or engineer early in the planning stages. Discuss areas of concern, water flow patterns, and potential solutions to water management issues, and develop a plan with him or her to deal with specific situations.
- Consider the use of temporary measures such as straw bales or ‘silt fences’ in concentrated flow areas to interrupt water flow.
- Leave plenty of room for grassed filter strips around headlands and grassed waterways in concentrated flow areas.
- Design your vineyard with row breaks around swales, where possible. Low areas are often frost pockets. Maintaining them in sod will help filter runoff and reduce erosion.
- Seed a cover crop in row middles by late summer to protect against winter runoff and erosion.
Martinson, T. E. 2007. Conservation Practices for Vineyards. Sustainable Viticulture in the Northeast issue 2. Cornell University.
Pool, R. M., R. Dunst, and J. Kamas. 1988. Managing Weeds in New York Vineyards. V: Managing Vineyard Floors using no-tillage. Cornell University, NYS Agricultural Experiment Station, Geneva, NY.
Weigle, T. 1995. Grape IPM in the Northeast. Appendix 3: Weed Management. NYS IPM Publication 211.
Reviewed by Helen Fisher, University of Guelph
and Dave Lockwood, University of Tennessee