Central Coast Vineyard Team.
Napa County vineyards are under extreme pressure to address view-shed concerns, water quantity and quality issues and soil erosion. Napa County's Hillside Farming Ordinance restricts new vineyards to slopes of less than 30% and limits annual soil loss to 5 tons/acre/year. This ordinance also specifies straw as the mulching material to be used for erosion control. Several limitations of straw include its cost and need for reapplication each year. (Straw washes into drains and waterways if nor crimped in properly.) Finally, straw has very little effect on soil organic matter levels. Green landscaping mulch could provide an alternative to straw mulch, with added benefits of improving organic matter levels.
Through a grant from the California Integrated Waste Management Board, Paul Skinner, from a local waste management company and UC Davis soil scientist Vic Claasen, studied a potentially beneficial use for green waste. The waste material being evaluated as mulch in this study is chipped yard trimmings that have not been composted but have been passed through a screen. It is relatively free of plastic and glass. Organic waste materials have been applied to German and French vineyards for decades, and many of these vineyards are farmed straight down 30% sloping hillsides, with low levels of pollutants entering the waterways. Napa County soils vary widely, but many of them, like German and French soils, are more stable if farmed downhill.
Treatments that Skinner utilized were surface applied mulch to cover and noncover cropped rows in 1 and 3 inch-thick layers. Controls were straw-mulched only. Plastic aprons were placed below the treated rows, and 55-gallon barrels were positioned sub-grade below the aprons to catch initial storm runoff. Soil moisture monitoring was also conducted.
One of the sites treated had a 16% slope. The 1 and 3-inch layers of mulch applied over the tilled soil reduced soil erosion by 5% and 10%. Three inches of mulch over a grass cover crop reduced soil loss by 70% in comparison to the straw mulch control. Another site had 28% slopes and the 1 and 3-inch mulches reduced soil loss by 28% and 70%.
Mulch contributed very low levels of salts to runoff, and in the case of nitrate, less was contributed than from the straw control. There were some sediment surges coming from the mulched plots, but U.S. Geological Survey water quality parameters, considered typical for freshwater streams, were not exceeded. In a newly planted vineyard, and at the end of the first rainy season, soil loss in the treated area was reduced by 60% and 80% in the 1 and 3-inch mulches, compared to the control.
Mature vines, in the composted mulch plots, had increased nitrogen and potassium in leaf samples during mid-season of the first year. Mature vines also had increased pruning weights and cluster weights at the end of the first growing season. Mature and young vines had increased shoot lengths in the 3-inch mulch treatment at the beginning of the second growing season. The best overall treatment proved to be the 5-inch mulch combined with the cover crop. Some nutrients are supplied by the mulch, soil moisture conditions are improved and less soil leaves the site under this combined treatment.
Mulch applications are definitely beneficial. Costs of mulch are low, often a few dollars per ton. Hauling and application are expensive, but specialized trucks and application equipment are available.
(For more information, contact the Central Coast Vineyard Team at P.O. Box 840, Templeton, Calif. 93465, phone (805) 434-4848 or fax (805) 434-4854.)
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|Title Annotation:||mulch study|
|Publication:||Wines & Vines|
|Article Type:||Brief Article|
|Date:||Jun 1, 2002|
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