Composting has been shown to increase soil quality by increasing organic matter and altering concentrations of nitrogen and phosphorous, as well as changing bulk density, porosity, and water holding capacity. These changes could be beneficial for soil conservation, particularly in soils that are degraded or damaged and prone to erosion. Not only is composting beneficial for the soil, but the changes to the soil could also be very beneficial for those plants and animals/insects growing in it.
In terms of wine, it is been well documented that soil characteristics play a role in the quality of the wine produced from the grapes growing in that soil. Though the chemical composition of grapes is well known, very few studies have examined the effects of composting on this composition. Therefore, the goal of the short study presented today was to examine the long-term effects of composting on the yield and quality of Chardonnay grapes grown in a Tuscan vineyard.
The experimental vineyard was located in Cesa (Italy) inside the Centro Sperimentale per l’Agricoltura e l’Innovazione – ARISA Toscana. The climate is Mediterranean (dry subhumid) with an annual rainfall of 550mm. Autumn is prone to heavy rainfall events, which can cause problems with soil erosion and soil nutrient loss. The experimental vineyard belonged to the DOC region of Bianco Vergine di Valdichiana, with a slight slope of 2.5% and a NE exposure. Soil type was a loamy soil rich in alluvial sediments with limited water reserve.
The grapes used for this experiment were Chardonnay (Entav-Inra 95 clone) vines that were grafted on SO4 in 1996 and cordon trained with a density of 2700 plants/ha. Vineyard management practices included maintaining soil covered by grass between rows. In 2001, the vineyard was split into three experimental plots and treated with different fertilization types. Treatments were applied with the following:
- Treatment A: Control treatment with chemical fertilization (50kg N/hectare/year, 30kg P/hectare/year, 70kg K/hectare/year)
- Treatment B: Organic compost treatment with 15tons/hectare/year applied.
- Treatment C: Organic compost plus chemical fertilizer treatment with 15tons/hectare/year applied for the compost, and 25kg N/hectare/year, 15kg P/hectare/year, and 35kg K/hectare/year applied for the chemical fertilizers.
Compost was applied as mulch over inter-rows in the experimental plots. The organic compost was derived mainly from source separated organic urban waste that was selectively collected.
For all treatments, topsoil samples (0.3m depth) were collected twice (N = 5 per treatment), at the beginning and end of the experiment and before the application of compost/fertilizers. Composite soil samples were collected by combining two 60mm diameter soil auger cores that were taken in the middle of the inter-row. Soil physiochemical parameters were measured on all soil samples.
Leaf area was calculated for all treatment plots. Leaves were removed from half of a plant canopy (three plants per treatment) at veraison, and the following were measured three times throughout the season (May, July, and September): SPAD index, Net CO2 assimilation, and stomatal conductance.
Three grape clusters from each experimental sample vines were randomly collected and weighed. For the berries, the following were measured: soluble solids concentration (oBrix), titratable acidity, pH, malic acid, and tartaric acid.
- Long-term use of compost to the vineyard (alone or with fertilizers) significantly (and positively) affected soil parameters.
o There was a slight alkalinization of the soil.
o There was a significant increase in organic matter in the soil with compost treatment.
§ From 2001 to 2009, organic matter increased 3.5x with the compost treatment, and 2.5x with the compost plus chemical fertilizer treatment.
§ At the end of the entire experiment, soil treated with compost alone had an organic matter content 2.5x higher than the soil treated with the chemical fertilizers alone.
o There was the same trend for organic carbon content as organic matter (increase with compost treatment).
o There was a significant increase in total nitrogen content with the compost treatment alone.
§ Total nitrogen was 2x higher in compost only soil compared to chemical fertilizer only soil.
o Ammonium concentrations significantly increased in the compost treatment, while nitrate concentrations were significantly lower.
- Application of compost led to an increase in soil nitrogen, with a mineralizable and stable nitrogen pool and a decrease in soil nitrate levels compared to the chemical fertilizer treatments.
- Compost treatment did not significantly affect Chardonnay grapevine growth.
o Leaf area values were nearly the same for all treatments.
o There were no significant differences in leaf gas exchange parameters (i.e. net CO2 assimilation, stomatal conductance, and SPAD index).
§ Since CO2 assimilation and stomatal conductance are linked to photosynthesis, these results indicate that compost treatment did not affect photosynthetic performance of the grapevines.
§ There were significant decreases in CO2 assimilation and stomatal conductance at the end of the season, compared to earlier measurements (the same for all treatments), as well as a peak in SPAD index levels.
· This result is due to the senescence of leaves and does not affect quantity/quality of the grapes.
o Compost treatment did not have a significant influence on vine growth, nor were there differences between treatments in regards to plant physiological characteristics (CO2 assimilation, stomatal conductance, and SPAD index).
- Compost treatment gave varied results over time, depending upon the year/vintage.
o The number of clusters per plant and the average berry weight were not affected by compost treatment and were not significantly different than the chemical fertilizer control EXCEPT in 2002, 2005, and 2006.
o Cluster weight was significantly affected by compost treatment EXCEPT in 2003, 2004, and 2005 (no differences detected for those three years).
o Compost treatment led to a higher production in 2002, 2005, 2007, and 2008 compared to the control chemical fertilizer treatment and a lower production in 2001 and 2006 compared to the control.
o On average throughout the course of the entire experiment, there were minimal differences among treatments when considering grape production levels.
- The pH and oBrix of the grapes was not affected by compost treatment, except in 2006 when oBrix were higher in the compost treatment compared with the control.
Based on the results of this study, the benefits of organic composting are seen primarily in the soil itself, and not as much in the quality/quantity of the grapes produced from the vines planted therein. The long-term treatment of organic compost to a vineyard can be beneficial for soil characteristics such as organic matter and nitrate content. Though some years showed significant effects on grape quality, the average for the long-term treatment showed no differences in grape quality with compost-treated soils versus chemical fertilizer-treated soils.
One thing I would have liked to see is how the chemical composition of the grapes changed with organic compost treatment, and not simply berry weight. Perhaps production remains the same regardless of treatment type, but does the chemical profile of the grape remain the same or change? How would this affect the resulting wine?
Even though, according to this study, grape quality/quantity remained unchanged with the organic compost treatment, the sheer benefit to the soil itself is reason enough to justify potentially employing the treatment in routine viticultural management practices. Of course, more work would need to be done.
I’d love to hear what you all think about this study/topic. Feel free to leave your comments below (no html tags, please).
Source: Mugnai, S., Masi, E., Azzarello, E., and Mancuso, S. 2012. Influence of Long-Term Application of Green Waste Compost on Soil Characteristics and Growth, Yield and Quality of Grape (Vitis vinifera L.). Compost Science and Utilization 20(1): 29-33.
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