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w i n e G R O WIN G plow horizon. Much of this additional growth was in the form of fine roots. This supports the importance of maintaining these treatments for long time periods. It is likely that roots proliferate into this horizon in spring prior to tillage or may grow between the first tillage event (April) and second event (May). Thus root biomass changes were increasing carbon sequestration for the minimum tillage treatment. Carbon sequestered into soil organic carbon pool A long-term increase of carbon in soils occurred under the minimum-tillage treatment. Between 1991 and 2003, soil carbon content (% by weight) remained constant without a significant change in the Ap horizon (0 to 15 cm). After seven years (2003 – 10) of imposed minimum tillage, soil carbon in the plow horizon of the minimum-tilled rows had significantly increased by an average of 8.4%. Taking into account a soil bulk density at approximately 1.32 grams cm-3, and the drip zones where no change is expected, this translates into an overall sequestration of 2,640 kg carbon per hectare; annually, 377 kg C or 1,383 kg CO2 were removed from the atmosphere. The tilled-only once per year treatment, Figure 2: Grape root biomass distributions (kg per m3) measured at five 30 cm depths in the three tillage treatments. Fine-root biomass (less than 2 mm) increased in the top plow (Ap) horizon under minimum tillage. which was a control, also showed increased soil carbon, so treatment differences had to be adjusted. A slight decline in soil carbon was reported for the treatment tilled twice per year, although it was not statistically significant. Grape production and ripening Yield generally declined following initiation of the trial (2004 – 06). In 2009 and 2010, yields were also low, from 1.8 tons to 3.3 tons per acre. Production from minimum-tilled plots was consistently lowest among the three management practices. In all treatments, canopy size (leaf production) declined, which was reflected in pruning weights of one-year-old canes, and was significantly lower under minimum tillage over the course of the study. There were no significant differences in individual berry weight, pH, or °Brix for the 2009 and 2010 vintages among the three tillage treatments. The decreased yield and growth in the minimum tillage treatment seemed to be primarily due to long-term water stress.7 Most water consumed by these vines in summer is derived from deeper soil reservoirs and late spring rains. In the summer of 2009, after a winter of low rainfall, significantly greater water stress occurred in the minimum-tilled vines, and it occurred early in the summer (Figure 4). In contrast, in the subsequent year, after a winter of heavy rainfall, there were no significant differences.7 Production and consumption of greenhouse gases Carbon dioxide from soil respiration We monitored the flux of CO2 from the soil, commonly referred to as soil respiration (Figure 5). The majority of this flux pr actica l win ery & vin eya r d N OVEM B ER 20 13 87