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w i n e G R O WIN G Figure 1: Minirhizotron images capture the maturation of grapevine roots over two weeks in July. average ANPP-C for the vineyard across all treatments was about 3.43 metric tons of carbon per hectare per year in 2009 (mT C ha-1 year-1). In 2010, a wetter year, an average ANPP of 3.55 mT C ha-1 year-1 was produced. These sums include carbon in the fruit. In 2009, the conventional tillage treatment with a barley cover crop assimilated 18% more carbon than the minimum-tilled cover crop, while the difference jumped to 37% in 2010. In the 2009 fruit harvest, approximately 17.4% of ANPP-C (or about 0.6 mT C ha-1 year-1) was removed from the vineyard, whereas in 2010 this percentage was somewhat higher at 27.3%, or roughly 1.0 mT C ha-1 year-1. Biomass carbon other than harvested fruit is either retained as wood in trunk and cordon growth or incorporated into the tractor row by mowing and tillage (canes and leaves). A decline in pruning weights and yield under minimum tillage was noted during the course of the experiment. In 2009 this treatment produced 29% less fruit and 25% less ANPP-C than the tilled cover crop treatment. In 2010, these discrepancies progressed to 33% and 28% less. Yield under conventional tillage was intermediate in both years. The "devigoration" noted in the minimum-till treatment offset about 5% of the carbon it sequestered into soils, because vines were accumulating less woody biomass. It is surmised that this devigoration was due mainly to water competition, because the cover crop consumes water and is likely to compete with vines in early spring. The wider differences seen in 2010 may be the result of long-term competition in the eighth year of treatment. The impact of these changes in production in the minimum-tillage treatment depends on site characteristics. This is a moderate-vigor site where reduction in vigor is somewhat desirable, so yield reductions may contribute to improved quality. Overall yields in 2009 and 2010 ranged from approximately 1.7 to 3.9 tons per acre, with lowest yields from the minimum-tillage treatment and highest yields from the tilled cover-crop treatment. Belowground carbon sequestration into roots Several key findings emerged from efforts to quantify the influence of minimum tillage on grape-root biomass production and distribution. In Figure 2 are root biomasses at 30 cm intervals of soil depth. Results indicated that with the cessation of tillage in the minimum-tilled treatment, roots grew back into the soil horizon that was previously disturbed annually, best characterized as an Ap or 86 p r acti c al w i ne ry & v i n e yard NOVEMBER 20 13