A Vineyard Agroecosystem: Disturbance and Precipitation Affect Soil Respiration under Mediterranean Conditions

We investigated impacts of agricultural management practices on soil respiration (R-s) in a Cabernet Sauvignon (Vitis vinifera) vineyard (Oakville, CA; November 2003-December 2005). We determined (i) response of R-s to covercropping, mowing and tillage; (ii) environmental factors controlling R-s; and (iii) total annual C lost through R-s. A winter cover crop was either mown (CC+mow), or mown and tilled (CC+Till), and resident vegetation was tilled (RV+Till). Precipitation amount and pattern differed between years, and low R, rates occurred during summer drought and high rates during wet periods. Total CO2 emissions differed only in Year 2 (RV+Till: 10.99 0.30, CC+Till: 10.11 +/- 0.49, CC+mow: 8.57 +/- 0.54 Mg CO2-C ha(-1)). After tillage or mowing, R-s increased five- to six-fold in tilled treatments and two-fold in the mown treatment (Year 1). In Year 2, R, increased two-to three-fold after tillage Only. R, increased after 'post-management' rainfall in spring and was 1.5- to 2-fold greater in tilled than mown treatments in both years due to prior incorporation of plant biomass during tillage. After fall rainfall, R-s was 1.7-fold greater in mown than tilled treatments (Year 1). Our findings suggest that the interaction of management practice with climate and soil conditions before disturbance (i.e., management and rainfall) influenced R-s. Polynomial regressions of R-s on GWC and soil temperature indicated that R-s increased until gravimetric water content (GWC) reached 14 to 15% in tilled treatments and 20% in the mown treatment, subsequently declining, indicating thresholds of GWC at which soil temperature more strongly influences R,.