Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/13/2009
Publication Date: 1/31/2010
Citation: Steenwerth, K.L., Pierce, D.L., Carlisle, E.A., Spencer, R.G., Smart, D.R. 2010. A Vineyard Agroecosystem: Disturbance and Precipitation Affect Soil Respiration under Mediterranean Conditions. Soil Science Society of America Journal. 74:231-239.
Interpretive Summary: Due to the lack of intensive tillage in perennial cropping systems (e.g., vineyards) that occurs in annual cropping systems, there is potential to store increased carbon (C) in vineyards to mitigate greenhouse gas emissions that are linked global warming. For two years, we studied effects of cover crops, tillage and mowing on soil respiration in a vineyard (Napa Co., CA). Soil respiration (Rs), or soil CO2 efflux, is composed of root and microbial respiration. We determined 1) Rs’s response to cover cropping, mowing and tillage, 2) environmental drivers of Rs and 3) total annual carbon (C) lost through Rs. A winter cover crop was either1) mown or 2) mown and tilled, and 3) resident vegetation was tilled in spring in years 1 and 2. Dynamic increases in CO2 efflux occurred after rainfall and tillage, soil water content largely controlled soil CO2 efflux, and the two tilled soils had greater annual CO2 efflux than the mown treatment.
Technical Abstract: We investigated impacts of agricultural management practices on soil respiration (Rs) in a Cabernet sauvignon (Vitis vinifera) vineyard (Oakville, CA; November 2003 – December 2005). We determined 1) Rs’s response to cover cropping, mowing and tillage, 2) environmental drivers of Rs and 3) total annual carbon (C) lost through Rs. A winter cover crop was either1) mown ('CC + mow') or 2) mown and tilled ('CC + till'), and 3) resident vegetation was tilled ('RV+till'). Annual differences in Rs among treatments were associated with distinct patterns of precipitation and gravimetric water content (GWC). Among all treatments, low Rs rates occurred during summer drought and high rates during wet periods. Rs increased after spring rainfall, but was greater in the tilled treatments (year 1: 6-7 µmol CO2 m-2 s-1; year 2: 4-5 µmol CO2 m-2 s-1) than ‘CC+mow’ (years 1 and 2: 3.5 µmol CO2 m-2 s-1) due to recently tilled residues. Conversely, after rainfall in fall (year 1), Rs was 1.7-fold greater in ‘CC+mow’. After tillage or mowing, Rs increased 5-6-fold in the tilled treatments and 2-fold in ‘CC+mow’. In year 2, Rs increased 2-3 fold only after tillage in ‘CC+till’ and ‘RV+till’. We attribute Rs’s increase the tilled plots to soil disturbance and in ‘CC+mow’ to increases in GWC. Total CO2 efflux 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; P<0.05). Through multiple regression, we demonstrate that GWC is a primary driver of Rs, and that Rs increased until GWC reached 14-15% in tilled treatments and 20% in ‘CC+mow’, subsequently declining, implying the existence of ‘tipping points’ for control of Rs by GWC and soil temperature.