Nutrient Management Research Database

Impacts of soil tillage and cover crops on soil carbon (C) dynamics and microbiological
function were investigated in a vineyard grown in California’s mediterranean climate. We
(1) compared soil organic matter (SOM), C dynamics and microbiological activity of two
cover crops [Trios 102 (Triticale  Triosecale) (‘Trios’), Merced Rye (Secale cereale) (‘Rye’)] with cultivation (‘Cultivation’) and (2) evaluated seasonal effects of soil temperature, water content, and precipitation on soil C dynamics (0–15 cm depth). From treatments established in November 2001, soils were sampled every 2–3 weeks from November 2005 to November 2006. Gravimetric water content (GWC) reflected winter and spring rainfall. Soil temperature did not differ among treatments, reflecting typical seasonal patterns. Few differences in C dynamics between cover crops existed, but microbial biomass C (MBC), dissolved organic C (DOC), and carbon dioxide (CO2) efflux in ‘Trios’ and ‘Rye’ were consistently 1.5–4-fold greater than ‘Cultivation’. Cover crops were more effective at adding soil C than ‘Cultivation’. Seasonal patterns in DOC, and CO2 efflux reflected changes in soil water content, but MBC displayed no temporal response. Decreases in DOC and potential microbial respiration (RESPmic) (i.e., microbially available C) also corresponded to or were preceded by increases in CO2 efflux, suggesting that DOC provided C for microbial respiration. Despite similar MBC, DOC, RESPmic, annual CO2 efflux and aboveground C content between the two cover crops, greater aboveground net primary productivity and SOM in ‘Trios’ indicated that ‘Trios’ provided more soil C than ‘Rye’.

This study was conducted in a Chardonnay vineyard on Teleki 5C rootstock that was planted in 1996.  The cover crop and cultivation treatments were established four years before this study began.  

• 3 treatments were established, one with a Trios (Triticale x Triosecale) cover crop, one with a Merced Rye (S. cereale) cover crop, and a cultivated ("Cultivation") treatment without a cover crop. There were two treatment plots of each treatment, in an experimental randomized complete block design.
• The study was conducted in late fall 2005 and late fall 2006, resulting in one season of cover crop and grapevine growth.
• Vine spacing was 2.4m between rows and 1.8m within rows. Grapevine rows measured 506m long, and were oriented from west to east
• The cover crop treatments were sown at a rate of 112 kg seeds ha^-1, mowed in mid-April 2006, and the residue was left on the soil surface.  The cultivated treatment was tilled about once every 2 months using a tandem disc and ring roller.
• Aboveground cover crop and weed biomass was sampled biweekly from emergence through mowing.  Root biomass was collected at the end of the growing season. Total C of aboveground and root biomass was analyzed.
• Soil was sampled biweekly for gravimetric water content (GWC), microbial biomass C (MBC), dissolved organic C (DOC), Potential microbial respiration, and total soil C content.
• Soil CO₂ emissions were also measured.

• When precipitation frequency was high, soil water content was greater in the cover crops treatments than in treatments with cultivation, suggesting reduced runoff and increased infiltration.
• The Trios cover crop tended to have higher weed biomass than the Rye cover crop.
• Both cover crop treatments had 1.4 times greater soil organic matter than the cultivation treatment.
• Cover crop soils also had greater C content in microbial biomass, greater microbial activity (potential microbial respiration), and soil CO2 emissions than the cultivated treatment.