Abstract
There is little information available on the evolution and stratification of soil C content (SCC) at the medium- to long-term in semiarid vineyards with cover crops. The objective was to determine SCC at different depths in the medium term (5 and 8 years) in a semiarid vineyard with different cover crops. The field experiment was conducted on Typic Haploxerept soil with a loam texture, pH 8.2, situated in a vineyard (cv. Tempranillo) located in the La Rioja region (northeast Spain) on Miocene sandstones, siltstones, clays and marlstones. Two different soil managements were evaluated: conventional tillage (CT) and continuous cover crop of resident vegetation (RV). Soil samples were collected from four soil layers (at depths of 0-2.5, 2.5-5, 5-15, and 15-25 cm) in June 2009 and June 2012, 5 and 8 years respectively after cover crop establishment. The SCC was determined and the SCC variation with respect to tillage treatment was determined considering the percentage of soil &lt; 2 mm and soil bulk density. The results showed that the greatest increase in SCC occurred at 0-2.5 cm soil depth, increasing less with depth. The SCC annual increment in the whole soil sampled (0-25 cm) was 2.78 Mg C ha<sup>-1</sup> year<sup>-1 </sup>after 5 years and decreased to 1.98 Mg C ha<sup>-1</sup> year<sup>-1</sup> after 8 years of cover crop establishment. The lower SCC annual increase was not due to the maximum increase being reached in the whole of the sampled soil (0-25 cm). From 2009 to 2012, the SCC did not increase at the soil surface (0-2.5 cm), but did so in the subsurface zone (2.5-5 cm), although with an annual increment lower than that found at soil surface (0-2.5 cm). In conclusion, the steady state in SCC would not have been reached in the medium term (8 years) under cover crop, since there is still a increment of SCC in the subsurface layers.
Highlights
Increasing the soil C content (SCC) with conservation agriculture techniques has attracted great interest in its ability to improve soil quality, because soil C sequestration can attenuate the negative effects of increasing CO2 concentration on atmosphere (Lal 2004).Spain is the country with the largest vineyard area worldwide, with 1,032,000 ha, and in La Rioja winegrowing area (NE Spain) where the field experiment was carried out, there are 60,000 ha of vineyard soils
Soil Carbon content in CT (Table 2) was similar to SCC found in vineyards soil from La Rioja under conventional tillage (Peregrina et al 2010a)
In the 0-2.5 and 2.5-5 cm soil depths at year 2009, resident vegetation (RV) increased soil organic C (SOC) compared to CT
Summary
Increasing the soil C content (SCC) with conservation agriculture techniques has attracted great interest in its ability to improve soil quality, because soil C sequestration can attenuate the negative effects of increasing CO2 concentration on atmosphere (Lal 2004).Spain is the country with the largest vineyard area worldwide, with 1,032,000 ha, and in La Rioja winegrowing area (NE Spain) where the field experiment was carried out, there are 60,000 ha of vineyard soils. The use of cover crops has been studied in La Rioja as a strategy to reduce the excess vigor of grapevines and to improve must and wine quality (Perez-Álvarez et al 2015). In these studies, in La Rioja, it has been found that cover crops in the short term (4 years) can increase SCC with rates in the order of 1.5 Mg C ha-1 year-1 and with a high degree of stratification (Peregrina et al 2010b). There is very little information on how the SCC evolves over time and when the maximum level of SCC in equilibrium will be reached at different depths in agro-systems such as vineyard with cover crops under Mediterranean climatic conditions
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