Influence of two different cover crops on soil N availability, N nutritional status, and grape yeast-assimilable N (YAN) in a cv. Tempranillo vineyard

[Aim] The aim was to study the effects of two different cover crops (leguminous versus gramineous) on soil NO3−-N availability, grapevine N status, and yeast-assimilable N (YAN) and amino acid profile in the must of a cv. Tempranillo vineyard from La Rioja (Spain) over 3 years.
[Methods] Three treatments were established: gramineous (barley) and leguminous (Persian clover) cover crops and conventional tillage. Soil total N and extractable NH4+-N at bloom, soil NO3−-N content from budbreak to postharvest, leaf N content at bloom, and free amino acids and ammonia in must were monitored.
[Results] Each year, the barley cover crop treatment had lower soil NO3−-N than tillage, while the clover treatment showed lower soil NO3−-N than tillage in 2009 and showed higher values in 2010 and 2011. In 2011 leaf N content, yeast-assimilable N (YAN), and some amino acids in the grapes were lower in barley cover crop treatment thus affecting the amino acid profile. Meanwhile, the clover cover crop did not have these effects. Furthermore, relationships between leaf N content and various amino acids were also found.
[Conclusions] With the barley cover crop treatment, soil N availability decreased from the first year of the experiment, provoking a decrease in N grapevine status and in content of YAN and various amino acids at the third year. In contrast, clover cover crop maintained N grapevine status, YAN, and amino acid profile similar to conventional tillage. Therefore, our study shows how soil N can be managed both within a year and from year to year when two different cover crops are sown and how the grapevine N nutritional status and YAN content and amino acid profile can be modified in the must.