SOIL NITRATE AND ORGANIC CARBON IMPROVEMENT BY USE OF LEGUMINOUS PLANTS AS COVER CROPS IN AN ORGANIC OLIVE ORCHARD

Abstract

The organic olive orchard represents about 0.5 Mio ha in EU and 36% are locatedin Spain. This production system implies an economic opportunity for rural areas.The use of cover crops between the rows of olive trees is an agricultural practicethat farmers are progressively adopting since they reduce soil erosion whileimprove soil quality. Due to an usual fertilisation strategy in organic farming is theuse of leguminous plants, three legumes (Vicia sativa, Vicia ervilia and Viciavillosa) used as cover crops were compared to study their capacity to protect thesoil and improve soil fertility during 4 years. Two soil managements wereconsidered after mowing cover crops: plant residues left on surface or incorporatedinto the soil. Soil nitrate and coverage were monitored monthly and soil organiccarbon (SOC) was analysed at the end of every growing season. Despite not beingthe best species to protect the soil, the coverage at the end of decomposition periodincreased by 32% in 4 years in the management without incorporation, providingvalues over 30% of cover. The soil nitrate recorded in May, when the demand forN by the olive tree is greater, increased in the study period by 70% with theresidues left on surface and by 50% when the residues were buried. A carbonsequestration rate of 1.08 Mg C ha-1 y-1 was reached by V. villosa withoutincorporation. Where residues were incorporated, V. sativa obtained the highestcarbon fixation with 1.21 Mg C ha-1 y-1.