Biochar and compost application for improving soil properties and plant physiology: the case of an intensive-olive orchard under deficit irrigation

Abstract

Biochar is the solid by-product of the pyrolysis of residual biomass. Numerous authors have previously demonstrated that biochar addition to soils improves soil physical properties and plant growth (De la Rosa et al., 2014; Campos et al., 2020, 2021). Additionally, the production of biochar has taken attention during the last decade as a way to valorise abundant residual biomasses, such as waste from the olive oil agro-industry. Another important issue is the need for irrigation in super-intensive olive plantations, which are mainly located in the Mediterranean region, with a semi-arid climate. In this work, the application of biochar to the soil is proposed to increase water retention, improve soil permeability, and at the same time valorise a waste product such as the residual olive pomace. Green compost was also used to compare biochar with the traditional amendment. Soils at a super-intensive plantation of arbequina olive trees under deficit irrigation (“La Hampa” field station, Coria del Río, Seville, Spain) were amended with 40 t ha-1 of biochar, green-compost or a 50% w/w biochar-compost mixture. Un-amended plots were used as control. The field experiment lasted 380 days. Soil properties (pH, electrical conductivity, water holding capacity), soil humidity and resistance to penetrability at field, physiological status of olive trees [midday stomatal conductance (gs), net photosynthesis rate (AN) and maximum rate of electron transport (ETRmax)] were determined on a monthly basis. At harvest (October 2021) the productivity in olives and oil per tree was determined. All the organic amendments showed high porosity and water retention capacity. Biochar application resulted the most effective in reducing soil compaction and improving the water status of olive trees in this super-intensive olive trees plantation. Moreover, the use of biochar increased about 15% olive yields, although net olive production was maintained

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