Straw mulching increases soil health in the inter-row of citrus orchards from Mediterranean flat lands

The inter-rows in woody crop plantations such as citrus orchards are usually not more than alleyways for agricultural operations thus leading to soil health decline spinning around the compaction and soil organic carbon (SOC) loss. In the present scenario of global warming, the soil on the inter-rows of citrus orchards should be recovered for organic carbon trapping with benefits for climate change mitigation and for adaptation through soil health enhancement. Therefore, the aim of this work was to evaluate the effect of a conservation agriculture soil management, specifically, no-till rice straw mulching, on soil health parameters, including SOC, in the inter-rows of two citrus plantations jointly fairly representative of the semi-arid hot-summer Mediterranean climate on flat lands. Temperature, water content, saturated hydraulic conductivity, bulk density (ρb), root abundance, dehydrogenase (DHA) and β-D-glucosidase (GLA) activities, CO2 emission, nitrogen, phosphorus, potassium and organic carbon in the topsoil layer (0 – 20 cm) were studied for almost three years. The rice straw mulching increased the surface albedo by between 0.015 and 0.115, thus reducing mean temperature in the inter-row topsoil by between 0.5 and 1.2 ºC regarding bare soil. The more moderate temperature under the straw mulch fostered a 4-fold higher crop root growth and the subsequent soil macrofauna development, as revealed by the significantly higher DHA and, overall GLA, as well as CO2 emission. Under the straw mulch, the macroporosity rose as revealed by the hydraulic conductivity between twice and 14 times higher. Ultimately the SOC mass fraction increased 10% more under straw than in the bare soil. Therefore, rice straw mulching enhances soil health in citrus orchards of Mediterranean flat lands. However, in remarkably compacted soils, i.e., with ρb over 1.6 g cm-3, the beneficial effects of straw mulching on soil health are still limited after three years of treatment. With such high initial compaction, the search of a kick-off effect by means of adding organic fertilizers and/or amendments alongside a surface tillage operation, might be recommended.