A research team from the agriculture and environment area of the Agrarian and Fisheries Research and Training Institute (Alameda del Obispo center, Córdoba) has measured how much organic matter incorporates the presence of three types of cultivated herbs into the soil of the olive grove, together with the that arises spontaneously. The quantity fluctuates between 10’5 and 14’5 tons at the end of the four-year period analyzed. This contribution is facilitated by both the deposit of remains of these species and the protection against erosion, especially rain.
According to Mercacei, the study supports the idea launched at COP21 (the United Nations summit against climate change held in Paris in 2015) to mitigate this global crisis with better management of agricultural soils. «The objective set by the 4 per thousand initiative, which aims, through good agricultural practices, to increase soil organic carbon by at least 0.4% per year to compensate for human-caused emissions is more than met,» he said. the Discover Foundation, Miguel Ángel Repullo, researcher from the Alameda del Obispo center, first author of the study «Soil organic matter and nutrient improvement through cover crops in a Mediterranean olive orchard», published in the journal Soil & Tillage Research.
Organic matter and, specifically, three of the main nutrients -carbon, nitrogen and potassium- increased in the four years of presence of the covers. The one known as vegeta (Brachypodium distachyon) generally improved the fertility of the soil more on the surface, up to 5 centimeters deep. At the same time, white mustard (Sinapis alba) had better results in depth. They also verified that potassium was the element with the highest release rate, followed by nitrogen, despite not selecting among the legume sown species, which have the property of fixing it to the soil.
The work focused on an olive grove whose management prior to the beginning of the trial was traditional, with several tillage passes per season to control the weeds, leaving the soil of the «streets» very unprotected. Vegeta was planted the first year as it had a great regeneration capacity, while white mustard and caterpillar (Eruca vesicaria) were planted every year. The control of the covers was made with two annual clearings, at the end of winter and spring. «The evaluation of the decomposition of the biomass of the herbaceous species was sampled periodically, analyzing the concentration of elements both on the surface and in depth,» said Repullo.
The use of this vegetal cover also kept the soil protected against erosion, something that the experts verified when observing the rain streaks in areas of the farm where the herbaceous plants had not been installed.