Learning about green covers and their contributions to the soil
From olive to almond trees, experiences in soil management
About twenty people attended the workshop on vegetable covers organized by the AlVelAl association, given by Milagros Saavedra, Doctor in Agricultural Engineering, from the IFAPA Alameda del Obispo centre, and Miguel Ángel Gómez, AlVelAl researcher.
The workshop has focused on the soil of olive and almond trees, making a comparison between both crops, understanding their phenological cycles and fruit ripening among other aspects, important factors to manage the covers.
Through the transference of results, with studies made throughout the years in different fields, a key factor has been insisted on, as it is the one to contribute nutrients to the ground (organic matter) and of the importance to make a good manage of the ground, although the maintenance of vegetal covers supposes to assume a certain loss of water. The effects of these good practices are not immediate, but they are showing that when there is good green cover, one of the great problems suffered by our land can be avoided: erosion and soil degradation. When soils are susceptible to erosion problems, it is advisable to maintain the cover, made up of spontaneous or cultivated plants, which covers the maximum possible surface area of the soil.
Milagros pointed out that "the cover should be functional, not pretty", and explained the diversity of flora adapted to the soil of olive and almond trees, providing data from research over many years, which enriched the course of the workshop.
Types of cover Different types of covers and their proper manage were addressed as an essential part of their functionality: Spontaneous or selected weed cover, These covers are composed of the weeds present in the soil. The farmer can either let this flora grow without control, or select some species from it. Spontaneous cover is recommended in soils where the orography of the land makes it difficult to sow species and in historically cultivated areas, where there will surely be a large number of species that allow us to have a dense protective cover. Sown green cover: grasses, leguminous and cruciferous. Cover sown with grasses (barley, bromine brachiopodium, etc). This cover is composed of one or several species. Sowing is done with a conventional machine or, what is more economical, broadcast. No certified seeds are needed, so they can be obtained at an economical price. Cover sown with legumes (vetch, clover, others). They have a high environmental interest in fixing nitrogen and thus fertilizing the crop.
The problem they present is that their plant remains, once dry, are not sufficiently persistent in the field. This inconvenience makes them less efficient against erosion processes, especially in autumn. Cover sown with cruciferous plants (white mustard, caterpillar, others). This is a very suitable alternative, because of the need to find species capable of rotating with grass covers, since after several years of using the same species as a cover, there is a deterioration of the same and a decrease in soil protection, compaction and flora investment towards species that are difficult to control. They are very interesting in soil biofumigation, that is, incorporating them into the soil to disinfect it, for example against verticillosis (with the cruciferous species Sinapis alba) or Phytophthora (with species of Brassica). Covered with plant debris. They are composed of non-living plant elements, unlike the previous ones, which are living plants. They can be crushed pruning remains, leaves, straws or residues from the agro-food industry. They should be on the surface to protect it. As they decompose slowly, they provide prolonged and sufficient protection of the soil. Over time, a layer of several centimetres can be created that increases water infiltration.
It is very important to note that these wastes should not be contaminated with pathogenic propagules, for example, of Verticillium dhaliae. Inert covers. These are elements that cover the soil, but do not provide nutrients, normally stones. They increase the water content of the soil by reducing erosion and increasing infiltration. In addition, evapotranspiration is reduced, managing to maintain more water through this route as well. Its main advantage is that there is no competition for water and nutrients with the crop, as is the case with plant species. We believe that it has been very interesting to highlight the mosses inside the green covers, since research is beginning and there is a high diversity, showing trials on them. Management of the green cover
Live green cover, in other words, spontaneous and sown plant cover, requires in most cases management to limit competition with the crop for water and nutrients. This management can be done by chemical mowing, mechanical mowing or grazing. It is also possible to incorporate it into the soil as green manure.
Chemical mowing, that is, applying herbicides, presents the risks inherent in the use of these agrochemicals.
Mechanical mowing has an influence on the vegetation that can evolve into perennial species, which can easily regrow, all of which are difficult to control with a brushcutter.
Grazing, presents the difficulty of choosing the right moment to graze and that animals can select species and make the cover evolve towards species that we do not want.
In any case, it is advisable not to enter the field with wet soil to avoid soil compaction that leads to loss of water storage capacity.
Management experiences in almond farms
The second part of the event presented by AlVelAl researcher, Miguel Ángel Gómez, focused more on almond crops in the AlVelAl territory, presenting the results of the research carried out, to begin to lay the foundations for further work and research. Key questions have been addressed, such as: What do I have to put in? How do I fertilize the farm?
Due to the climate that we have in our territory, low rainfall and sometimes torrential (rainfall data have been shared in different parts of the territory) it is essential to manage to infiltrate the water into the soil so that it is not lost and that it does not cause damage, Miguel Ángel points out that "between 1 and 2 millimetres of soil in the fertile layer are lost annually", not only due to water erosion but also due to wind erosion.
Therefore, soil management is essential in agriculture. The researcher points out that "organic matter is very important and modifies the structure of the soil and modifies water management" and describes different types of management to increase organic matter levels, according to the type of farm in question.
It is important to know that before installing a green cover it is necessary to add nutrients to the soil and that its success will depend on how it is managed. The participants had the opportunity to see different graphic files to see the differences between a soil to which nutrients are added and another that is not, in addition Miguel Ángel shared data extracted from different farms, with various very interesting managements to complete the visual information.