Abstract
In Southwest Germany, the renaturation of quarry areas close to settlements is usually based on the planting of native species of trees and shrubs, which are then neither cultivated nor used. This study investigates whether a species-rich agroforestry system based on Ernst Goetsch’s syntropic agriculture approach would be suitable for both renaturation in the form of soil fertility improvement and diverse food crop production under temperate climate. The quarry syntropy project was launched in summer 2019. Two shallow stony sections of a spoil heap of the quarry in Ehningen, Southwest Germany were available for demonstration plots. An interdisciplinary project team was set up both to obtain the official permits from five governmental institutions and to begin the study. The demonstration plots were each divided into three broad strips, which differ in three vegetation types: trees, shrubs, and annual food crops. The tree and shrub areas are mainly used for biomass production for a continuous mulch supply on the entire cultivated area in order to rapidly increase soil fertility. The food crops and also partly the trees and shrubs were intended to provide organically produced food (vegetables, fruit, berries and herbs). Most of the trees (eleven species) were planted in November 2019. In March 2020, soil samples were taken (0–30 cm), and a solar-powered water storage system was installed. Currently, the shrub and annual food crop strips are under preparation (pre-renaturation phase). In this initial phase, the priority is fertility improvement of the topsoil through intensive mulching of the existing grassland stock dominated by top grasses and the legumes hybrid alfalfa (Medicago × varia Martyn) and common bird’s-foot trefoil (Lotus corniculatus L.). The food crop strip should then start in 2021 after one year of mulching. Depending on the success of growth, the tree strips should then also gain in importance for mulch application in the following years. The strategy is to gradually build up food crop cultivation under organic low-input agricultural practices while simultaneously enhancing the biophysical growth conditions guided by natural succession.
Highlights
Agroforestry is considered one of the most important cultivation methods, which serves the production of biomass but can provide many other ecosystem services, such as carbonAgriculture 2020, 10, 603; doi:10.3390/agriculture10120603 www.mdpi.com/journal/agricultureAgriculture 2020, 10, 603 storage [1,2], crop yield increase [3,4,5], climate change adaptation [6], biodiversity conservation [7,8], habitat functions [9] and landscape improvement
According to Goetsch and Colinas, “syntropic agriculture” is to be understood as an agricultural strategy according to which soil-physical cultivation parameters such as humus cover, soil fertility, water infiltration and erosion mitigation of agroforestry systems are improved through (i) the introduction of a high diversity of plant species and (ii) an intensive cutting and pruning frequency to foster both light penetration into the system and photosynthesis rate
Syntropic agriculture aims at regaining agricultural productivity of marginal agricultural land in the long term, so that food crops can be cultivated on those areas in the near future [15]
Summary
Agroforestry is considered one of the most important cultivation methods, which serves the production of biomass but can provide many other ecosystem services, such as carbonAgriculture 2020, 10, 603; doi:10.3390/agriculture10120603 www.mdpi.com/journal/agricultureAgriculture 2020, 10, 603 storage [1,2], crop yield increase [3,4,5], climate change adaptation [6], biodiversity conservation [7,8], habitat functions [9] and landscape improvement. In view of the increasing competition for land use [11], it might be important to deal with this in the future, as the areas that are released for renaturation by quarries every year must be enormous in view of the exorbitant production volumes, for example 10 billion tons of concrete per year [12] These areas are to be renaturalized following the local nature conservation guidelines, i.e., they are left to controlled succession through controlled planting of native tree and shrub species. Following Andrade et al 2020, this triggers an interplay of natural succession and stratification, resulting in an increased number of vegetation layers consisting of various plant species and stages [15] Due to this spatial and temporal stratification, syntropic agriculture could lead to an increased biomass productivity compared to standardized mono-cropping-based cultivation methods [14,15]. It must be kept in mind that syntropic agriculture requires agricultural and social (socio-economic) adaptation by bridging the gap between agriculture and ecosystems
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