Abstract
The soils of Mediterranean semiarid environments are commonly characterized by low levels of organic matter and mineral elements, as well as severe weed infestations, which, taken together, cause an intensive use of auxiliary inputs (tillage, fertilizers, herbicides). Although cover crops are recognized to sustainably improve soil health, the impact of Trifolium subterraneum L. cover cropping needs specific attention. This research investigates for the first time the effects over 4 years of T. subterraneum and spontaneous flora cover crops, after either incorporating their dead mulches into the soil or leaving them on the soil surface, on soil organic matter (SOM), macroelements, mineral nitrogen, microelements, and weed seedbank dynamics as indicators of soil quality in an apricot orchard. Compared to a conventional management control, the T. subterraneum cover crop with the burying of dead mulch into the soil increased the amount of SOM (+ 15%), ammoniacal (+ 194%) and nitric (+ 308%) nitrogen, assimilable P2O5 (+ 5%), exchangeable K2O (+ 14%), exchangeable Na (+ 32%), exchangeable K (+ 16%), Fe (+ 15%), Mn (+ 28%), Zn (+ 36%), and Cu (+ 24%), while it decreased the weed seedbank size (‒ 54%) and enhanced weed biodiversity. These findings suggest that T. subterraneum cover cropping may be an environment-friendly tool to enhance soil quality and limit auxiliary input supply in Mediterranean orchards.
Highlights
The weaknesses of agricultural activity (i.e., release of agrochemicals, loss of water resources, generation of ammonia from grazing (GAG) emission, soil degradation, and loss of biodiversity) are attributed to the irrational or inefficient use of auxiliary inputs and to the excessive biological homogeneity typical of intensive farming systems
In recent researches conducted in Sicily, important improvements have been observed in the weed control and nutritional status of soil in an apricot orchard managed with subterranean clover compared to spontaneous flora cover cropping and conventional soil management (Restuccia et al 2020; Scavo et al 2020)
The incorporation of T. subterraneum dead mulches into the soil significantly decreased the weed seedbank size and the weed aboveground biomass compared to other studied managements, while it increased the amount of ammonia-oxidizing (Nitrosomonas europaea) and N-fixing (Azotobacter vinelandii) bacteria involved in the soil N-cycle, which resulted in a significant enhancement of ammoniacal and nitric N-availability in the soil
Summary
The weaknesses of agricultural activity (i.e., release of agrochemicals, loss of water resources, generation of ammonia from grazing (GAG) emission, soil degradation, and loss of biodiversity) are attributed to the irrational or inefficient use of auxiliary inputs and to the excessive biological homogeneity typical of intensive farming systems. The loss of soil minerals, relevant for macronutrients such as nitrogen (N) and phosphorous (P), combined with the severe weed infestations, represents two critical aspects of Mediterranean agroecosystems, where an intensive and indiscriminate use of auxiliary inputs (tillage, fertilizers, and herbicides) is adopted In this framework, subterranean clover (Trifolium subterraneum L.), a self-pollinated annual legume with remarkable geocarpism, native to the Mediterranean Basin and widely diffused throughout the world in regions with Mediterranean-type climates (Australia, New Zealand, The Americas and South Africa), is considered an eligible cover crop, owing to its self-reseed and N-fixation ability, rapid growth, and weed suppressive ability (Enache and Ilnicki 1990; Restuccia et al 2020; Scavo et al 2020). The incorporation of T. subterraneum dead mulches into the soil significantly decreased the weed seedbank size and the weed aboveground biomass compared to other studied managements, while it increased the amount of ammonia-oxidizing (Nitrosomonas europaea) and N-fixing (Azotobacter vinelandii) bacteria involved in the soil N-cycle, which resulted in a significant enhancement of ammoniacal and nitric N-availability in the soil
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