Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Quantifying the role of soil microbial activity in cover crops on newly established fruit trees in the Western Cape

Auteur : Burger, Jani

Université de soutenance : Stellenbosch University

Grade : Master of Science (MScAgric) 2022

Résumé partiel
Limited research is available on the role of cover crops in newly established deciduous fruit orchards in South Africa. Thus, three field studies were conducted to evaluate the contribution of cover crops towards soil health/fertility. The effect of cover crop combinations on soil characteristics (mineral composition, soil moisture, soil compaction, water holding capacity, microbial activity and tree performance) and the contribution towards weed suppression and biomass production for mulching in a perennial orchard were quantified during two and three consecutive seasons in two locations. In addition, soil microbial activity and diversity were quantified with three locally available methods (Molecular fingerprinting, CO 2-burst test and gas chromatography). A two-year field study (Trial 1 and 2) was conducted in Stellenbosch, (33°56’51.27" S 18°52’19.29" E) and a three-year field study (Trial 3), in Elgin (34°09’16.83’ S, 19°02’28.01” E), Western Cape. Trial 1 (Multi species : forage rye, radish and white mustard) and trial 2 (Single specie : forage rye) comprised four treatments each : i) Control (natural vegetation), ii) Cover crop with no fertilizer application (MNFA ; SNFA), iii) Cover crop with a single organic fertilizer application (MSFA ; SSFA) and iv), Cover crop with a double organic fertilizer application (MDFA ; SDFA). Trial 3 consisted of five annual winter cover crop treatments : i) Phacelia (PC) ii) Forage rye & vetch (FRVC) iii) Forage radish & white mustard (FRWMC), iv) Forage barley & peas (FBPC) v), Forage rye (FRC). Cover crops provided a significantly higher above- and below ground biomass compared to natural vegetation in trial 1 and 2, however, biomass differed amongst cover crop treatments. Biomass production differed significantly between cover crop treatments in trial 3. FRC performed the best, followed by FRVC and FRWMC. Crop species were the primary factor in plant performance and other factors contributed less towards biomass. However, weed suppression efficiency was affected by cover crop biomass and species. In trial 3, Forage rye, in combination or monoculture, performed the best in terms of consistency, biomass for mulching purposes, root length and weed suppression.

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