The effect of cover crop mixtures on N mineralization and on spring barley (Hordeum vulgare) performance

• Autor(a) principal: Nascimento, José Gonçalo Bettencourt
• Data de Publicação: 2020
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10348/10778
• topic: agriculture; cover crop mixture

Cover crop mixture residues, through complementarity, can supply a larger biomass to the soil than monoculture cover crops resulting in a higher nitrogen (N) input into the soil. Moreover, one can control the cover crops quality by mixing species with different N content. By doing this, N can also be transferred between the species residues, avoiding soil N immobilization, potentially resulting in higher N availability for the next crop. We hypothesised that N mineralization in mixtures would be higher than the expected based on sole cover crops, resulting in a better than expected performance of the following crop. A field experiment was conducted to assess the ability of 3 cover crop species, oat (Avena strigosa), radish (Raphanus sativus), and vetch (Vicia sativa), and all possible 2 and 3- species mixtures to provide mineral N to spring barley (Hordeum vulgare). Besides this, a laboratory incubation was performed to investigate if the residue quality, in terms of the N, carbon (C), lignin, N in the cell wall, N in the readily decomposable fraction and cellulose content, could explain the observed N mineralization of mixed residues. In the field experiment, only the vetch-oat mixture has shown a higher than expected N mineralization. However, differences in quantity (biomass) or quality (C:N ratio) of the cover crop did not explain this difference. Conversely, barley performance was higher than expected only when preceded by the oat-radish mixture. The mixtures in the laboratory incubation did not present signs of enhanced N mineralization, not giving a clear explanation for the observed enhanced N mineralization in the field. Although the C:N ratio was a good predictor of N mineralization in the laboratory incubation, cellulose and the N content in the cell wall also showed a high correlation, indicating that the C:N ratio may not be enough to predict N mineralization in mixed residues. Cover crop mixtures do not perform consistently better than expected at providing mineral N to the main crop, however similar yields as the corresponding best performing sole crop can be reached.