Soil management and vegetation control effects on soil water content in olive orchards in Alentejo

C. Alexandre¹, J. Andrade¹ & T. Afonso²

RESUMO

Este trabalho compara o teor de água do solo, entre Janeiro de 2004 e Abril de 2005, em resultado da aplicação de 3 técnicas de controlo da vegetação herbácea em olivais jovens: cobertura com luzerna, Medicago spp. (L), mobilização tradicional (M) e não mobilização (N). A área em estudo localiza-se na Herdade dos Lameirões (DRAAl), Safara, a leste de Moura, envolvendo 6 parcelas de olival (var. “Galega”) situadas numa encosta com 4-5% de declive, num Solo Calcário Vermelho Para Barro derivado de calcários não compactos associados a xistos (Vc‘), Cambissolo Vértico-Calcárico (Crómico) na terminologia WRBSR. A humidade do solo foi objecto de três tipos de monitorização: irregular (humidade gravimétrica), principalmente na camada 0-10 cm; periódica, quase quinzenal, com sondas PR1 (Delta-T)* até aos 40 cm; e contínua, com as mesmas sondas e profundidades anteriores. Atendendo às limitações das sondas PR1 em solos argilosos, os resultados são analisados comparativamente. O tratamento L teve uma redução mais rápida da humidade na camada 0 a 20 cm nos períodos com maior desenvolvimento vegetativo e durante o Inverno de 2005 (com temperaturas mínimas muito baixas, grandes amplitudes térmicas diárias e extrema secura). O tratamento M evidencia maior descontinuidade do perfil hídrico dos 10-20 cm para os 20-30 cm, indiciando menor drenagem para as camadas subjacentes aos 20 cm. O mesmo tratamento registou maiores variações de humidade entre os 0 e os 20 cm, durante o Verão de 2004, em que se manteve com solo nu, diferença que pode dever-se a uma maior intercepção e evaporação pelos resíduos vegetais existentes à superfície nos tratamentos L e N. O tratamento N indicia um perfil hídrico mais homogéneo: a ausência de mobilizações permite uma maior variação da humidade nas camadas subjacentes aos 20 cm do que no tratamento M e o controlo da vegetação (com herbicida na linha e corte na entrelinha) origina menores perdas de humidade entre os 0 e os 20 cm do que no tratamento L. (^* Referência apenas com fins informativos).

ABSTRACT

This paper compares results of soil water content, measured between January of 2004 and April of 2005, under 3 different methods of soil management and weed control in young olive orchards: alfalfa cover, Medicago spp. (L), conventional tillage (M), and no tillage (N). This study is being carried out in trials of olive orchards set up near Moura, Alentejo. The plots used for soil water measurements are located on a slope with 4-5% gradient with a Calcaric-Vertic Cambisol (Chromic), according to the WRBSR. Soil water content was measured with three different methods and frequencies: irregular, by the gravimetric method, mainly for the 0-10 cm layer; periodic, approximately twice a month, with a probe PR1 (Delta-T)* from 0 to 40 cm depth, and continuously, with the same probes and depths. Considering the limitations of PR1 probes for clayey soils, results are discussed comparatively. Alfalfa treatment reveals a quicker decrease of the soil water content for the layer 0 to 20 cm on periods of greater plant growth, and also during the winter of 2005 (with very low minimum temperatures, high daily thermal amplitudes and extreme dryness). Conventional tillage shows some signs of greater discontinuity in soil water content profile between 10-20 cm and 20-30 cm layers, suggesting worse drainage around 20 cm depth. Soil under conventional tillage was kept bare during the summer of 2004 and showed greater variation on soil water content between 0 and 20 cm. This difference might be the result of a greater amount of intercepted rain, trapped on the mulch residues at soil surface, on the alfalfa and no tillage treatments. The soil under no tillage shows a more homogeneous soil water profile: no tillage allows a greater variation of soil water content under 20 cm depth than the conventional tillage, and weed control makes a lower soil water loss above 20 cm depth than the alfalfa cover. (^* Mention made only for information).

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¹ Dep. de Geociências e ICAM, Universidade de Évora, Apartado 94, 7002-554 Évoratel: 266745301; fax: 266745397; e-mail: cal@uevora.pt;

² Colaboradora no Projecto AGRO nº298