Water-Deficit Stress and Soil Type Effects on Spring Onion Growth

ABSTRACT

Soil type and management practices can affect Allium growth and quality. This study investigated the effects of water-deficit stress and soil type on tissue water content, plant growth and dry-matter production of spring onion (Allium cepa L.) cv. White Lisbon. Seedlings were grown in a glasshouse in pots containing clay (Alluvial Gley) or sandy loam (Brown Earth). Irrigation treatments were watering to near field capacity (−0.01 MPa), or re-watering to near field capacity when the available soil moisture level was depleted to either ≤ 50% (−0.80 MPa) or ≤ 25% (−1.19 MPa). Watering to field capacity significantly (P < 0.05) increased relative water content and water potential of leaf tissue. Periodic water-deficit stress increased leaf number, but reduced leaf length. At −0.01 MPa, plant fresh weight and dry-matter content were increased, especially for plants grown on clay as compared with the −0.80 or −1.19 MPa treatments. Irrigation to near field capacity improved growth and dry-matter production. A greater proportion of colloids, and greater water storage capacity of the clay soil, compared to the sandy loam, caused an increase in plant growth and dry-matter. Attainment of functional equilibrium maintained a balance between shoots and roots fresh weight ratio, irrespective of irrigation treatment and soil type. In conclusion, deficit irrigation especially on the sandy loam caused physiological stress that reduced spring onion growth and dry-matter yield compared to regular irrigation. The good water retention capacity of the clay soil compensated for deficit irrigation compared to the sandy loam.

KEYWORDS:

• Allium
• growth
• roots
• soil water potential
• spring onion