Waterlogging

Waterlogging is a condition rather than a single fixed threshold: it describes soil pore space remaining saturated, or very nearly so, for long enough that oxygen supply to roots and aerobic soil organisms becomes limiting. How quickly this becomes damaging depends on temperature, soil type, and the crop involved.

• Surface waterlogging: standing or slow-draining water at or near the soil surface
• Subsurface waterlogging: saturation within the root zone even without visible surface water, often linked to a high water table

Waterlogged, oxygen-depleted soil impairs root respiration, nutrient and water uptake, and can trigger root death in sensitive species within a period of hours to a few days depending on temperature and species. Anaerobic conditions also favour different microbial processes, including denitrification, which can increase nitrogen loss, and can promote some root-disease organisms.

Waterlogging is often identified through direct field observation of standing water or slow infiltration after rain or irrigation, through soil profile inspection for grey or mottled colours that indicate a history of saturation, and through monitoring of water-table depth where a shallow water table is a contributing factor.

Management generally focuses on removing excess water more quickly, through surface or subsurface drainage systems, and on avoiding practices that slow drainage further, such as compaction from field traffic on wet soil.

• Install or maintain surface drains and subsurface tile drainage where chronic waterlogging occurs
• Avoid heavy field traffic on wet soil, which compacts pores and slows drainage
• Schedule irrigation to match crop demand and avoid over-application
• Select waterlogging-tolerant crops or varieties on sites where drainage cannot be fully corrected