Recent high rainfall events across most of the Eastern Australia has seen many cotton crops inundated with water and experiencing prolonged periods of overcast weather. The timing of the event has coincided with cotton planting up to the squaring stage where the plant is particularly susceptible to the effects of water logging. Waterlogging is a complex stress as it affects both the soil environment and crop growth.

A range of responses to this event may have eventuated from complete crop establishment failure to reductions in growth rate and yield potential. The crop impact depends on the severity (depth, water quality, flow) and length of inundation. Coupled with waterlogged soils, cloudy weather (low light) and low temperatures also impacts crop growth. Under these conditions, cotton plants are likely to cease growth (e.g. production of new nodes), and then shed squares and fruit as assimilate in the plant becomes limited.

Flooding and waterlogging can impact soil nutrient availability and plant uptake as many nutrients become deficient when the soil is saturated (low in soil oxygen (anaerobic)). In the soil the availability of nitrogen (N), iron (Fe) and zinc (Zn) are reduced, and manganese (Mn) is increased, directly affected by the decline in soil oxygen; while the uptake of N, K, P and Fe by the plants roots that are oxygen deprived is also impaired. The severity of yield loss is directly related to the number of days the plant spends in waterlogged conditions as seen in Figure 1.

It is also important to consider that following flooding or waterlogged events that there is a high probability that the soil N supply will be significantly depleted, as a result of denitrified (N loss to the atmosphere). Crop management decisions for after a flooding/waterlogged event depends on at what crop growth stage it occurred, the severity of the damage, and how quickly remedial action takes effect.