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Fellow CSIRO research agronomist Dr Ian Rochester, who specialises in cotton nutrition, said he had received a lot of enquiries regarding cotton crop’s health during and after water logging events.
“When looking at crop symptoms it’s often hard to pick out which is the problem nutrient but commonly its deficiencies of nitrogen, zinc, potassium, and sulphur. Some of those nutrients are mobile in the soil and with a lot of rain, get washed into the subsoil so the roots must get down there into the subsoil to take them up. Many cotton crops have shallow root systems where the soil has been constantly saturated. As many growers did not apply much N fertiliser presowing, it is important to apply sufficient N for the crops needs and not to stimulate excessive vegetative growth. Some growers who applied N fertiliser before the rain stopped and may have lost a substantial amount of that N.
Dr Rochester said while many people had been applying foliar fertilisers to minimise the problem, their impacts would only be short-term.
“Foliar fertilisers are something you can be proactive in doing but it’s of marginal importance – the real problem is getting oxygen to the roots and getting sunshine on the leaves so the plants can produce sugars that go down to the roots to help them to take up nutrients and water.”
“Putting on foliars might help in the very short term until the plants get going again – so the nitrogen, iron, zinc, sulphur applied in a band might help in the short term but eventually the plants will probably recover on their own accord as the soil drains.”
“Past research by Arthur Hodgson has shown applying foliar nitrogen before a water logging event may help in overcoming some of the damage. When that work was done, he applied nitrogen to the foliage of plants before irrigation, knowing that there might be rainfall coming.”
“I don’t think many people are doing it these days and I don’t think it would have helped this year because we’ve had such long periods of cloudy weather and long periods of saturated soil as well,” he said.
According to Dr Rochester the most important ways to minimise water logging related to how growers managed their soil.
“Soil management is important – so having a decent slope on the ground, good grade, and good drainage is the primary concern of avoiding water logging. Hill height is important – flat hills are more prone to water logging than high hills but that all depends on your soil.”
“Having well aerated soil – not having compacted soil is a good way to reduce the effects of waterlogging and you can help that by increasing organic matter in the soil, conserving stubble by putting crop stubble back into the soil.”
Dr Rochester said it was almost impossible to calculate how much nitrogen fertiliser would be lost from soils during water logging events and the best way to calculate the crop’s needs was via regular leaf blade testing for the rest of the season.
“Petiole testing this year is probably a bit of a waste of time because of the amount of cloudy weather and water logging so leaf blade analysis is much more reliable than petioles in years like we’re experiencing now.”
