Making the most of flooded crops

11 February, 2011

CSIRO researchers have provided some insight for cotton growers managing crops damaged by floods during December and January.

Speaking on CSD’s Web on Wednesday broadcast, CSIRO Narrabri-based research scientists Dr Mike Bange and Dr Ian Rochester said crops affected by flooding would have lower yield potential but by careful monitoring and management, there were some techniques growers could use to minimise losses.

Dr Bange, a specialist in crop physiology who has recently visited some of the flood affected regions said three factors were conspiring against crops inundated by flood water – the first being the delay in crop development that has occurred during the season.

“There is generally a defined end to the season so if we lose two or three weeks from crops being delayed either due to inundation or the fact that it has been cooler – that’s two to three weeks less yield potential. Based on research, we work on a 0.3 to 0.6 bales per hectare yield reduction for every week of lost time of fruit growth in the crop,” he said.

“We need to consider that in a lot of regions, crops have been delayed because the season has been cooler – there are situations where crops are two to three weeks later from when flowering or fruiting has started.”

“The second thing is the loss of plant stand – in some cases plant stand will have been reduced and become gappy which can reduce yield potential.”

“Finally, there’s the actual affect of the inundation, flooding and water-logging itself. Roots systems have been impaired or damaged considerably from being inundated and photosynthesis would have also been reduced. The crop’s reaction to water-logging stress is reduced growth of nodes and shedding of fruit leading to less fruit. Inundated crops also provide excellent conditions for plant diseases,” he said.

Dr Bange said people needed to be realistic in determining how long crops could be grown to recover.

“The best way to work how much time is left to produce fruit is to look at local knowledge of when the last effective flower or last effective square occurs for your district. The last effective flower or last effective square is that fruit that is going to have time to mature and produce yield. It will take about 80 days at average temperatures for a square to become a boll.”

“Attempting to grow crops into autumn runs into the risk of fruit that may not be mature and thus contribute little to yield. Immature fruit also will have lower micronaire, and potentially neps which are small knots in the fibre. Late crops can sometimes have difficulty with defoliation which can lead to lower colour and leaf grades in the sample and can be attractive to whitefly and aphids – all of which can lead to increased costs and lower returns,” he said.

Dr Bange said the plant growth regulator mepiquat chloride, commonly referred to as Pix, was a useful tool in managing damaged crop if used correctly.

He said Pix, when applied to the crop, reduces vegetative growth and if applied incorrectly could restrict the plant’s recovery at a time when you need to be putting on more growth to get more yield.

“The first way it can be used effectively is to maintain a balance between vegetative and reproductive growth as the plants recover – making sure it doesn’t get too rank as it regrows. This requires careful and regular monitoring of vegetative growth rate.”

“The second use of Pix is to aid in crops cutting out to manage last effective flower – looking after the fruit that you’ve got which is going to be mature in time for harvest.”

Dr Bange also warned against under-irrigating flooded crops in attempt to encourage roots deeper into the soil profile.

“The danger of putting this stress on these crops is that you’re restricting the growth of the fruit that are already on the plant and restricting the potential to grow more fruit. With the limited season length left you need to ensure you continue growing fruit while you can. It’s a balance to ensure you’re not watering too much and repeat the water-logging problems but to encourage the crop to keep growing,” Dr Bange said.

Another dilemma for growers facing the prospect of managing crops damaged by flood is determining whether there is enough nutrition left in the soil to achieve the best yield possible in a bad situation.

According to Dr Ian Rochester, a research scientist specialising in cotton crop nutrition, estimating how much fertiliser has been lost after the flood waters recede is a complicated and difficult task.

He said the crop nutrients most prone to loss are the ones most mobile in the soil – notably nitrogen and sulphur

“Generally, if you’ve got flooding you can expect to lose some of the nitrogen in the soil. If you’re starting off with higher levels of nitrate and higher levels of stubble, your losses are probably going to be greater,” he said.

According to Dr Rochester, soil testing in-crop was of little value because most nitrogen fertiliser applied has gone through to be in organic forms which won’t show up on soil tests and that testing of leaf blades was a more accurate way of assessing if the crop had access to enough nitrogen.

“People who traditionally use high fertiliser levels should have some nitrogen left. I’d suggest leaf testing one to three times to make sure your crop is on track and not running out of nitrogen.”

“Adding more would be useful depending on how much nitrogen you’ve lost – if there have been huge losses, you might have to add a little bit more nitrogen but generally in the past when people have assessed their crops that were starting to regrow again, if they had enough nitrogen on at the start there’s probably not a need to add any more particularly if those crops have a substantially reduced yield potential.”

“There is a danger in over-fertilising those crops as it will produce vegetative matter rather than bolls,” he said.

Dr Rochester said he had fielded many calls from people asking about the benefits of foliar fertiliser applications in a bid to improve flood-damaged crops.

“Foliar fertilisers will offer a benefit in the short term if there’s a substantial deficiency in one or more of the nutrients. Really the idea is to get the root system growing and that requires aeration in the soil so the roots can get deeper into the soil profile and access the water and nutrients that might have been washed down there – and that’s particularly true for nitrogen and sulphur,” Dr Rochester said.

Dr Bange and Dr Rochester recommended people get more information from Cotton CRC publications such as the Australian Cotton Production Guide and FibrePAK which are available for download from the Cotton CRC website.

11 February 2011

Further Information:

Dr Mike Bange 0267 991500
Dr Ian Rochester 0267 991500