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Planning ahead for in-crop nutrition management
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Global urea prices have climbed in 2021 and remain at frustratingly high levels. As much as ever, this makes the 2021/22 season a perfect opportunity to get nutrient application on point, reducing significant costs and establishing the crop for the best possible growing season.
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The application of synthetic fertilisers should be aimed at meeting the plant’s requirements for the expected yield. With high input prices persisting, it’s a good year to tailor your own nutrition management strategy, following the 4 Rs: Right product, Right rate, Right time, and Right place. Critically, early season nitrogen (N) losses can be significant in cropping systems that have excessive soil nitrate levels present when crop N demands are low.
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Plant N uptake:
Nitrogen (N) management should ensure there is sufficient N available to the plant at its critical growth stages. Early season N requirements are low, with cotton requiring less than 0.5 kg N/ha/day prior to the onset of flowers. Not until the initiation of flowering does the demand for plant N start to increase.
The increase for plant N uptake is substantial, increasing exponentially from the start of the season. Ian Rochester found cotton required 55 percent of its N uptake during the flowering period (80-130 days after sowing, or DAS), with a maximum N uptake rate of 2.1 kg/ha/day at 102 DAS. This is the key period you should aim to target with your N application management.
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Plant N uptake through the growing season (Rochester, 2012)
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Early season N loss pathways:
Nitrogen (N) management should ensure there is sufficient N available to the plant at its critical growth stages. Early season N requirements are low, with cotton requiring less than 0.5 kg N/ha/day before the onset of flowers. Not until the initiation of flowering does the demand for plant N start to increase.
The increase for plant N uptake is substantial, increasing exponentially from the start of the season. Ian Rochester found cotton required 55 percent of its N uptake during the flowering period (80-130 days after sowing, or DAS), with a maximum N uptake rate of 2.1 kg/ha/day at 102 DAS. This is the key period you should aim to target with your N application management.
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Management options:
Splitting your fertiliser application between upfront and in-crop is one management strategy that has proven to reduce potential percent N losses. If we reduce the amount of fertiliser applied pre-plant and increase the percentage applied in-crop, we can reduce losing N to the air through denitrification or in our tailwater. We can keep it in the paddock, where the crop needs it.
There are three options to apply N in-crop when it’s in the form of Urea: side-dressing; water running; or spreading and irrigating it in.
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Matching nutrition with irrigation management:
Matching the irrigation schedule to soil type is key to maximising crop N uptake. Work conducted by NSW DPI's Jon Baird in northern NSW and Deakin University's Wendy Quayle in southern NSW has confirmed this.
Changes to irrigation deficit introduce complex interactions with maturity and crop development that influence management decisions later in the season. Physiology studies by Jon Baird found that frequent irrigation with high N availability can hinder the retention of first position fruit between the 5th and 15th nodes. Longer growing seasons were required to compensate for the loss of fruit.
For irrigation systems on duplex and/or sodic soils, scheduling of irrigation needs to consider the implications water will have on the soil’s structure. A high frequency of applied water early in the growing season leads to soil structural collapse, causing poor plant N recovery.
Transformations and losses of N from the soil and cropping system can be complex, but crop monitoring using such tools as petiole and leaf tests offers you the ability to evaluate plant N status before further N applications are made. This is especially the case where loss events have occurred, such as rainfall during or following irrigation.
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Ag Econ is conducting a survey into nitrogen management to help inform future industry research, funded by CRDC. Please help by completing this short survey
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