The application of nutrients to ratoon crops harvested late in the season might be reduced in order to improve nutrient use efficiency and reduce input costs without affecting productivity.
Late harvested ratoon crops are generally impacted by less favourable climatic conditions, often with the onset of the wet season (or drought conditions in some regions) shortly after harvest.
Late harvested crops could potentially have reduced productivity, increased nutrient losses and, consequently, are less likely to respond to nutrient inputs than crops ratooned and fertilised earlier in the season.
Lawes et al. (2002) showed that the time of ratooning had a large influence on cane yield, with crops ratooned after October yielding significantly less than those ratooned earlier in the season. The impact on yields due to harvesting late in the season has been supported by Di Bella et al. (2008), McDonald et al. (1999) and Moller (1975).
The following information could be considered when refining nutrient rates using Steps 5 & 6 of the SIX EASY STEPS for crops harvested and ratooned late in the season.
Poor crop condition may be associated with several factors including harvest damage, pest or disease damage, loss of stools, high weed pressure and generally poor ratooning.
Older crop classes are often ratooned later in the season than younger crop classes. Therefore, crops ratooned late in the season are likely to be older ratoons and potentially in poorer condition.
Reducing nutrient inputs for crops harvested late in the season is likely to have lower risk of productivity loss if these crops are also in poorer condition.
Reducing nutrient inputs for a crop that is in good condition, even if harvested late in the season, may not be an appropriate strategy, particularly if the climate outlook is for favourable growing conditions. A recent research trial highlighted this issue (Skocaj et al. 2019).
The position of a soil in the landscape can give an indication of the soil properties, help describe the formation processes, physical and chemical characteristics and which nutrient loss pathways may be dominant.
Soils located low in the landscape that are prone to waterlogging are at risk of losing nitrogen by denitrification. Waterlogging also reduces the ability of roots to function and take up nutrients.
Reductions in yield may be more pronounced and the response to nutrients reduced for crops harvested late in the season on soils in low lying positions, particularly during severe wet seasons.
Where possible, heavy textured soils low in the landscape should be harvested early in the season to provide sufficient time for crop establishment and early nutrient uptake prior to the onset of the wet season.
Light textured soils (sands to loams) higher in the landscape are prone to losses by leaching.
Crop performance on these soils may not be impacted as much as those on low lying positions in seasons experiencing early onset of the wet season, prolonged or high rainfall.
Climate outlooks are an important tool to consider when determining an appropriate nutrient management strategy. By having an indication as to the likelihood of future weather events and seasonal climate outlook, suitable management decisions can be made.
In years experiencing excessive spring summer rainfall (typical of La-Niña events) and low solar radiation, crop growth and responsiveness to applied nitrogen may be reduced.
For those years where spring summer rainfall is likely to be normal to drier than normal (typical of Neutral and El-Niño events), crop responsiveness to applied N is unlikely to be adversely impacted.
In Southern regions, excessive rainfall rarely limits productivity. Reducing nitrogen application rates for crops harvested late in the season may still be considered but guidance related to climate outlooks above may not be applicable.
It is recommended that any change in management is tested on-farm. This will build confidence in both the new nutrient rates but also the process of fine tuning a nutrient management program as part of steps 5 & 6 in the SIX EASY STEPS. A guideline for conducting on-farm trials is included in the SIX EASY STEPS toolbox.
Leaf testing also provides a valuable method for checking on the adequacy of nutrient inputs.
A reduction to fertiliser application rates of up to 20% could be tested on farm.
In the Burdekin, as crops age and are ratooned under less than ideal conditions late in the season, the likelihood of them responding to the higher N application rate based on a DYP of 180 t cane/ha decreases. In this case, adjusting to lower N rates based on a DYP of 150 t cane/ha could be considered.
Any reduction in fertiliser application rates should not be used multiple times in a crop cycle as this would increase the risk of productivity and profitability losses.
Crops ratooned late in the season should always be fertilised as soon after harvest as practical to avoid application in the wet season.
Enhanced efficiency nitrogen fertilisers (EEFs) may provide benefit when fertilising late in the season. Nitrification inhibitors (Entec®, eNtrench®, other) temporarily protect nitrogen from losses whilst still being available to the crop. Current research suggests these products can be applied at lower rates (~20%) without affecting productivity (further guidance for the use of EEF’s will be available in the near future).
If dry, irrigate to ensure quick crop establishment and nutrient uptake.
Papers published from the Australian Society of Sugar Cane Technologists annual conference are also available at www.assct.com.au
Version: April 2020
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