Study finds pineapples may not need excessive pre-plant fertiliser

Study finds pineapples may not need excessive pre-plant fertiliser

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HARVEST: Pineapple harvesting in full swing on the Steemson family's Litabella Pines property, north of Bundaberg, Qld.

HARVEST: Pineapple harvesting in full swing on the Steemson family's Litabella Pines property, north of Bundaberg, Qld.

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A pineapple grower has worked with the Qld DAF to explore nutrition options.

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JOHN Steemson, along with his wife Linda and sons Daniel and Justin, operate Littabella Pines, a pineapple farm located north of Bundaberg in the Burnett Mary catchment.

Given the farms proximity to Littabella Creek and the Great Barrier Reef, water quality is currently an important topic for this pineapple farmer.

Understanding the importance of optimal nutrient use for both farm productivity and water quality targets, is increasingly important for horticulture.

John took a proactive approach to understand where refinements in his nutrient program could be made.

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He was curious to find out if applying his full standard rate of pre-plant fertiliser was necessary for successful pineapple crop production.

"I wanted to determine whether the plants can be sustained through my usual foliar application program without the need to supplement this with a large amount of pre-plant fertiliser," John said.

John established a pre-plant fertiliser rate trial over about 7 hectares, to compare three different rates of application.

DOCUMENTED: The paddock layout showing the trials of the varying rates of pre-plant fertiliser applied.

DOCUMENTED: The paddock layout showing the trials of the varying rates of pre-plant fertiliser applied.

Field-based soil survey investigations confirmed soil type to be consistent throughout the study area.

Fertiliser rates used in the trial are shown in the table below.

Pre-plant fertilisers can present a risk to water quality due to large inputs of nutrients, particularly nitrogen, at a time when crop uptake is minimal.

TABLE 1: Fertiliser rates used in the trial.

TABLE 1: Fertiliser rates used in the trial.

Depending on conditions, excess nitrates associated with these fertilisers can be transported off-farm in surface and groundwater.

Optimising nutrient programs can therefore have environmental and economic benefits.

To keep things simple, John laid the trial out in three sections.

The bays were planted with the 'Smooth Cayenne' pineapple variety, with planting spanning June to August 2018.

Southern 'low rate' bays were planted first, proceeding northwards to 'medium rate' bays, and finally 'full rate' bays.

INSIGHT: Examining the growth rates of pineapple plants.

INSIGHT: Examining the growth rates of pineapple plants.

A brief period of wet weather slightly delayed planting in the full rate bays.

Any zones of poor crop establishment within blocks were avoided where possible during sampling for plant and fruit size assessment.

"I did this trial to better understand how I can get the best results from the amount of nutrients I apply," he said.

All bays were farmed conventionally.

Plants received Littabella Pines standard practice of 100kg/ha urea and 100kg/ha potassium sulphate applied as a foliar spray at roughly monthly intervals.

Pests and diseases were controlled as required. Rainfall during the growing period was well below average.

Plant growth sampling

THE plants were sprayed with ethylene to induce flowering in August 2019. Plant growth was compared between the three pre-plant fertiliser rates.

John contacted the Department of Agriculture and Fisheries (Queensland DAF) to assist in a strategic plant sampling analysis.

Seventy-two plants were sampled from 36 random locations within the trial area.

GRAPH 1: This graph displays the plant dimensions from the trial.

GRAPH 1: This graph displays the plant dimensions from the trial.

Plant growth was assessed in terms of total plant weight, leaf weight, roots weight, stem weight and stem diameter.

The results showed growth for all measured plant components to be similar between the full, medium and low rate of pre-plant fertiliser application.

There was no evidence of adverse impacts on plant growth due to lowering the rate of pre-plant fertiliser application from the full Littabella Pines standard rate in the trial area.

SAME: In the plant growth analysis, there was no evidence of adverse impacts on plant growth due to lowering the rate of pre-plant fertiliser application from the full Littabella Pines standard rate in the trial area.

SAME: In the plant growth analysis, there was no evidence of adverse impacts on plant growth due to lowering the rate of pre-plant fertiliser application from the full Littabella Pines standard rate in the trial area.

Harvest fruit sampling

FRUIT harvesting of the trial area occurred in February and March 2020.

Fruit weight and brix was compared between the different pre-plant fertiliser rates.

GRAPH 2: This graph shows the fruit weight and Brix levels from the three fertiliser rates.

GRAPH 2: This graph shows the fruit weight and Brix levels from the three fertiliser rates.

With the help of the grower, DAF strategically collected and weighed fruits in groups of 20, from 54 random locations throughout the trial area.

In total, more than 1000 fruits were sampled. Brix was also measured on one fruit from each group of 20.

The results showed similar weight and brix for fruits produced on plants grown using the full, medium and low rates of pre-plant fertiliser.

RESULTS: The results showed similar weight and brix for fruits produced on plants grown using the full, medium and low rates of pre-plant fertiliser.

RESULTS: The results showed similar weight and brix for fruits produced on plants grown using the full, medium and low rates of pre-plant fertiliser.

There was no clear negative impact on fruit weight or brix associated with reductions of pre-plant fertiliser application in the trial area.

"Visually, there was no apparent difference in plant and fruit size between the three rates," John said.

Take home messages

LOWER pre-plant fertiliser rates did not impact pineapple crop productivity in the investigated trial area.

Plant and fruit size were similar for the full rate and reduced rates of pre-plant fertiliser application.

At lower rates, crops were supplied adequate nutrients from foliar fertiliser sprays and uptake from residual soil sources.

Room exists for refinement of Littabella Pines current standard application rate of pre-plant fertilisers.

John said the findings have given him confidence to continue reduced pre-plant fertiliser rate trials in different blocks and planting windows.

Further trial work will help realise the potential economical returns associated with reductions in pre-plant fertiliser input costs.

"I'm now a firm believer that we can certainly apply what the crop needs nutritionally in a foliar manner in smaller amounts, more regularly throughout the growth cycle of the plants," John said.

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