Nutrient management is a key component of high-quality fruit production – the human analogy is ‘we are what we eat’.

The same applies to plants – and particularly to apples and pears, where the goal is to produce high-dry matter, crunchy, high-colour fruit. Unlike a vegetable grower, where it’s all about leafy green yield, the apple grower must manage the nutritional balance to ensure the fruit is of high eating quality.

As with many Future Orchards orchard walks, the spring walks returned to the nutrition component of the production jigsaw. 

Before the walks, soil samples were taken, and during the walks, leaf tests.

The presenters were also able to observe the crop and talk to the growers about their historical fruit outcomes.

Sampling, timing and frequency

There are a range of nutrient analysis techniques which offer insights into plant nutrient composition and, therefore, block performance and crop quality.

In combination, these tests help quantify nutrient levels through the different stages of the plant nutrient cycle, and how these nutrients exist in the soil, plant and are then removed as crop.

Best practice is to incorporate various testing techniques into orchard management, to better understand your block-specific nutrient budgets. These include:

• Soil tests
• Leaf tests
• Fruitlet and fruit tests
• Fertiliser/nutrient application history
• Crop outcomes.
   

Soil testing

Soil testing best practice is to test each block (or distinct soil type) at least every two years.

This helps growers understand the soil nutrient balance, as well as the implications of the soil test results and how these translate through to block performance.

In soil, the relationship between nutrients, their ratios and the soil pH result all have a bearing on nutrient availability and uptake.

Fertiliser input history provides background and validates recommendations, especially when aiming to alter nutrient ratios, maintain/optimise available nutrients, or fix identified deficiencies.

It can also highlight historical nutrient applications that may have contributed to elevated levels.

Leaf testing

Best practice leaf testing involves seasonal testing of each distinct block, with a test taken in mid-November followed by a secondary test in late January (pre-harvest).

The mid-November leaf test highlights any nutrient deficiencies the plant has experienced over spring.

The aim of this test is to capture this information before visual symptoms occur and the damage has been done.

Once a nutrient deficiency can be diagnosed through visual leaf symptoms, the plant potential has already been compromised.

Leaf tests should then be retaken in late January.

These will show if changes made to block-specific nutrient plans have achieved the desired results.

This test also guides any post-harvest nutrient requirements.

If you are targeting high yields, the second test will validate that nutrient levels are changing at the correct rates throughout the season and remaining within the target ‘zone’ – outlined in Table 2.

Paired leaf tests (tests taken from two separate areas of a block) could be carried out if a grower was trying to narrow the focus of a block-specific issue.

For example, one of the 10 case study blocks analysed had a long history of poor fruit colour at harvest.

Both ends of the block were tested, both showed elevated nitrogen levels.

Both the N:P ratio and the N:K ratio were above optimum due to the elevated nitrogen levels.

The identified N percentage was likely to remain above the desired ‘pre-harvest leaf test’ parameters (mentioned in Table 2) and is understood to be a key cause of the crop’s inability to colour at harvest.

Pre-harvest fruit samples could also be taken to show the internal nutrient content of the fruit and highlight specific block challenges.

Examples of this include:

• N:K ratios and, therefore, the impacts on ability of fruit colouring at harvest
• Mg:K ratios in the fruit at harvest can confirm fruit quality issues
• Calcium levels can highlight any concerns around calcium-related storage disorders, allowing for changes to the post-harvest management of the fruit.

Leaf test targets

Different stages of the season have different leaf test targets.

These targets are aimed at optimising plant health and crop quality.

As an example, nitrogen should be around 2.5–2.7 per cent at the mid-November leaf test, but by late January, nitrogen should have dropped to around 2.0 per cent to support fruit pigmentation at harvest.

Late January leaf nitrogen levels will guide post-harvest application requirements, such as the decision to make a post-harvest nitrogen application to support bud quality and return bloom.

It is important to consider the influence from the following factors when making decisions on block-specific nutrient management programs:

• Seasonal crop loads (nutrient removal)
• Block vigour status
• Local nutrient delivery sources
• Natural composition of the soil bedrock (K, P, Ca, Mg)
• Soil organic matter, compost application or a legume dominated sward (N)
• Rainfall, ground water and irrigation composition (N, Ca, P)
• Historical nutrient inputs.

Crop removal rates

Crop nutrient removal in apples has been widely studied by analysing the nutrient composition of the fruit at harvest. Although this varies depending on the variety, generally, the numbers in Table 3 can be used to understand block-specific nutrient budgets.

To ensure understanding of Table 3, a 100t per ha crop removes 85kg of nitrogen and 120kg of potassium.

For the trace elements, the removals are 100g of iron and 400g of zinc. These are extremely low – an important aspect to understand.

Soil CEC balance

The cation exchange capacity (CEC) determines the number of cation binding sites within the soil profile.

The more positive the charge, the more sites available.

Sand tends to have a low CEC with few available sites.

A little-and-often approach to fertiliser application (potentially fertigation) would be a good option for low CEC soils.

Compost applications or specific management strategies to improve the organic matter in low CEC soils is essential.