RESEARCH & EVENTS
It ' s not just about NPK
The ABA ’ s Peter Jealous is reviewing the ABA factsheets on nutrition with industry members including Brett Rosenzweig and Peter Reynolds to provide an update on planning a post harvest nutrition program .
IN almond orchards , fertigation schedules often focus on the primary macronutrients : Nitrogen ( N ), Phosphorus ( P ) and Potassium ( K ). These are indeed essential for tree growth and crop production , but several other micronutrients also play critical roles and their importance should not be overlooked . A typical annual nutritional program or forecast analysis includes not only N , P , and K but also Calcium ( Ca ), Magnesium ( Mg ), Sodium ( Na ), Chloride ( Cl ), Zinc ( Zn ), Manganese ( Mn ), Iron ( Fe ), Copper ( Cu ), Boron ( B ) and Sulphur ( S ). To maintain a healthy and productive orchard , it is essential to replace the nutrients removed by the crop at harvest . The ABA fact sheet on crop nutrient removal emphasizes the need to apply nutrients in amounts that match or exceed the removal rates , allowing for not only fruit production but also root and shoot growth , age and size of trees as well as losses due to factors such as leaching or soil nutrient lock-up .
Sampling and Nutrient Analysis To better understand nutrient use , regular sampling and lab analysis can provide insights by comparing nutrient levels in the crop with cumulative fertiliser inputs . In many cases , fertiliser applications exceed the amount removed by the crop , though specific nutrients like potassium or phosphorus may occasionally be under-applied . It is important to determine the aim of the fertiliser program , is it desirable to increase tree growth above normal growth or to apply just enough to maintain the crop and some small amount of growth ? Nutrient inputs and removals can vary depending on fertiliser products chosen , application method and timing , management practices and seasonal conditions . Nutrients are utilised not only for fruit production but also for tree growth and processes such as nutrient recycling in leaves , wood and roots with additional losses occurring through leaching ,
A forthcoming ABA factsheet on crop nutrient removal will incorporate key messages from the ABA Almond Skills workshop on nutrition held in the Riverland , Sunraysia and the Riverina during winter .
volatilisation and pruning removals .
Nutrient Inputs : How Much is Enough ? The amount of nutrient input required extends beyond what is removed by the crop . There will need to be a forecast for the next season ’ s crop load , how much the tree will naturally grow ( 1 year older ) and how much tree growth is desired . A common approach is to increase nutrient inputs by 20-30 % to account for root and shoot growth , as well as other nutrient losses . This adjustment helps ensure a balanced nutrient supply , though application rates and timing of specific products may vary depending on fertilisation strategies , with some applying more than necessary while others achieve a closer balance to tree and crop needs .
Consequences of Over-application When nutrient inputs significantly exceed crop removal , the excess nutrients can either accumulate in the soil or in the case of highly mobile forms like nitrates , be leached away from the root zone . Over-application might not lead to increased yields , especially in seasons where the crop load is lower . In fact , too much vegetative growth can occur , which may reduce fruitfulness by shading the canopy and hindering flower bud development . Other risks of over application may include immediate root damage ( for example , extremely high nitrate levels ), locking up other essential nutrients ( for example ,
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very high rates of Phosphorus can inhibit Zinc uptake ) or altering soil characteristics ( e . g . changing soil pH ). In such situations , it may be more economical to reduce fertiliser inputs to match the tree ’ s actual demand , particularly in years with lighter yields . This can save costs in the short term while preserving the tree ’ s health and productivity for the following season .
The Role of Calcium and Magnesium Calcium and magnesium , though sometimes overlooked , are essential macronutrients that should be factored into fertiliser programs . Calcium supports root tip growth , cell wall development , kernel , shell & hull strength and soil structure , while magnesium is vital for chlorophyll production and other plant functions . Some orchards may not actually apply enough calcium or magnesium to match crop removal , though many growers successfully meet calcium needs through products like calcium nitrate . Both nutrients are crucial for maintaining the soil ’ s cation exchange capacity , which affects nutrient retention and availability , especially in sandy soils with low capacity , potentially impacting tree health and productivity . Calcium also plays a role in helping to displace sodium in the soil , thereby reducing the damaging impact of salinity . It is also important to avoid over supplying Magnesium as it can lead to diminished soil structure ( slaking ). Continued page 43
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