Nutrient analysis in almond production

Soil analysis

Soil analysis can be used to provide baseline initial information for a fertilizer programme – particularly as an indication of potassium and phosphorus requirements. It is also used to assess soil pH and organic matter levels.

There is though often a poor relationship between soil and plant nutrient levels in nut tree crops and so soil analysis alone does not aid accurate nutrition.

Tissue analysis

Leaf tissue analysis should be used to confirm that the balance between elements within an applied fertilizer programme is sufficient to support both leaf canopy and nut production.

Tissue analysis will also confirm visible deficiency symptoms and indicate any excessive nutrient concentrations which may be causing other nutrient imbalances or toxicities.

Note that nutrient concentrations change during the growing season (Figure 22), therefore, a defined sampling date is necessary to ensure the nutrient contents found in leaf analysis comparable to critical values.

Some advisors are utilizing in-season leaf analysis of nitrogen to more closely match demand needs – particularly in regions where N use is restricted due to legislation. Thus, if N-status in July is sufficient, post-harvest nitrogen applications will be omitted or reduced, minimizing leaching and other nutrient loss risks. In contrast, if the leaf nitrogen concentration is inadequate, or if the trees are supporting a greater than normal yield, then foliar or fertigation nitrogen applications can be used to improve their nitrogen status.

Whether tissue testing in April or July, ensure you collect a representative sample to obtain an even sample from each tree and take a composite sample of leaves from across the area being analyzed. Samples are normally taken of recently matured leaves from non-fruiting shoots .

They should contain enough material from different sites within the grove; typically 5-10 leaves per tree from 10-20 randomly selected trees resulting in around 100 leaves per sample. Prepare different samples for different varieties, soil types, rootstocks etc. If leaf analysis aims to compare year by year performance, leaf samples should ideally be taken from the same trees at the same time/growth stage.

Trees must be healthy, free of dust, pesticide or foliar fertilizer residues. Do not include leaves that are damaged by insects or pests, or by mechanical injury. Sampling time is usually several weeks after flowering, mid July/beginning August, when the leaf nutrient content is relatively stable (Figure 22).

Common practice is to take tissues from trees as set out below. Different countries have different sampling procedures and it is important to maintain consistency of techniques when assessing all crops in a region:

Almonds

There is a move in almonds to take tissue samples earlier on in the season in April – 37-49 days after full bloom – most notably for the variety, Nonpareil. Then – on the back of early season yield estimates – to adjust in-season and/or fruit maturity/post-harvest nitrogen rates accordingly.

When sampling at this earlier time, sample all leaves from 5-8 non-fruiting spurs on a tree, around 6 weeks after full bloom. Most leaves will have reached full size by this stage. Collect these leaves from 18 to 28 trees per orchard, gathering at least 100 leaves. Each tree sampled must be around 30m from other samples trees.

When sampling in July, take around 100 fully expanded non-fruiting spur leaves.

Hull analysis

Hull analysis at harvest is a better indicator for tree boron status than leaf analysis in almonds (see boron chapter on page 50 for explanation and typical range of values).

Best practice is to sample 40-50 hulls per tree from different trees at around 1.8m height at harvest.

Alternatively pick at least 40 hulls from the wind-rows. Keep the hulls separate by grove and variety. Make sure that there is no contamination from soil when picking the hulls from the ground.