Soil analysis is an indicator of the soil nutrient status of fruit trees, however, the concentration of a nutrient in the soil does not always mean it is available to the tree.  A soil characteristic that can directly or indirectly affect tree fruits growth and productivity is soil pH. The pH affects the nutrient availability and should be maintained between 6.0 and 7.0 in orchard for optimum nutrient availability (Hanson, nd).  Soil pH need to be monitored in established orchards (Crassweller, 2018).  Soil pH in Okanagan valley is usually neutral or alkaline (>7). Agricultural or dolomitic lime can be incorporated into the soil by cultivation if the pH is found to be low. High soil pH will reduce the availability of important micronutrients such as Fe, Zn and Mn. High soil pH can be managed by sulfur, or sulfur-based fertilizers application over time.    

Soil analysis is also useful to do prior to planting since it is easier to adjust nutrient levels before trees are established.  If replanting, take a soil sample after all roots are removed and grading is completed (Crassweller, 2018). Soil analysis at the end of a season can also be useful to check for excess fertilizer application particularly N.   

Soil Sampling Methods for Orchards

Soil sampling is typically done in the fall or spring.  If replanting, it is best to collect a soil sample in the fall preceding planting.  Such analyses can reveal unsuitable soil conditions that may need to be corrected before planting.

There can be significant differences in the soil in a block. Natural land variations, irrigation, and orchard practices can result in changes to the nutrient content of the soil, thus sample location can make a difference in the results.   Common land variations can be areas of high calcium carbonate from runoff of nearby hills. Irrigation can impact soil nutrient content by reducing the presence of soluble nutrients through leaching and will impact where the majority of roots will be growing.  Orchard practices such as the use of mulch, fertilizer placement, cultivation, equipment traffic and herbicide application can result in distinct soil differences in soil organic matter and nutrients between row and alleys in the orchards (Midwood et al. 2020).

Soil samples should be collected as a composite sample (single sample resulting from the combination of several smaller samples).  If soil is uniform throughout an orchard, a single composite sample may be sufficient.  Separate composite samples may need to be collected  from each unique area when land contours or soil types obviously vary. For trees planted greater than 13 feet between rows, select five to ten trees for sampling in an orchard block where the soils are similar (Figure 1).  For large areas of similar soil, a minimum of 30 trees per ha (12 trees per acre) should be used.  Take one sample beneath each tree at 1 m from the tree trunk and make a composite sample for analysis. 

Figure 1. Selection of trees for soil sampling when greater than 13 feet between rows

For young trees, select young trees which are similar in growth characteristics and height such as less than 0.5 m, 0.5-1.0 m and so on in an orchard block where the soils are similar.  Obtain individual samples from within 60 cm from the trunk beside four to eight young trees and make a composite sample for analysis.  A composite sample for analysis from two or more locations can also be made depending on the height as showed in Figure 2.

Figure 2. Selection of composite soil samples for trees of different heights

 

When replanting an old orchard, at least 2 composite samples should be taken and kept separately.  One composite sample from the sites of removed trees where fertilizer applications have been heavy and one on sites between tree rows (alleys) that have received little or no fertilizer. 

Soil probes, augers, or shovels can be used to take samples as seen in Figure 5.  Be sure all tools and containers are clean.  If a shovel is used, clear away the surface litter and dig a U-shaped hole in the soil.  A 2.5 cm (1 “) slice to a depth of 0-30 cm (0-12”) is taken.  It should be noted that lime recommendations are based on lime requirement analysis of composite samples taken from the 0-30 cm (0-12”) depth. This is an individual sample which should be mixed in a clean pail or plastic sample bag to make a composite sample.  Samples can also be taken from 30-45 cm in order to analyse the subsoil for soil acidity. Samples taken from these depths are obtained in a similar manner to the 0-30 cm method described above.  After the individual soil samples are mixed together well, fill the soil sample box with soil and label with date of sample and sample identification (name of orchard, block ID, location of sample, etc).  Fill out a soil information sheet for each sample.  Draw a rough sketch of the orchard indicating the various sampling locations.

Hutchinson et al. (2009) suggest sampling soils in orchards at least 2 times at pre-plant prior to replant and prior to tree establishment, no sampling at non-bearing and at least every 3 years during bearing.  Soil and leaf tissue samples should be collected in the same year to allow comparing.

Figure 3. Examples of tools and method used for soil sampling    

Assessing Soil Nutrient Content

Sallato et al. (2019) describe optimal levels of nutrients in soils for orchards in Washington state.  A summary of their findings is found in Table 1.

Table 1. Optimal soil test levels for fruit trees from Sallato et al. (2019)

Soil test	Units	Low	Optimal	Excessive	Methoda
pH	-	<5.0	6.0-7.5	>8.0	1:1 CaCl2
EC	mmhos/cm	-	<2.6	>4.0	Paste
EC 1:2:5 or 1:1	mmhos/cm	-	<0.5	>1.0	1:1
P-Olsenb	ppm	<10	15.40	>50	NaHCO3
Potassium (K)	ppm	<120	150-250	>300	NH4OAc
Potassium (K)	meg/100 g	<0.3	0.4-0.6	>0.7	NH4OAc
Calcium (Ca)	meg/100 g	<3.0	4.1-20	-	NH4OAc
Magnesium (Mg)	meg/100 g	<0.5	0.5-2.5	>2.5	NH4OAc
Sodium (Na)	meg/100 g	-	<0.5	>0.5	NH4OAc
Boron (B)	ppm	<1.0	1.0-1.5	>1.5	CaCl2 0.01 mol/L
Sulfur (S)c	ppm	<4.0	9-20	>20	Ca3(PO4)2
Zinc (Zn)	ppm	<0.25	0.6-1.0	-	DTPA
Copper (Cu)	ppm	<0.1	0.6-1.0	>20	DTPA
Manganese (Mn)	ppm	-	1-5	>50	DTPA
Iron (Fe)d	ppm	>4.5	-	-	DTPA
Molybdenum (Mo)	ppm	-	0.11-0.20	-	DTPA

^a Methods: derived from Soil, Plant and Water Reference Methods for the Western Region, 2005, by Gavlak et al.

^b P-Olsen is recommended for the mildly acid to alkaline soils of eastern Washington (Gavlak et al. 2005).

^c The method has a detection limit of 2.0 mg kg-1 (dry basis) and is generally reproducible to within ± 15%. Better to look at in-tissue analysis.

^d Soil analyses for Fe do not correlate well with Fe availability.

Note: mg/kg = ppm. ppm = meq/100 g*MW/charge*10.

Soil testing requirements under the new Agricultural Environmental Management Code of Practice

The Agricultural Waste Control Regulation (AWCR) was replaced by the Agricultural Environmental Management Code of Practice (AEM CoP) in 2019. The AEM CoP applies to all agricultural operations in BC, including orchards.  Some requirements of the AEM CoP have already been implemented, while others are being phased in. Here, we briefly outline the requirements for soil testing and record keeping that currently apply to orchards under the AEM CoP, provide links to information on the requirements for processing, storing and applying sources of soil nutrients (e.g., fertilizer, manure, compost), and outline the new requirements for nutrient management planning that are being phased in.

Current requirements under the AEM CoP that apply to orchards:

A. Soil testing

 

Under the AEMCoP, most orchard soils must now be tested for post-harvest soil nitrate and soil available P on a regular basis. The figure below should help you figure out if, and how frequently, you will need to conduct these tests.

More information about soil sampling, analysis, and interpretation of soil test results can be found here and here. Recommended soil sampling dates based on the location of your orchard can be found here.

B. Record keeping

You will also need to keep records to demonstrate that you are applying nutrients at appropriate rates for your site, soil and crop.  Records should include information on:

1. the location and size of your orchard;
2. annual crop nutrient needs;
3. annual crop yield;
4. dates, locations, type and rates of nutrient applications;
5. details of how nutrient application rates were determined;  and
6. results of any soil nutrient analyses (post-harvest soil nitrate and soil test P, at a minimum). 

Leaf nutrient analyses are not required, but if you use leaf analyses to determine nutrient application rates, this information should also be included in your records.  Moving forward, you will need to retain at least 5 years’ worth of records.  More information about recording-keeping for nutrient applications can be found here.

C. Management of nutrient sources

The AEMCoP also includes requirements for processing, storing and applying nutrients to the soil.  You can find more information at the links below:

• Production, distribution and use of agricultural compost
• Storage and use of manure and other agricultural by-products, e.g., pruning debris,
• Maintenance of setbacks for the storage, processing and application of fertilizer, compost, manure and woody residue
• Timing of nutrient applications to the soil

Phased-in requirements under the AEM CoP that will apply to orchards:

D . Nutrient management plans (NMP)

The requirement to complete nutrient management plans is being phased in over the next several years. 

• Initially, only orchards ≥ 5 ha that fell within the ‘Hullcar aquifer recharge area’ and that have post-harvest soil test nitrate ≥100 kg N/ha were required to have a nutrient management plan. To find out if your orchard falls within this area, check out this map.
• Beginning in July 2021, some orchards ≥ 5 ha that fall within a ‘vulnerable aquifer recharge area’, that keep > 5 animal units (equivalent to about 5 cows or 17 ewe/lamb pairs) and that have post-harvest soil test nitrate ≥100 kg N/ha may also be required to have a nutrient management plan.  To find out if your orchard falls within one of these areas and when these requirements will apply to you, check out the maps and table accessible here.
• Beginning in July 2023, the requirement to complete a nutrient management plan for other orchards will be based on:

1. orchard size;
2. whether the orchard falls within a ‘vulnerable aquifer recharge area’ or a ‘phosphorus-affected area’;
3. the date (additional areas will be phased in each year); and
4. the results of your orchard’s post-harvest soil nitrate and soil P tests.

By July 2026, all agricultural operations ≥ 5 ha located in a ‘high-risk’ area, with soil test nitrate ≥100 kg N/ha and soil test phosphorus ≥100 ppm P will require a nutrient management plan.  The Okanagan Lake Basin, among others, is considered a ‘phosphorus-affected area’.  Osoyoos, Okanagan Falls, Oliver, and Penticton, among other locations, are considered ‘vulnerable aquifer recharge areas.

Once you know whether your orchard falls within a ‘vulnerable-aquifer recharge area’ or a ‘P-affected area’, and you have the results of your soil tests, check out the table here to figure out if you will need a nutrient management plan for your orchard and who will be able to prepare it.  Information about preparing nutrient management plans can be found here.

More detailed information can be found on the province’s AEM CoP webpage: gov.bc.ca/Agricultural-Environmental-Management, or on the BC Agriculture Council’s AEM CoP webpage: https://bcac.ca/aemcop/.  You can also get answers to specific questions, via email, at: [email protected].