Page 96 - Nutrient Management Planning Guide

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Chapter 3.3

Recall that soil analysis requirements under AOPA require a sample representing the entire 0 to 60 cm (0 to 24 in) depth to measure NO

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s i d e b a r

Under AOPA, fields that will receive manure must be soil tested a minimum of once every three years.

s i d e b a r Sampling for Phosphorus and Potassium

Phosphorus and K recommendations are based on the amounts of crop available P and K contained in the 0 to 15 cm depth sample. Generally, most of the plant available P in soil is confined to the plow layer because P is relatively immobile.

Sampling Frequency

Ideally, all fields should be sampled and tested annually, but this may not always be practical. Alternatively, samples may be taken from representative fields and the resulting recommendations can be used to manage un-sampled fields. Fields could also be sampled every other year, with estimates used in years between samplings to make fertility decisions. In both cases, the cost and time requirements associated with sampling are reduced; however, nutrient management decision-making may be less precise.

Sampling Strategies

Soil variability is a major concern when trying to obtain a representative soil sample. The strategy used to sample a field can address this challenge. Information collected during a site assessment can assist in choosing an appropriate strategy for a particular field.

Some of the sampling strategies that can be followed include:

Random composite sampling • Directed random composite sampling • Benchmark sampling • Landscape-directed benchmark sampling • Grid sampling •

General Soil Sampling Guidelines

For any soil sampling strategy: Take 15 to 20 cores for each representative bulk •

sample. This number of samples is based on statistical precision.

Each core will be segmented into lengths that •

represent depths of 0 to 15 cm, 15 to 30 cm and 30 to 60 cm.

Separate the segmented cores by depth into •

clean, labeled plastic pails. Thoroughly mix the content of each pail, crushing any lumps in the process. Avoid using metal pails to collect samples because they can alter the results of micronutrient tests.

Take a single sub-sample (0.5 kg) for each •

sampling depth and submit for analysis.

For hilly fields with knolls, slopes, or •

depressions, take samples from mid-slope positions to get a representative sample of the field average.

Avoid sampling obvious areas of unusual •

variability such as: saline areas, eroded knolls, old manure piles, burn piles, haystacks, corrals, fence rows, old farmsteads or any other unusual areas.

Soils within 15 m (50 ft) of field borders or •

shelterbelts and within 50 m (150 ft) of built-up roads should be avoided or sampled separately.

Always sample prior to manure or fertilizer •

applications.