Soil sampling 11

BY4215

Taking soil samples

Process of collecting soil from a field to assess nutrient status and properties

Composite sample

A sample made by mixing multiple soil cores from an area to get a representative sample

Creating a composite sample

Collect 10-20 cores, mix thoroughly in a clean bucket, take a portion for analysis, seal and submit to a lab

Random sampling

Collecting soil samples from a field in a non-patterned way, suitable for uniform soil areas

Grid sampling

Dividing a field into uniform blocks and collecting a composite sample from each block, provides high detail

Zone sampling

Dividing a field into areas based on characteristics like soil type or slope and collecting composite samples from each zone

Random sampling advantage

Low cost and simple

Random sampling disadvantage

Not suitable for highly variable fields

Sampling area uniformity

Sample areas should have uniform soil type, texture, structure, slope, drainage, organic matter, cropping history, and fertilizer treatment

Sampling plan

A strategy to decide which areas to sample, typically 2-4 hectares per sample

Sampling frequency

Depends on rate of nutrient change influenced by fertiliser input, stocking rate, nutrient removal, and soil type

Grid sampling specifics

Field divided into 2-2.5 acre cells, 15-20 cores per cell, collected within 10-foot radius of georeferenced point

Grid sampling advantage

Good assessment of variability

Grid sampling disadvantage

Expensive

Zone sampling specifics

Areas <10-15 acres, 20 cores per zone, collected in zig-zag pattern, borders can be georeferenced

Zone sampling advantage

Cost-effective and better assessment of variability than random

Zone sampling disadvantage

Not as detailed as grid

Zone delineation

Based on field knowledge, soil maps, topography, past history, yield maps, nutrient maps

Sampling depth

All cores taken to 10 cm, equal volume per core

Number of cores per area

20 cores per 2-4 ha sampling area

Avoidance in sampling

Dung, urine patches, gateways, feeding areas

Sample timing

Same time each year, 4-6 months after fertiliser for P and K, 2 years after lime for lime requirement

Sample processing

Air dry if wet, store separately in labeled plastic bags, bulk to create representative sample

Precision agriculture sampling

Each sample analyzed individually to reflect variation

Diagnostic soil tests

Fast, cheap, simple, correlate to plant response, good tests for P, K, and pH

Soil heterogeneity

Requires mixing of subsamples for representative analysis

Soil analysis steps

Crush, air dry, sieve through 2 mm, extract mineral N with KCl, available P with Morgan’s reagent, K, Mg, Ca with Morgan’s extracts

Recommended P application rate

Based on soil P Index, varies from 0-45 kg/ha depending on soil level and treatment

Soil N reserves

90% in organic forms, mineralized to NH₄⁺ and NO₃⁻ for crop uptake

Min-N availability

Depends on crop rotation and soil type, faster in light soils, slower in heavy soils

N supply status

Deduced from previous cropping and manurial history, categorized into N Index

N Index for tillage crops

Index 1-4 based on previous crops, N input, and pasture history

Recommended N application for malting barley

Varies by soil N Index and soil type (limestone/heavy, mineral, peat)

Comparing soil types

Consider bulk density, texture, structure, colour, depth, pH, and organic content

Site-specific management

Adjusts fertilizer recommendations to field variation using sampling, analysis, GIS, and computer-controlled spreading

High-technology sampling

Facilitates site-specific nutrient management, uses multiple cores per zone to create representative samples