- D. Cressman, Ecologistics Limited, Waterloo, Ont.
Evaluation Summary (Tech. Transfer Report Summaries)
View / Download Final Report [458 KB pdf] (appendices included)
Associated SWEEP/LSP Research
Completed: December, 1990
reduced tillage, conventional tillage, no-till, nutrient stratification,
bulk density, phosphorus, potassium
Under conservation tillage systems using broadcast placement of phosphorus
(P) fertilizers, there is a tendency for phosphorus to remain at or near
the surface of the soil, resulting in vertical stratification. Band placement
of P fertilizer in soils under conservation tillage may also lead to stratification
of nutrients in a horizontal dimension.
In order to study the extent and severity of nutrient stratification
in Ontario soils, a survey was conducted of the distribution of P and other
nutrients, such as potassium (K), magnesium (Mg) and calcium (Ca), in a
vertical and horizontal grid over a number of field conditions and management
histories. The distribution of pH and organic matter and several soil physical
properties (bulk density, cone penetrometer resistance, surface water infiltration)
were also studied in relation to the distribution patterns of nutrients
in the soil.
In the first of two experiments, a study of vertical stratification of
nutrients, the effects of conservation tillage were compared with the effects
of conventional tillage over a range of soil textural groups. At each of
36 sites, the soil was sampled at 2 cm increments to a depth of 20 cm, and
below that at 5 cm increments to a depth of 45 cm. Samples were analyzed
for plant-available P, K, Mg and Ca in addition to pH and organic matter.
Soil physical property data (bulk density, cone penetrometer resistance
and surface water infiltration) were also collected at each site.
A questionnaire was given to each farm cooperator requesting information
regarding management history of the field. Based upon this information,
the management of each field was classified as conventional tillage (CT),
reduced tillage (RT) or no-till (NT).
Nutrient data were grouped into three strata (0-10 cm, 10-20 cm and 20-45
cm) corresponding to expected average depths of secondary and primary tillage.
The data within these strata were statistically summarized to determine
means and regressed to find the slope over depth. The slope provided a relative
index of change in nutrient concentration with depth and thereby an indication
of stratification. The slopes of nutrient concentrations were analyzed for
differences among tillage methods and soil types (clay, loam, sand). The
stratum means of the measured soil physical properties and the gradient
slope of organic matter were incorporated into the analyses. Questionnaire
data were also included when possible.
Tillage systems had a significant effect on the vertical distribution
of nutrients in the soil sampling layer. Soil under CT practices displayed
a relatively even distribution of nutrients within the plough layer as indicated
by a slower decline in nutrient concentrations with depth. Soil in fields
managed under NT systems had a significantly greater rate of decline in
nutrient concentration with depth. The lack of soil mixing resulted in an
accumulation of nutrients at or near the soil surface. Soil organic matter
content was similarly stratified with depth under NT conditions.
Soil texture was also a significant factor affecting the stratification
of nutrients. Higher water infiltration rates associated with sandy soil
enhanced the leaching of nutrients from the soil surface and reduced the
development of a stratified surface layer by moving the nutrients down through
the soil profile.
The second experiment was a study of horizontal distribution and stratification
of soil nutrients, pH and organic matter over a range of soil textural groups.
Nine sites were chosen for the study in fields which had been fertilized
using a band application method and managed under a NT cropping system.
Three sites were selected within each textural group: sand, clay and loam.
As in the first experiment, a questionnaire was given to each farm cooperator
requesting management history of the field.
At each location, a trench was dug along a 100 cm transect positioned
perpendicular to the crop rows. Sample points were located every 20 cm along
the transect starting at 0 cm giving a total of six points. The first point
along the transect (0 cm) was always located within a crop row. Soil samples
were taken by hand trowel at each transect point at 2 cm increments to a
depth of 20 cm. These samples were analyzed for soil nutrient content (P,
K, Mg, Ca) and pH. Similar samples to a depth of 16 cm were analyzed for
organic matter content.
To identify horizontal stratification of nutrients, the standard deviations
of the nutrient concentrations at each depth across the transect were determined.
An analysis of variance was conducted on these results. A numerically high
standard deviation was considered indicative of a relatively high degree
of stratification or variance in concentrations across the transect.
The number of years that each field had been managed under a NT system
was significantly related to the horizontal variation in nutrient concentrations;
the severity of horizontal stratification of nutrients increased with the
number of consecutive years under NT. Soil texture was a significant factor
affecting the severity of horizontal stratification of K, Mg and to lesser
extent, P. Only P stratification was significantly affected by the soil
sample depth; the horizontal variation in P concentrations was greatest
at 6 cm.
The results of the two experiments show that the stratification of nutrients
in soils does exist, primarily within the soil sampling zone, and that its
severity is directly related to tillage practice.
(From Technology Transfer Report Summaries - A. Hayes, L. Cruickshank,
The study examined the effect of various field management systems on
the distribution patterns of P, K, Mg, and Ca at various soil sampling depths.
The tillage system used affected the vertical distribution of nutrients
in the soil sampling layer. Severe vertical stratification was found in
no-till systems and to lesser degrees in reduced tillage and conventional
tillage systems in the 0 to 10 cm depths. At greater depths the amount of
stratification in the no-till system decreased but increased in the reduced
tillage and conventional tillage systems, due to mixing of the soil. The
longer a field had been under no-till the greater the severity of nutrient
stratification in the sampling layers.
The following factors were found to affect the development of vertical
Clayey soils in the study tended to have more stratification than sandy
soils. The higher infiltration rates associated with sandy soils enhanced
the leaching of nutrients from the upper layers therefore decreasing the
potential for vertical stratification. Clay particles fix or retain P and
K, therefore there is little movement from the point of application.
Horizontal stratification of nutrients is associated mainly with banding
of fertilizers under no-till systems. Generally horizontal stratification
did not vary greatly with soil depth except for P which varied significantly
with sampling depth.
Consistency in crops, and row widths were difficult to obtain. Extensive
field histories were also difficult to obtain. Climatic conditions varied
from location to location. It is difficult to make a direct and valid comparison
between locations under such conditions.
No comment was made as to the possible effect of the rushed data collection
or the incomplete questionnaires on the results of the survey. The agronomic
effects of nutrient stratification or the effects on plant growth or yield
were not discussed.
Future Research: ( ) indicates reviewers suggestion for
priority, A - high, C - low.
(C) The impact of vertical stratification with respect to nutrient loss
due to soil erosion needs further study. Horizontal stratification on fields
with known histories and similar cropping patterns should be examined. The
impact of vertical nutrient stratification on plant growth and yield needs
further study. There should be further study on the effects of specific
management practices under controlled conditions.
Thursday, May 19, 2011 02:55:36 PM