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SWEEP Report #35

Nutrient Distribution and Stratification Resulting
from Conservation Farming

Researchers: 
D. Cressman, Ecologistics Limited, Waterloo, Ont.

Executive Summary

Evaluation Summary (Tech. Transfer Report Summaries)

View / Download Final Report  [458 KB pdf]  (appendices included)

Associated SWEEP/LSP Research

 

 

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Completed: December, 1990

Key Words:

reduced tillage, conventional tillage, no-till, nutrient stratification, bulk density, phosphorus, potassium

Executive Summary

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.

 

Evaluation Summary

(From Technology Transfer Report Summaries - A. Hayes, L. Cruickshank, Co-Chairs)

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 nutrient layers:

  • soil mixing

  • soil texture

  • soil physical properties

  • soil fertility prior to fertilizer application

  • soil organic matter content

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.

Comments:

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.

Associated SWEEP/LSP Research:

  • SWEEP Report #44 - Comparison of Planters and Fertilizer Applications Systems for No-Till Corn

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.

 

 

 

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Created: 05-28-1996
Last Revised: Thursday, May 19, 2011 02:55:36 PM