Micronutrient management in the early years of no-till

R. Mohr¹, R. Karamanos²and C. Grant¹

¹Brandon Research Centre – Brandon, MB
²Western Co-operative Fertilizers Ltd. – Calgary, AB

Micronutrients

• Are elements essential for plant growth but that are required in very small amounts

• Boron (B)

• Chlorine (Cl^-)

• Copper (Cu)

• Iron (Fe)

• Manganese (Mn)

• Molybdenum (Mo)

• Zinc (Zn)

Micronutrient removal by crops (lb/ac)

Micronutrient removal by crops (lb/ac)

Sources of micronutrients in soil

• Parent material from which soils developed

• Organic matter

Question: Micronutrients -
When do we need them?

Answer: When their application results in an economic benefit to the farmer!

How is the economic benefit measured?

• Increased yield

• Improved quality (mostly perception)

How is the economic benefit not measured?

• In most cases, when soil test value above critical level – “marginal” range

• Increased tissue level as a result of a micronutrient application

How is the economic benefit measured?

• Best way is to define by yield responses

• Responses can be obtained as a result of:

• Soil deficiencies

• Plant physiological effects

• In Manitoba and North Dakota, most soils have adequate levels of micronutrients…

…however certain conditions may reduce micronutrient availability…

Soil and environmental conditions that may reduce the availability of micronutrients:

• Soils low in organic matter à B, Cu, Zn

• Coarse-textured soils à Cl, Cu, Zn, B, Mo

• Peat soils or with >30% OM à Cu, Mn, B

• Cool, wet soils

• may reduce the rate and amount of micronutrients take up by the crop

• High soil pH

^•êavailability for all but Mo and Cl^-

• Highly calcareous soils, or soils with a high lime content à Zn, Fe

• Soils with exposed subsoil due to erosion or land levelling à Zn

• Soil with excess P à Zn

Accurate identification of micronutrient deficiencies is important because…

• The range of micronutrient concentrations at which plants grow well is not great (e.g. B)

• Micronutrients are relatively costly

Diagnosing micronutrient deficiencies

What are the steps?

1. Is it a micronutrient deficiency or something else?

• Eliminate other possible causes of poor growth

• drought, flooding, herbicide damage, salinity, disease, macronutrient deficiency, etc.

2. Is your particular soil or crop likely to be deficient in micronutrients?

• Have there been deficiencies in the area previously?

• Soil and crop characteristics?

3. Are the visual symptoms in the crop typical of a micronutrient deficiency?

• Type of symptoms

• Location of symptom

• Within field (e.g. patchy vs uniform)

• On plant (e.g. old vs new growth)

4. Do soil and tissue tests indicate a micronutrient deficiency?

• Take soil and tissue samples from both affected and unaffected areas, and submit to a lab for complete nutrient analysis

5. When a micronutrient deficiency is indicated…

• Apply nutrients in a test strip in the field

• Evaluate crop recovery and yield in treated and untreated areas

What Micronutrient Criteria Have Been “Scientifically” Established in Western Canada?

• Copper (Cu)

• Boron (B)

• Manganese (Mn)

• Zinc (Zn)

• Iron (Fe)

• Molybdenum (Mo)

Copper

Copper

• Symptoms may include excess tillering, aborted heads, poor grain fill, increased root rot and stem and head melanosis

• Symptoms appear in irregular patches in field

• Patches have “drought-like” appearance

Copper soil criteria

• Criteria were developed in 1980-85

• Manitoba 0.2 ppm

• Saskatchewan 0.4 ppm

• Alberta 0.6 ppm

(DTPA extraction)

• But most of marketing/selling is happening between 0.4 and 2.5 ppm!

Interpretation of soil test – Wheat (Saskatchewan and Alberta)

Statistical and Economic Characteristics for Deficient

Statistical and Economic Characteristics for Deficient

Statistical and Economic Characteristics for Marginal

Statistical and Economic Characteristics for Marginal

Interpretation of Soil Tests for Copper

• Based on 102 tests with spring wheat in western Canada

• Deficient < 0.4 ppm (52 tests):

• Average Cu test 0.24±0.09 ppm

• 94% probability of an agronomic response

• 62% probability of an economic response

Interpretation of Soil Tests for Copper

• Marginal 0.4 –0.6 ppm (50 tests)

• Average Cu test 0.68±0.24 ppm

• 16% probability of an agronomic response

• 2% probability of an economic response

Boron

Boron

• Mobile in soil

• Narrow range between deficiency and toxicity

• Suspected B deficiencies in alfalfa and canola on sandy and eroded sandy soils in the grey soil zone

Interpretation of Soil Tests
W. Canada 40 sites; Yield 18-63 bu/ac

Interpretation of Plant Tissue Tests
(18 sites in 1999)

Tissue B and yield (low yield)

Tissue B and yield (high yield)

Soil testing criteria for assessing boron in prairie mineral soils

Manganese

Manganese

• Responses on organic soils only

• No documented responses mineral soils

• DTPA extraction

• Manitoba: 7 ppm

• Mn/Cu ratio but requires modification

• routine method 1:2; proposed 1:5 soil:DTPA extractant

• Mn/Cu < 1 Mn deficiency

• Mn/Cu > 15 Cu deficiency

Manganese

• Responses on organic soils only

• No documented responses mineral soils

• Mn/Cu ratio suggested but requires modification

• routine method 1:2; proposed 1:5 soil:DTPA extractant

• Mn/Cu < 1 Mn deficiency

• Mn/Cu > 15 Cu deficiency

Soil testing criteria for assessing manganese in prairie mineral soils

Zinc

Zinc Identification

• Extensive database in western Canada

• No responses with cereals and oilseeds

• Responses with corn and beans

• DTPA extraction but proven unsuitable for mineral soils!

Soil test critical level (dry bean in Manitoba)

Soil testing criteria for assessing zinc in prairie mineral soils

Iron (Fe) and Molybdenum (Mo)

• Least-research micronutrients in Canadian prairies because parent material typically rich in these nutrients. No calibration work done.

• Iron

• Ca-induced iron chlorosis in trees and garden vegetables

• Soybeans grown on poorly-drained soils with high carbonate and salinity levels may be prone to iron chlorosis, causing interveinal yellowing

Molybdenum (Mo)

• Cu-Mo imbalances in east-central SK and west-central MB due to excess Mo in pasture soils à molybdenosis in cattle

What about managing micronutrients in direct-seeded systems?

Some aspects of zero-till systems could potentially influence micronutrients…

• Cooler, wetter soils

• Stratification of nutrients

• Soil pH

However, the same principles apply in terms of identifying deficiencies…

One consideration for no-till systems…

…placement of micronutrient fertilizers

Recommended application methods

• Broadcast & incorporation often found to be most efficient and effective placement method for Cu and Zn (Karamanos et al., 1985)

• Seed-placing smaller and more economic amounts??

Copper Source, Placement and Rates

Economic returns over five years of seedrow (1 kg/ha/yr) versus broadcasting and incorporation (4 kg/ha once) of various products (Karamanos et al. 2005)

Why is Seed-placement an Ineffective Method of Applying Micronutrients?

Foliar Application

May provide an option in some cases

• E.g. for Cu deficiency

• Potential disadvantages

• May cause leaf burn in some cases

• Additional application may be required

• Not always as effective as B&I

Seed-placed Copper Products - 1998

Some alternatives to broadcast/incorporated:

Summary

• Properly identify micronutrient deficiencies

• Assess the economic benefit of a micronutrient application

• If micronutrients are required, determine the most appropriate rate, source and placement method for your situation

Thank-you