Long term soil p and k trends in relation to nutrient removal in corn soybean rotations
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Long-Term Soil P and K Trends in Relation to Nutrient Removal in Corn-Soybean Rotations. Antonio Mallarino Iowa State University. Joint Meeting NEC-17, NCERA-13, SERA-6 June 22-25 2008. Basis of Soil P and K Testing Use. Soil test correlation and calibration

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Long term soil p and k trends in relation to nutrient removal in corn soybean rotations

Long-Term Soil P and K Trends inRelation to Nutrient Removal inCorn-Soybean Rotations

Antonio Mallarino

Iowa State University

Joint Meeting NEC-17, NCERA-13, SERA-6June 22-25 2008


Basis of soil p and k testing use
Basis of Soil P and K Testing Use

  • Soil test correlation and calibration

  • Interpretation: interpretation categories

  • Fertilizer recommendations

    • Response-based and often some buildup for the low-testing categories, those with high probability of response.

    • Maintenance of desirable soil-test levels, those with low probability of response. Based on nutrient removal and/or empirical data.


Removal based p and k maintenance
Removal-Based P and K Maintenance

Example from Iowa

Pounds per unit of yield

Crop

Unit of Yield

P

O

K

O

2

5

2

Corn

bu

0.375

0.30

Corn silage

bu grain equiv.

0.55

1.25

Corn silage

3.50

8.0

ton, 65% H2O

Soybean

bu

0.80

1.5

Oat and straw

bu

0.40

1.0

Oat straw

ton

5.0

33.0

Wheat

bu

0.60

0.30

Alfalfa

ton

12.5

40.0

Red clover

ton

12.0

35.0

Pm-1688 pub, ISU


Some relevant questions
Some Relevant Questions

  • Are assumed buildup and maintenance rate appropriate?

  • Does maintenance make sense? What level should be maintained?

  • Does removal-based fertilization really maintain STP and STK levels?

  • How do yield, removal, and soil-test values in the short term and long term?

  • What are the impacts of wrong yield and nutrient concentration estimates?


Long term studies in iowa
Long Term Studies in Iowa

  • 5 trials for P, 12 years each, no-till

  • 5 trials for K, 10 years each, no-till

  • Corn/Soybean rotations, both crops each year on adjacent identical trials

  • 3 P rates: 0, 14, and 28 kg P/ha

  • 3 K rates: 0, 33, and 66 kg P/ha

  • Broadcast and band placement methods

  • Measured yield from all plots and soil tests for the control and the high rate









Grain k concentration and yield
Grain K Concentration and Yield

Avg = 1.2 lb K2O/bu

Current (dry basis) = 1.7 lb K2O/bu


Grain k concentration and yield1
Grain K Concentration and Yield

Avg = 0.22 lb K2O/bu

Current (dry basis) = 0.35 lb K2O/bu








Grain p concentration yield

Mean = 0.57%

Avg = 0.78 lb P2O5/bu

Current (dry basis) = 0.92 lb P2O5/bu

Grain P Concentration & Yield


Grain p concentration yield1

Mean = 0.24%

Avg = 0.31 lb P2O5/bu

Current (dry basis) = 0.44 lb P2O5/bu

Grain P Concentration & Yield






Cumulative p removal soil p
Cumulative P Removal & Soil P

Averages of Non-Fertilized Plots Across Locations

47 lb P2O5/acre/year for

1 ppm/year decrease


P removal soil p increase
P Removal & Soil P Increase

Averages of Fertilized Plots Across Locations


Grain yield and concentrations
Grain Yield and Concentrations

  • Crop yields vary greatly across field and years. We overestimated yield, as most farmers do with yield goals.

  • Grain P and K concentration also vary across field and years

    • Estimates of P and K concentration in grain were much higher than observed averages.

    • Increased up to a certain plateau with the fertilizer rate and soil-test values

    • Grain P and K concentrations were not correlated with yield level across sites.


Removal and soil test values
Removal and Soil Test Values

  • Our overestimation of yield levels and nutrient concentrations resulted in a significant overestimation of removal.

  • Removal was well reflected on soil-test values in the long term, but very poorly or not at all in the short term

    • slow P recycling of residue P and K?

    • slow equilibria between soil P and K pools?


Implications for management
Implications for Management

  • Major errors at estimating P and K removal is caused by error in grain yield estimates.

  • Removal-based P and K maintenance based on good yield and concentration estimates maintain or only slightly increase soil-test P and K it over time.

  • Removal-based maintenance rates must be based on yield averages over time, not from year to year changes.


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