Copper and zinc antagonism on low phosphorus soils

When Cu and Zn fertilizers were applied to phosphorus (P) deficient soils at 4.5 lbs/ac (5 kg/ha) rate, wheat yields were reduced. Symptoms of micronutrient metal toxicity were observed at early growth stages, and included purplish-red colour and chlorotic leaves.

Liebig’s Law of the Minimum states that growth is dictated not by total resources available, but by the scarcest resource or limiting factor. In the case of soil fertility, these resources of macro and micronutrients need to be available in a balanced supply for optimum crop yield. Previous research has found antagonism between P, copper (Cu) and zinc (Zn) in wheat.

This study was conducted to reveal the nutrient transformation process related to antagonistic effects of micronutrient fertilization on wheat yield when Cu and Zn sulfate fertilizers were applied separately or combined at different rates.

Greenhouse and field studies were used to assess hard red spring wheat response to P, Cu, and Zn fertilization. Soil was collected from 0 to 15 cm layer of Levine (Gleyed Cumulic Regosol) and Waskada (Orthic Black Chernozem) soils in Manitoba, and Tisdale (Dark Gray Chernozem) in Saskatchewan for the greenhouse study at the University of Saskatchewan. The field study was conducted near Central Butte, Saskatchewan on a Brown Chernozem (Echo association) soil. All soils were P-deficient with less than 10 ppm modified Kelowna extractable P soil test levels.

Eight fertilizer treatments were compared. The Cu and Zn fertilizers were added as Cu and Zn sulfate salts. These Cu and Zn rates are often considered as the recommended rate of application for deficient soils:

  • T1: Control (no micronutrient and no phosphorus);
  • T2: Control (no micronutrient, but phosphorus added at 17.8 lbs P2O5/ac (20 kg P2O5/ha);
  • T3: Cu at 2.2 lbs/ac;
  • T4: Zn at 2.2 lbs/ac;
  • T5: Cu + Zn at 2.2 lbs/ac;
  • T6: Cu at 4.5 lbs/ac;
  • T7: Zn at 4.5 lbs/ac;
  • T8: Cu + Zn at 4.5 lbs/ac.

Other fertilizers applied across all treatments included urea at 179 lbs N/ac (200 kg N/ha) and potassium sulfate (0-0-44-17) at 18 lbs S/ac (20 kg S/ha) and 42 lbs K20/ac (47 kg K2O/ha).

For the greenhouse study, the fertilizer was applied and incorporated to a 2 cm depth. Wheat was grown in small pots. In the field study, wheat was grown in small plots 1 m x 3 m with fertilizer broadcast and incorporated. The field site was split into 4 blocks running from upper slope to lower slope position.

Grain and straw yields were measured and nutrient concentrations were determined in the grain, straw and soil after harvest.

Micronutrient fertilizer reduced yield

When added at the high rate of 4.5 lbs of micronutrient metal per acre of soil to the P deficient soils in the pot study, symptoms of micronutrient metal toxicity were observed at early growth stages, and included purplish-red colour and chlorotic leaves. Tissue analysis found higher levels of Zn in wheat grown on the Waskada soil. In addition, in the Waskada and Tisdale soils, an imbalance in the P:Zn concentration was observed.

Wheat yield was higher when phosphate fertilizer was applied at 18 pounds per acre without micronutrients compared to the control with no fertilizers applied in all three soils in the greenhouse study. However, when Cu and Zn fertilizers were applied to the P deficient soils without P fertilizer at the 4.5 lbs/ac rate, yields were reduced on two of the three soils (Waskada and Tisdale) under the controlled environment conditions.

The field site had similar results, with higher grain yield with P fertilization than the control, but yield was unaffected when Cu and Zn were applied at the 4.5 lbs/ac rate.

Soil test DTPA-extractable Zn concentration from the Waskada soil appeared to be high enough to create toxicity problems in wheat production especially under P deficiency, potentially due to the imbalance in P:Zn ratio.

Most of the Cu and Zn fertilizer remained in the soil in plant available form post-harvest.

This work was funded by Western Grains Research Foundation and Agriculture and Agri-Food Canada Agri-Innovation Program.

Noabur Rahman, Derek Peak, and Jeff Schoenau. 2022. Antagonistic effect of copper and zinc in fertilization of spring wheat under low soil phosphorus conditions. Canadian Journal of Soil Science. 102(3): 797-809.

Related articles:

Noabur Rahman & Jeff Schoenau (2022) Zinc and copper interactions under variable soil phosphorus and moisture conditions in selected Saskatchewan soils, Journal of Plant Nutrition, 45:3, 311-331, DOI: 10.1080/01904167.2021.1952223

Md. Noabur Rahman, Ryan Hangs & Jeff Schoenau (2020) Influence of soil temperature and moisture on micronutrient supply, plant uptake, and biomass yield of wheat, pea, and canola, Journal of Plant Nutrition, 43:6, 823-833, DOI: 10.1080/01904167.2020.1711941

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