Boron Deficiency and Toxicity in Soil

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Questions and Answers

What is a significant risk associated with using elevated concentrations of boron fertilizers?

  • Impaired photosynthesis in crops
  • Fluctuations in soil pH
  • Seedling toxicity and yield reduction (correct)
  • Nutrient lockout in plants

Which boron source has been recognized for its slow-release properties?

  • Colemanite (correct)
  • Sodium borate
  • Borax
  • Calcium borate

What is one benefit of using slow-release boron fertilizers?

  • Lower cultivation costs
  • Reduced risk of nutrient leaching (correct)
  • Immediate availability of boron
  • Higher seed germination rates

Which statement best describes the mobility of boron in soil solutions?

<p>Boron is usually present as an uncharged molecule and is highly mobile. (B)</p> Signup and view all the answers

What is a common challenge when applying boron in high-rainfall environments?

<p>Excessive leaching of applied boron (C)</p> Signup and view all the answers

How can slow-release coatings and matrices potentially improve boron fertilizer efficiency?

<p>By reducing application rates or frequency (D)</p> Signup and view all the answers

What is a common condition that can lead to boron deficiency in crops?

<p>High-rainfall environments with sandy soils (B)</p> Signup and view all the answers

What aspect of boron fertilizers needs further research to enhance prediction of their behavior?

<p>The release rate under differing soil and climatic conditions (D)</p> Signup and view all the answers

What is the recommended boron fertilizer application rate for crops generally?

<p>0.25 to 3 kg ha-1 (C)</p> Signup and view all the answers

Which boron source has been found to be about 10 times more soluble than colemanite?

<p>Ulexite (C)</p> Signup and view all the answers

Which method of boron application is typically more effective for correcting deficiencies in fruit trees?

<p>Foliar spray (D)</p> Signup and view all the answers

In what pH condition does the solubility of colemanite and ulexite increase?

<p>pH 5 (D)</p> Signup and view all the answers

Which of the following effects can result from repeated application of boron fertilizers?

<p>Boron toxicity (C)</p> Signup and view all the answers

What is the reaction type of BPO4 compounds when mixed in water?

<p>Acid reaction (D)</p> Signup and view all the answers

How does the synthesis temperature affect the solubility of BPO4 compounds?

<p>Solubility decreases with temperature (D)</p> Signup and view all the answers

Why is comparison between studies on boron fertilizers often not possible?

<p>Different studies use various methods and crop types (D)</p> Signup and view all the answers

What is the primary form of boron present in soil solution under normal conditions?

<p>Boric acid (H3BO3) (A)</p> Signup and view all the answers

What can lead to boron toxicity in plants?

<p>Irrigation water with high B concentrations (C)</p> Signup and view all the answers

Which of the following describes the challenge with boron fertilization?

<p>Narrow window between deficiency and toxicity (C)</p> Signup and view all the answers

In which soil conditions is boron leaching most likely to occur?

<p>High rainfall regions with coarse-textured soils (A)</p> Signup and view all the answers

Which factor is known to increase boron adsorption in soils?

<p>Increase in pH levels (B)</p> Signup and view all the answers

What is a common consequence of high boron concentrations at the seedling stage?

<p>Seedling toxicity (A)</p> Signup and view all the answers

What aspect does the phenomenological adsorption equation developed by Keren et al. take into account?

<p>Influence of pH on boron adsorption (A)</p> Signup and view all the answers

What is a characteristic of slow-release fertilizers for boron?

<p>Reduced potential for toxicity (A)</p> Signup and view all the answers

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Study Notes

### Boron Deficiency and Toxicity

  • Boron (B) is an essential nutrient needed for plant growth, it is typically present as boric acid (H3BO3) in soil.
  • Boron is highly mobile in soil, so deficiency is common in high rainfall areas, and particularly on sandy soils.
  • Boron toxicity occurs most commonly in arid or semi-arid regions.
  • Boron fertilizers are used to address deficiency, but are challenging due to the narrow margin between deficiency and toxicity, and the fact that boron is relatively immobile in plants.
  • Excess boron at the seedling stage can cause toxicity, and leaching can lead to insufficient boron later in the growing season.

Boron in Soil

  • Boron adsorption by soil components (e.g. clays, oxides, hydroxides) is generally weak and increases with increasing pH, reaching a maximum around pH 9.
  • Boron fertilizers can be applied to soil or as a foliar spray. Soil-applied is generally used for field crops, while foliar is used to correct deficiencies in fruit trees.

Slow-Release Boron Sources

  • Slow-release boron sources reduce the risk of seedling toxicity and leaching.
  • Slow-release sources provide a more consistent and longer-lasting supply of boron, allowing for lower application rates and longer intervals between applications.
  • Colemanite is a commonly used slow-release boron source.
  • More research is needed to predict the release rates of boron from various sources under different soil and climate conditions.

Boron Chemistry

  • Boron is a metalloid with properties of both metals and non-metals.
  • Boron is primarily present in soil solution as boric acid (H3BO3).
  • At higher pH, borate (B(OH)4-) is also present.

Boron Fertilization and Applications

  • Boron fertilizer recommendations are dependent on crop type, application method, soil’s boron status, and the fertilizer source.
  • Foliar fertilization is generally more effective than soil application, but requires repeated applications due to boron immobility within the plant.
  • The solubility of boron sources (e.g., colemanite, ulexite) can vary significantly.
  • The solubility of boron phosphate compounds (BPO4) decreases with increasing synthesis temperature.

Future Research

  • New technologies for slow-release coatings and matrices for nitrogen (N) fertilizers may be applicable for boron-containing fertilizers.

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