Ammonium boron uptake may be higher in

Correct option is D

The correct answer is (D) Clayey soil

Explanation:
• Boron ($B$) is a micronutrient that exists in soil as boric acid ($H_3BO_3$) or borate ions.
• In clayey soils, the high surface area and the presence of iron and aluminum oxides provide more sites for the adsorption of boron compared to sandy or organic soils.
• Clay minerals (especially illite) have a high affinity for boron. While this can sometimes lead to lower immediate availability due to tight binding, the total reservoir and potential uptake in specific conditions (where ammonium may interact with clay interlayer spaces) can be higher.
• Furthermore, clayey soils have higher water-holding capacity, and since boron moves primarily through mass flow with water, better water retention can facilitate consistent uptake.

Information Booster:
• Boron is essential for cell wall formation, pollen tube growth, and sugar translocation.
• The range between boron deficiency and toxicity is very narrow compared to other nutrients.
• Boron availability is highest at a pH of $5.0$ to $7.0$ and decreases significantly in alkaline soils due to adsorption on calcium carbonate.

Additional Knowledge:
• Acidic soil of humid regions (Option C): Boron is highly susceptible to leaching in these regions; therefore, these soils are often boron-deficient.
• Organic soil (Option A): Organic matter can bind boron, but it usually releases it easily; however, sandy soils (often contrasted with clayey) are the most prone to boron deficiency.