Phosphorus (P) is critical for crop production but also poses a threat to water quality in Ohio. Therefore, a better understanding of optimizing the P availability to crops while minimizing the potential of P to pollute water bodies is important.
Plant P Use
Plants require P to generate adenosine triphosphate (ATP), which is an energy currency. It is also part of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) that make genetic code and synthesize proteins. A deficiency of P also negatively affects fundamental processes such as photosynthesis, seed production, maturation, and root growth. A P-deficient plant is often stunted and can develop dark green or purple pigmentation on older (lower) leaves (Fig.1).
Soil P Pools
Phosphorus is less abundant in soil than nitrogen and potassium. The total P content in soil varies from 0.0005% to 0.15%, but most of this total P is not readily available to crops. Some of the P is in the organic form, which is derived from plant residues, manure, or other organic sources. In Ohio’s relatively young soils, most of the P is in the inorganic P form. Inorganic P is bound to primary and secondary minerals, and a proportion of it can be bound to clay. Organic and inorganic P forms are in equilibrium with soil-solution P that provides P to growing crops.
When an external organic P source such as crop residue is added to soil, it can be immobilized or mineralized based on the carbon-to-phosphorus (C to P) ratio. If the C to P ratio of organic matter is greater than 300 to 1, the P can be immobilized into organic form and become relatively unavailable for uptake by plants. If the C to P ratio of organic matter is less than 200 to 1, the P from organic matter is mineralized into plant-available P forms. Similarly, when P fertilizers are added to soil, they increase the soil-solution P concentration.
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Categories: Ohio, Crops