**7. Effect of soil properties on phosphorus use efficiency (or phosphorus dynamics)**

The efficiency of P-use depends mostly on the complex interactions among the physical, chemical and biological characteristics of soils, and the processes involved with these properties. These properties can directly influence root growth and development, restricting P-uptake. Soil depth, structure, stoniness, moisture retention, and composition of the soil atmosphere can influence P-dynamics. Notably, the prevailing soil properties such as soil texture, mineralogical composition, total surface area, pH, CaCO3 content, organic matter content, the presence of Fe and Al-hydroxides, etc., can considerably alter the solubility, availability, and extractability of P in soil [90]. Due to the presence of dense subsurface layers (e.g., plow pans) and surface-soil compaction, the diffusion of phosphate ions in soil is decreased, and root growth and development are hindered. Although the slow movement of P by diffusion is usually attributed to the tortuosity of the pore system, the reactive sites for P-adsorption on soil minerals around the pores can hold phosphate ions, temporarily or permanently, that slow or prevent their movement along the pore [91]. Soil texture influences the chemical behavior and hydrology of soils and affects the formation of Al-organic bonded stable P and leaching of P from soils [92, 93]. By practicing zerotillage, cultivating permanent crops, and maintaining a crop-residue cover, and by minimizing traffic over the soil surface and reducing invasion of livestock in wet and heavy-textured soils in humid temperate regions, the physical limitations of P-uptake can be controlled to some extent. Besides, soil-borne fungal pathogens and nematodes injure plant roots and limit P-uptake and to overcome this problem, crop rotation is a suitable option.

Soil acidity is a chemical limitation to the efficient use of P-fertilizers as it has adverse effects on P-uptake. Soil pH regulates the release of Al from various clay minerals and the dissolution of Al hydroxy compounds in soil. At low pH with high Al-concentrations in the soil solution, root tips and lateral roots are thickened and turn brown, causing the reduction in P-uptake. As a result, P translocation in the

upper parts of the plant decreases, and P metabolism is hampered. These problems can be ameliorated by adding lime and other acid-neutralizing materials that can increase pH as well as base saturation percentage. P-distribution in different soil P pools is an inherent soil property, and changes in the P-distribution in the pools are difficult to achieve. Scientists around the globe investigated the impact of pH change by adding lime to acid soils on retention and extractability of P and found no consistent influence on soil P availability [94–97]. The amount of readily available plant P increases with the increase of organic matter in the soil [98]. In P-deficient soils, applying a material that can compete with the phosphate ion for the adsorption sites within the soil such as silica or silicate might be a suitable option to increase P-availability [99].
