Total and Available Phosphorus Concentrations in Major Rice Growing Soils and Their Relationships with Rice Grain Phosphorus Concentration

Abstract

Phosphorus (P) is an essential macro nutrient for plant growth and development. Soil P exists in organic and inorganic forms. However, only a fraction of soil P is readily available to plant. Plant available and total P concentrations in soils vary among soil types due to the differences in soil mineralogy, structure, physical & chemical properties, and fertilizer application. Therefore, this research was conducted to estimate the concentrations of plant available and total P in major rice growing soils (i.e. 18 soil types) in Sri Lanka, and to study their relationships with grain P concentration. Total of 200 soil samples and grain samples were collected representing paddy lands across the country using a stratified random sampling approach. Available P (Olsen-P) and total P in soils, and grain P concentrations were measured. Available P concentration in paddy soil samples ranged from 5.4-76.9 mg kg−1. The highest available P concentration was recorded in Reddish Brown Earths & Immature Brown Loams soil (RBE_IBL) (34 mg kg−1) and the lowest in Red-Yellow Latosols soil (RYL) (12 mg kg−1). Soil total P concentration had a wide range of values i.e., 142-5685 mg kg−1. The Red-Yellow Podzolic soils with soft or hard laterite (RYP) had the highest soil total P concentration (2525 mg kg−1). Grumusol soil and RYL soil reported the lowest total P, i.e., < 1000 mg kg-1. Grain P concentration varied among soil types and it ranged between 0.6-1.8 mg g-1. However, there was no correlation between the grain and soil P concentrations. This information would be important for sustainable P-nutrient management in Sri Lankan rice soils.