Investigation of effects of soil pH and P concentration on phosphorus adsorption of paddy soil

Abstract

Phosphorus (P) is one of the most important macro-nutrients for plant growth. Given the fact that soil minerals and organic matter are two main sources of P, plant can only uptake P in form of anions HPO₄^2- and H₂PO₄^-, the larger part of soil P is absorbed on clay minerals or precipitated by oxide or hydroxide aluminum (Al) or iron (Fe), calcium (Ca) and magnesium (Mg). The Red River delta attributes to the biggest rice-production field in the north of Vietnam, which is now under threat of soil degradation as a consequence of fertilizer abuse to boost productivity. Therefore, the research was conducted by sampling soil of 3 provinces of the Red river delta including Hai Phong, Nam Dinh and Ninh Binh to evaluate P adsorption capacity to generate recommendation for sustainable agriculture purposes. Fluvisols samples were taken from the study sites and undertaken under lab condition in terms of P adsorption of different soils and effects of pH value on the adsorption. Our hypotheses are (i) at low concentration, P adsorption increase was associated with the P addition but attaining maximum volume at high P concentration in soil solution; and (ii) P adsorption was strongly affected by pH value but distinct in different range values. Our result supported our first hyphothesis, which showed the fact that at low concentration there was a positive correlation between P addition and P adsorption. At 500 mg/kg P concentration, the P adsorption attained a saturation. On the other hand, pH strongly impacted P adsorption capacity but the effects were different according to soil particle ratio among 3 soil samples. The research has contributed the scientific base for accurate calculation of P fertilizer in field condition and also open an important research orientation aiming at sustainable cultivation development under Vietnam condition.