Sokrat Sinaj

Interference of colloidal particles in the determination of orthophosphate concentrations in soil water extracts

Abstract Accurate determination of orthophosphate (P) in soil solutions is a prerequisite for rigorously assessing soil P availability for plants as well as the potential risk of P transfer to water bodies. Although P is usually measured on extracts filtered at 0.45 μm, little is known on the potential interfences due to the presence of colloidal particles. This work was conducted to study the influence of colloidal particles on P concentration by measuring it both by the phosphoantimonylmolybdenum blue colorimetry and ion chromatography in soil water extracts filtered at 0.45, 0.2, or 0.025 μm. Results strongly suggest that direct measurements with colorimetry might lead to an overestimation of the P concentration due to the solubilization of P‐containing particles in the acid medium prevailing in the solution during colorimetric essay. In the present study, the largest overestimations were observed in soil extracts rich in iron (Fe) and aluminum (Al) that had been filtered at 0.45 μm, on the opposite th...

Modeling of phosphorus dynamics in contrasting agroecosystems using long-term field experiments

Morel, C., Ziadi, N., Messiga, A., Bélanger, G., Denoroy, P., Jeangros, B., Jouany, C., Fardeau, J. C., Mollier, A., Parent, L. E., Proix, N., Rabeharisoa, L. and Sinaj, S. 2014. Modeling of phosphorus dynamics in contrasting agroecosystems using long-term field experiments. Can. J. Soil Sci. 94: 377-387. Long-term field experiments on phosphorus (P) fertilization were originally designed to study crop needs in different soil types by analyzing the effects of several rates of P fertilization on yields, their P concentrations and dynamics of plant-available soil P. The objective of this study was to test a computer-based model to simulate the P dynamics at the field scale using plant database and analyzing for plant-available P by a hierarchical process-based approach. It predicts both the concentration (CP) of phosphate ions (Pi) in soil solution and the associated Pi amounts that in time equilibrate with Pi in solution. Five experiments, representative of contrasting soil types, land-use, and climates were selected. Our model equilibrates the change in plant-available P in the upper soil layer to the P budget between annual P inputs and outputs. Rates of P fertilization affected simulations following the same expected pattern across sites. Field-observed and simulated values are in good agreements in all sites. The field-observed variations of CP per unit of P budget ranged from 0.007 to 2.49 (µg P L-1) (kg P ha-1)-1. The predictions are of the same order of magnitude. Predictions were compared with empirical long-term data and mismatches were discussed. This investigation highlights the scientific interest of long-term field P experiments to test and validate models describing P dynamics at the scale of the agricultural fields under different agricultural management practices.

Soil test phosphorus and cumulative phosphorus budgets in fertilized grassland

We analyzed the linearity of relationships between soil test P (STP) and cumulative phosphorus (P) budget using data from six long-term fertilized grassland sites in four countries: France (Ercé and Gramond), Switzerland (Les Verrières), Canada (Lévis), and Finland (Maaninka and Siikajoki). STP was determined according to existing national guidelines. A linear-plateau model was used to determine the presence of deflection points in the relationships. Deflection points with (x, y) coordinates were observed everywhere but Maaninka. Above the deflection point, a significant linear relationship was obtained (0.33xa0<xa0r2xa0<xa00.72) at four sites, while below the deflection point, the relationship was not significant, with a negligible rate of STP decrease. The relationship was not linear over the range of STP encountered at most sites, suggesting a need for caution when using the P budget approach to predict STP changes in grasslands, particularly in situations of very low P fertilization. Our study provides insights and description of a tool to improve global P strategies aimed at maintaining STP at levels adequate for grassland production while reducing the risk of P pollution of water.