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Comparison of P- availability from monocalcium and diammonium phosphates using a mechanistic nutrient uptake model (1990)

Ernani, P. R. ; Barber, S. A.

Springer

Nutrient cycling in agroecosystems 22 (1990), S. 15-20

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ISSN: 1573-0867

Keywords: Phosphate fertilizers ; soil solution phosphorus ; exchangeable soil phosphorus ; soil phosphorus diffusion coefficient

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract Calcium and ammonium phosphates are the most commonly used phosphate fertilizers. Since they differ in some chemical aspects it is important to compare their ability for supplying P to plant roots in different soils. The objective of this research was to compare the predicted effectiveness of monocalcium phosphate (MCP) and diammonium phosphate (DAP) for supply of P to maize in 13 soils. Phosphorus was applied at rates varying with soil from 50 to 400 mg kg−1. Thirty days later P, Ca, pH, and Al were measured in the soil solution and in the solid phase. We calculated buffer power (b) and effective diffusion coefficient (De) for P, and used them, together with solution P (Cli), in the Barber-Cushman mechanistic nutrient model to predict P uptake. Monocalcium phosphate and DAP were similarly effective in supplying P to plant roots. Predicted P uptake differed between fertilizers in only three soils, and maximum differences between fertilizers in Cli or resin-exchangeable P (Csi) in any one soil were always less than 30%. The determinations most highly correlated with predicted P uptake were De (r = 0.93**) and Cli (r = 0.60*). Resin-exchangeable P was not significantly correlated with Cli, De, b or P uptake. Calcium, Al, and pH varied with source of P and soil: soils treated with DAP had lower extractable Al, lower Al in solution, and higher soil pH than soils where MCP was applied. Monocalcium phosphate increased extractable Ca whereas DAP did not affect it.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01054802

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The effect of ionic strength on soil P reactions is negligible (1995)

Ernani, P. R.

Springer

Nutrient cycling in agroecosystems 45 (1995), S. 193-197

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ISSN: 1573-0867

Keywords: cation activity ; phosphorus ; potassium chloride ; soil solution

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract The electrolyte concentration of the soil solution affects the availability of some nutrients in the soil, especially of P, but it is not know at what salt concentration the reactions start to be significantly affected and their magnitude. This study was carried out to evaluate the effect of rates of potassium chloride (KCl) on some soil parameters that determine supplying of P, K, Ca, Mg, and Al in an unlimed acid soil. Increasing rates of KCl (from zero up to 2000 mg K kg−1) were applied to soil samples fertilized with 360 mg P kg−1. Solution (Cli) and exchangeable (Csi) forms of P, Ca, Mg, K, and Al were determined in the treated soil samples after 30-days of incubation; cation activity in solution and their selectivity coefficients were then calculated. Addition of KCl at rates equal to or above 500 mg K kg−1 caused a large relative increase on P in the soil solution (Pli) but a small and insignificant increase on the absolute value of Pli. All forms of soil K increased with increases on K applied, and buffer power for K varied according to the range of soil K. At all KCl rates, K displaced Ca, Mg, and Al from the solid phase to the soil solution, but had no effect on the extractable values. The relative preference of cations for the adsorption sites increased with increase on cation valency, and only those selectivity coefficients involving K were affected by K applied.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00748589

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