Sorption of Phosphorus from Fertilizer Mixture

*Augustine Muwamba, Kelly T. Morgan and Peter Nkedi-Kizza*

## **Abstract**

Studying phosphorus (P) sorption behavior is among the prerequisites for P management in the crop fields. The work presented in this chapter described P sorption data when fertilizer mixture (NH4NO3, KH2PO4, and KCl) was used to characterize sorption on soil. In addition to using fertilizer mixture, sorption experiments were also conducted using KH2PO4 prepared in 0.01 M KCl, 0.005 M CaCl2, and deionized water. The 24-h batch sorption experiments were conducted using a sandy soil to solution ratio of 1:2, and the equilibrium solution and sorbed data were described using Freundlich isotherm. Sorption kinetics experiments were conducted using times, 4, 8, 12, and 24 h. The Freundlich isotherm constant and sorbed P kinetics data for 0.005 M CaCl2 were significantly greater (*p* < 0.05) than for 0.01 M KCl and/or fertilizer mixture. The Freundlich isotherm constant and sorbed P kinetics data for deionized water were significantly lower (*p* < 0.05) than for 0.01 M KCl and/or fertilizer mixture. There was no significant difference in Freundlich isotherm constant and sorbed P kinetics data for 0.01 M KCl and fertilizer mixture. The sorption data showed the importance of using the fertilizer mix applied to the field when conducting sorption experiments.

**Keywords:** fertilizer mixture, isotherm, sorption coefficient, sorption kinetics

## **1. Introduction**

Phosphorus (P) is applied with different nutrients to crop fields. Examples of field crops that need fertilizer mixture are shown in **Table 1**. Varying nutrients combinations can significantly affect the interactions of P with soil due to varying ionic strength and pH [1–7]. For example ionic strength was positively correlated to P sorption [2]. The specific affinity and the valence of the cation on the soil exchange site were also associated to P sorption capacity [7]. Supporting electrolytes are used for conducting P sorption experiments assuming representation of the true chemistry of the field solutions without necessarily considering the varying fertilizer mix applied to the soil. **Table 2** shows examples of supporting electrolytes that were used to characterize P sorption in the past studies. In this chapter, it was hypothesized that P sorption isotherm constants and kinetics data for fertilizer mix were significantly different from supporting electrolytes commonly used for conducting P sorption.

Sorption isotherms are used to describe relationships between sorbed and solution P in a given sorption experiment at constant temperature and act as indicators


#### **Table 1.**

*Field crop and fertilizer mixture distributions.*

of field P retention potential [24–27]. Sorption coefficient is among the coefficients described in the isotherms that is used to model P movement in the field [28]. Phosphorus sorption capacity has also been used as an important management tool in many crop fields [29]. Therefore, there is a need to identify the appropriate chemistry of the field solutions before conducting P sorption experiments and modeling P movement in the crop fields. Sorption kinetics data trends were reported to provide clues on the mechanisms of sorption reactions [30]; appropriate solution chemistry should also be carefully chosen for the sorption kinetics experiments. It was also hypothesized that the isotherms that describe sorption data from fertilizer mixture are different from isotherms that describe data from typical laboratory supporting electrolytes.

The importance of laboratory P sorption and kinetics data in modeling and understanding of the P dynamics in crop fields has been documented [31, 32]. The P sorption characteristics help to properly calibrate theoretical models that aim at mimicking field processes [31, 32]. Accurate laboratory sorption data collected using true field solution chemistry will therefore improve models as predictive tools for P movement. The objective of the study was to determine the differences in P sorption behavior for P in fertilizer mixture (N, P, and K) prepared in deionized water and in P fertilizer (KH2PO4) prepared in 0.01 MKCl, 0.005 M CaCl2, and deionized water.

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**2. Sorption experiments and trends in sorption data**

*Supporting electrolytes, soils, and sorption isotherms for the literature studies.*

The soil samples used for sorption experiments were air dried, passed through 2-mm sieve and first analyzed for pH, total carbon, oxalate extractable iron, oxalate extractable aluminum, and exchangeable calcium. Particle size distribution of the

**2.1 Determination of soil properties**

*Sorption of Phosphorus from Fertilizer Mixture DOI: http://dx.doi.org/10.5772/intechopen.80420*

0.01 M CaCl2 - Langmuir

0.01 M KCl - Langmuir

0.05 M KCl - Langmuir



0.001 M CaCl2

Deionized water

*ND, not determined.*

**Table 2.**

0.1 M CaCl2 ND - Typic Argiudolls


**Electrolyte Isotherm Soil Reference**



0.02 M KCl - Langmuir - Loamy, siliceous, hyperthermic Arenic Glossaqualf [20]

0.1 M NaNO3 - Langmuir - Sandy, siliceous, hyperthermic Ultic Alaquod [23] 0.1 M NaCl ND - Aquic or Oxyaquic Haplocryods [3]










ND - Aquic or Oxyaquic Haplocryods [3]



[8]

[1, 9–14]

[15]

[16–19]

[4, 21, 22]





Paleudults

Paleudults

Humaquepts

Udorthents

Fluvaquents

Udorthents


*Advanced Sorption Process Applications*

**Field crop Fertilizer mixture distribution**

Sugarcane 200 kg N, 50 kg P2O5, and 200 kg K2O per acre Canola spring type 160 lb N, 30 lb P2O5, and 40 lb K2O per acre Canola winter type 175 lb N, 30 lb P2O5, and 40 lb K2O per acre Corn (for grain) dryland 120 lb N, 20 lb P2O5, and 20 lb K2O per acre Corn (for grain) irrigated 180 lb N, 70 lb P2O5, and 70 lb K2O per acre Cotton (1500 lb yield goal) 105 lb N, 140 lb P2O5, and 80 lb K2O per acre Grain sorghum 80 lb N, 80 lb P2O5, and 80 lb K2O per acre Peanuts 0 lb N, 80 lb P2O5, and 80 lb K2O per acre Small grain-barley 100 lb N, 80 lb P2O5, and 80 lb K2O per acre Small grain-oats 105 lb N, 80 lb P2O5, and 80 lb K2O per acre Small grain-cover crop 60 lb N, 80 lb P2O5, and 80 lb K2O per acre Small grain-wheat 120 lb N, 80 lb P2O5, and 80 lb K2O per acre Small grain silage 160 lb N, 100 lb P2O5, and 160 lb K2O per acre Sorghum silage 150 lb N, 80 lb P2O5, and 160 lb K2O per acre Soybeans 0 lb N, 70 lb P2O5, and 100 lb K2O per acre Sunflower 80 lb N, 80 lb P2O5, and 80 lb K2O per acre Sweet sorghum 80 lb N, 80 lb P2O5, and 80 lb K2O per acre Tobacco 50 lb N, 100 lb P2O5, and 180 lb K2O per acre Kenaf 175 lb N, 100 lb P2O5, and 100 lb K2O per acre Truffles 50 lb N, 80 lb P2O5, and 80 lb K2O per acre

of field P retention potential [24–27]. Sorption coefficient is among the coefficients described in the isotherms that is used to model P movement in the field [28]. Phosphorus sorption capacity has also been used as an important management tool in many crop fields [29]. Therefore, there is a need to identify the appropriate chemistry of the field solutions before conducting P sorption experiments and modeling P movement in the crop fields. Sorption kinetics data trends were reported to provide clues on the mechanisms of sorption reactions [30]; appropriate solution chemistry should also be carefully chosen for the sorption kinetics experiments. It was also hypothesized that the isotherms that describe sorption data from fertilizer mixture are different from isotherms that describe data from typical

The importance of laboratory P sorption and kinetics data in modeling and understanding of the P dynamics in crop fields has been documented [31, 32]. The P sorption characteristics help to properly calibrate theoretical models that aim at mimicking field processes [31, 32]. Accurate laboratory sorption data collected using true field solution chemistry will therefore improve models as predictive tools for P movement. The objective of the study was to determine the differences in P sorption behavior for P in fertilizer mixture (N, P, and K) prepared in deionized water and in P fertilizer (KH2PO4) prepared in 0.01 MKCl, 0.005 M CaCl2, and

**30**

**Table 1.**

deionized water.

laboratory supporting electrolytes.

*Field crop and fertilizer mixture distributions.*


#### **Table 2.**

*Supporting electrolytes, soils, and sorption isotherms for the literature studies.*
