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Mitigating Ammonia Volatilization from Urea in Waterlogged Condition Using Clinoptilolite Zeolite.

Byline: Perumal Palanivell Osumanu Haruna Ahmed1 Kasim Susilawati and Nik Muhamad Ab Majid


Besides causing environmental pollution ammonia volatilization from nitrogenous fertilizers such as urea reduce urea-N use efficiency in agriculture. Amending urea with Clinoptilolite zeolite may reduce ammonia loss from urea as well as improving chemical properties of soils. This study was conducted to determine the effects of amending an acid soil with Clinoptilolite zeolite on ammonia loss and selected soil chemical properties. An acid soil (Typic Paleudults) was mixed with three rates of Clinoptilolite zeolite. Treatments were evaluated using closed-dynamic airflow system. Standard procedures were used to determine soil pH total nitrogen exchangeable ammonium available nitrate available phosphorus exchangeable cations organic matter total organic carbon and cation exchange capacity (CEC). Application of Clinoptilolite zeolite significantly reduced ammonia loss up to 25.33% increased soil pH exchangeable ammonium

Available nitrate (treatment with highest amount of Clinoptilolite zeolite) and exchangeable cations. However there was reduction in total titratable acidity exchangeable Al3+ and H+ ions. Mixing acid soil (Typic Paleudults) with Clinoptilolite zeolite minimized ammonia loss from urea and improved selected soil chemical properties (under laboratory condition).

Keywords: Ammonia loss; Urea; Clinoptilolite zeolite; Soil chemical properties; Exchangeable ammonium; Available nitrate


Unbalanced use of urea does not only lead to ammonia (NH3) loss but it also causes eutrophication groundwater pollution acid rain soil acidification and greenhouse gas emissions (Tang et al. 2008; Adesemoye and Kloepper 2009; Ju et al. 2009; Moose and Below 2009). Furthermore NH3 volatilization from urea causes nutrients leaching from leaves of plants besides increasing plants' sensitivity to stress factors (Francis et al. 2008). When urea is surface applied approximately 90% of N is lost in sandy soils with low buffering capacity (Francis et al. 2008).

Ammonia loss from urea occurs when it is hydrolyzed to ammonium carbonate [NH2CONH2 + 2H2O (NH4)2CO3] by urease. Afterwards ammonium carbonate decomposes into NH3 CO2 and H2O. Ammonia loss is also high under warm-dry and cool-wet conditions (McGarry et al. 1987). Ammonia loss is higher under waterlogged or anaerobic condition compared to aerobic condition (Zhengping et al. 1991). For example photosynthetic activities of aquatic organisms (photoautotroph) in rice fields (anaerobic condition) are reduced by rice canopy. As a result it reduces carbon dioxide depletion in rice fields and increases the possibility of NH3 loss (Fillery et al. 1983). Application of algaecide in anaerobic condition reduces water pH.

Ammonia loss from urea can be reduced with application of materials which are high in CEC (Sommer et al. 2006; Omar et al. 2010; Latifah et al. 2011a b c) or materials which lower soil microsite pH (Stevens et al. 1992) moisture and temperature (Sommer et al. 1991). In a study zeolite was mixed with dairy slurry to reduce ammonia volatilization (Lefcourt and Meisinger 2001). Zeolite has also been mixed with acid sulphate soil (Ahmed et al. 2010) or cellulose (He et al. 2002) or triple superphosphate and humic acids (Ahmed et al. 2006a b) to control ammonia loss from urea in non-waterlogged soils. Mixing zeolite with sago waste water and peat water reduced ammonia loss from urea in waterlogged soils (Omar et al. 2010; Latifah et al. 2011c). However unlike previous studies where researchers used expensive acidic materials (corrosive and difficult to handle) such as acid sulphate soil triple superphosphate and peat water to control ammonia loss

In this present study an acid soil was mixed with Clinoptilolite zeolite alone to control ammonia loss in waterlogged condition. We hypothesized that mixing Clinoptilolite zeolite with an acid soil will effectively reduce ammonia loss from urea. This is possible because the high affinity of Clinoptilolite zeolite for cations such as ammonium will enhance retention of ammonium ions which are produced during urea hydrolysis and release these ions timely to minimize the rate of converting ammonium to NH3. Therefore this study was carried out to determine the effect of mixing an acid soil (Typic Paleudults) with Clinoptilolite zeolite at different rates on ammonia volatilization from urea exchangeable ammonium available nitrate and other selected soil chemical properties.

Materials and Methods

Soil Sampling Preparation and Characterization

Typic Paleudults (Bekenu Series) soil was sampled at 0 to 25 cm in an undisturbed area of Universiti Putra Malaysia Bintulu Sarawak Campus Malaysia (latitude 3 12' 14.6" N and longitude 113 4' 16.0" E). The soil was air-dried ground and sieved to pass to a 5 mm sieve. The soil was analyzed before and after the incubation study for texture using a hydrometer method pH in distilled water and 1 M KCl (at ratio of 1:2.5 soil:water or KCl) using a glass electrode (Peech 1965) organic matter and total carbon using loss-on-ignition method (Piccolo 1996) total N using Kjedahl method (Bremner 1965) available NO3 exchangeable NH4 (Keeney and Nelson 1982) exchangeable cations and available P were extracted using the Double Acid Method (Mehlich 1953) and cations determined using Atomic Absorption Spectrometer (AAnalyst 800 Perkin Elmer Instruments Norwalk CT) whereas available P was determined using the Blue Method (Murphy and Riley 1962).

Cation exchange capacity of the soil was determined using the leaching method (Cottenie 1980) followed by steam distillation (Bremner 1965). Total titratable acidity exchangeable H+ and exchangeable Al3+ were determined using acid-base titration method (Rowell 1994).

The selected chemical and physical properties of the soil (Table 1) used in this study were typical of Typic Paleudults (Bekenu series) and they are consistent with those reported by Paramananthan (2000) except for CEC exchangeable calcium and magnesium.

Clinoptilolite Zeolite Characterization

The Clinoptilolite zeolite used in this study was characterized for pH (Tan 2005) CEC using CsCl method (Ming and Dixon 1986) total N (Bremner 1965) total P and cations were extracted using the Aqua Regia method (Tan 2005). Phosphorus in the extractant was determined using the Blue method (Murphy and Riley 1962) total cations were determined using atomic absorption spectrophotometry. pH of the Clinoptilolite zeolite was higher as expected but its CEC and total N content were lower (Table 2).

Treatments Evaluation for Ammonia Loss from Urea

The ammonia loss incubation study was conducted using close-dynamic air flow system (Siva et al. 1999; Ahmed et al. 2006a b). Treatments were arranged in a Complete Randomized Design (CRD) with three replications for 33 days. The treatments per 250 g of soil evaluated in 500 mL conical flask were: T1: soil alone T2: soil + 1.31 g urea T3: soil + complete fertilization T4: soil + complete fertilization + 20 g Clinoptilolite zeolite T5: soil + complete fertilization + 40 g Clinoptilolite zeolite and T6: soil + complete fertilization + 60 g Clinoptilolite zeolite. The complete fertilization is equivalent to 1.31 g urea + 1.39 g ERP + 0.88 g MOP + 0.16 g Kieserite + 0.53 g chelated ZnCoBor per experimental unit. The amounts of the fertilizers used were a scaled down for plant density of 3 rice plants hill-1. This fertilizer rate for macronutrients (151 kg ha-1 N 97.8 kg ha-1 P2O5 130 kg ha-1 K2O and 7.6 kg ha-1 MgO)

(Muda Agricultural Development Authority Malaysia) was based on the recommended fertilizer for rice whereas micronutrients (2.3 kg ha-1 B 4 kg ha-1 Cu and 4 kg ha-1 Zn) fertilization was based on the recommendation of Liew et al. (2010). The amounts of Clinoptilolite zeolite used were deduced from the literature and Sepaskhah and Barzegar 2010) where rates of 5 10 and 15 tons ha-1 are equivalent to 20 40 and 60 g hill-1 respectively.

The incubation study was carried out by mixing soil with Clinoptilolite zeolite for the treatments with zeolite alone after which the mixture was moistened to 100% of field capacity and left over night to equilibrate. Before the fertilizers were applied the water level in each conical flask was maintained at 3 cm from the soil surface to ensure the system was waterlogged. The water level was marked on the conical flasks. The water level in the conical flask was maintained throughout incubation period (33 days) by adding distilled water as the deficit of the original water level. The fertilizers were applied on the soil surface air was passed through the volatilization system at a rate of 2.5 L min-1 and volatilized ammonia from urea was captured in 75 mL of 2% boric acid solution with bromocresol green and methyl red indicator. The rate of air flow was measured using a Gilmont flow meter (Gilmont Instrument Great Neck NY USA).

The boric acid solution was replaced every 24 h and back titrated with 0.05 M HCl to determine ammonia loss from urea. This measurement was continued until the ammonia loss decreased to 1% of the N added in the system (Ahmed et al. 2006a b c). This incubation study was conducted in a laboratory with an average temperature of 29.7 1.4C and an average relative humidity of 70.1 10.5%.

Statistical Analysis

Analysis of variance (ANOVA) was used to detect significant differences among treatments whereas Tukey's HSD test was used to compare treatment means using Statistical Analysis System version 9.2 (SAS 2008).

Table 1: Selected chemical and physical properties of Typic Paleudults (Bekenu Series) soil before incubation




CEC (cmolc kg-1)###11.97

Total organic carbon (%)###2.43

Total N (%)###0.08

Exchangeable NH4+ (mg kg-1)###21.02

Available NO3- (mg kg-1)###7.01

Available P (mg kg-1)###4.85

Exchangeable K+ (cmolc kg-1)###0.10

Exchangeable Ca2+ (cmolc kg-1)###0.25

Exchangeable Mg2+ (cmolc kg-1)###0.34

Exchangeable Na+ (cmolc kg-1)###0.22

Exchangeable Fe2+ (cmolc kg-1)###0.19

Exchangeable Cu2+ (cmolc kg-1)###Trace

Exchangeable Zn2+ (cmolc kg-1)###0.01

Exchangeable Mn2+ (cmolc kg-1)###0.02

Bulk density (g cm-3)###1.16

Sand %###71.04

Silt %###14.58

Clay %###14.38

Table 2: Selected chemical properties of Clinoptilolite zeolite

Property###Clinoptilolite Zeolite


CEC (cmolc kg-1)###71.30

Total N (%)###0.22

Total P (%)###0.01

Total K (%)###0.37

Total Ca (%)###0.67

Total Mg (%)###0.10

Total Na (%)###0.76

Total Fe (%)###0.11

Total Cu (mg kg-1)###15.42

Total Zn (mg kg-1)###16.75

Total Mn (mg kg-1)###125.08


Ammonia Volatilization

Ammonia volatilization was observed for complete fertilization without Clinoptilolite zeolite (T3) on the first day of incubation (Fig. 1). For T2 T4 T5 and T6 the ammonia volatilization started on the second day of incubation. At day 8 of incubation the highest ammonia volatilization (9.58%) occurred in urea alone (T2). Ammonia loss from urea alone (T2) lasted for 23 days whereas those of T3 T4 T5 and T6 lasted for 32 30 29 and 29 days respectively. Ammonia volatilization decreased at 12 and 19 days of incubation and it has increased at 13 and 20 days of incubation in all the treatments except for T1. No ammonia volatilization was observed in soil alone (T1). Treatments with Clinoptilolite zeolite (T4 T5 and T6) significantly decreased total NH3 loss and available P compared to treatments without Clinoptilolite zeolite (T2 and T3) (Fig. 2). The total NH3 loss and available P decreased (T4 greater than T5 greater than T6) with increasing rate of Clinoptilolite zeolite.

Soil Chemical Properties

Clinoptilolite zeolite in T4 T5 and T6 increased soil pHwater pHKCl and exchangeable NH + compared with T1 T2 and T3 (Fig. 3 and 4). The treatment with the highest amount of Clinoptilolite zeolite (T6) showed higher available NO - compared with T3 (Fig. 5). There were no significant differences among treatments in terms of organic matter and total carbon contents after incubation (Table 3). Soil alone (T1) showed the highest total titratable acidity exchangeable H+ and exchangeable Al3+ compared with other treatments. At 33 days of incubation the treatments with Clinoptilolite zeolite (T4 T5 and T6) showed higher exchangeable Ca Mg Na Fe and Mn compared with treatment T3 (complete fertilization without Clinoptilolite zeolite) (Fig. 6 7 8 and 9). The contents of exchangeable Ca Na Fe and Mn increased with increasing rate of Clinoptilolite zeolite (T4 T5 and T6).

Table 3: Selected soil chemical properties over 33 days of incubation


Decrease in total NH3 loss as compared to T2 (%)###nd###nd###nd###6.75###14.90###25.33

OM (%)###4.00a (0.12) 4.33a (0.13)###4.07a (0.18)###3.87a (0.18)###3.73a (0.07) 3.93a (0.18)

TOC (%)###2.32a (0.07) 2.52a (0.08)###2.36a (0.10)###2.24a (0.10)###2.16a (0.04) 2.28a (0.10)


Total N (%)###0.10 (0.01) 0.15 (0.01) 0.13 (0.01) 0.16 (0.01)###0.18 (0.01) 0.18a (0.01)

Available P (ppm)###0.35e (0.02) 23.14d (2.36) 110.24a (5.70) 44.89bc (2.82) 52.25b (0.81) 29.45cd (3.28)

Total titratable acidity (meq)###0.37a (0.01) 0.20b (0.01)###0.15c (0.00)###0.21b (0.01)###0.22b (0.01) 0.21b (0.00)

Exchangeable H+ (meq)###0.27a (0.01) 0.20b (0.01)###0.15c (0.00)###0.21b (0.01)###0.22b (0.01) 0.21b (0.00)

Exchangeable Al3+ (meq)###0.11a (0.01) 0.00b (0.00)###0.00b (0.00)###0.00b (0.00)###0.00b (0.00) 0.00b (0.00)

However T3 (complete fertilization without Clinoptilolite zeolite) showed the highest exchangeable K Cu and Zn compared with other treatments (Table 4). Exchangeable K Cu and Zn contents in the soil with Clinoptilolite zeolite decreased with increasing rate of Clinoptilolite zeolite.


Higher evolution of ammonia from the treatment with urea alone (T2) suggests that urea hydrolyzed and volatilized rapidly. Inclusion of rock phosphate in T3 T4 T5 and T6 delayed ammonia volatilization compared with T2 because of phosphoric acid from acidic phosphate hydrolysis. This reaction may have reduced urea hydrolysis and ammonia volatilization (Ahmed et al. 2006b).

The fluctuation of ammonia volatilization during the incubation study was caused by the reaction between urea and soil water to form NH4 . As the soil surface rapidly dried due to air velocity in the chamber NH3 from urea decreased at 12 and 19 days of incubation. Ammonia loss decreased when soil water was insufficient for the chemical reaction but it increased at 13 and 20 days of incubation upon addition of water. This observation is consistent with that of Bundan et al. (2011). No ammonia volatilization in T1 suggests that the soil alone did not contribute to ammonia loss. This observation is consistent with findings reported in previous studies (Siva et al. 1999; Ahmed et al.2006a b c; Omar et al. 2010; Bundan et al. 2011).

The treatments with Clinoptilolite zeolite (T4 T5 and T6) increased soil pH because of the basic cations in the Clinoptilolite zeolite (Fig. 6 7 and 8). CEC of the Clinoptilolite zeolite may have partly contributed to reduction of NH3 loss because of the improvement in the retention of NH + and NO - (Ahmed et al. 2010). No 4 3 change in organic matter and total carbon contents regardless of treatment was because there was no addition of organic matter rich materials to the soil. Total titratable acidity exchangeable H+ and exchangeable Al3+ of the soil alone (T1) were higher because this treatment showed lowest soil pH and highest exchangeable Fe compared with the other treatments (Gotoh and Patrick 1974; Williams 1980). At lower pH H+ activity and exchangeable Al are higher. Hence increase in soil pH to 5.2 or higher normally reduces H activity and precipitates exchangeable Al3+ (Zhu et al. 2009; Azura et al. 2011).

The CEC of the Clinoptilolite zeolite may have caused adsorption of the cations at the exchange sites of the Clinoptilolite zeolite. This process renders cations readily available for plant uptake (He et al. 1999; Ahmed et al. 2010). The higher Na (almost double the amount of K in

Table 4: Selected soil exchangeable cations (cmolc kg-1) at 33 days of incubation

Exchangeable cations###T1###T2###T3###T4###T5###T6

K+###0.14e (0.003)###1.16c (0.106)###2.91a (0.029)###1.67b (0.008)###1.16c (0.010)###0.85d (0.014)

Cu2+###0.030bc (0.005)###0.040b (0.003)###0.062a (0.003)###0.038b (0.000)###0.018cd (0.001)###0.012d (0.000)

Zn2+###0.002c (0.0001)###0.012b (0.0010)###0.026a (0.0009)###0.002c (0.0002) 0.002c (0.0000)###0.001c (0.0001)

Clinoptilolite zeolite) content compared with K in Clinoptilolite zeolite may have reduced K availability in the soil after 33 days of incubation via antagonism. The lower contents of Cu and Zn (bivalent cations) in the Clinoptilolite zeolite compared with Ca Mg Fe and Mn may have caused lower availability of Cu and Zn in the soil. Increasing amount of Clinoptilolite zeolite reduced exchangeable Cu and Zn in the soil. This was because the Clinoptilolite zeolite has higher affinity for Cu and Zn than Fe and Mn (Erdem et al. 2004; Iskander et al. 2011).


Mixing an acid soil (Typic Paleudults) with Clinoptilolite zeolite under waterlogged condition reduced ammonia loss from urea and successfully improved ammonium and nitrate ions retention soil pH and selected exchangeable cations. Thus Clinoptilolite zeolite could be used to amend waterlogged acid soils in rice fields to minimize urea-N loss and as well improve soil chemical properties but long term field evaluation is essential to consolidate the findings in this study. This aspect is being embarked on in our field experiments.


Authors acknowledge Ministry of Education (MOE) Malaysia for the Long-term Research Grant Scheme LRGS (Food Security-Enhancing sustainable rice production) and Universiti Putra Malaysia for funding this research project. The authors would also like to acknowledge Asean Bintulu Fertilizer Sdn Bhd and MB Plus Sdn Bhd for supplying research materials for this research.


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