I.INTRODUCTION

Animal manure is considered important nutrient source for plant growth. Manure is recognized as resource like supply of organic matter and ameliorant to soil. Roy et al. (2002) have predicted global utilization of N from animal manure is going to be 50 million tons by 2070. The application of manure to soil not only improves physical and chemical properties of soil but also provides nutrient such as N for plant growth (Mӧller and Stinner, 2009). However, plant cannot directly uptake the organic N in manure. Thus, it should be mineralized as ammonium (NH₄⁺) and nitrate (NO₃^-) to form plant available N (Park et al., 2016). Generally, N mineralization process consists in two steps. Ammonification is the first step which is conversion of organic nitrogen into NH₄⁺ by soil microorganism. After ammonification of N occurs, ammonium is rapidly converted to nitrate by soil bacteria through a process known as nitrification, which is the second step. Therefore, mineralization is the key process for controlling to obtain plant -available N (Badia, 2000).

It has been well reported that soil N mineralization are affected by many factors such as manure composition, soil physical and chemical characteristic, management, and microorganisms (Harris 1981; Haynes, 1986; Eckard et al., 2003; Li and Li, 2014). For example, N mineralization increases with increasing temperature under agricultural soils (Eghball, 2000). Mineralization increases by nearing field capacity (Cassman and Munns, 1980). In addition, mineralization is significantly affected by manure characteristics (Eghball et al., 2002). However, few studies have specifically compared the effects of various kinds of manures on mineralization.

NH₃ volatilization from agricultural soils occur a direct loss of plant N (Salazar et al., 2014). Once volatilized to the atmosphere, it is going to be stored on soil and water after deposition, contributing to soil acidification, water eutrophication eventually influences on human health (Hristov et al., 2011). Moreover, NH₃ is considered as indirect greenhouse gas because ammonium deposition could induce the formation of nitrous oxide in the atmosphere (Sanderson et al., 2006). Several studies reported that NH₃ volatilization depends on the manure characteristics and the environmental conditions. Pagans et al. (2006) reported that ammonia emissions rapidly increased by high temperature during first few days. Matsusada et al. (2002) have shown that NH₃ emissions from composting animal manure varied from 15 mg/kg to 2840 mg/kg in swine manure, dairy manure and poultry. However, NH₃ emission occurred during soil mineralization with different animal manure has not been well documented.

Therefore, this study was conducted to evaluate soil ammonification rate and ammonia emission from different animal manures having same amount of N content. To test this experiment, 4 kinds of animal manures as cattle manure (CtM), goat manure (GM), chicken manure (ChM) and pig slurry (PS) were applied to soil in vitro condition.

Ⅱ.MATERIAL AND METHODS

1.Experiment design

The present study based on an incubation experiment conducted in laboratory. The soil was collected from the surface layer (0-15cm) in Gwangju, South Korea (N35º10', E126º54'). Cattle, goat, chicken manure and pig slurry were sourced from Barebong fertilizer, farming association articles of incorporation (Namwon-si, Korea). The soil was sifted through a 6 mm mesh sieve. Air-dried soil was adjusted to attain at 50 % water hold capacity (WHC) by adding distilled water and packed to the bulk density of field at 1.40 g cm^-3 to be pre-incubated for one week under 25°C. Both manures and soil were ground to 0.2 mm and stored in 4°C to measure total N content and inorganic N content. Chemical property of soil and animal manures used for the experiment were provided in Table. 1. The experiment was allocated with five treatments; control (unfertilized soil), cattle manure (CtM), goat manure (GM), chicken manure (ChM) and pig slurry(PS). The 2 kg of soil was adjusted to 60% WHC and mixed with manures as 200 mg N kg^-1. Soil and manure mixture were transferred into 5.7 L chamber and incubated. The chamber was opened 1 hour for sample harvest, air change and maintain soil moisture every day for the first 7 days and then once per week until 84 days. NH₃ gas was collected when chamber was opened. The soil mixed with manures samples collected at day 0, 14, 28, 49 and 84.

2.Chemical analysis

N property of pig slurry used for this study was determined according to the method of Bremner (1996). The pH measurement was regularly done after shaking a 1:5 (sample:water, w/v) solution for 1 h on a rotary shaker. Total nitrogen was determined by digestion using the Kjeldahl procedure. Inorganic nitrogen was extracted with 2 M KCl and the NH₄⁺-N was determined by distillation in an alkaline medium (MgO). The same procedure was used for NO₃^--N after reduction with Devarda’s alloy (Lu, 2000). For the determination of NH₃ volatilization, the N concentration in collected samples by beakers placed on the soil surface which containing 10 mL, 0.2 M sulfuric acid to collect NH₃. The solution in the form of (NH₄)₂SO₄ was quantified by a colorimetric determination with ammonium color reagent (Nessler’s reagent, Sigma, 72190) as described by Kim and Kim (1996). The net ammonification rate was calculated by following equation, where t is incubation time (Kirkham and Bartholomew, 1954).

Net ammonification rate = ( NH 4 + Dt - NH 4 + D0 ) /t

3.Statistical analysis

Statistical analyses were conducted using the SAS 9.1.3 package. Duncan’s multiple range tests were used to compare means of three replications between different animal manure amended soils. Statistical significance was set at p ≤ 0.05.

Ⅲ.RESULTS AND DISCUSSION

In this study, sandy loam soil which contained 0.25 ± 0.02 g kg^-1 total-N including 10.5±0.88 mg kg^-1 NH₄⁺-N and 7.0 ± 4.38 mg kg^-1NO₃^--N, was used for experiment. The soil and manures nitrogen components were presented in Table 1. Chicken manure (ChM) contained the highest total-N (38.3 g N kg^-1),whereas pig slurry(PS) contained lowest total-N (4.8 g N kg^-1).Thecattle manure (CtM), goat manure (GM) and ChM is consisted of mostly organic N (more than 90%), whereas PS was mainly composed of inorganic N (NH₄⁺ and NO₃^-).

The ammonium nitrogen (NH₄⁺-N) and ammonification rate in the soil with unfertilized control, CtM-, GM-, ChM-, and PS-amended soil were shown in Fig. 1. The NH₄⁺-N was decreased in all treatment during incubation period (Fig. 1A). After 84 days of inoculation, NH₄⁺-N was decreased by 56, 55, 57, 52 and 73% in the soil with unfertilized control, CtM-, GM-, ChM- and PS-amended soil compared to initial level (day 0), respectively. The NH₄⁺-N was continuously decreased in GM- and PS-amended soil for the whole experimental period. On the other hand, in CtM- and ChM-amended soil it was slightly increased after 14 days of experiment. A significant decrease of NH₄⁺-N in early period of experiment might be due to volatilization of NH₃. Similar results were recorded that organic fertilizer increased the amount of ammonium nitrogen at initial period and then it was decreased until 90 days in incubation period (Khalil et al., 2005). The decrease of NH₄⁺-N influenced ammonification rate (Fig. 1B). The ammonification is the conversion of organic nitrogen as animal manure into ammonium nitrogen (NH₄⁺-N) by soil microbes. At initial period of experiment (0 to 14 days), all of treatments recorded negative ammonification rate. The ChM-amended soil increased ammonification rate during 14-28 day while NH₄⁺-N was increased. The decrease of NH₄⁺-N and ammonification rate was result from nitrogen volatilization as ammonia (NH₃) emission. The lowest amount of NH₄⁺-N and ammonification rate was due to a large amount of gas losing (Wolter et al., 2004).

It is well known that ammonia volatilization is closely related to manure characteristics such as total nitrogen, NH₄⁺-N and percentage of dry matter (%, DM) during manure application to soils. The NH₃ was emitted approximately 41.22 μg kg^-1, 33.2 μg kg^-1, 25.2 μg kg^-1 and 7.0 μg kg^-1 in PS-, CtM-, ChM- tand GM-amended soil, respectively, for the first day (Fig. 2A). Afterwards, the NH₃ emission was dramatically decreased in CtM- and ChM-amended soil, whereas NH₃ was gradually decreased in PS-amended soil. The highest NH₃ emission was observed in PS-amended soil. Similar results observed by Park et al. (2015) who reported that ammonia gas was more emitted in pig slurry than cattle manure. Generally, liquid manure and slurry have a high rate of ammonia loss compared to solid manure. It probably related to abundant uric acid in pig slurry (Krogdahl and Dalsgard, 1981). On the other hand, NH₃ emission was low in GM-amended soil for the whole experimental period. The cumulative NH₃ emission was the highest in PS-amended soil with 0.6 mg kg^-1 for 84 days, while less than 0.1 mg kg^-1 in three other plots (Fig. 2B). The cumulative NH₃ emission in PS-amended soil was rapidly increased until 35 days and then it was maintained. A similar tendency was observed ChM-, GM- and CatM-amended soil, but the rate of emission was much less than in PS-amended soil throughout experimental period. Similarly, Chambers et al. (1997) found that emissions of NH₃ from applied solid manure follow a similar pattern over time as slurry but at a lower initial rate and continue for longer because the total ammoniacal N would not infiltrate into the soil to the same degree as that in slurry. These results suggested that manures addition provided a beneficial environment for microorganism lead to accelerate N mineralization.

Taken together, in present study, different manures showed different soil ammonification and ammonia emission even though same amount of N supply. For future study needs soil incubation by using isotope method for N use efficiency and plant available nitrogen for herbage yield.