1. Analysis of Nitrogen Dynamics and Fertilizer Use
Efficiency in Rice using the Nitrogen-15 Isotope
method following the application of Biogas Slurry
or Chemical Fertilizer
15
Adel Ghoneim, H. Ueno, A. Ebid, N. Asagi and I.Abou El-darag
International Journal of Soil Science 3 (1): 11-19, 2008

2. Introduction
Biogas slurry is a by-product of the biological
breakdown of organic wastes such plants, crop residue,
food waste, human and animal manure under anaerobic
conditions. Biogas slurry is a valuable source of crop
nutrients and organic matter and improve soil physical
properties.
Use of 15
N tracer is the most powerful tool to
distinguish between the fate of particular N source and
background soil N.
Objectives
To determine the impact of 15
N labeled biogas slurry
and chemical fertilizer on N uptake, N distribution and
fertilizer use efficiency.

3. Nitrogen fertilizer is the most costly input element.
Therefore, it is important to maximize N use efficiency and
minimize N losses to the environment. These losses occur from
the soil-plant system via denitrification, volatilization and by
leaching.
By understanding N movement in the soil, we can characterize
how these losses occur and seek to increase N use efficiency.

4. Problem Statements
• Utilization of large amounts of chemical fertilizer
in paddy field.
• Low nitrogen use efficiency.
• Large quantity of post harvest rice residues.

5. Treatments
• Chemical fertilizer @ 80 Kg N ha-1
labeled with
1.0 atom% 15
N. Nitrogen fertilizer applied 3 splits
(40, 20, and 20) during transplanting, 30 and 60
DAT.
• Soil amended with biogas slurry @80 Kg N ha-1
applied at different growth stages

6. Soil samples and analysis
• Collected at 0, 2, 4, 6 and 8 days after BS
application. Samples were categorized as 0-2
and 2-5 cm depth.
• Soil pH and soil mineral N were determined
• Rice growth parameters were measured

7. Nitrogen Dynamics and 15
N Recovery Calculation
• Atom% 15
N excess was calculated as the difference
between 15
N atom% in plant – natural abundance in the
atmosphere
• Fertilizer N Use Efficiency (FUE)
FUE CF = (atom% 15
N excess plant )/ (atom% 15
N excess CF) x N plant
/ N applied CF x 100.
FUE BS = N plant BS /N BS
• Relative efficiency (%) = FUE BS/ FUE CF x100

8. Materials and Methods
Properties Value
pH 6.7
EC 0.37 dS m-1
CEC 9.24 cmol kg-1
Total C 14.6 g kg-1
Total N 1.5 g kg-1
Clay 13.4 %
Sand 58.5 %
Silt 18.1 %
Table 1. Soil chemical properties

9. Characteristic Mean (n, 3)
pH 7.6
EC 1.7 dS m-1
Total C 14 g kg-1
Organic N 1.10 g kg-1
Total Volatile Acids 70.6 %
C/N ratio 7.6
Phosphate 180 mg kg-1
Exchangeable K 0.57 mg kg-1
SO4
-2
380 mg kg-1
Table 2. Chemical properties of biogas slurry

10. Treatment Yield
g pot-1
No of panicle
pot-1
1000-
grain wt.
g
Chemical Fertilizer (CF) 24.6 18.5 23.2
Biogas Slurry (BS) 23.1 16.5 22.1
F test NS NS NS
Table 3. Yield and yield component

11. Treatment Rice part DW (g pot-1
)
Chemical fertilizer 25.9 a
Biogas slurry grain 28.5 a
Chemical fertilizer 37.6 a
Biogas slurry straw 34.7 a
Chemical fertilizer 14.9 a
Biogas slurry root 10.8 a
Chemical fertilizer 78.4 a
Biogas slurry Whole plant 74.0 a
Table. Dry weight
Means in a column followed by the same letter were not
significantly different (Tukey-Kramer test: P =0.05)

12. Treatment N uptake (mg pot-1
)
Rice part Ndf Ndfs Total
Chemical
Fertilizer (CF)
63.9 (16.8)a 316.9 (3.2)a 380.8a
Biogas slurry
(BS)
grain 26.9 (8.93)b 274.2 (9.1)a 303.1a
CF 48.3 (14.7)a 280.9 (88.3)a 329.9a
BS straw 27.3 (9.7)b 257.6 (90.2)a 285.9a
CF 20.8 (14.1)a 127.2 (85.9)a 148.0a
BS root 14.7 (11.4) b 113.9 (88.6)a 128.6a
CF 133.0 (15.5)a 725.0 (84.5)a 858.0a
BS whole plant 68.9 (9.64)b 65.7 (90.4)a 714.6a
Table. N uptake from chemical fertilizer and biogas slurry

13. Treatment NUE
(%)
Relative
Efficiency
(%)
N distribution (%)
Soil Uptake Loss
Chemical
Fertilizer
70.3 a 100 6.2 a 70.3 a 23.5 a
Biogas
Slurry
50.5 b 71.8 13.2 b 50.5 b 50.5 b
Means in a column followed by the same letter were not
significantly different (Tukey-Kramer test: P =0.05)
Table. Nitrogen use efficiency, relative efficiency and N distribution

14. Conclusion
 N uptake was highest in chemical fertilizer treatment
compared with biogas slurry
 The highest proportion of N uptake by rice was from soil
 About 6.2 and 13.3% of applied N remained in the soil
treated with chemical fertilizer and biogas slurry,
respectively
 Significant amount of N was lost from the soil-plant
system