| nitrogen loading 
oggles, Holywell 
Is are of the form: 
;alculated nitrogen 
rved discharge in 
ssion coefficients. 
Model 
B1 r2 
4 1883.5 97.6 
; + 1130.5 97.6 
+ 9143 95.3 
; + 1059.88 94.3 
) + 1267.0 93.8 
)+ 1152.0 85.3 
y+ 8730. 98.1 
ntrogen loading 
icient model with 
Nitrogen loss 
(tonnes/year) 
ved Predicted 
ha) 128.33 
.76 124.36 
36 92.39 
61 84.87 
87 533.68 
73 470.50 
.07 603.80 
nerally successful 
and the export 
estimate nitrogen 
ions can be seen 
ated values which 
use of rating 
bserved loads and 
fficients selected 
li et al., 19953). 
ionstrate that the 
ding with a fair 
nitrogen for the 
rs are presented in 
igure that nitrogen 
1931-89. Nitrogen 
O tonnes/year in 
r in 1989. This 
  
increase in solute loading in the surface water is 
due to the combined effect of increased arable 
land and an increased rate of application of 
nitrogen fertilizer. The marked increase of 
nitrogen loading during 1971-1984, may be 
attributed to an increased rate of nitrogen 
fertilizer application (i.e. 200 kg/ha) in 1984 as 
compared to the much smaller rate in 1971. 
388888 
Nitrogen loading, tonnes/year 
3 
1 
  
  
© 
| 
bd en — “+ > > 
e \O > oo oo oo 
ON AN Oo ON Os ON 
vod vw Land vw — -— 
Figure 2. Predicted losses of nitrogen loading for 
the entire study area: 1931-89. 
In the export coefficient model, nitrogen 
loading is dependent on both land-use and 
fertilizer application rates. Therefore, the analysis 
of nitrogen loading presented above portrays the 
combined effect of both land-use change and 
fertilizer usage. An analysis was carried out to 
identify the separate effects of land-use change 
and fertilizer usage on nitrogen loading. This was 
achieved by predicting nitrogen loading for 
different rates of fertilizer application on the 
historical land-use data (Mattikalli et al., 1995c). 
The results of such an analysis for different cases 
were used to produce bar graphs of nitrogen 
loading (figure 3). 
(a) Predicted Nitrogen Loading 
Using Fertiliser Application Rates of 1931 
100 - 
80 4 
  
  
60 a HEHE 
40 4 
20 — 
Nitrogen loading, tonnes/year 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
1963 ud 
1971 
(b) Predicted Nitrogen Loading 
Using Fertiliser Application Rates of 1971 
E E 
3 
8 
Nitrogen loading, tonnes/year 
tA A 
e e 
© 
  
(c) Predicted Nitrogen Loading 
Using Fertiliser Application Rates of 1963 
250 - 
200 + 
150 — 
100— 
50— 
Nitrogen loading, tonnes/year 
  
  
(d) Predicted Nitrogen Loading 
Using Fertiliser Application Rates of 1984 
7004 
600 — 
5004 
400 rz 
300 4 
200 — 
Nitrogen loading, tonnes/year 
1004 
  
  
E Wm reas 
-—- — v— -— — ve 
Figure 3. Bar graphs illustrating effect of land- 
use change on nitrogen loading. Each diagram 
shows the variation of nitrogen loading with 
respect to the land-use change during 1931-89 
for constant fertilizer application rates of: (a) 
1931; (b) 1963; (c) 1971; and (d) 1984. Source: 
Mattikalli (1993).