96 The best fit equations describing response curves for cumulative K uptake
versus application rate of K fertilizers with their values of RAE are presented in Table 5.5. As shown in this table, gneiss was about half as effective as K
2
SO
4
for growing ryegrass up to 6 months H1 – H2, but was slightly more effective for
plants harvested at 9 and 12 months H3 – H4. This interpretation should be treated with some caution as the plants supplied with K
2
SO
4
had removed most ≈ 34 of
applied K from soil by H2. K-feldspar was much less effective than K
2
SO
4
for all growth periods.
5.3.4. Internal Efficiency IE of Nutrient Elements
Various confounding effects may occur when comparisons are made between fertilizers of quite different composition and particularly for fertilizers that
provide several nutrient elements, dissolve at very different rates and which may have various liming effects. One way of testing data for the presence of these
confounding effects is to determine if plant yield and plant nutrient test nutrients content data conform to a single curve relationship for all the fertilizers under
comparison. These relationships are often called ‘internal efficiency’ Yang et al. 2003; Pathak et al. 2003 or ‘physiological efficiency’ Sahrawat et al. 1997 curves
as they provide an indication of the efficiency with which increments of nutrient uptake content produce increments of plant growth response. The trends in IE
were identified by plotting the yield of dry shoot versus uptake of nutrient concerned for each growing period H1 – H4, and plots are presented in Figures 5.7 – 5.9. The
plots for experiments A using soil MR-5 and B using soils WP-6 and MR-5 were excluded from this analysis due to the minor response of plants to applications of
fertilizers. The slopes of these plots indicate the values of the parameters IE as defined
in this thesis, and these values as indicated in Figures 5.8 and 5.9 change with application rate of fertilizers. To provide appropriate estimates for relative internal
effectiveness RIE of SRF over that of the reference fertilizer only for K experiment, the IE value for K
2
SO
4
was defined as the mean IE values for the application rates of 0 control to 90 mg Kkg soil e.g., the slopes of broken lines
shown in Figures 5.8 and 5.9, whereas the IE value for SRF was defined as the initial slope of the curve for application rates of 0 control to 225 mg K as gneiss
97
Figure 5.7. Plots of yield versus Ca uptake for each harvest H1 – H4 of plants grown on soil WP-6 receiving Ca fertilizers Ca experiment. The plots for nil Ca
and +CaCl
2
was not presented due to insufficient data most plants for the nil Ca and +CaCl
2
treatments dead. SRFkg soil and to 450 mg K as K-feldspar SRFkg soil. The IE values for K
experiment are presented in Table 5.6. As shown in Figure 5.7, the IE values of H1 for basalt and dolerite SRFs
were similar, which was about 0.4 g dry topsmg Ca uptake, and IE tends to decrease with increasing application rate of the Ca fertilizers. The IE values for H2 –
H4 were about zero to negative, indicating that for applications of basalt and dolerite SRFs at rates greater than 333 mg Cakg soil to soil WP-6 increased Ca uptake but
did not increase yield H2 – H4 see Figure 5.1. As discussed in earlier sections, the main limiting factor for plant growth on
soil WP-6 was the low pH of the soil rather than it being deficient in Ca. Some of the applied basalt and dolerite SRFs may have rapidly dissolved releasing about
H-1 Basalt
Dolerite
1 2
3
2 4
6 8
10 Cumulative Ca uptake mgpot
C u
m u
lat iv
e Y
ield g
p ot
H-2 Basalt
Dolerite
1 2
3 4
5 6
7 8
9
4 8
12 16
20 Cumulative Ca uptake mgpot
C u
m u
lat iv
e Y
ield g
pot
H-3 Basalt
Dolerite
5 10
15
5 10
15 20
25 30
Cumulative Ca uptake mgpot C
u m
u lat
iv e
Y ield
g pot
H-4 Basalt
Dolerite
5 10
15 20
5 10
15 20
25 30
35 40
Cumulative Ca uptake mgpot C
u m
u la
tiv e
Y ield
g pot
98
Figure 5.8. Plots of yield versus K uptake of each harvest H1 – H4 for plants grown on soil BSN-1 receiving K fertilizers.
10 of total Ca see Figure 4.1, Chapter 4 during the first 3 months while also
increasing soil pH. For a longer growing period, more Ca was released from Ca-SRF which was associated with an increase in soil pH which may also have increased
microbial activity and released initially soil-fixed Ca e.g., OM-Ca to plants Gillman 1980. Consequently, a large amount of Ca was taken up by plants. This
large Ca uptake, however, did not increase plant yield which actually decreased, which was probably due partly to the confounding effect of SRF reducing Cu uptake
to deficient level see section 5.3.2.. For K experiment see Figures 5.8 - 5.9 and Table 5.6, the IE values for H1
are in the order gneiss K
2
SO
4
K-feldspar BSN-1 and K-feldspar gneiss K
2
SO
4
SCP-11. With increasing growing period, the IE values for K
2
SO
4
become much higher than for both K-SRFs.
H-1
Gneiss
K-feldspar
K
2
SO
4
1 2
3
20 40
60 80
100 K uptake mgpot
Y iel
d g
pot H-2
Gneiss K-feldspar
K
2
SO
4
1 2
3 4
5 6
7 8
9
20 40
60 80
100 K uptake mgpot
Y iel
d g
pot
H-3
Gneiss K-feldspar
K
2
SO
4
1 2
3 4
5 6
7 8
9
20 40
60 80
100 K uptake mgpot
Y iel
d g
pot H-4
Gneiss
K-feldspar K
2
SO
4
1 2
3 4
5 10
15 20
25 30
35 40
K uptake mgpot Y
iel d
g pot
99
Figure 5.9. Plots of yield versus K uptake of each harvest H1 – H4 for plants grown on soil SCP-11 receiving K fertilizers.
Table 5.6. Internal efficiency IE and relative internal efficiency RIE for application of K fertilizers calculated based on initial slope of response curves in
Figures 5.8 and 5.9.
IE g dry shootmg K uptake RIE
Harvest +K
2
SO
4
Gneiss K-feldspar
+K
2
SO
4
Gneiss K-feldspar
H1 H2
H3 H4
H1 H2
H3 H4
0.0148 0.1025
0.5570 0.8550
0.0108 0.2444
0.9503 0.6565
0.0174 0.0548
0.0998 0.1723
0.0170 0.0502
0.1061 0.1251
Soil 0.0072
0.0668 0.2313
0.0695
Soil 0.0192
0.2115 0.3108
0.2048 BSN-1
100 100
100 100
SCP-11 100
100 100
100 118
53 18
20
157 21
11 19
49 65
42 8
178 87
33 31
H-1
Gneiss K-feldspar
K
2
SO
4
1 2
3 4
20 40
60 80
100 K uptake mgpot
Y ie
ld g
p ot
H-2
Gneiss K-feldspar
K
2
SO
4
1 2
3 4
5 6
20 40
60 80
100 K uptake mgpot
Y ie
ld g
p ot
H-3
Gneiss K-
feldspar K
2
SO
4
1 2
3 4
5 6
7
20 40
60 80
K uptake mgpot Y
ie ld
g p
ot H-4
Gneiss K-feldspar
K
2
SO
4
1 2
3 4
5 10
15 20
25 30
35 K uptake mg Kpot
Y ie
ld g
p ot
100 Values of IE are commonly used to provide information on the relative
efficiency of genotypically different plants in utilizing a nutrientfertilizer Baligar et al.
2001; Yang et al. 2003; Pathak et al. 2003; Sahrawat et al. 1997, in which experiments the plants under comparison receive the same amounts of
nutrientfertilizer. In this present research, however, the same plants were grown, so the differences in IE values mostly reflect the external and sometimes confounding
effects discussed above. During the first 3 months, the plants grown on soils BSN-1 and SCP-11 were
sufficient in K, so there was less response in plant yield to the application of K- fertilizers although there was an increase in K uptake low IE values. For growing
periods of 3 – 12 months, the plants receiving K
2
SO
4
were severely deficient in K due to rapid depletion of K in the first 3 months so that the plants were highly
responsive in yield to K uptake, thus the IE values increased with increasing growing period. In contrast, the plants receiving ground gneiss and K-feldspar
applications were less severely deficient in K for H2 – H4 due to additional K dissolving from applied K-SRFs during this growth period. Moreover, dissolution of
K-SRFs produced a liming effect increased soil pH which may have increased the amount of K released from indigenous soil K reserves. In summary, the internal
efficiency for K
2
SO
4
was higher than for ground gneiss and K-feldspar applications for plants grown on soils deficient in K. This relatively lower IE values for K-SRF
application was due to the large supply of K and the liming effect of the applied K- SRFs. Moreover, the confounding effects of K-SRF application including reduced
uptake of several plant nutrients as discussed in section 5.3.2 may also have contributed to these low IE values.
5.3.5. Extractable Nutrients, pH, and EC of Residual Soils
