Long-Term Mineral Fertilization and Soil Fertility
99
2.1 Changes in soil acidity forms
2.1.1 Soil acidity forms for the 0-400 cm profile
The soil acidity forms, averaged for the investigated depth of the 0-400 cm profile, were significantly affected by the type of fertilizer combination. The independent effect of the factor mineral fertilization was higher on exchangeable Al3+, Ca2+ and the sum of Са2+ and Mg2+, and significantly lower - on the values of residual hydrolytic acidity and the rate of alkali saturation. The depth of the investigated profile was the factor with decisive effect on all forms of soil acidity. Its effect on the pH values, the residual hydrolytic acidity and the alkali saturation degree was over 90 %. Significantly lower was its influence on the
exchangeable Al3+ (22.5%) and the sum of exchangeable Са and Mg (45.8%).
pH – H2O
Ca+Mg
Ca
Al
4,7 2,0
7,6
7,2
20,3
7,0
46,6
22,5
45,8
70,6
72,5
93,3
Fert.variants (A) Depth (B) Fert.variants * Depth
Fert.variants (A)
Depth (B)
Fert.variants * Depth
Fert.variants (A) Depth (B) Fert.variants * Depth
Fert.variants (A)
Depth (B)
Fert.variants * Depth
Fig. 1. Power of factors influence
In spite of the maximum degree of significance of the effect of mineral fertilization on the forms of soil acidity, the amplitude of variation of the separate indices was not so well expressed as in the separate soil layers up to 400 cm down the soil profile. Averaged for the fertilization variants, pH varied from 6.35 (10-20 cm) to 8.53 (260 – 300 cm). Soil reaction increased down the soil profile and at the 4th meter there was well expressed correlation between the soil layers forming it. It, however, showed similarities to layers 160-180, 180-200
and 200-220 cm. The layers from 220 to 300 cm possessed higher pH values in comparison to the layers of the 4th meter.
The amount of exchangeable Ca2+ showed a gradual tendency toward decreasing down the
depth profile. Amplitude of variation was from 28.49 cmolckg-1 (60-80 cm) to 18.79 cmolckg-1
(380-400 cm). The surface layers 0-10 and 10-20 cm had lower content of exchangeable Ca2+ in comparison to the layers under them up to depth of 100 cm, being more similar to the amounts found in the 2nd meter. Highest amounts were detected in layers 60-80 cm and 80-100 cm.
The amount of exchangeable Mg2+ had a clear tendency toward increasing down the soil
profile, being highest in the 340-360 cm layer (8.10 cmolckg-1). In the trial field, layers 80-100, 120-140 and 60-80 cm had lowest content of exchangeable Mg2+ – about 1-2 cmolckg-1. The
surface layers within the 1st meter were comparatively richer in it, but their content
considerably conceded to the content in the deeper layers of the 3rd and 4th meter.
The sum of the two exchangeable cations down the profile varied from 25.38 cmolckg-1 (120-140 cm) to 30.51 cmolckg-1 (60-80 cm). The surface layers (0-10 cm and 10-20 cm) had lower sorption capacity, ∑Ca+Mg and degree of saturation with bases than the 0-20 cm layer
according to the trial beginnig. According to Nankova (2005, Personal Communication) at
the start of this long-term experiment the values of these parameters were 34,44 cmolckg-1 , 30,80 cmolckg-1 and 91,2% respectively. Further down the profile the sorption capacity
100
Agricultural Science
decreased. What is very impressive is that it significantly increased in the 4th meter
regardless of the occurrence of Ha in the 360-380 and 380-400 cm layers. The main reason for this is the higher amount of exchangeable Mg2+ in the 4th meter, which makes it very
distinctive from the layers above it.
The degree of saturation with bases was lowest in the surface layers 0-10, 10-20 and 20-40 cm due to the intensive anthropogenic activity on the one hand, and on the other – due to the presence of plants. From the 40-60 cm layer the values of this index increased. In the entire 2nd meter the degree of saturation with bases was more than 99 %, and in the third meter it was 100 %. This value remained the same in the upper part of the 4th meter but in the layers 360-380
and 380-400 cm decreased slightly and was closer to the values registered in the 2nd meter. The reason for this is the occurrence of residual hydrolytic acid in the lower part of the 4th meter.
The separate meters up to depth 400 cm, as well as the sub-layers (horizons) at each meter (every 20 cm) affected to a maximum degree of significance the investigated indices
characterizing the soil acidity forms in the investigated fertilization variants. The
comparison of the results for the indices characterizing soil acidity revealed clear
differentiation by each meter down the investigated soil profile.
Exchangeable cations
Degree of
Т
saturation
pH/
8.2,
Depth, cm
pH/H
Sorption
∑Ca+M
with
KCl
2O
Н 8.2 Al3+
Ca2+
Mg2+
capacity
g
bases, V%
In cmolckg-1. soil
0-10
5,54 b
6,46 b
33,21 p 5,65 k
,17 b
23,80 k 3,60 h
27,40 h
82,99 b
10-20
5,38 a
6,35 a
33,06 o
5,90 l
,26 c
23,27 i
3,62 h
26,89 f
82,17 a
20-40
5,72 c
6,74 c
33,06 o
4,65 j
,00 a
25,09 m 3,33 g
28,42 l
85,93 c
40-60
6,45 d
7,48 d
32,83 n
2,88 i
,00 a
27,44 n
2,52 e
29,95 n
91,17 d
60-80
6,80 e
7,89 e
32,13 m 1,62 h
,00 a
28,49 p
2,02 c
30,51 o
94,91 e
80-100
7,15 f
8,21 f
30,83 l
,97 g
,00 a
28,28 o
1,58 a 29,86 m
96,89 f
100-120
7,35 g
8,30 g
28,37 k
,47 f
,00 a
24,97 l
2,94 f
27,90 j
98,38 g
120-140
7,43 jk
8,34 h
25,56 a
,19 e
,00 a
23,64 j
1,74 b
25,38 a
99,29 h
140-160
7,41 i
8,40 i
26,00 d
,09 d
,00 a
23,67 j
2,25 d
25,91 c
99,67 i
160-180
7,39 h
8,48 jk
26,54 f
,03 b
,00 a
23,58 j
2,94 f
26,51 e
99,91 k
180-200
7,41 i
8,51 klm
26,53 f
,04 b
,00 a
23,08 h 3,41 g
26,49 e
99,86 k
200-220
7,42 ij
8,47 j
26,97 g
,00 a
,00 a
23,11 h
3,86 i
26,97 f
100,00 l
220-240
7,43 k
8,52 m
26,51 f
,00 a
,00 a
22,05 g 4,46 k
26,51 e
100,00 l
240-260
7,49 m
8,52 lm
25,88 c
,00 a
,00 a
21,62 f
4,25 j
25,88 c
100,00 l
260-280
7,47 l
8,53 m
25,88 c
,00 a
,00 a
21,55 f
4,32 j
25,88 c
100,00 l
280-300
7,47 l
8,53 m
25,70 b
,00 a
,00 a
19,88 b
5,82 l
25,70 b
100,00 l
300-320
7,49 m
8,48 j
27,24 h
,00 a
,00 a
21,09 e 6,15 m
27,24 g
100,00 l
320-340
7,49 m
8,48 jk
28,25 j
,00 a
,00 a
20,79 d 7,46 n
28,25 k
100,00 l
340-360
7,52 n
8,49 jkl
28,33 jk
,00 a
,00 a
20,23 c
8,10 p
28,33 k
100,00 l
360-380
7,51 n
8,49 jkl
27,75 i
,06 c
,00 a
19,98 b 7,71 o
27,69 i
99,79 j
380-400
7,53 o
8,49 jkl
26,36 e
,06 c
,00 a
18,79 a
7,51 n
26,30 d
99,79 j
Table 1. Sorption capacity (T8.2), exchangeable cations and degree of saturation with bases down the soil profile
Long-Term Mineral Fertilization and Soil Fertility
101
Exchangeable cations
Degree of
pH/
pH/
Т
∑Ca+M saturation
Depth, cm
8.2
Н
KCl
H
8.2 Al3+
Ca2+
Mg2+
2O
g
with bases
In cmolckg-1. soil
0-100
6,32 a
7,35 a
32,40 d 3,18 d
,043 b
26,57 d
2,61 a
29,186 d
90,30 a
100-200
7,40 b
8,41 b
26,60 b
,16 c
,000 a
23,79 c
2,65 a
26,44 b
99,42 b
200-300
7,46c
8,51 d
26,19 a
,00 a
,000 a
21,64 b
4,54 b
26,19 a
100,00 d
300-400
7,51 d
8,48 c
27,59 c ,025 b
,00 a
20,18 a
7,39 c
27,56 c
99,91 c
Table 2. Sorption capacity (T8.2), exchangeable cations and degree of saturation with bases by meter down the soil profile
Averaged for the investigated fertilization variants, the 1st meter had lowest pH values, exchangeable Mg2+ and degree of saturation with bases. This meter, at the end of the 40-year period of investigation, showed harmful exchangeable acidity untypical for the natural
status of this soil type. The first meter was also characterized by significantly higher content of residual hydrolytic acidity and higher sorption capacity in comparison to the other
depths down the profile. In the 2nd and 3rd meter, with the exception of pH and the degree of saturation with bases, all other indices decreased their values. The third meter was
characterized with complete absence of residual hydrolytic acidity, 100 % saturation with bases and increased content of exchangeable Mg2+ - with 73.9 % more above the 1st meter
and with 71.2 % more above what has been established in the 2nd meter. What was typical
for the separate layers of the 4th meter, besides the visually distinct coloration of these layers, was once again the occurrence of residual hydrolytic acidity, comparatively high increase of the content of exchangeable Mg2+ in comparison to the 3rd meter (62.6 %). Averaged for this depth, a higher sum of exchangeable bases was determined in the trial field in comparison to the 2nd and the 3rd meter, as well as higher sorption capacity of soil.
In spite of the average data for 400 cm, 40 years mineral fertilization caused a big difference on the forms of soil acidity accorfing to kind of fertilizer variant. The differentiation between variants of fertilization is very well expressed (Table 3). Soil reaction varied in narrow limits, but in spite of this it was established decreasing of pH in variants N180P60K60 и N60P180K0
according to the control variant. By the Waller-Duncan test there were established a very well expressed differences in all soil acidity forms, as well as in degree of saturation.
The lowest values of residual hydrolytic acidity (H8,2) were registered in the variant with independent fertilization with 180 kg P2O5/ha (0.87 cmolckg-1 soil). Residual hydrolytic acidity is one of the forms strongly affected by the long-term mineral fertilization, especially in the variant with N180P60K60 (1.36 cmolckg-1 soil). High amplitude of variation was determined for residual hydrolytic acidity down the soil profile: from its complete lack to 5.90 cmolckg-1 soil.
As was shown the highest values were established in the surface layers, 0-10 and 10-20 cm, which are most influenced by the agronomy practices fertilization and tillage.
The strongest evidence for the high effect of the long-term mineral fertilization with various norms and ratios on the agrochemical condition of the slightly leached chernozem soil in the trial field was the occurrence of exchangeable Al3+ in the soil absorption complex. It was detected in the surface layers (0-10 and 10-20 cm) in the variants N180P0K0 and N180P60K60. It was not present in the soil absorption complex further down the profile.
102
Agricultural Science
Exchangeable Degree
of
saturation
Fertilizer
pH/
pH/
Т8.2
Н 8.2 Al Ca Mg Ca+M
with b
g
ases –
variants
KCl
H2O
V %
cmolckg-1. почва
N0P0K0
7,12 c 8,14 d 28,55 d 1,03 c
,00 a
24,60 f
2,92 a
27,52 d
96,83 f
N60P0K0
7,18 f 8,13 d
28,71 e 1,13 f
,00 a
23,16 d
4,41 d
27,58 e
96,50 c
N120P0K0
7,13 d 8,15 d 28,96 g
,89 b
,00 a
23,79 e
4,29 c
28,07 h
97,30 g
N180P0K0
7,13 d 8,23 e
27,45 a 1,11 e
,07 b
21,63 a
4,64 e
26,27 a
96,59 d
N0P180K0 7,15
e 8,21 e
28,72 e
,87 a
,00 a
23,19 d
4,65e
27,84 g
97,39 h
N60P180K0
6,98 a 7,96 b
27,94 b 1,16 g
,00 a
22,92 c
3,87 b
26,78 b
96,41 b
N120P120K120
7,04 b 8,06 c
28,79 f 1,05 d
,00 a
22,88 c
4,86 f
27,74 f
96,69 e
N180P60K60
6,98 a 7,93 a
28,30 c 1,36 h
,10 c
22,36 b
4,48 d
26,84 c
95,89 a
Table 3. Sorption capacity (T8.2), exchangeable cations and degree of saturation with bases according to variants of fertilization, average for 0-400 cm depth
The variant with independent nitrogen fertilization with 180 kg/ha has the lowest ∑ Са+Mg and the lowest value of sorption capacity. Intensive mineral fertilization with N180P60K60
caused decreasing of degree of saturation with bases.
2.1.2 Compare the changes of soil acidity forms after 30th and 40th years mineral
fertilization
For the first time in Bulgaria in such long-term trial we compared the obtained results for the individual indices which characterize the forms of soil acidity for the end of the 30th and the end of the 40th year since the initiation of the experiment in some of the variants to 60 cm depth.
At the end of the 40th year, the tendency towards lower values of pH and sorption capacity of soil became more prominent to various degrees according to the type of fertilization
variant . This tendency was most evident in the variant with N120P120K120, where a decrease with 17.2 % according to the end of the 30th year was determined.
A serious change was observed also towards decrease of the values of acidity on the
strongly acid positions (TCA) of the soil adsorbent with the increase of the duration of
mineral fertilization in the above variants, and respective significant increase of this acidity, but this time on the slightly acid positions of the soil adsorbent. The indicated change led also to decrease of the rate of alkali saturation. The decrease varied from 4.4% (N120P0K0) to 8.1% (N120P120K120).
Т
Т
Degree of
Т
СА
А
Fertilizer
pH/H
8.2
2O
Strongly acid
Slightly acid
saturation with
Sorption capacity
varia