**2. Influence of long-term mineral fertilization on some agrochemical characteristics of slightly leached chernozems (Haplic Chernozems)**

One of the main degenerative processes in soil is the so called acidification. Various acid complexes are formed in soil as a result from soil formation processes on the one hand (erosion, humification, leaching, podzolization), and on the other – as a result from the activity of micro organisms and plants. Soils also possess buffer systems to counteract the acidification, which differ by their capacity.

#### **2.1 Changes in soil acidity forms**

98 Agricultural Science

Picture 1. Position of Dobrudzha Agriculture Institute on Bulgaria map (43о 40' northen

The potential nitrogen-supplying ability of soil was determined through incubation under constant temperature of 30o C at 60 % humidity from its total moisture absorption capacity in order to develop optimal conditions for nitrification. Incubation was done in thermostate to investigate its dynamics at the 14th, 28th and 56th day. The samples were analyzed to determine the amount of nitrate nitrogen in 1 % K2SO4 extract. The ability of NO3-N to form intensive yellow coloration when interacting with disulphurphenoloc acid

Carbon contend was valuated using the Tyurin modification (oxidizing with K2Cr2O7/H2SO4 solution in thermostate at 1250С, 45 min, at presence of Ag2SO4 and titration with (NH4)2SO4.FeSO4.6 H2O (Kononova&Belchikova,1961; Spiege at al, 2007; Hegymegi at al, 2007). Composition of soil organic matter was determined by Konnova (1963) and

Data were analysed with Excel and SPSS 16.0 (2007) and means separated by the Waller-

One of the main degenerative processes in soil is the so called acidification. Various acid complexes are formed in soil as a result from soil formation processes on the one hand (erosion, humification, leaching, podzolization), and on the other – as a result from the activity of micro organisms and plants. Soils also possess buffer systems to counteract the

**2. Influence of long-term mineral fertilization on some agrochemical characteristics of slightly leached chernozems (Haplic Chernozems)** 

The soil acidity forms were determined by Ganev&Arsova (1980).

latitude and 28о 10' eastern longitude)

[C6H3OH(HSO3)2] in alkali media was used.

acidification, which differ by their capacity.

Filcheva&Tsadilas (2002).

Duncan test (P<0,05).

#### **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%).

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

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

Long-Term Mineral Fertilization and Soil Fertility 101

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

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

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

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,

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

well expressed differences in all soil acidity forms, as well as in degree of saturation.

which are most influenced by the agronomy practices fertilization and tillage.

was not present in the soil absorption complex further down the profile.

Exchangeable cations Degree of

g

with bases <sup>Н</sup> 8.2 Al3+ Ca2+ Mg2+ ∑Ca+M

In cmolckg-1. soil

saturation

Depth, cm pH/

KCl

meter down the soil profile

pH/ H2O

Т8.2

to the 2nd and the 3rd meter, as well as higher sorption capacity of soil.

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.


Table 1. Sorption capacity (T8.2), exchangeable cations and degree of saturation with bases down the soil profile

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

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

**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

Exchangeable cations Degree of

g

<sup>Н</sup> 8.2 Al3+ Ca2+ Mg2+ ∑Ca+M

In cmolckg-1. soil

saturation with bases, V%

differentiation by each meter down the investigated soil profile.

Т8.2, Sorption capacity

distinctive from the layers above it.

Depth, cm pH/

down the soil profile

KCl pH/H2O


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.

Long-Term Mineral Fertilization and Soil Fertility 103

Furthermore, during the last decade the balanced treatment with NPK at norm 120 kg/ha was the variant with lower values of Т8,2 and ТСА, while at the end of the 30th year of this trial the values of the above indices were higher than the values of the check variant and the values of the variants with independent nitrogen fertilization with increasing norms. The negative changes in the absolute values of these indices occurred also when determining the

30th year

40th year

N0P0K0 N120P0K0 N180P0K0 N120P120K120

Fig. 2. Acidity on the highly acid positions of the soil adsorbent as percent of T8.2 according

The changes caused by the long-term agricultural usage of the land concerned also changeable Ca and Mg and their respective sum (Table 5). During the last investigated period changeable Са2+ decreased in all tested variants, most strongly in the variants treated annually with N120P120K120. The check variant (N0P0K0), as well the variants with independent nitrogen fertilization, were less affected by this process. The amount of exchangeable Са2+ at the end of the 40th year averaged for the investigated variants was 88.76 % from the amount at the end of the 30th year. A tendency was found towards lower amounts of exchangeable Mg2+ in the check variant and the variants with independent nitrogen fertilization, and towards significant increase in the variant with systematic balanced introduction of the main macro elements (N120P120K120). At the end of the 30th year the investigated variants were characterized with a mean content of exchangeable Mg2+ of 3.66 cmolckg-1 soil, and at the end of the 40th year – of 3,05 cmolckg-1 soil. The comparison of the results for ∑ Са+Mg revealed their decrease with averagely 12 % according to the data

from the end of the 30th year, the decrease being greatest in the variant N120P120K120.

Exchangeable cations Ha Ca2+ Mg2+ ∑Ca+Mg 30th 40th 30th 40th 30th 40th 30th 40th

N0P0K0 2,57 a 4,73 d 28,63 b 25,12 b 3,63 b 3,00 ab 32,27 b 28,12 b N120P0K0 2,58 a 3,80 a 28,23 b 26,98 c 4,33 c 2,38 a 32,57c 29,36 d N180P0K0 2,60 a 4,33 b 25,82 a 25,49 b 3,78 b 3,11 bc 29,60 a 28,60 c N120P120K120 2,92 b 4,56 c 31,17 c 23,43 a 2,88 a 3,72 c 34,05 d 27,15 a Table 5. Comparison of the changes in the exchangeable cations at the end of the 30th year and at the end of the 40th year from the trial depending on the type of the fertilization variant

to the fertilization variant at the end of the 30th and the 40th year of the trial.

percent of acidity on the highly acid positions of the soil adsorbent (Fig. 2).

50,0

60,0

70,0

80,0

**%**

Fertilizer variants

90,0

100,0


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).


Table 4. Comparison of the soil acidity forms at the end of the 30th and at the end of the 40th year from the initiation of the trial according to the fertilization variant applied

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

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

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

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

> ТСА Strongly acid positions

**30th 40th 30th 40th 30th 40th 30th 40th 30th 40th** 

N0P0K0 7,60 c 6,85 a 34,87 b 32,93 b 32,33 b 23,92 b 2,53 ab 9,01 b 92,63 b 85,65 a N120P0K0 7,48 b 7,09 c 35,17 b 33,15 c 32,55 b 24,11 b 2,62 b 9,03 b 92,59 b 88,55 c N180P0K0 7,14 a 6,99 b 32,74 a 32,92 b 29,57 a 24,83 c 3,18 c 8,09 a 91,09 a 86,84 b N120P120K120 7,44 b 6,84 a 38,32 c 31,71 a 35,87 c 22,23 a 2,45 a 9,48 c 93,15 c 85,65 a Table 4. Comparison of the soil acidity forms at the end of the 30th and at the end of the 40th

year from the initiation of the trial according to the fertilization variant applied

ТА Slightly acid positions

Degree of saturation with bases

**2.1.2 Compare the changes of soil acidity forms after 30th and 40th years mineral** 

Exchangeable Degree of

Н 8.2 Al Ca Mg Ca+Mg

cmolckg-1. почва

saturation with bases – V %

Fertilizer variants

**fertilization** 

8.1% (N120P120K120).

Fertilizer variants

pH/ KCl

pH/ H2O

Т8.2

according to variants of fertilization, average for 0-400 cm depth

with 17.2 % according to the end of the 30th year was determined.

Sorption capacity

pH/H2O Т8.2

caused decreasing of degree of saturation with bases.

Furthermore, during the last decade the balanced treatment with NPK at norm 120 kg/ha was the variant with lower values of Т8,2 and ТСА, while at the end of the 30th year of this trial the values of the above indices were higher than the values of the check variant and the values of the variants with independent nitrogen fertilization with increasing norms. The negative changes in the absolute values of these indices occurred also when determining the percent of acidity on the highly acid positions of the soil adsorbent (Fig. 2).

Fig. 2. Acidity on the highly acid positions of the soil adsorbent as percent of T8.2 according to the fertilization variant at the end of the 30th and the 40th year of the trial.

The changes caused by the long-term agricultural usage of the land concerned also changeable Ca and Mg and their respective sum (Table 5). During the last investigated period changeable Са2+ decreased in all tested variants, most strongly in the variants treated annually with N120P120K120. The check variant (N0P0K0), as well the variants with independent nitrogen fertilization, were less affected by this process. The amount of exchangeable Са2+ at the end of the 40th year averaged for the investigated variants was 88.76 % from the amount at the end of the 30th year. A tendency was found towards lower amounts of exchangeable Mg2+ in the check variant and the variants with independent nitrogen fertilization, and towards significant increase in the variant with systematic balanced introduction of the main macro elements (N120P120K120). At the end of the 30th year the investigated variants were characterized with a mean content of exchangeable Mg2+ of 3.66 cmolckg-1 soil, and at the end of the 40th year – of 3,05 cmolckg-1 soil. The comparison of the results for ∑ Са+Mg revealed their decrease with averagely 12 % according to the data from the end of the 30th year, the decrease being greatest in the variant N120P120K120.


Table 5. Comparison of the changes in the exchangeable cations at the end of the 30th year and at the end of the 40th year from the trial depending on the type of the fertilization variant

Long-Term Mineral Fertilization and Soil Fertility 105

balance between economic and non-economic part of the produce and avoid possible losses (Cantero-Martinez et al.,1995). It is well known that the availability of the nitrogen from the mineral fertilizers depends strongly on the type of the nitrogen source, the soil type, the crop, the fertilization norm, etc. Many farmers tend to apply higher nitrogen norms to ensure higher yields (Franzluebbers et al., 1999). This in many cases is not necessary due to changes in the distribution of the nitrogen in the surface of the soil profile and its improved

The ability of soil to nitrify nitrogen under optimal conditions was significantly affected by the mineral fertilization and the investigated layer up to depth 400 cm (Table 7). During all three investigated periods of increasing incubation, this effect was significant to a maximum degree both under the independent influence of the investigated factors and under their interaction.

Fertilizer variants (A) 14 days 7 1201,997 1071,012 ,000

Soil depth (B) 14 days 20 3566,615 3177,951 ,000

A x B 14 days 140 84,304 75,117 ,000

The depth of the soil layer was the factor with higher effect on the values of the soil's mineralization ability in comparison to mineral fertilization during all three incubation periods (Figure 1). The longer the period of incubation was, the higher its effect, reaching a maximum at 28-day incubation. Regardless of a slight decrease in the effect of this factor at 56-day incubation, the longer incubation had higher effect on the obtained results in comparison to 14-day incubation. The effect of mineral fertilization was lowest in the second incubation period and slightly increased in the third incubation period. The long-term mineral fertilization affected the amount of the established NO3-N to a highest degree at 14-

> **After 28-days of incubation** 4,5 3,2

Fertilizer variants (A) Soil depth (B) A x B

92,3

**After 54-days of incubation** 4,0

5,1

90,9

Fertilizer variants (A) Soil depth (B) A x B

Table 8. Variance analysis of the mineralization ability during a 40-year period of

day incubation. The same was valid for the interaction between the two factors.

**After 14-days of incubation**

77,9 Fertilizer variants (A) Soil depth (B) A x B

Fig. 3. Effect of factors according to the period of incubation, %

12,9 9,2

Variable df Mean Square F Sig.

28 days 7 895,323 644,004 ,000 56 days 7 1760,257 808,230 ,000

28 days 20 9128,237 6565,923 ,000 56 days 20 14022,587 6438,532 ,000

28 days 140 63,912 45,972 ,000 56 days 140 113,244 51,997 ,000

mobility (Rice et al., 1986).

investigation

Source Dependent

At the end of the 40th year the acidity on the highly acid positions averaged for depth 0-60 cm was 23.77 cmolckg-1 soil, compared to 32.58 cmolckg-1 soil at the end of the 30th year, i.e. there was a decrease with 27.04 % (Table 5). pH variations affected most strongly the 20-40 cm layer. The established negative tendencies affected the 40-60 cm layer as well, where a significant decrease of the sorption capacity of soil was determined: with 9.6 % according to the values at the end of the 30th year.

At the same time the acidity on the slightly acid positions strongly increased in all three layers, the mean increase being almost three times higher, and affected mostly the 40-60 cm layer. These results also concern the rate of alkali saturation, which, too, demonstrated a tendency towards decrease. The decrease was highest in the surface 0-20 cm layer (8.1 %), in the 20-40 cm layer (6.5 %) and in the 40-60 cm layer (4.1 %).


Table 6. Comparison of the soil acidity forms at the end of the 30th year and at the end of the 40th year of the trial depending on the depth of the layer

The changes which occurred down the investigated profile confirmed the established tendencies towards change in the values of the exchangeable cations during the respective periods of investigation depending on fertilization. The increase of the values of residual hydrolytic acidity affected most the surface 0-20 cm layer (Table 6). This layer was characterized with highest decrease of the changeable Са2+ values, the amount of exchangeable Mg2+ remaining practically the same. Within both periods of analysis the sum of exchangeable alkali increased down the profile due to the exchangeable Са2+.


Table 7. Comparison of changes in the exchangeable cations between the 30th and the 40th year from the trial depending on the depth of soil layer
