**2.3.2 Soil organic mater composition along the soil profile to 400 cm depth**

The variance analysis of the composition of the soil organic substance down the layers of the soil profile up to depth 400 cm revealed the dynamics in the degree of significance of the changes of C in the respective groups and fractions as a result from the long-term mineral fertilization. Although the indices of variations of the respective fertilization variants were not significant, the established differences between the investigated fertilization combinations were significant to a maximum degree, averaged for depth 0-400 cm.


Table 12. Variance analysis of the soil organic matter composition after a 40-year mineral fertilisation

0,000 0,500

> N oP o K o

N 6 0P oK o

N 1 2 0P oK o

fertilization variants

**Depth cm Corganic** 

fertilisation

N 1 8 0P oK o

N oP 1 8 0K o

0 - 10 10 - 20 cm 20 - 40 cm 40 - 60 cm 60 - 80 cm 80 - 100 cm

**% C in 1st meter**

N 6 0P 1 8 0K o

0,000 0,100 0,200 0,300 0,400 0,500 0,600 0,700

> N oP o Ko

**Humic acides (HA)** 

N 6 0 P o K o

N 1 2 0 P o K o

N 1 8 0 P o K o

N oP1 8 0 K o

100 - 120 cm 120 - 140 cm 140 - 160 cm 160 - 180 cm 180 - 200 cm

**%C in 2nd meter**

N 6 0 P 1 8 0 K o

Fig. 4. Content of Сtotal (%) by layers for every meter up to 400 cm averaged for the

**2.3.2 Soil organic mater composition along the soil profile to 400 cm depth** 

combinations were significant to a maximum degree, averaged for depth 0-400 cm.

0-20 ,000 ,000 ,000 ,000 ,000 ,000 ,000 ,001 20-40 ,000 ,000 ,000 ,000 ,000 ,055 ,023 ,006 40-60 ,000 ,102 ,008 ,001 ,052 ,000 ,000 ,000 60-80 ,000 ,001 ,006 ,000 ,001 ,000 ,000 ,006 80-100 ,000 ,000 ,001 ,000 ,000 ,013 ,002 ,001 100-120 ,001 ,003 ,001 ,001 ,003 ,001 ,001 ,000 120-140 ,002 ,004 ,006 ,000 ,003 ,001 ,001 ,001 140-160 ,001 ,000 ,000 ,000 ,000 ,001 ,001 ,001 160-180 ,000 ,000 ,001 ,001 ,000 ,000 ,000 ,008 180-200 ,002 ,000 ,005 ,000 ,000 ,000 ,007 ,239 200-220 ,003 ,000 ,381 ,073 ,000 ,000 ,009 ,003 220-240 ,001 ,000 ,004 ,000 ,000 ,000 ,107 ,001 240-260 ,000 ,000 ,022 ,069 ,000 ,000 ,011 ,000 260-280 ,008 ,003 ,008 ,023 ,001 ,003 ,007 ,000 280-300 ,002 ,000 ,012 ,022 ,000 ,000 ,032 ,001 300-320 ,004 ,003 ,001 ,009 ,007 ,000 ,074 ,003 320-340 ,000 ,000 ,000 ,000 ,000 ,000 ,000 ,008 340-360 ,000 ,000 ,000 ,000 ,000 ,026 ,001 ,000 360-380 ,000 ,000 ,000 ,000 ,000 ,007 ,002 ,001 380-400 ,000 ,000 ,000 ,000 ,000 ,000 ,000 ,000 **0-400 cm ,000 ,000 ,000 ,000 ,000 ,000 ,000 ,000**  Table 12. Variance analysis of the soil organic matter composition after a 40-year mineral

**Fulvic acides (FA)** 

The variance analysis of the composition of the soil organic substance down the layers of the soil profile up to depth 400 cm revealed the dynamics in the degree of significance of the changes of C in the respective groups and fractions as a result from the long-term mineral fertilization. Although the indices of variations of the respective fertilization variants were not significant, the established differences between the investigated fertilization

0,000 0,050 0,100 0,150 0,200 0,250 0,300

> N o Po Ko N 6 0P oK o N 1 2 0P oK o N 1 8 0P oK o N oP1 80K o N 6 0P 1 8 0K o N 1 2 0P 1 2 0K1 2 0 N 1 8 0P 6 0K 6 0

**% C in 3rd meter**

200 - 220 cm 220 - 240 cm 240 - 260 cm 260 - 280 cm 280 - 300 cm

0,000 0,050 0,100 0,150 0,200 0,250 0,300 0,350 0,400 0,450

**HA/FA HA-Ca HA-R2 O3 Humin FA in** 

N oP o K o

N 6 0P oK o

N 1 2 0P oK o

N 1 8 0P oK o

N oP 1 8 0K o

300 - 320 cm 320 - 340 cm 340 - 360 cm 360 - 380 cm 380 - 400 cm

**% C in 4th meter**

N 1 8 0P 6 0K6 0

**H2SO4** 

1,000

1,500

2,000

Organic C of soil was also subjected to dynamic changes averaged for the entire 4 m depth. In this index the differentiation between the variants was less expressed in comparison to total C. Its amount was lowest in the untreated check variant.

Highest differentiation in the content of organic C according to the type of the fertilization variant was established in layers 40-60 cm and 60-80 cm, and lowest variation was found in the 260- 280 cm layer.

The independent nitrogen fertilization with 180 kg N/ha contributed most significantly to the increased amount of Corganic averaged for a considerable depth down the profile. In this case, however, Сhumin had lowest values. A similar tendency was found in the independent nitrogen fertilization with 120 kg N/ha, as well. In these two variants the amount of Сhumin, also called "guard of humus", was below the level of the check variant. The independent nitrogen fertilization with 60 kg N/ha, the independent phosphorus fertilization with 180 kg P2O5/ha, the combination between them and the systematic balanced introduction of NPK at norm 120 kg/ha did not in practice affect the insoluble fraction of organic substance of soil under systematic agricultural cultivation of the land. Not only in the respective layers, but also in the entire 0-400 cm depth, the long-term independent nitrogen fertilization with 120 and 180 kg/ha lead to lower amounts of the insoluble residue. This is valid to a higher degree for the norm 180 kg/ha. Lowest differentiation in the values of Cresidue between the fertilization variants was determined in the 320-340 cm layer. Highest variations between the fertilization variants were established in the 0-20 cm, 60-80 cm and 380-400 cm layers.


The systematic introduction of N180P60K60 had most significant contribution for Cresidue increase average for 0-400 cm profile.

Table 13. Content of Corganic by layers up to 400 cm according to the fertilization variants

Long-Term Mineral Fertilization and Soil Fertility 111

Fig. 5. Content of СHA and CFA by layers up to 400 cm according to the fertilization variants


Table 14. Content of Cresidue by layers up to 400 cm according to the fertilization variants

The percent of Corganic in comparison to Ctotal of soil varied within a wide range: from 43.11 % in the variant with N180P60K60 to 71.51% in N18P0K0. With the exception of systematic introduction of N180P60K60, all other fertilization variants involved in the study contributed to the higher percent of the total humus substances in Ctotal of soil. The results from the investigation on the changes of organic C of soil showed that the independent nitrogen fertilization, especially with annually applied high norms, had a strong negative effect on the mobility of the organic substance and caused serious decrease of the percent of carbon in the insoluble residue.

The carbon of humic and fulvic acids (HA and FA) also varied considerably depending on the mineral fertilization (Fig.5). Regardless of the lower values of C of HA and FA down the soil profile, the variations between the fertilization variants were significant to a maximum degree, averaged for 0-400 cm depth. They were not significant for C-HA in the 0-40 cm layer and for C-FA in the 200-220 cm and 240-260 cm layers. Highest differentiation in the values of C-Ha between the fertilization variants was found in the 80-100 cm and 360-380 cm layers, and of the values of C-FA – in the 360-380 cm layer. Averaged for the investigated depth of 400 cm, variant N180P0K0 had highest content of C-HA, exceeding the check variant with 24.9 %. A considerable increase of C-FA according to the check was determined after systematic application of N180P0K0 – with 60.1 %, of N60P180K0 – with 72.3 %, and of N180P60K60 – with 70.0 %.

Depth cm N0P0K0 N60P0K0 N120P0K0 N180P0K0 N0P180K0 N60P180K0 N120P120K120 N180P60K60 0-20 ,8055 d ,6837 a ,8779 e ,7366 bc ,7667 c ,7124 ab ,7553 c ,8085 d 20-40 ,7490 bc ,7655 bc ,7892 c ,6235 a ,7154 abc ,6840 ab ,7716 bc ,8045 c 40-60 ,5700 b ,6889 d ,6494 cd ,5053 a ,5762 b ,5785 b ,7479 e ,6384 c 60-80 ,4805 c ,5654 e ,4028 b ,4616 c ,3326 a ,5526 de ,5132 cde ,5096 d 80-100 ,3492 b ,4146 bc ,4150 bc ,2585 a ,4840 d ,3856 bc ,3653 b ,4376 cd 100-120 ,2241 b ,2325 b ,1707 a ,2147 ab ,3262 cd ,2901 c ,3586 d ,2979 c 120-140 ,1989 bc ,2370 c ,0489 a ,0885 a ,2082 bc ,1558 b ,2142 c ,2211 c 140-160 ,1329 b ,1777 bc ,0402 a ,1344 bc ,1820 c ,0694 a ,1748 bc ,1767 bc 160-180 ,0798 b ,0552 ab ,0415 ab ,0563 ab ,1250 c ,0206 a ,1545 c ,1497 c 180-200 ,1188 c ,0204 a ,1216 c ,0341 ab ,1549 c ,0427 ab ,0988 bc ,1592 c 200-220 ,0995 b ,1000 b ,1256 bc ,0341 a ,1239 bc ,1777 c ,1348 bc ,1795 c 220-240 ,1286 abc ,0880 ab ,1196 abc ,0804 a ,1548 bc ,1608 c ,1513 abc ,1239 abc 240-260 ,1342 bc ,1367 bc ,0848 ab ,0341 a ,1509 c ,1502 c ,1346 bc ,1549 c 260-280 ,1467 c ,1021 bc ,0540 ab ,0321 a ,1084 bc ,1555 c ,1230 c ,1254 c 280-300 ,1379 b ,1083 b ,0942 ab ,0313 a ,1258 b ,1366 b ,1230 b ,1557 b 300-320 ,2020 c ,1802 bc ,0924 a ,1182 ab ,1471 abc ,1635 abc ,1389 abc ,1438 abc 320-340 ,1886 b ,1904 b ,2096 b ,0460 a ,1674 b ,1667 b ,0783 a ,1726 b 340-360 ,1857 b ,1663 b ,1377 b ,0624 a ,1597 b ,1870 b ,0655 a ,2473 c 360-380 ,1364 bc ,1877 c ,1283 bc ,0277 a ,1075 b ,1610 bc ,1151 b ,2565 d 380-400 ,0804 abc ,1706 e ,1012 bcd ,1330 cde ,0466 ab ,1403 de ,0387 a ,2483 f **0-400 cm 0,2557 c 0,2629 c 0,2339 b 0,1860 a 0,2569 c 0,2544 c 0,2641 c 0,3000 d**  Table 14. Content of Cresidue by layers up to 400 cm according to the fertilization variants

The percent of Corganic in comparison to Ctotal of soil varied within a wide range: from 43.11 % in the variant with N180P60K60 to 71.51% in N18P0K0. With the exception of systematic introduction of N180P60K60, all other fertilization variants involved in the study contributed to the higher percent of the total humus substances in Ctotal of soil. The results from the investigation on the changes of organic C of soil showed that the independent nitrogen fertilization, especially with annually applied high norms, had a strong negative effect on the mobility of the organic substance and caused serious decrease of the percent of carbon in

The carbon of humic and fulvic acids (HA and FA) also varied considerably depending on the mineral fertilization (Fig.5). Regardless of the lower values of C of HA and FA down the soil profile, the variations between the fertilization variants were significant to a maximum degree, averaged for 0-400 cm depth. They were not significant for C-HA in the 0-40 cm layer and for C-FA in the 200-220 cm and 240-260 cm layers. Highest differentiation in the values of C-Ha between the fertilization variants was found in the 80-100 cm and 360-380 cm layers, and of the values of C-FA – in the 360-380 cm layer. Averaged for the investigated depth of 400 cm, variant N180P0K0 had highest content of C-HA, exceeding the check variant with 24.9 %. A considerable increase of C-FA according to the check was determined after systematic application of N180P0K0 – with 60.1 %, of N60P180K0 – with 72.3 %, and of

the insoluble residue.

N180P60K60 – with 70.0 %.

Fig. 5. Content of СHA and CFA by layers up to 400 cm according to the fertilization variants

Long-Term Mineral Fertilization and Soil Fertility 113

The similarities found between the separate fertilization variants with regard to the amount of HA linked to calcium were the reason for the lower rate of differentiation in their values. Systematic fertilization with N180P60K60 and N120P120K120 led to lower amount of HA-Ca, below the level of the check and all other investigated fertilization variants (Fig. 7). There was a well expressed tendency towards increase of carbon in HA-Ca as a result from the independent phosphorus and nitrogen fertilization, regardless of the nitrogen norm. Averaged for the 400 cm depth, the independent nitrogen fertilization with 180 kg/ha contributed most to the higher carbon in HA-Ca. The greater amounts of CHA were due to

As a result from the long-term mineral fertilization averaged for the investigated depth, the degree of humification of the organic substance (OS) varied according to the type of the fertilization variant. The differentiation in the values of this index was extremely high regardless of the similarity and sameness in some of the variants. The 4 m profile had "very high" degree of humification of OS after systematic independent fertilization with 120 and 180 kg N/ha. Only at systematic application of NPK=3:1:1 the rate of humification averaged for the investigated profile was lowest (25.57 %) and according to Orlov and Grishina (1981) can be considered "moderate". In the other variants the values were 30-40 %, which determined humification as "high". It should be noted that in the check variant and in the variant with independent nitrogen fertilization with 60 kg/ha, the humification rate was at the upper limit tending towards "very high", while in the independent phosphorus fertilization and in the variants with N60P180K0 and N120P120K120 the values were closer to the

Averaged for the tested variants of long-term fertilization, the slightly leached chernozem soil in the trial field can be referred to the low humic type according to the classification of Orlov and Grishina. Ctotal was highest in the 0-20 cm layer (1.62 %) and gradually decreased down the 4-m profile. In the last investigated layer (380-400 cm) its content was 0.26 %, but

Along the entire investigated profile, organic C was represented by humic acids which exceeded fulvic acids. The amount of HA was highest in the 0-20 cm layer and gradually decreased down the profile and at 380-300 cm it was 0.0919 %. Similar to organic carbon (total humic substances, THS), the amount of HA also slightly increased at depth below 300 cm. The above tendencies remained the same with regard to the changes in FA down the profile. According to the classification of Orlov and Grishina (1981), the slightly leached chernozem soil in the trial field possessed high to very high content of HA, expressed as percent from the organic C in soil. The values of this ratio were more than 80 % at depth from 20 to 80 cm. They gradually decreased down the profile but nevertheless remained within 60 – 80 %. The greater part of HA along the entire 400 cm profile was linked to calcium. Down the profile their amount gradually decreased and in the 220-300 cm zone the lowest concentrations were detected. At the 4th meter their concentration slightly increased. At depth 40-100 cm the amount of HA-Ca was very high (>80 % of HA). At all other depths the percent of HA-Ca/HA was 60-80 % and can be considered high. The amount of C in HA, free and linked to R2O3, was lower than the amount of the HA linked to Ca and also slightly decreased down the profile, the lowest values being registered in the 320-340 cm layer

this higher content of C in the HA fraction linked to calcium.

lower limit.

the 260-280 cm layer had lowest content.

еspecially at N180P60K60 .

The variants with independent introduction of all three nitrogen norms as well as of phosphorus had more C in HA in comparison to the check, as well as the variants with combinations of the main macro elements. The differentiation with regard to C content in FA was even better expressed. The check variant and the independent nitrogen fertilization with 60 and 120 kg N/ha had lowest amounts. In all other variants with combinations of the three macro elements, as well as in independent introduction of the highest nitrogen norm, the amount of FA increased. It reached maximum values after systematic application of N60P180K0, similar to the fraction of aggressive FA. Averaged for this high depth profile, a tendency was observed towards higher HA content as a result from the long-term systematic mineral fertilization regardless of the norms and ratios of the main macro elements.

The changes in the content of HA and FA averaged for the 400 cm profile led to distinct differentiation between the fertilization variants with regard to the values of the ratio HA/FA (Fig.6). Variation was within a wide range: from 1.72 to 3.75. The long-term systematic nitrogen fertilization with 180 kg N/ha in combination with low fertilization norms of phosphorus and potassium determined the type of humus as fulvic-humic, averaged for the investigated depth 0-400 cm. In all other fertilization variants, regardless of the norms and ratios between the macro elements and in the check variant, the values of this ratio were above 2, which determined the type of humus as humic.

Fig. 6. Values of the ratio HA/FA average for the 0- 400 cm depth according to the fertilization variants

The variants with independent introduction of all three nitrogen norms as well as of phosphorus had more C in HA in comparison to the check, as well as the variants with combinations of the main macro elements. The differentiation with regard to C content in FA was even better expressed. The check variant and the independent nitrogen fertilization with 60 and 120 kg N/ha had lowest amounts. In all other variants with combinations of the three macro elements, as well as in independent introduction of the highest nitrogen norm, the amount of FA increased. It reached maximum values after systematic application of N60P180K0, similar to the fraction of aggressive FA. Averaged for this high depth profile, a tendency was observed towards higher HA content as a result from the long-term systematic mineral fertilization regardless of the norms and ratios of the main macro

The changes in the content of HA and FA averaged for the 400 cm profile led to distinct differentiation between the fertilization variants with regard to the values of the ratio HA/FA (Fig.6). Variation was within a wide range: from 1.72 to 3.75. The long-term systematic nitrogen fertilization with 180 kg N/ha in combination with low fertilization norms of phosphorus and potassium determined the type of humus as fulvic-humic, averaged for the investigated depth 0-400 cm. In all other fertilization variants, regardless of the norms and ratios between the macro elements and in the check variant, the values of this

> N180P60K60 1,72

> > 3,17

Fig. 6. Values of the ratio HA/FA average for the 0- 400 cm depth according to the

N0P0K0 3,75

3,50 N180P0K0

N60P0K0 3,27

N120P0K0

ratio were above 2, which determined the type of humus as humic.

N0P180K0 2,47

N120P120K120 2,23

N60P180K0 2,72

fertilization variants

elements.

The similarities found between the separate fertilization variants with regard to the amount of HA linked to calcium were the reason for the lower rate of differentiation in their values. Systematic fertilization with N180P60K60 and N120P120K120 led to lower amount of HA-Ca, below the level of the check and all other investigated fertilization variants (Fig. 7). There was a well expressed tendency towards increase of carbon in HA-Ca as a result from the independent phosphorus and nitrogen fertilization, regardless of the nitrogen norm. Averaged for the 400 cm depth, the independent nitrogen fertilization with 180 kg/ha contributed most to the higher carbon in HA-Ca. The greater amounts of CHA were due to this higher content of C in the HA fraction linked to calcium.

As a result from the long-term mineral fertilization averaged for the investigated depth, the degree of humification of the organic substance (OS) varied according to the type of the fertilization variant. The differentiation in the values of this index was extremely high regardless of the similarity and sameness in some of the variants. The 4 m profile had "very high" degree of humification of OS after systematic independent fertilization with 120 and 180 kg N/ha. Only at systematic application of NPK=3:1:1 the rate of humification averaged for the investigated profile was lowest (25.57 %) and according to Orlov and Grishina (1981) can be considered "moderate". In the other variants the values were 30-40 %, which determined humification as "high". It should be noted that in the check variant and in the variant with independent nitrogen fertilization with 60 kg/ha, the humification rate was at the upper limit tending towards "very high", while in the independent phosphorus fertilization and in the variants with N60P180K0 and N120P120K120 the values were closer to the lower limit.

Averaged for the tested variants of long-term fertilization, the slightly leached chernozem soil in the trial field can be referred to the low humic type according to the classification of Orlov and Grishina. Ctotal was highest in the 0-20 cm layer (1.62 %) and gradually decreased down the 4-m profile. In the last investigated layer (380-400 cm) its content was 0.26 %, but the 260-280 cm layer had lowest content.

Along the entire investigated profile, organic C was represented by humic acids which exceeded fulvic acids. The amount of HA was highest in the 0-20 cm layer and gradually decreased down the profile and at 380-300 cm it was 0.0919 %. Similar to organic carbon (total humic substances, THS), the amount of HA also slightly increased at depth below 300 cm. The above tendencies remained the same with regard to the changes in FA down the profile. According to the classification of Orlov and Grishina (1981), the slightly leached chernozem soil in the trial field possessed high to very high content of HA, expressed as percent from the organic C in soil. The values of this ratio were more than 80 % at depth from 20 to 80 cm. They gradually decreased down the profile but nevertheless remained within 60 – 80 %. The greater part of HA along the entire 400 cm profile was linked to calcium. Down the profile their amount gradually decreased and in the 220-300 cm zone the lowest concentrations were detected. At the 4th meter their concentration slightly increased. At depth 40-100 cm the amount of HA-Ca was very high (>80 % of HA). At all other depths the percent of HA-Ca/HA was 60-80 % and can be considered high. The amount of C in HA, free and linked to R2O3, was lower than the amount of the HA linked to Ca and also slightly decreased down the profile, the lowest values being registered in the 320-340 cm layer еspecially at N180P60K60 .

Long-Term Mineral Fertilization and Soil Fertility 115

The systematic introduction of macro elements at different norms and ratios during a period of 40 years of cultivation of the trial field lead to formation of different reserves of total carbon in soil at depth up to 60 cm with well expressed differentiation (Fig 8). The long-term 2-field agricultural use of the trial field without mineral fertilization was characterized with lowest reserves of total C. The independent nitrogen fertilization with increasing norms caused their increase according to the check variant with 12.6 %.This increase, however, was lower than the increase registered in all other variants. Highest reserve in absolute values at the moment of taking samples was found in the variants with 40-year fertilization with N0P180K0 and N60P180K0. The main reason for this fact is that besides the variation in the content of total C, respectively humus, variation in the values of the other component was found when determining reserves – volume density of soil. According to Yankov (2007, Personal Communication), highest values of volume density averaged for the 0-60 cm layer were demonstrated by the variant with systematic introduction of phosphorus (180 kg/ha) – 1.43 g/m3, and lowest mean values – by the variant with N180P60K60 (1,22 g/m3). Over 36 % of the total carbon reserves in soil at depth up to 60 cm were concentrated in the 20-40 cm layer, followed by the layer lying beneath (Table 12). Regardless of the low differentiation in the content of total C down the soil profile up to the 60th cm, the differentiation of the layers according to their reserves was very well expressed. Humus reserves in soil were highest in the 20-40 cm layer. The layer 10-20 cm have a negative C balance according to check variant. The maximum increase according to the control in 0-10 cm and 10-20 cm layer was established in the variants with N180P0K0 and N0P180K0 (136,3 and 135,6 %, respectively for 0-

**2.3.3 Soil organic matter reserves in depth up to 60 cm** 

10 cm layer and 103,2 % and 105,3 % for 10-20 cm layer).

(N180P60K60)

Fig. 8. Total Carbon reserves for layer 0-60 cm, C kg/m2

13,076 (N120P120K120)

> 12,810 (N60P180Ko)

C kg/m2

(NoPoKo) 12,690

13,256 (NoP180Ko)

tendency was established also for long-term fertilization with N180P60K60.

Combination between macroelements affected positively the humus reserves in soil. The variant with balanced fertilization N120P120K120 contributed enrichement of soil carbon reserves in 40-60 cm layer with 37,1% according to the same layer in check variant. This

12,204 (N180PoKo)

10,837

11,830 (N120PoKo)

12,056 (N60PoKo)

Fig. 7. The amount of C in HA, linked to Ca and free and linked to R2O3 by layers up to 400 cm according to the fertilization variants

Fig. 7. The amount of C in HA, linked to Ca and free and linked to R2O3 by layers up to 400

cm according to the fertilization variants

#### **2.3.3 Soil organic matter reserves in depth up to 60 cm**

The systematic introduction of macro elements at different norms and ratios during a period of 40 years of cultivation of the trial field lead to formation of different reserves of total carbon in soil at depth up to 60 cm with well expressed differentiation (Fig 8). The long-term 2-field agricultural use of the trial field without mineral fertilization was characterized with lowest reserves of total C. The independent nitrogen fertilization with increasing norms caused their increase according to the check variant with 12.6 %.This increase, however, was lower than the increase registered in all other variants. Highest reserve in absolute values at the moment of taking samples was found in the variants with 40-year fertilization with N0P180K0 and N60P180K0. The main reason for this fact is that besides the variation in the content of total C, respectively humus, variation in the values of the other component was found when determining reserves – volume density of soil. According to Yankov (2007, Personal Communication), highest values of volume density averaged for the 0-60 cm layer were demonstrated by the variant with systematic introduction of phosphorus (180 kg/ha) – 1.43 g/m3, and lowest mean values – by the variant with N180P60K60 (1,22 g/m3). Over 36 % of the total carbon reserves in soil at depth up to 60 cm were concentrated in the 20-40 cm layer, followed by the layer lying beneath (Table 12). Regardless of the low differentiation in the content of total C down the soil profile up to the 60th cm, the differentiation of the layers according to their reserves was very well expressed. Humus reserves in soil were highest in the 20-40 cm layer. The layer 10-20 cm have a negative C balance according to check variant. The maximum increase according to the control in 0-10 cm and 10-20 cm layer was established in the variants with N180P0K0 and N0P180K0 (136,3 and 135,6 %, respectively for 0- 10 cm layer and 103,2 % and 105,3 % for 10-20 cm layer).

Fig. 8. Total Carbon reserves for layer 0-60 cm, C kg/m2

Combination between macroelements affected positively the humus reserves in soil. The variant with balanced fertilization N120P120K120 contributed enrichement of soil carbon reserves in 40-60 cm layer with 37,1% according to the same layer in check variant. This tendency was established also for long-term fertilization with N180P60K60.

Long-Term Mineral Fertilization and Soil Fertility 117

soil. Systematic use of N180P60K60 contributed most for the increase of its content at average depth 0-400 cm. Fertilizer variants N180P60K60 and N120P120K120 led to lower amount of HA-Ca, below the level of the check and all other investigated fertilization variants. There was a well expressed tendency towards increase of carbon in HA-Ca as a result from the

The ratio CHA/CFA putted under average for the 400 cm profile to distinct differentiation between the fertilization variants.Variation was within a wide range: from 1.72 to 3.75. The long-term systematic nitrogen fertilization with 180 kg N/ha in combination with low fertilization norms of phosphorus and potassium determined the type of humus as fulvichumic, averaged for the investigated depth 0-400 cm. In all other fertilization variants, regardless of the norms and ratios between the macro elements and in the check variant, the values of this ratio were above 2, which determined the type of humus as humic. Independent nitrogen fertilization, especially with annually applied high norms, had a strong negative effect on the mobility of the organic substance and caused serious decrease

As a result from the systematic mineral fertilization in the 20-40 cm layer, higher reserves were formed by the layers lying above and below. Triple NPK combinations (N120P120K120

These results showed that regardless of the intensive agricultural activities and changes of some agrochemical characteristics, slightly leached chernozem soil (Haplic chernozems) in Sough Dobrudzha region in Bulgaria preserved its main genetic characteristics at the lower

The effect of long-term fertilizer treatments on detail nutrient balances, technological quality of crops, concentration of available forms of macro elements and trace elements in soil and plant biomass dynamics and many other aspects of this experiment await detailed analysis.

The author is deeply indebted to Prof Maria Petrova for the initiated of this long term trail in 1967. The author thank to Dobrudzha Agricultural Institute and staff of Agrochemistry lab

Filcheva E., Tsadilas, C. (2002). Influence of Cliniptilolite and Compost on Soil Properties.

Ganev,S.& Arsova, A. (1980). Methods for determining weak acid cation exchange of soil.

Goulding K.W.T., Poulton P.R., Webster C.P., Howe M.T. (2000). Nitrate leaching from

Iliev I., Nankova M. (1994). Another type motor-driven portable soil sampler. *ESNA XXIV th Annual Meeting*, September 12-16, 1994, Varna, BULGARIA: 140-147

Broadbalk wheat experiment, Rothamsted, UK, as influenced by fertilizer and

independent phosphorus and nitrogen fertilization, regardless of the nitrogen norm.

of the percent of carbon in the insoluble residue.

depths of the soil profile.

**4. Acknowledgment** 

for correct support.

**5. References** 

and N180P60K60) enriched organic mater reserves in 40-60 cm layer.

FAO, (2006). World Reference Base of Soil Resources. Rome, Italy.

*Commun. Of Soil Sci. and Plant Analysis, 33, 3-4, 595-607* 

manure inputs and the weather. *Soil Use Manage, 16, 244-250* Iliev I. (2000). Mechanized soil sampler. *BG 385 Y1. Patient of useful model*

*Soil science and agrochemisty*, Vol XV, No 3,pp. 22-32


Table 15. Reserves by depth up to 60 cm according to fertilization, C – kg/m2
