**2.2 Changes of the soil mineralization ability after 40-years mineral fertilization**

Transportation, redistribution and transformation of nitrogen down the soil profile was affected by a number of factors such as the structure of soil units, aeration, macro pores, composition, amount and depth of post harvest residue incorporation, mineral fertilization and nitrogen norm, mineralization of organic substance, leaching, productive moisture, etc (Goldbi et al., 1995; Karlen et al., 1998). The size of the nitrogen norm is significant for agricultural production under moist, semi-dry and dry conditions to obtain acceptable

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

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

> ТСА Strongly acid positions

30th 40th 30th 40th 30th 40th 30th 40th 30th 40th

Exchangeable cations Ha Ca Mg Ca+Mg 30th 40th 30th 40th 30th 40th 30th 40th

0-20 6,99 a 6,42 a 34,77 a 32,69 b 31,21 a 22,89 a 3,56 c 9,80 c 89,49 a 82,29 a 20-40 7,44 b 6,86 b 35,24 b 32,96 c 32,39 b 24,01 b 2,85 b 8,96 b 92,51 b 86,49 b 40-60 7,81 c 7,55 c 35,81 c 32,38 a 34,14 c 24,42 c 1,67 a 7,96 a 95,11 c 91,25 c Table 6. Comparison of the soil acidity forms at the end of the 30th year and at the end of the

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

0-20 3,65 c 5,79 c 27,25 a 22,96 a 3,76 b 3,90 c 31,01 a 26,86 a 20-40 2,62 b 4,45 b 27,46 a 25,52 b 4,61 c 2,99 b 32,08 b 28,52 b 40-60 1,74 a 2,83 a 30,68 b 27,28 c 2,60 a 2,26 a 33,28 c 29,54 c Table 7. Comparison of changes in the exchangeable cations between the 30th and the 40th

**2.2 Changes of the soil mineralization ability after 40-years mineral fertilization** 

Transportation, redistribution and transformation of nitrogen down the soil profile was affected by a number of factors such as the structure of soil units, aeration, macro pores, composition, amount and depth of post harvest residue incorporation, mineral fertilization and nitrogen norm, mineralization of organic substance, leaching, productive moisture, etc (Goldbi et al., 1995; Karlen et al., 1998). The size of the nitrogen norm is significant for agricultural production under moist, semi-dry and dry conditions to obtain acceptable

of exchangeable alkali increased down the profile due to the exchangeable Са2+.

ТА Slightly acid positions

Degree of saturation with bases

the values at the end of the 30th year.

pH/H2O

Soil depth, cm

Soil depth, cm

the 20-40 cm layer (6.5 %) and in the 40-60 cm layer (4.1 %).

40th year of the trial depending on the depth of the layer

year from the trial depending on the depth of soil layer

Т8.2 Sorption capacity 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 mobility (Rice et al., 1986).

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.


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

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

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

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

Long-Term Mineral Fertilization and Soil Fertility 107

application of N120P120K120 for a period of 40 years showed lowest amounts of nitrified nitrogen following the check variant. Averaged for the 4-m soil profile, they were lower than the amounts after independent application of the same nitrogen norm. The main reason for this was that after this type of fertilization the highest yields from wheat were obtained, averaged for the 40-year period of investigation, which, on its part, was an indication for their uptake and respective realization into cash crop. The results with regard to the nitrification capacity from the analysis of this fertilization variant revealed considerable similarities to that of the check variant. The comparatively low amounts of nitrified nitrogen after systematic fertilization with N120P120K120, combined with high agronomy effect, showed that this fertilization combination can not lead to accumulation of inorganic nitrogen in soil

The incubation periods of soil under conditions favorable for the nitrification process also significantly affected the values of nitrified nitrogen (Table 10). With the longer incubation periods, the mean total amount of nitrified nitrogen increased with increasing the days of incubation. This lead to clear differentiation of the incubation periods and to formation of

incubation Value Group 14 7,2081 a 28 11,0113 b 56 15,7811 c Table 11. Mean content of NO3-N according to the incubation period (mg NO3-N/1000 g soil)

Systematic mineral fertilization carried out for 40 years in two-field crop rotation (wheat – maize) affected the content of Ctotal deep down the profile of the slightly leached chernozem soil. Annual fertilization with N180P60K60 during 40 years contributed most for the increase of its content at average depth 0-400 cm. Independent nitrogen fertilization with increasing norms, especially with 120 and 180 kg N/ha, had low effect on the content of Ctotal, averaged for depth 0-400 m (Fig 4). This type of fertilization contributed less to the total carbon reserves in soil, averaged for the 60 cm layer. The fertilization variants involving phosphorus and phosphorus plus potassium in the norms and ratios investigated in this study had more significant effect on the increase of these reserves; in this case there was an average increase with 18.7 % in comparison to the check

Along the soil profile, the sub-depths forming the 3rd meter had lowest Ctotal (respectively humus). No differentiation affected by the fertilization variant was found in this zone. The layers comprising the 4th meter had higher Ctotal content in comparison to the 3rd meter, and the differentiation in its content depended on the

**2.3 Changes of the soil organic matter after long-term mineral fertilization** 

**2.3.1 Carbon concentration along the soil profile to 400 cm depth** 

Days of

(in nitrate form) down the soil profile.

the results into separate groups.

variant without fertilization.

applied fertilization variant.

The distribution of the amount of nitrified nitrogen averaged for the periods of incubation by meters down the soil profile showed interesting results (Table 8). The soil layers of the 1st meter had highest potential nitrogen-supplying capacity. The layers forming the 2nd and the 3rd meter (loess horizon) had lowest nitrification capacity regardless of the favorable conditions for this process. The Waller-Duncan test did not reveal differences between them. It, however, differentiated the results obtained for the content of NO3-N averaged for the 4th meter in a separate group after what was established in the 1st meter.


Table 9. NO3-N content by meters down the soil profile (mg NO3-N/1000 g soil)

The effect of mineral fertilization of the different variants averaged for depth 0-400 cm and the incubation periods was strongly expressed depending on the norms and ratios between the three macro elements (Table 9).


Table 10. Mean content of NO3-N according to the type of fertilization variant (mg NO3- N/1000 g soil)

The check variant (N0P0K0) reflected the natural fertility of *Haplic Chernozems* in the trial field after its long-term cultivation. The check variant had lowest content of NO3-N after incubation among all tested variants. The fertilization variants were well differentiated on the basis of the total amount of NO3-N after incubation. The independent nitrogen fertilization with increasing norms was accompanied with proportional increase of the amount of nitrified nitrogen, the values of which fell within separate groups of higher orders, compared one to another.

When combining nitrogen with phosphorus and potassium depending on the norms and ratios between the three elements, the 4-m soil layer had variable capacity to supply nitrates as a result from incubation. Highest amounts of this inorganic nitrogen form were found after systematic application of N180P60K60 – 21.63 mg NO3-N/1000 g soil. The systematic

The distribution of the amount of nitrified nitrogen averaged for the periods of incubation by meters down the soil profile showed interesting results (Table 8). The soil layers of the 1st meter had highest potential nitrogen-supplying capacity. The layers forming the 2nd and the 3rd meter (loess horizon) had lowest nitrification capacity regardless of the favorable conditions for this process. The Waller-Duncan test did not reveal differences between them. It, however, differentiated the results obtained for the content of NO3-N averaged for the 4th meter in a separate group after what was

> Meters Value Group 2 3,59 a 3 3,74 a 4 5,08 b 1 32,92 c

The effect of mineral fertilization of the different variants averaged for depth 0-400 cm and the incubation periods was strongly expressed depending on the norms and ratios between

variants Value Group N0P0K0 5,95 a N120P120K120 8,64 b N0P180K0 9,17 c N60P0K0 10,28 d N60P180K0 10,71 d N120P0K0 11,36 e N180P0K0 12,93 f N180P60K60 21,63 g Table 10. Mean content of NO3-N according to the type of fertilization variant (mg NO3-

The check variant (N0P0K0) reflected the natural fertility of *Haplic Chernozems* in the trial field after its long-term cultivation. The check variant had lowest content of NO3-N after incubation among all tested variants. The fertilization variants were well differentiated on the basis of the total amount of NO3-N after incubation. The independent nitrogen fertilization with increasing norms was accompanied with proportional increase of the amount of nitrified nitrogen, the values of which fell within separate groups of higher

When combining nitrogen with phosphorus and potassium depending on the norms and ratios between the three elements, the 4-m soil layer had variable capacity to supply nitrates as a result from incubation. Highest amounts of this inorganic nitrogen form were found after systematic application of N180P60K60 – 21.63 mg NO3-N/1000 g soil. The systematic

Table 9. NO3-N content by meters down the soil profile (mg NO3-N/1000 g soil)

established in the 1st meter.

the three macro elements (Table 9).

orders, compared one to another.

N/1000 g soil)

Fertilizer

application of N120P120K120 for a period of 40 years showed lowest amounts of nitrified nitrogen following the check variant. Averaged for the 4-m soil profile, they were lower than the amounts after independent application of the same nitrogen norm. The main reason for this was that after this type of fertilization the highest yields from wheat were obtained, averaged for the 40-year period of investigation, which, on its part, was an indication for their uptake and respective realization into cash crop. The results with regard to the nitrification capacity from the analysis of this fertilization variant revealed considerable similarities to that of the check variant. The comparatively low amounts of nitrified nitrogen after systematic fertilization with N120P120K120, combined with high agronomy effect, showed that this fertilization combination can not lead to accumulation of inorganic nitrogen in soil (in nitrate form) down the soil profile.

The incubation periods of soil under conditions favorable for the nitrification process also significantly affected the values of nitrified nitrogen (Table 10). With the longer incubation periods, the mean total amount of nitrified nitrogen increased with increasing the days of incubation. This lead to clear differentiation of the incubation periods and to formation of the results into separate groups.


Table 11. Mean content of NO3-N according to the incubation period (mg NO3-N/1000 g soil)

#### **2.3 Changes of the soil organic matter after long-term mineral fertilization**

#### **2.3.1 Carbon concentration along the soil profile to 400 cm depth**

Systematic mineral fertilization carried out for 40 years in two-field crop rotation (wheat – maize) affected the content of Ctotal deep down the profile of the slightly leached chernozem soil. Annual fertilization with N180P60K60 during 40 years contributed most for the increase of its content at average depth 0-400 cm. Independent nitrogen fertilization with increasing norms, especially with 120 and 180 kg N/ha, had low effect on the content of Ctotal, averaged for depth 0-400 m (Fig 4). This type of fertilization contributed less to the total carbon reserves in soil, averaged for the 60 cm layer. The fertilization variants involving phosphorus and phosphorus plus potassium in the norms and ratios investigated in this study had more significant effect on the increase of these reserves; in this case there was an average increase with 18.7 % in comparison to the check variant without fertilization.

Along the soil profile, the sub-depths forming the 3rd meter had lowest Ctotal (respectively humus). No differentiation affected by the fertilization variant was found in this zone. The layers comprising the 4th meter had higher Ctotal content in comparison to the 3rd meter, and the differentiation in its content depended on the applied fertilization variant.

Long-Term Mineral Fertilization and Soil Fertility 109

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

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 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

cm N0P0K0 N60P0K0 N120P0K0 N180P0K0 N0P180K0 N60P180K0 N120P120K120 N180P60K60 0-20 ,7969 a ,8940 c ,7868 a ,8962 c ,8284 b ,8827 c ,8949 c ,9461 d 20-40 ,7824 a ,8209 b ,7625 a ,8962 d ,7782 a ,8705 c ,8583 c ,8660 c 40-60 ,6539 b ,7235 d ,5919 a ,6954 c ,7406 de ,7730 f ,7486 e ,7479 e 60-80 ,5172 a ,5773 cd ,5311 ab ,5448 abc ,7782 f ,5901 de ,5657 bcd ,6245 e 80-100 ,3556 a ,3947 b ,3971 b ,4694 c ,5021 cd ,5047 d ,5047 d ,4818 cd 100-120 ,2312 ab ,3244 d ,2498 bc ,2059 a ,3264 d ,3219 de ,2853 cd ,3026 de 120-140 ,1318 a ,1632 ab ,2498 d ,2508 d ,2385 cd ,1951 bc ,2121 cd ,2227 cd 140-160 ,1572 ab ,1617 abc ,2498 d ,1933 bc ,2008 c ,2438 d ,1268 a ,1424 a 160-180 ,1697 b ,2348 cd ,2583 d ,2222 c ,1883 b ,2926 e ,1268 a ,1172 a 180-200 ,1074 a ,2348 d ,1249 a ,2008 cd ,1757 bc ,1951 cd ,1390 ab ,0990 a 200-220 ,1499 c ,1349 bc ,1413 c ,2008 d ,1255 bc ,0834 a ,1146 abc ,0990 ab 220-240 ,1324 d ,1267 cd ,1357 d ,1255 cd ,0628 a ,0771 a ,0866 ab ,1053 bc 240-260 ,0949 a ,0780 a ,1385 b ,2008 c ,0753 a ,0992 a ,0829 a ,0743 a 260-280 ,0824 a ,1125 ab ,1520 b ,1506 b ,1004 a ,0708 a ,0829 a ,0806 a 280-300 ,0999 ab ,1267 b ,1291 b ,1933 c ,1004 ab ,1244 b ,0829 a ,0619 a 300-320 ,1199 ab 1389 bc ,1745 cd ,2008 d ,1255 ab ,0975 ab ,0902 a ,1231 ab 320-340 ,1449 b ,2099 c ,0804 a ,3306 d ,1255 b ,1146 ab ,1073 ab ,1261 b 340-360 ,1449 bc ,1876 d ,1291 abc ,3393 e ,1506 c ,1146 a ,1317 abc ,1240 ab 360-380 ,1449 cd ,1632 d ,1269 bc ,2987 e ,1506 cd ,1204 ab ,1024 a ,1177 ab 380-400 ,1574 c ,1369 bc ,1047 ab ,2436 d ,1506 c ,0975 a ,1354 bc ,1055 ab **0-400 cm ,2585 a ,2972 c ,2757 b ,3429 d ,2962 c ,2934 c ,2740 b ,2784 b**  Table 13. Content of Corganic by layers up to 400 cm according to the fertilization variants

total C. Its amount was lowest in the untreated check variant.

the 260- 280 cm layer.

increase average for 0-400 cm profile.

Depth

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