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 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.
Dependent
Source
df
Mean Square
F
Sig.
Variable
Fertilizer variants (A)
14 days
7
1201,997
1071,012
,000
28 days
7
895,323
644,004
,000
56 days
7
1760,257
808,230
,000
Soil depth (B)
14 days
20
3566,615
3177,951
,000
28 days
20
9128,237
6565,923
,000
56 days
20
14022,587
6438,532
,000
A x B
14 days
140
84,304
75,117
,000
28 days
140
63,912
45,972
,000
56 days
140
113,244
51,997
,000
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.
After 14-days of incubation
After 28-days of incubation
After 54-days of incubation
5,1
4,0
12,9
9,2
4,5
3,2
92,3
90,9
77,9
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, %
106
Agricultural Science
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.
Meters
Value
Group
2
3,59
a
3
3,74
a
4
5,08
b
1
32,92
c
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).
Fertilizer
Value
Group
variants
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-
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
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 (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.
Days of
Value
Group
incubation
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) 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.
