EFFECT OF MINERAL AND BACTERIAL FERTILIZERS ON THE OAT YIELD ON A DRAINED PEAT BOG

V. S. Boiko, M. G. Degtyareva, A. Ya. Khromov

In the literature on the agricultural development of drained peat bogs, the instability of the effectiveness of fertilizer application and large fluctuations in yields are noted. This is often associated with the reaction of the peat bogs, suppressed microbiological activity, or poor aeration of the upper soil layer.

The aim of our experiment was to determine the effectiveness of applying various forms of mineral and bacterial fertilizers on a drained peat bog. Field experiments were carried out on a peat bog at the Pobeda state farm, Tomsk district, Tomsk oblast. The peat bog is of the lowland type; the depth of the peat deposit is up to 2 meters; the degree of decomposition is 25–30%; ash content is 23–30%. The reaction of the peat is neutral. The peat contains inclusions of vivianite and lime. The weather conditions of 1965 were characterized by severe drought.

When the peat bog reached physical ripeness, the experiment was laid out. The area of the experimental plots was 100.8 sq. m. The crop was oats, variety “Golden Rain.” Mineral fertilizers were applied at a dose of \(N_{30}P_{60}K_{30}\) by active ingredient. Bacterial fertilizers were prepared in the microbiology laboratory of the Novosibirsk Agricultural Institute on a peat substrate. Oat seeds were inoculated with this suspension. The experiments were laid out in duplicate.

During the experiments, soil samples from the drained peat bog were analyzed for the content of nitrates, ammonia, and phosphoric acid in the 0–20 cm layer. In addition to agrochemical analyses, microbiological studies were conducted. The biological yield was recorded by the method of meter plots in fivefold replication.

Agrochemical analyses were carried out in June, July, and August for all variants of the experiment. The results are summarized in Table 1.

It is evident from the table that the application of mineral and bacterial fertilizers to the peat bog increases the content in it of forms of nitrogen and phosphoric acid available to plants. It should be noted, however, that by the end of the growing season their content in the experimental variants had decreased. With the application of bacterial fertilizers, the content of mobile forms of nitrogen and phosphorus is somewhat lower than with the application of mineral fertilizers, but their content toward the end of the growing season shows a tendency to increase. This may be explained by the increasing microbiological activity of the drained peat bog.

The activity of microbiological processes may be influenced by the content of ash, water-soluble humic substances, and total nitrogen. To characterize the variants by these indicators, on June 5 samples were taken for the corresponding analysis.

Table 1

Effect of mineral and bacterial fertilizers on the nitrogen–phosphorus regime in a drained peatland
(in mg/100 g of air-dry peat)

The results of the analysis are given in Table 2.

In terms of ash content, the peat samples differed among the experimental variants. In the control the percentage of ash was the lowest, while with NPK and with cellulose-decomposing bacteria it was the highest. In the content of water-soluble humic substances, there was no substantial difference among the experimental variants,

Table 2

Content of ash, water-soluble humic substances,
and total nitrogen in a drained peatland (in % of air-dry peat)

but in the content of total nitrogen, the variants with phosphorobacterin and the control were distinguished by a somewhat larger reserve. It may be assumed that the fertilizers applied at the end of May, by the time of the analysis (June 5), could not yet have exerted a substantial influence on peat mineralization, and therefore the data presented may be used as an initial characterization of the development of the microflora.

Simultaneously with the taking of samples by experimental variants for agrochemical analyses, samples were taken, with sterility observed, for microbiological analyses. In conducting the microbiological investigations, the method adopted at the Institute of Microbiolo-

GII of the USSR Academy of Sciences. The investigations were carried out at two times, June 2 and August 5. The results of the investigations are summarized in Tables 3 and 4.

Table 3

Microbiological characteristics of drained peatland fertilized with mineral and bacterial fertilizers. Analysis of June 2, in mln./g

Peat samples taken from the plots of the experimental site contain all the groups of microorganisms that we recorded, capable of participating in the destruction of the organic matter of peat. The abundance of ammonifying bacteria is especially great in all soil samples. There was low contamination with bacteria decomposing mineral phosphate salts and organic phosphorus compounds. There were many cellulose-decomposing bacteria in all variants, but their enzymatic activity

Table 4

Effect of mineral and bacterial fertilizers on the microbiological activity of the soil of a drained peatland, analysis of August 5, in mln. per 1 g

was unequal and reduced. The abundance of Azotobacter cells was high. Conditions for nitrogen assimilation were quite favorable.

The number of ammonifying bacteria at the second analysis date, compared with the previous study, increased significantly in the variants with phosphorobacterin and with the mixture of bacteria. Inoculation with rhizospheric bacteria decreased in the control and in the mixture of bacteria.

Table 5

Effect of mineral fertilizers on the yield of oat grain

Nitrification remained at the level of the previous study. Inoculation with phosphorus bacteria dissolving mineral phosphates increased significantly, especially in the variants with cellulose-decomposing bacteria applied alone and in a mixture with Azotobacter and phosphorus bacteria.

The application of mineral fertilizers in growing oats on drained peatland had a substantial effect not only on changes in the content of available nutrients and the microbiological activity of the soil, but also on the magnitude of the grain yield. The results of the accounting of the biological yield are given in Table 5.

Complete mineral fertilizer produced a higher yield increase than the other combinations and single fertilizers, especially nitrogen fertilizers.

Table 6

Effect of bacterial fertilizers on the yield of oat grain on drained peatland

Inoculation of oat seeds with bacterial fertilizers, as was already shown above, had a substantial effect on changes in the microbiological activity of the soil of the drained peatland and on the content of mobile nutrients for plants. The bacterial fertilizers also affected the grain yield, as is evident from Table 6.

Phosphorobacterin produced an almost twofold greater yield increase than Azotobacterin. Their mixture somewhat exceeded the yield increase given by the sum of the increases from separately applied Azotobacterin and phosphorobacterin.

Conclusions

On the basis of the results of the experiment conducted in 1965, the following preliminary conclusions may be drawn.

1. The application of mineral and bacterial fertilizers on drained peatland increased the microbiological activity of the soil and the content of mobile forms of nitrogen and phosphoric acid.

2. Complete mineral fertilizer and a mixture of bacterial fertilizers increased the yield of oat grain, respectively, by 27.0 and 23.1 percent relative to their controls.

3. To clarify more fully the effect of bacterial and mineral fertilizers on drained peatland, the investigations must be continued.