EFFECT OF VARIOUS MULCH MATERIALS ON SOD-PODZOLIC SOIL AND FIELD CROPS YIELD - Fertilizers: Components, Uses in Agriculture and Environmental Impacts - page 268

of humic acids, fulvic acids, amino acids, proteins and other organic compounds. In this way
up to 65-85 % of ions are bound. The chemical absorption is associated with structural
changes of organic compounds in peat. As a results, ions are bound in inactive forms. In this
manner about 10-30% of ions are bound. Physical, mechanical and biological absorption of
ions by peat under normal conditions is irrelevant (Lishtvin et al., 1984). In our experiments
we used peat with a total cationic capacity of 160-180 mmol/100g BDH.
The use of post-harvest residues, including crops straw, as mulch materials has a long
history and a wide practical application in all agricultural zones all over the world. It is
connected with the low cost and general availability of the material, the ease of its use and its
high efficiency.
The effect of straw mixed with the soil layer of 0-5 cm at the proportion of 5 t/ha on the
physical and chemical properties of the plow horizon is contradictory. In some cases, it led to
soil acidification and reduced the amount of exchangeable bases in the plow horizon, while in
other cases it reduced the acidity and increased the amount of exchangeable bases. The
marked variations of these parameters are explained by the strong dependence of the straw
decomposition rate on the environmental conditions. In the case of slow decomposition, there
is a significant amount of acidic intermediate decomposition products, mainly in the form of
organic acids (acetic, propionic, butyric, salicylic, etc.). However, this does not happen under
favorable environmental conditions. Application of straw on the top of the plow horizon
accelerates its mineralization, so there was a slight decrease in the soil acidity and an increase
in the amount of exchangeable bases during the five years of observation.
2. Effect of Mulches on Chemical Properties of the Soil
A characteristic feature of podzolic soils is their low humus content, which often limits
the ecological state and productivity of soils. As expected, the greatest impact on this
indicator was achieved by the application of organic mulches (peat and straw).
Incorporating peat in the soil layer of 0-5 cm at the proportion of 40 t/ha increased the
content of organic matter in the plow horizon by 523%. During the five years of observation
it was on average 15.1% higher than in the control (without mulch) (Figure 4).
This well-known effect was possible because about 80-95% of the peat dry substance is
comprised of various organic compounds. The organic matter of peat consists of
carbohydrates (cellulose, hemicellulose, bitumen, lignin), protein and humic acids. Each
group of the organic compounds plays a different role when peat is applied. Easily
hydrolysable fractions are wonderful energetic material for the development of soil
microflora. They decompose quickly and enrich the soil with mineral elements, primarily
nitrogen and carbon dioxide. Hardly hydrolysable and non-hydrolysable fractions are highly
resistant to biodegradation. Nevertheless, they transform gradually and make up a specific
part of organic matter in the soil. The humic part is of the greatest value to agriculture. It has
been found to consist of acidic compounds and contain aromatic complexes and
proteinaceous components that split off amino acid in the hydrolysis (Tishkovich, 1993).
Humic acids in peat, like humus in soil, are involved in the regulation and maintenance of
redox reactions in the soil, improve root formation, increase the permeability of membranes
and stimulate respiration enzymes and other vital processes of plants (Khristeva, 1977).