Allelotoxicity of Greenhouse Substrates after Vegetable Cultivation.

Crop exposure to stress during cultivation is known to reduce the yield and to cause the release of allelotoxins from plants into soil. It was assumed that allelotoxin release may considerably affect the vegetable growth in greenhouses and that a decrease in the allelotoxin concentration in greenhouse substrates may improve the plant growth. To verify the assumptions, allelotoxicity and microbial contents were determined in greenhouse substrates in which cucumber, tomato, and pepper plants grew well or poorly. The allelotoxin content was found to be higher and the prokaryote content, lower in the substrates of poorly growing plants. The finding confirmed the assumption that allelotoxins significantly influence the cultivation of vegetables in greenhouses. Treating the plant root zone with humate solutions having a high allelotoxin absorption capacity appreciably improved the cucumber plant growth and was assumed to provide a promising means to increase the vegetable yields in greenhouses.

State of Soil Gels in Soddy-Podzolic Soil Samples Prepared for Viscosimetry by Different Methods.

As is well known from the mid-20th century, films of organomineral gels cover and bind soil particles in soils. Soil contact with water has been shown to lead to water absorption by gels and gel swelling. The change of gel properties in soils should manifest itself in a change in the viscosity of soil pastes. A vibrating viscometer was proposed to use to determine the viscosity of soil pastes. The physical meaning laid down in Einstein's formula was used to interpret the results. This made it possible to assess the degree of gel swelling by the amount of water that remained capable of moving independently of soil particles, that is, was not included in soil gels (free water). The effect on the degree of swelling of soil gels was studied for (1) the moisture content in soil samples used to prepare soil pastes, (2) the time after adding water during the preparation of soil samples used subsequently to obtain soil pastes, and (3) the sample preparation of soil samples (initial, autoclaved, or dried to air-dry and absolutely dry states and re-moistened) used to obtain soil pastes. Experiments showed that (1) the degree of swelling of soil gels increased with the increasing moisture content in soil samples, (2) a longer time of interaction of soil samples with water led to a greater degree of swelling of soil gels, and (3) different degrees of swelling of soil gels were observed in pastes prepared from soil samples that had the same moisture content, but differed in sample preparation protocol.

Allelotoxicity and Water Stability of Sod-Podzolic Soil after Growing Wheat on It.

It is well-known that soil allelotoxicity and the water stability of soil structure are determined by the entry of plant residues into the soil, but the relationship of these soil properties has not been investigated. Soil samples from the fields of the Federal Research Center "Nemchinovka" after growing 25 cultivars of spring and winter wheat on plots with sod-podzolic soil are selected in this study. The effect of the soil's allelotoxicity of plot samples on the germination of spring wheat seed of the Liza cultivar is studied by the biotesting method. The water stability of the soil structure is determined for the same samples. The existence of a sigmoid dependence between the allelotoxicity of soil samples and their water stability with a correlation greater than 95% is established. The presence of this dependence is apparently related to the increase in the soil's water stability with an increase in the amount of fresh plant residues entering them, which is known from the literature, and the transition of the allelotoxins' effects from stimulation to suppression with a growth in their concentration in soils.