Abstract
The present experiment was carried out in the period 2006-2008. The aim of this study was to determine the effect of aqueous soil extracts from the soil of a spring wheat monoculture on seed germination energy and capacity, the length of the first leaf and of the longest radicle as well as the number of radicles. Moreover, the content of 0-dihydroxyphenols in the soil was compared in the last year of the study. The soil used to prepare the solutions came from a field experiment established on medium heavy mixed rendzina soil. Spring wheat, cv. Zebra, was grown using plough tillage and two conservation tillage methods in the presence of undersown crops (red clover, Westerwolds ryegrass) and stubble crops (lacy phacelia, white mustard). Germination energy of the seeds watered with the soil extracts from the ploughed plots was significantly higher than this trait in the seeds watered with the extracts from the conservation tillage treatments with spring disking of the catch crops. Germination energy and capacity of spring wheat in the control treatment watered with distilled water were significantly higher compared to the other treatments under evaluation. Spring wheat watered with the aqueous extract prepared from the soil obtained from the plough tillage treatment produced a significantly longer first leaf compared to the treatments in which both conservation tillage methods had been used. The shortest leaf and the lowest number of radicles were produced by the seedlings watered with the soil extract from the treatment with the white clover stubble crop. Radicle length was not significantly differentiated by the soil extracts under consideration. The content of 0-dihydroxyphenols in the rendzina soil determined during the spring period was higher than that determined in the autumn. The content of 0-dihydroxyphenols in the soil was lower in the conservation tillage treatments with autumn incorporation of the catch crops than in the plots in which plough tillage and conservation tillage with spring disking of the catch crops had been used. The type of catch crop used did not have a significant effect on the soil content of these compounds. At the same time, it was found that the treatments in which the catch crops had been sown tended to have higher contents of these compounds compared to the plots without catch crops.
Highlights
The essential phenomena in which the role of allelopathy in the cultivation of plants is perceived are as follows: soil exhaustion, which is most frequently observed in monocultural cropping, mutual modification of plant growth among the plants in agrophytocenoses, crop self-regulation, and plant responses to the presence of the companion crop in mixed crops (Wójcik - Wojtkowiak, 1980, 1987; Ahmed and Wardle, 1994; Jaskulski, 1997)
The present study found a significantly lower content of 0-dihydroxyphenols in the soil in the conservation tillage treatments with autumn disking of the catch crops compared to the ploughed plots and in the conservation tillage treatments with spring incorporation of the catch crops
The presence of these compounds in the soil extracts obtained from the conservation tillage treatments with spring disking of the catch crops could have resulted in lower germination energy of the seeds compared to the treatments in which the seeds were watered with the soil extract from the ploughed plots
Summary
The essential phenomena in which the role of allelopathy in the cultivation of plants is perceived are as follows: soil exhaustion, which is most frequently observed in monocultural cropping, mutual modification of plant growth among the plants in agrophytocenoses, crop self-regulation, and plant responses to the presence of the companion crop in mixed crops (Wójcik - Wojtkowiak , 1980, 1987; Ahmed and Wardle , 1994; Jaskulski , 1997). Soil exhaustion caused by the presence of allelopathic compounds may lead to disturbances in bio-chemical and physiological processes in plants. This results in the inhibition of developmental processes, in particular the growth process, which leads, as a consequence, to reduced plant productivity (S m y k , 1969/1970; Wójcik - Wojtkowiak , 1997). Cast et al (1990) found that there were much fewer inhibitory compounds in the ploughed soil compared to direct sowing. This is associated with the specificity of such a cropping system that does not promote the dispersion of these compounds. Jaskulski et al (1997) are of opinion that under direct sowing or minimum tillage conditions, and under conditions that do not permit ploughed-in plants to be covered completely, a part of seeds planted during sowing in the immediate vicinity of the decomposing tissues of post-harvest crops or mulch plants can be exposed to the effect of allelopathic compounds
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