Soil Bioassay 

• 000 - initial level of fertility, without the application of fertilizers and means of protection of plants from pests, diseases and weeds;
• 111 - average level of the fertility of the soil, the minimum dose of fertilizer, the biological protection of plants from pests and diseases;
• 222 - initial level of the fertility of soil, the average dose of fertilizers, the chemical protection of plants from weeds;
• 333 - high level of the fertility of soil, a high dose of fertilizers, chemical protection of plants from pests and diseases.

As the objective of this work it was intended to study the inhibition of chloroplast movements and the coefficient of instantaneous growth as the tesed indices for contamination of the soil, in the diverse variants of the multifactor experimental design.  To achieve the stated goal, statistical analysis was conducted to detect the influence of each factor on the growth and development of Lemna minor.

Inhibiting phototaxis of the chloroplasts of Lemna minor was investigated in different levels of the soil: 0-20, 20-40 cm. The analysis of the response of phototaxis to the different experimental variations showed the reliable influence of each of the factors (fertility of soil, the system of fertilizers and the system of the protection of plants).  The portion ofhe common variance of the fertility of soil composed 39,7%, the systems of fertilizers - 30,7%, and the system of the protection of plants - 30,7 %.

Reliable differences in terms of the average value of the coefficient of inhibition of phototaxis are noted between all versions with different factors (Table 1).
 

Table 1.  Sums of rank test on the confidence of a difference in the average values of group average of the united versions according to the indices: inhibition of chloroplast phototaxis and the coefficient of instantaneous growth, at the soil level of 0-20 cm.

Version	United Versions	Average	Rank Test
factor - fertility of the soil
3	333, 331, 313, 311	8,44 ± 0,55	*
2	222, 220, 200, 202	5,78 ± 0,29		*
1	111, 131, 133	5,43 ± 0,18		*
0	000, 002, 022, 020	3,80 ± 0,36			*
factor - system of the fertilizers
3	333, 331, 131, 133	7,85 ± 0,57	*
2	111, 313, 311	6,23 ± 0,34		*
1	222, 022, 220, 020	5,82 ± 0,27		*
0	000, 002, 200, 202	3,75 ± 0,36			*
system of  plant protection
1	111, 331, 311, 131	7,90 ± 0,60	*
3	333, 313, 133	6,23 ± 0,27		*
2	222, 002, 022, 202	5,80 ± 0,28		*
0	111, 331, 311, 131	3,78 ± 0,36			*

Note:  Arrangement * in the different vertical lines reflects significant differences in the averages, on one - uncertain.

The 16 experimental variants being investigated were broken into groups during the study of each factor.  The results of the association of variants are represented in Table 1.

On the fertility of soil a reliable difference is noted between variants 3, 0 and variants 2 and 1.  Along the system of fertilizers the difference between the averages of variants 3, 0 (1 and 2).  Along the system for protection of plants - variant 1 from variant 0 and variants 3 and 2.

To investigate the joint influence of factors on inhibiting chloroplast phototaxis, we used different combinations of experimental variants:in the first case - 000, 002, 022, 222, 220, 200, 202, 020, in the second case - 111, 333, 331, 313, 133, 311, 131.

The results of two-factor variance analysis testify about the significant influence of those interactions of the system of fertilizers and the plant protection system on the differences in the phototaxis for the first case (fraction/portion in the general/common dispersion it comprised 10,3%).  For the second case a significant influence is discovered for the interactions of the fertility of soil and the system of fertilizers (53,2%).

Three-factor variance analysis showed in the first case the reliable influence of interaction of all three factors.  Fraction/portion in the general/common dispersion comprised 47,9%.

In the work two levels of soil  were studied:  0-20 cm and 20-40 cm.  Analysis of the test results showed the essential differences between the levels according to the index - inhibition of phototaxis.  The portion in the general/common dispersion of the fertility of soil comprised 8,8%, the systems of fertilizers - 17,5%, and the plant protection system - 30,8%.

On the average, for the index of the fertility of soil, a significant difference is noted between versions 2, 0 and 3, 1; along the system of fertilizers - between versions 2, 3 and 1, 0; and along the plant protection system - versions 1 and 2 version 3 and 0 (tabl.2.)
 
 

Table 2.  Sums of rank test on the significance of a difference in the average values of group average of the united versions according to the indices: inhibition of phototaxis of chloroplasts and the coefficient of instantaneous growth, at the level of 20 cm.

Version	United Versions	Average	Rank Test
factor - fertility of the soil
2	222, 220, 200, 202	5,41 ± 0,32	*
0	333, 331, 313, 311	4,92 ± 0,53	*
1	111, 131, 133	3,77 ± 0,40		*
0	000, 002, 022, 020	3,57 ± 0,38		*
factor - system of the fertilizers
2	222, 022, 220, 020	5,69 ± 0,33	*
1	111, 313, 311	4,66 ± 0,32		*
0	000, 002, 200, 202	4,64 ± 0,51		*
3	333, 331, 131, 133	2,88 ± 0,39			*
system of  plant protection
2	222, 002, 022, 202	6,18 ± 0,34	*
3	333, 313, 133	5,06 ± 0,37		*
0	000, 220, 200, 020	4,20 ± 0,46		*
1	111, 331, 311, 131	2,58 ± 0,30			*

 The results of two-factor variance analysis testify to the significant influence of the fertility of the soil and the system of fertilizers on the differences in the phototaxis for the second case - 53,2%.  For the first case the significant influence of the factors is determined to be the fertility of soil and system of fertilizers (33,0%).

Three-factor variance analysis showed in the first case the significant influence of interaction of all three factors.  Fraction/portion in the general/common variance comprised 46,0 %.

The coefficient of instantaneous growth  was investigated in diverse experimental variations, 000, 111, 222, 333, 002, 200, 220.  First stage of testing - before the introduction of herbicides on sowings of winter wheat (April), the second stage - after the introduction of herbicides (May) and the last stage - at the moment of harvest (July).  The precursor to the wheat crop - sunflower or corn.

The appearance of new fronds was observed after a short lag phase, with the average doubling time for wet weight was in the range of 2 - 4 days.

The coefficient of an instantaneous increase in the population (r) and the doubling time of the number of fronds (t _{of udv} ) were calculated on the basis of the obtained results for the control and for each variant. 
 

t of udv  = ln2/ r = 0,6931/r

 The calculation of these indices was carried out in the dynamics with the analysis of soil samples.  The analysis of data showed that the doubling time of the population of duckweeds to treatment of the soil was smallest in comparison with the data after processing and at the moment of harvest.  Common to the  two predecessors is the fact that after treatment we observed a suppression of the intensity of multiplication; therefore doubling time increased to 14 days.  In the observations larger interest causes the response of soil after the introduction of the herbicide and to the moment of harvest.  First of all interaction with the fertilizers and the level of fertility.  Thus, in versions 022, 202 - the negative effect of the pesticides was smoothed out (Fig. 1).
 

Predecessor - corn.

Predecessor - sunflower.

Fig. 1.  Change in the coefficient of instantaneous growth in lesser duckweed with diverse variants of agro-background.

 To sometimes obtain a direct response to the introduction of chemical preparations can be complicated by interaction of preparation with fertilizers either organic, or mineral (V.I.Tanskiy, et al., 1998; K. Fedke, 1985).  The data we obtained made it possible to trace the dynamics of the response of the introduced preparations, in all versions with the chemical means of protection, where the inhibtion of the growth of the indicator plant was noted.

Single-factor analysis of variance showed the significant influence of each index on the rates of increase in the Lemna minor during the first stage.  In the second stage the effect of differences on the fertility of the soil comprised 65,0 %, along the system of fertilizers and the system of the protection of plants - comprised 65,0%.  Factors showed significant differences on the average for the coefficient of instantaneous increase in version 222 and versions 000, 111, 333.  In the third stage the portion in the common variance of the fertility of soil comprised 42,9%, systems of fertilizers and system of the protection of plants - comprised  42,9%.  A significant difference in terms of the average values of versions 000 and 111, versions 333 and 222 is noted.

Analysis of variance showed the significant influence of the predecessor crop on the rates of increase in the Lemna minor.  The portion of the general variance for the factor predecessor was small and comprised 11,1%.  The portion in the general dispersion of the same factor during the analysis of the variability  of the coefficient of growth is equal to 10,9%.  No significant influence was seen for the fertility of the soil, system of fertilizers and system of plant protection, either separately or in interaction.

Thus, data shwon on the sensitivity of duckweeds to diverse variants of soil samples make it possible to make the following conclusions:

1. The samples of soil from the variants of field monitoring being investigated differ from each other in the index inhibition of phototaxis.  It is noted that the influence of the factors of fertility, the system of fertilizers and means of protection of plants with comprise portions of 30,7% and 39,7% by single-factor analysis, and with two factor and three-factor - they registered the combined influence of factors.
2. The analysis of the results of the tests showed significant differences between the levels of the soil according to the index - inhibition of phototaxis.  Differences are noted both in terms of the average values and on different crop predecessors.
3. On all variants, where there are means of protection of plants it is observed change in the position of chloroplasts and the growth inhibition in the Lemna minor.