STUDIES ON THE SEASONAL FLUCTUATION OF SOIL NEMATODES POPULATION IN SANDY AND LATERITE SOIL OF BALASORE AND MAYURBHANJ DISTRICTS OF ORISSA

INTRODUCTION The soil in a particular area contains various organic and inorganic matter and supports a number of plants and animals including micro organisms. Usually nematodes both free living and plant parasitic exist in communities containing many species which exhibit efficient dispersal, polyphagy, weak interspecific competition. As most of the workers like Choudhury (1985), Choudhury and Phukan (1990, 1992), Roy and Parija (1987), Khan and Sharma (1990), Khan et al. (1980), Khan, Adhami and Saxena (1971), Sabir (2000), Srivastava et al. (2000), Dwivedi and Upadhyay (2001), De et al. (2004), Sen et al. (2008) studied the population structure of soil nematodes associated with the different crops. Very few workers like Nilova (1961), Khakinov (1971), Das and Mukhopadhyay (1990), Choudhury ans Sivakumar (1999), studied the population fluctuation and vertical distribution of soil nematodes in cultivated and uncultivated soil and in different soil types. So an attempt was made to study the population structure together with the vertical distribution of the soil nematodes present in sandy and laterite types of soil in Balasore and Mayurbhanj districts of Orissa.


INTRODUCTION
The soil in a particular area contains various organic and inorganic matter and supports a number of plants and animals including micro organisms.Usually nematodes both free living and plant parasitic exist in communities containing many species which exhibit efficient dispersal, polyphagy, weak interspecific competition.As most of the workers like Choudhury (1985), Choudhury andPhukan (1990, 1992), Roy and Parija (1987), Khan and Sharma (1990), Khan et al. (1980), Khan, Adhami and Saxena (1971), Sabir (2000), Srivastava et al. (2000), Dwivedi and Upadhyay (2001), De et al. (2004), Sen et al. (2008) studied the population structure of soil nematodes associated with the different crops.Very few workers like Nilova (1961), Khakinov (1971), Das and Mukhopadhyay (1990), Choudhury ans Sivakumar (1999), studied the population fluctuation and vertical distribution of soil nematodes in cultivated and uncultivated soil and in different soil types.So an attempt was made to study the population structure together with the vertical distribution of the soil nematodes present in sandy and laterite types of soil in Balasore and Mayurbhanj districts of Orissa.

MATERIALS AND METHODS
The present study was undertaken during [2005][2006] in the specific areas of Balasore and Mayurbhanj districts of Orissa.In the Balasore district the soil is sandy in nature and in the forest area of Mayurbhanj district the soil is of laterite type.Four surveys was undertaken in January.March July and November, 2006.Collections were mainly made from the grass land and paddy field after harvest in the Balasore district and from the forest areas of the Mayurbhanj district.Collections were made in two depths one from 0 to 10 cm and other from 10-20 cm to study the vertical distribution.For the assessment of the nematode population 250 C.c. of soil samples were processed by sieving and decanting using 250 and 325 mesh and the nematodes were extracted by modified Baermann's funnel technique (Christie and Perry, 1951).The nematodes were counted under low power binocular microscope in a counting dish.
Apart from the extraction of the soil nematodes the soil samples were analysed to determine the pH and moisture content of the soil samples using Systronics pH metre and Infra red moisture balance respectively.Soil temperatures were recorded at the time of sampling the soil by inserting soil thermometer in the soil.

RESULTS AND DISCUSSION
The average moisture content of the sandy soil collected from Balasore district was 7.3%, 15.5% and 12% and that of laterite soil collected from Mayurbhanj district was 3%, 10.5% and 4.5% in premonsoon, monsoon and post monsoon period respectively.The moisture content of the upper and lower layer's soil samples (i.e., 0-10 cm and 10-20 cm depth) shows slight difference in both types of soil.In pre-and postmonsoon collections the moisture content of the lower layer's samples was slightly higher and this difference ranges from 0.5% to 1.5% in pre monsoon and 0.2% to 0.6% in postmonsoon period in sandy soil and in laterite soil it ranges from 0.7% to 0.8% in premonsoon and 1 % to 1.2% in post monsoon.But in the monsoon the moisture content of the upper layer (i.e., 0-10 cm) collections was more higher than that in the lower layer's collection in both types of soil and the difference of moisture content ranges from 2% to 5% and 1 % to 3% in sandy and laterite soil respectively.
The average soil temperature was 29°e, 28°e and 21 °e in sandy soil and 31 °e, 28°e and 21°e in laterite soil in pre monsoon, monsoon and post monsoon period respectively.The pH of soil samples were slightly alkaline in nature in both types of soil in all the seasons and it ranges from 7.1 to 7.8 and only the samples collected from paddy field the pH was slightly acedic in nature.
As regards the population of the soil nematodes in two types of soil the total population was always Rec. zooz.Surv.India higher in sandy soil than that in the laterite soil.The average number of soil nematodes in both the layers together (0-20 cm depth) in sandy soil was 42.5, 95 and 48 that in laterite soil was 30.2, 52.5 and 33.2 in pre monsoon, monsoon and post monsoon period respecti vel y.
The vertical distribution of the soil nematodes population in the sandy and laterite soil was also studied and it was observed that the total population was slightly higher in the lower layer (i.e., 10-20 cm depth) in pre monsoon and post monsoon period where as in monsoon the upper layer's population was almost double than that in the lower layer in both types of soil  37.96% and 35.35% of the total population in the premonsoon, monsoon and post monsoon respectively.
In the sandy soil the genus Aporcelaimellus occupying the second position but in the laterite soil the second position was occupied by the genus Dorylaimus (Fig.
Many factors are responsible for the seasonal fluctuations of nematodes.Among these fecundity, fertility, duration of life cycle, longivity and substrate g. '" 2! t'2   availability are important (Norton, 1978).Along with these factors, temperature, moisture content, relative humidity and agricultural practices also influence the population.
The higher number of nematodes in all the seasons in sandy soil than that in the laterite soil is may be due to the well aeration due to the presence of grass roots and higher moisture content of the soil in all the seasons.The low population in the pre-monsoon and post monsoon period than that in the monsoon in both types of soil is may be due to the high temperature and low moisture content of the soil.The influence of atmospheric temperature can be correlated to the change in nematode population mostly in the surface layers where there is little difference between soil temperature and atmospheric temperature (Norton, 1978).
So the low population of the nematodes in the upper layer in premonsoon in both the soil types may be due to the high temperature and low moisture content of the soil.The higher numbers of nematodes in the upper layer in the monsoon in both soil types is may be due to the high moisture of the soil in monsoon due to rainfall.

Fig. 2 .
Fig. 2. : Relative abundance of six different species of nematodes in different seasons in laterite soil.
Rec. zooz.Surv.India SUMMARY Population fluctuation and vertical distribution of the soil nematodes in sandy soil of Balasore and laterite soil of Mayurbhanj districts of Orissa was studied.Altogether seven species belonging to seven genera were identified and the relative abundance of the species in different seasons in both types of soil were analysed.In the monsoon the upper layer's population and the total population were higher in both types of soil The Genus Longidorous and Aporcelaimellus dominated the population in sandy soil and laterite soil respecti vel y.

Table - !
: Shows the average soil moisture, pH, soil temperature and nematode population in two types of soil in different seasons.