Effect of no-tillage and tillage on the ecology of mite, Acarina (Oribatida) in two different farming systems of paddy field in Cachar district of Assam

The present investigation was carried out in Cachar district of Assam over a period of one year (January 2011-December 2011) to understand the seasonal ecology of Acarina (Oribatida) in rice (Oryza sativa L.) cultivated fields. Population of Oribatida was found to be maximum during August 2011, both in no-tillage (6.32 +/- 0.66 No. /m(2) x 100(2)) and tillage (5.30 +/- 0.71 No. /m(2) x 100(2)) sites in Dorgakona area whereas the peak was recorded during August 2011, both in no-tillage (5.38 +/- 0.75 No./m(2)x 100(2)) and tillage (4.69 +/- 0.77 No./m(2)x 100(2)) in Durby area of study sites. Least population was encountered during January 2011, in both no-tillage (0.98 +/- 0.28 No. /m(2) x 100(2)) and tillage (0.98 +/- 0.30 No./m(2) x 100(2)) sites in Dorgakona area whereas the same was found during November 2011 in no-tillage (0.57 +/- 0.31 No./m(2) x 100(2)) and in February 2011 in tillage (0.45 +/- 0.21 No./m(2)x 100(2)) sites of Durby area. Linear regression analysis with all the environmental variables showed positive and significant influence on the population dynamics whereas relative humidity (R-2=0.26 p>0.05) in Dorgakona no-tillage and tillage (R-2=0.19 P>0.05) sites and relative humidity in tillage site (R-2=0.27 P>0.05) in Durby area showed no influence. Multiple regression analysis showed that the combined effect of climatic variables having a significant influence (p<0.05) on the oribatid mite population in no-tillage and tillage systems in both the study sites. Rainfall, relative humidity and temperature facilitated the soil moisture, microbial activity and litter decomposition, which in turn may favour the reproduction and growth rate of the species. Among microclimatic conditions all the parameters showed positive and significant influence (P<0.05) on the population in no-tillage and tillage system on both the sites except pH which showed negative correlation with the population. One way ANOVA revealed significant difference (F=6.53, P<0.01) of the Oribatid population between the systems.