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Keywords: Collembola/physical factors/agricultural practices. 1.INTRODUCTION:Soil animals promote the decomposition of organic matter by comminuting litter, The present experiment was conducted to study the Collembolan population of agricultural fields in which three crops (jute, paddy rice and wheat) were cultivated and supplemented with graded doses of N, P, and K fertilizers. Treatments were also designed to estimate the effects of organic manure and herbicides. 2.MATERIALS AND METHODS:Experimental plots were selected at the Jute Agricultural Research Institute (I.C.A.R.), Barrackpore, West Bengal, India (22°46'N, 88°24'E), in a long-term (15-yr) fertilizer experiment. In this experiment, three croppping systems using jute, paddy rice and wheat succeeded round the year. Nine different treatments (Table I) were replicated four times using a randomised block design. Soil samples were collected from experimental plots at monthly intervals for three consecutive years. Plot size was 20m x 10m.The soil was alluvium from the Gangetic plain. Fertilizer sources for NPK treatment were urea, superphosphate and potassium chloride, respectively. The three crop rotations consisted of two cereals, paddy rice (Oryza sativa L.) and wheat (Triticum aestivum L.) and one fibre crop, jute (Corchorus olitorius L.). Jute was sown in April and harvested in July. Paddy rice was transplanted in August and harvested in November. Wheat was sown in December and harvested in March. 4Hand weeding and hoeing were done at monthly intervals after sowing or transplanting. A herbicide was used for weed control in treatment 7. Soil samples were collected from all replicated plots at monthly intervals. Samplers were 9cm long and with a cross sectional area of 28cm 2 . Three cores were taken from each plot, at each time. Tullgren funnel extractors were used for collecting soil microarthropods.The extraction time was five days. Soil temperature, surface humidity and soil moisture were recorded each month from all replicated plots under each treatment.After extraction, animals were mounted in polyvinylalcohol and identified to the species or to the genus level under a phase contrast microscope. In the absence of a comprehensive account of Indian springtails, half of the species could only be identified at the genus level.Data pooled over three years for each experimental plot were used for the calculation of Spearman rank correlation coefficients, a posteriori comparisons among means using t-tests or non-parametric Kolmogorov-Smirnov tests according to normality of residuals [32] and correspondence analysis [16]. For correspondence analysis, data were transformed using refocusing (mean fixed to 20) and reweighting (variance fixed to 1) and variables were doubled in higher and lower values according to Ponge and Delhaye [28]. The latter procedure allowed to display changes in population densities. Each variable was thus represented by two points (higher and lower values) which were symmetrical around the origin. The farther these points were from the...

Two sublines from each of four flocks of White Leghorn were subjected to two cycles of selection for part year egg number and part year egg mass. A family index (combined selection) was the selection criterion for each of the two traits. The generation means of an unselected pedigreed randombred control, bred and maintained along with the selected sub-lines, were used for correcting short term environmental trends. The sublines selected for a common selection criterion were considered as replicates. The control corrected generation means, when averaged over replicates, gave the mean direct and correlated responses for the selected and different unselected traits. The average genetic change per generation was 2.16 eggs in egg number selected sublines and 146 g of egg mass in egg mass selected sublines. The direct response marginally exceeded the correlated response for both part period egg number and egg mass seen in the corresponding sublines. Except for egg weight the correlated responses for different unselected traits were in the same direction in both egg number and egg mass selected sublines. While the egg weight in egg number lines did not change, its response was positive in egg mass selected lines. A comparison between the lines revealed that the egg mass selected lines matured later and laid heavier but slightly less numerous eggs than the egg number selected sub-lines.

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