Naidid worms (Oligochaeta, Naididae) in paddy soils as affected by the application of legume mulch and/or tillage practice

Abstract

Reproduction, intrinsic rate of natural increase and population density of naidid worms were investigat- ed in submerged paddy fields and the laboratory. No till- age plus legume-mulching increased the population den- sity of naidid worms. Soil treatments with neither tillage nor legume mulch, and tillage practice alone, did not increase the number of worms. Dero dorsalis Ferro- nniere was dominant in soil of the no-tillage treatment. In laboratory experiments, legume-mulching with the proper amount of dissolved O2 accelerated asexual re- production of D. dorsalis through zooid budding. For the legume and aeration treatment, (N i+1 -N i ) N i -1 values (where Ni and Ni+1 are the populations at times t=i and t=i+1) were plotted against N i+1 . Utilizing this linear relation, this data fitted the logistic curve ( r2=0.885, P<0.05). Based on the linear relation, the intrinsic rate of natural increase (r), carrying capacity ( K), and doubling time (T) were calculated as 0.2125 day -1, 12,666 m-2, and 3.26 days, respectively. The amounts of legumes applied were highly correlated with the population of D. dorsalis, indicating that the weight of legume is a limiting factor with respect to carrying capacity. A litera- ture review indicated a significant correlation ( P<0.01) between intrinsic rate of natural increase and maximum body length of naidids with temperature conversion of the growth rate. Sexually mature worms were rarely found in submerged paddy fields. Sexual reproduction seems to be adopted in response to soil desiccation after paddy field drainage.