Effects of crop density and species upon surface casting by earthworms and implications for nutrient cycling in a tropical intercropping system

摘要

The effect of crop density upon surface cast production by earthworms was assessed in an intercrop of groundnut, maize, cassava and plantain in the humid forest zone of Southern Cameroon. Furthermore, cast production was compared under adjacent crops of the different species. The experiment was established at two sites of different fallow types: a four year old fallow dominated by Chromolaena odorata; and a secondary forest undisturbed for at least 25 years. Surface casts were collected from framestwice per week for 30 weeks. Dry weights were recorded for each sampling date. In total, 4.01 and 2.89 t/ha of surface casts were produced in the high crop density treatments at the chromolaena and secondary forest sites, respectively, significantly more than 2.18 and 0.34 t/ha in the low crop density treatments. 15.51 kg Ca2+, 3.44 kg Mg2+, 0.9 kg K+, 9.36 kg total N and 117.6 kg organic C/ha were deposited in surface casts in the high crop density treatment. In comparison, lower cast production in the low crop density treatment resulted in deficits of 6.41, 2.06, 0.39, 4.48 and 58.4 kg/ha of Ca2+, Mg2+, K+, total N and organic C, respectively. There were no significant differences between the quantities of casts produced under the four crop speciesat either site. The more intensive, high crop density treatment not only resulted in higher crop biomass production but also created the conditions for higher earthworm activity.