James P. Curry

Intensive cultivation can drastically reduce earthworm populations in arable land

AbstractThe impact of intensive cultivation for potato production on the earthworm populations was assessed in two adjacent large fieldplots. Three successive winter wheat crops had been grown in one plot while winter wheat was grown with minimum cultiva-tion in an understorey of white clover in the other. Both plots were ploughed in spring 1998 and intensively cultivated (grub-bing, ridging, bed-tilling, destoning, ridging) prior to planting potatoes. Earthworm populations were reduced from a meandensity of 319 individuals m –2 and 55 g m –2 biomass in the conventional wheat plot, and from 1160 individuals and 175 g m –2 biomass in the wheat–clover plot in the 1996/1997 cropping season, to 40–82 individuals and 4–19 g m –2 in June–October1998 following potato planting. Populations declined to virtually undetectable levels following mechanical potato harvesting inlate autumn 1998 and spring cultivation for barley in 1999, remained at very low levels throughout 1999 and had shown no signof recovering by May 2000. The results show that earthworm populations can be virtually eliminated within a single season bydrastic forms of soil cultivation.

Carbon and nitrogen stable isotope ratios in body tissue and mucus of feeding and fasting earthworms (Lumbricus festivus)

Abstract We used natural abundance stable isotope techniques to estimate carbon and nitrogen turnover rates in body tissue and mucus of earthworms. Isotope ratios of carbon (δ13C) and nitrogen (δ15N) were monitored simultaneously in body tissue and mucus for up to 101 days in feeding or fasting Lumbricus festivus kept in an artificial substrate. When the diet of the earthworms was switched from clover (C3 plant, legume) to maize (C4, non-legume), the new dietary δ13C signature manifested itself much more rapidly in the mucus than in the body tissue of the animals, causing a δ13C shift of about 4‰ in mucus and 1‰ in tissue after 13.5 days. Turnover of earthworm body tissue carbon, unlike that of mucus carbon, was described adequately by an exponential, single-pool model. Nitrogen turnover could not be assessed because the δ15N difference between sources was too small. Fasting for 56 days did not result in the expected whole-body 15N or 13C enrichment, but it caused a significant decrease in mucus and tissue C:N ratios and in the ratio (mucus C:N ratio):(tissue C:N ratio). We conclude that the separate analysis of body tissue and mucus has great potential for studying the ecophysiology, feeding ecology and role in elemental cycling of earthworms and other invertebrates.

Population dynamics of earthworms (Lumbricidae) and their role in nitrogen turnover in wheat and wheatclover cropping systems

Summary The temporal dynamics of earthworm populations were studied for three years in two farm-scale winter wheat production systems, conventionally monocropped wheat and low-input, direct-drilled wheat intercropped with white clover. Populations were estimated by soil sorting monthly in the first two cropping cycles and bimonthly in the third cycle. Earthworm population dynamics were strongly related to changes in soil moisture, with low population levels coinciding with low moisture content. Populations in conventional wheat were generally quite stable but showed a sharp drop after autumn ploughing followed by a marked recovery in the first two cropping cycles. In wheat–clover, drought conditions during the first summer probably disrupted population build-up. Population levels in the two systems diverged in the second cropping cycle and were widely separated in the third cycle when 319 individuals m —2 (55 g biomass m —2 ) were found in conventional wheat and 1160 individuals m —2 (175 g biomass m —2 ) in wheatclover. Nine earthworm species were present in both cropping systems and shifts in species composition were relatively small. Murchieona minuscula , a little known endogeic species previously unreported from Ireland, was abundant in both systems and appeared to benefit from annual ploughing. Earthworm tissue production was estimated to be 81–209 g m —2 in conventional wheat and 122–552 g m —2 in wheatclover, while N output resulting from mortality was calculated at 0.75–4.24 g m —2 in wheat and 1.16–10.61 g m —2 in wheatclover. N output via excretion and mucus was estimated to account for a further 2.93–3.65 g m —2 in the wheat and 4.98–10.69 g m —2 in the wheatclover crop.

Effects of earthworms on biomass production, nitrogen allocation and nitrogen transfer in wheat-clover intercropping model systems

The effects of earthworms (Lumbricidae) on plant biomass production and N allocation in model intercropping systems of winter wheat and white clover were evaluated in two pot experiments. Wheat and wheat-clover mixtures were grown in a low-organic loam soil, earthworms were added at densities comparable to field population densities and the experiments were terminated 48 and 17 d after earthworm introductions. In both experiments, earthworms significantly increased the biomass and N uptake of wheat while they had generally no effects on clover. As a result, earthworm activity increased the proportion of wheat biomass in the total plant biomass of the mixture. Nitrogen budgets of the experiment lasting 48 d indicated that additional N in the system made available by earthworm activity was primarily taken up by the wheat. Earthworms also affected intra-plant N allocation in wheat which had significantly higher shoot:root N ratios when earthworms were present. When clover was labelled with 15N in the experiment which lasted 17 d, endogeic earthworms significantly reduced the amounts of 15N excess transferred from living or decomposing clover roots to accompanying wheat plants. Earthworms assimilated small quantities of 15N tracer from decomposing clover roots but not from living clover roots. The results of these model experiments suggest that earthworms can affect the balance between intercropped cereals and legumes by altering intra- and inter-plant N allocation.

Successional changes in the arthropod fauna of a new ley pasture established on previously cultivated arable land.

In April, July and November 2002 and April 2003, a quadrat investigation of macrobenthos was conducted at four sampling profiles in the intertidal flat of Yangtze Estuary. The concentrations of Cu, Pb, Fe, Mn, Zn and Cr in several high biomass macrobenthos were determined, their absorbed amounts per square meter were calculated, and the biological quality of Corbicula fluminea and Siliqua minima was evaluated. The results showed that C. fluminea was widespread in the intertidal, especially in the low tidal flat of Yangtze Estuary, and heavy metals were mainly concentrated in its soft tissues. C. fluminea could selectively absorb Cu, leading to the little variation of Cu concentration in the tissues of C. fluminea sampled from different coastal region. Mollusks Rissoina sp. and Bullacta exarata, and all crustaceans could markedly accumulate Cu in their bodies, and the BSAF value reached 2.97-7.97. The mollusks and crustaceans had the greatest absorption of Fe per square meter, followed by Mn, Zn and Cu, and Pb and Cr. The amount of Cu, Pb, Fe and Cr absorbed by B. exarata larva from per square meter intertidal flat was obviously higher than that by other macrobenthos, while the absorbed amount of Mn and Zn in B. exarata larva was less than that in C. flunzinea collected from XuPu. The concentrations of Pb and Cr in the soft tissues of C. fluninea and S. miniema were relatively lower in the intertidal flat of Yangtze Estuary than in other coastal and estuarine areas, and those of Cu and Zn were also low but at appreciable level. Compared to the criterion for marine biological quality in China, the edible soft tissue of Corbicula fluminea and S. minima in the tidal flat of Yangtze Estuary was relatively safe for human beings.(1) Changes in the arthropod fauna of a newly established ley pasture were monitored in soil and vegetation. Soil and foliage communities increased in species richness during the 3-year study. Numbers in the soil to a depth of 5 cm increased in each successive year from 2317 to 114 413 individuals m-2. However, most groups extracted from the foliage by Tullgren funnel showed no significant change in abundance. (2) Various groups collected in suction net samples exhibited contrasting population trends. Insect numbers attained a late summer peak which became greater in successive years. Numbers of Cryptostigmata increased steadily throughout the study. Detritivorous Collembola exhibited population minima in midsummer when phytophagous species attained peak abundance. (3) A graphical method of tracing the accumulation of species in small samples was more useful for quantifying changes in the faunal complexity of the study site than were conventional indices of diversity.