C.W. Davoren

Earthworms as indicators of sustainable production in dryland cropping in southern Australia

Abstract Crop-monitoring by farmer groups has been established to identify agronomic and soil factors limiting crop yields and to promote the adoption of sustainable farming practices in South Australia. The use of earthworms as a potential indicator of sustainability has been investigated with a survey of 95 paddocks sown to wheat, barley or peas, within an area of about 3500 km 2 . Mean annual rainfall ranged from less than 350 mm to more than 500 mm, and soils varied from coarse sands through lighter loams to heavy clays. The dryland cropping soils in South Australia have been colonized by four immigrant earthworm species, Aporrectodea rosea (Savigny), Aporrectodea trapezoides (Duges), Microscolex dubius (Fletcher) and Microscolex phosphoreus (Duges); populations are generally dominated by A. rosea . Population differences, such as the higher numbers of A. rosea recorded under barley than peas and more juveniles under peas than wheat, and the occasional abundance of other species in some paddocks may be used to indicate changes in soil conditions associated with management. Conservation tillage, retaining plant-residues and reducing cultivation, is being promoted as desirable in developing sustainable farming systems and the inverse relationship between earthworm abundance and intensity of tillage (r = −0.69 ∗∗∗ ) provides support for earthworms as a potential indicator of sustainability. Earthworm abundance showed a small but significant correlation between earthworm activity and grain yields (r = 0.44 ∗∗∗ ) and grain protein content (r = 0.52 ∗∗∗ ). A positive correlation between nitrogen fertilizer levels and earthworm numbers (r = 0.48 ∗∗∗ ) and biomass (r = 0.43 ∗∗∗ ) may be related to increased soil organic matter, derived from increased plant growth. The distribution and abundance of earthworms is dependent not only on management related to crop production, but also on local soil and climatic factors. Density and biomass were significantly higher in paddocks with higher annual rainfall and inversely correlated with levels of coarse sand. The soils, crops, climate, management and history of a region of the geographic scale surveyed here is probably too diverse to provide simple relationships between earthworms and plant productivity. It is important to distinguish the broad concept of sustainable productivity on a regional basis from the reality of productivity and sustainability on the spatial and temporal scales of activity of the organisms studied and the production and management processes involved. At an appropriate scale, ecological data on both the species composition and on functional groups within earthworm communities, may be useful indicators of crop production and its sustainability.

Influence of the earthworms Aporrectodea trapezoides and A. rosea on the disease severity of Rhizoctonia solani on subterranean clover and ryegrass

Abstract The influence of the earthworms Aporrectodea trapezoides and A. rosea on subterranean clover and perennial ryegrass, grown in a red-brown earth soil artificially infested with R. solani , was examined. In soil artifically infested with R. solani on wheat chaff, the presence of A. trapezoides (at a number equivalent to 300 m −2 ) was associated with a significant reduction in the percentage length of roots containing Rhizoctonia lesions and a significant increase in shoot weight, root weight and root length of both subterranean clover and perennial ryegrass. The presence of A. rosea , at a number equivalent to 300 m −2 , was associated with a significant increase in the shoot weight and root length of subterranean clover, but A.rosea did not significantly influence the percentage root length containing Rhizoctonia lesions on either subterranean clover or perennial ryegrass. In the absence of R. solani inoculum, neither A. trapezoides or A. rosea influenced shoot weight, root weight or root length of subterranean clover. However, both earthworms significantly increased the shoot weight of perennial ryegrass in the absence of R. solani inoculum. These results demonstrate the potential of A. trapezoides and A. rosea to reduce the deleterious effect of R. solani on specific pasture plants.

Ability of the lumbricid earthworms Aporrectodea rosea and Aporrectodea trapezoides to reduce the severity of take-all under greenhouse and field conditions

Abstract The influence of the earthworms A. rosea and A. trapezoides on wheat plants, grown in soil artificially infested with the take-all fungus Gaeumannomyces graminis var. tritici (Ggt) was examined. In pot trials, using a red-brown earth soil artificially infested with Ggt , the presence of the earthworm A. trapezoides (at a density equivalent to 314 or 471 m −2 ) was associated with a significant ( P Ggt , shoot weight was not significantly ( P > 0.05) influenced by the presence of A. trapezoides .Two field trials were conducted, in which A. rosea and A. trapezoides were added, at an equivalent density of 100 or 300 m −2 , to cylinders driven into the soil. In a calcareous sandy loam artificially infested with Ggt , the presence of the earthworms A. rosea or A. trapezoides (at these densities) was associated with a significant ( P A. rosea or A. trapezoides (at an equivalent density of 300 m −2 ) caused a significant increase in shoot weight. In contrast, in the absence of added Ggt , shoot weight was not significantly ( P >0.05) influenced by the presence of A. rosea or A. trapezoides . In a second field trial in a red-brown earth, the presence of the earthworm A. trapezoides (at an equivalent density of 300 m −2 ) was associated with a significant ( P A. rosea or A. trapezoides did not cause a significant increase in shoot weight. In the absence of Ggt , shoot weight was not significantly ( P >.05) influenced by the presence of A. rosea or A. trapezoides .These results demonstrate the potential of the earthworms A. rosea and A. trapezoides , under both greenhouse and field conditions, to reduce the severity of take-all disease on wheat.

Reduced severity of rhizoctonia solani disease on wheat seedlings associated with the presence of the earthworm aporrectodea trapezoides (lumbricidae)

Abstract The influence of the earthworm Aporrectodea trapezoides on wheat plants grown in a calcareous sand loam and a red-brown earth soil, artificially infested with Rhizoctonia solani , was examined. Presence of the earthworm A. trapezoides , at a number equivalent to 471 m −2 was associated with a significant increase in shoot weight and a reduction in the root disease rating of wheat in both soil types artificially infested with R. solani on wheat chaff. In both soil types, the shoot weight of wheat grown in the presence of A. trapezoides and R. solani was equivalent to that of wheat grown in the absence of R. solani. One further treatment was applied to each soil type. In the calcareous sand inoculated with R. solani on wheat chaff, A. trapezoides was as effective as mechanical soil disturbance in reducing the root disease rating on wheat. In the red brown earth, in which R. solani was introduced via naturally infected roots, the presence of A. trapezoides was associated with a significant increase in shoot weight and a reduction in the root disease rating of wheat. These results demonstrate the potential of the earthworm A. trapezoides to reduce the effect of Rhizoctonia root rot on wheat.

Ability of the earthworms Aporrectodea rosea and Aporrectodea trapezoides to increase plant growth and the foliar concentration of elements in wheat (Triticum aestivum cv. spear) in a sandy loam soil

In a greenhouse study, the ability of the earthworms Aporrectodea rosea and A. trapezoides to influence the foliar concentration of elements and the growth of wheat plants was assessed 27 days after sowing in a sandy loam soil. The presence of A. rosea and A. trapezoides (at densities equivalent to 314 and 471 m-2, respectively) caused a significant increase in the shoot dry weight of wheat. The presence of A. rosea and A. trapezoides (at densities equivalent to 314 and 157 m-2, respectively) was also associated with a significant increase in the root dry weight of wheat. The presence of A. rosea caused a significant increase in the foliar concentration of Ca, Cu, K, Mn, N, Na, and P, but did not influence the foliar concentration of Al, B, Fe, Mo, Mg, S, and Zn. The presence of A. trapezoides was associated with a significant increase in the foliar concentration of Al, Ca, Fe, K, Mn, N, and Na, but did not influence the foliar concentration of B, Cu, Mo, Mg, P, S, and Zn. These results demonstrate the potential of A. rosea and A. trapezoides to increase the growth of wheat in a sandy loam soil and suggest that the mechanism by which they increased plant growth was, in part, through increasing the availability and uptake of nutrients from this soil.

Enhanced root nodulation of subterranean clover (Trifolium subterraneum) byRhizobium leguminosarium biovartrifolii in the presence of the earthwormAporrectodea trapezoides (Lumbricidae)

In a greenhouse study, the effect of the earthwormAporrectodea trapezoides on root nodulation in seedlings of subterranean clover (Trifolium subterraneum) was examined in the presence and absence of addedRhizobium leguminosarium biovartrifolii (strain NA 30). WhenR. trifolii NA 30 was inoculated into dung and placed on the soil surface, the total number of root nodules was five times greater (P<0.001) in the presence of earthworms than without earthworms and the number of nodules on the primary root of the plants 2–8 cm below the soil surface was 4 to 6 times greater (P<0.001) in the presence of earthworms. The additional nodulation did not affect plant growth or foliar N. When NA30 was dispersed through the soil at the beginning of the experiment, the presence of earthworms did not influence the level of root nodulation. The presence of earthworms increased root dry weight by 20–30%, plant top weight by up to 125% (P<0.001), and foliar N by 5–25% (P<0.001). Surface-applied dung increased the dry weight of plant tops (2-to 3-fold,P<0.001) but did not affect the concentration of foliar N (P<0.005).

Field evidence for reduced severity of Rhizoctonia bare-patch disease of wheat, due to the presence of the earthworms Aporrectodea Rosea and Aporrectodea Trapezoides

Abstract A study demonstrated the ability of the earthworms Aporrectodea rosea and Aporrectodea trapezoides (added at an equivalent density of 100 or 300 m −2 ) to reduce the disease severity of Rhizoctonia soiani Kuhn on wheat in the field. In a calcareous sandy loam artificially infested with R. solani , the addition of these earthworms caused a significant ( P = 0.02) reduction of the Rhizoctonia root disease rating and had a significant ( P = 0.01) positive effect on shoot weight. Neither earthworm number or earthworm species had a significant ( P R. solani , neither the presence of these earthworms, earthworm species nor earthworm number influenced root disease rating. However, under these conditions the addition of earthworms ( P = 0.01) had a significant positive effect upon shoot weight. To our knowledge these results demonstrate for the first time, the potential of earthworms to contribute to the disease suppression of a cropping soil in a field situation.

Effect of the lumbricid earthworm Aporrectodea trapezoides on wheat grain yield in the field, in the presence or absence of Rhizoctonia solani and Gaeumannomyces graminis var. tritici

Abstract In a field trial in a red-brown earth, the interaction between the earthworms Aporrectodea trapezoides and A. rosea (added at an equivalent density of 100 or 300 m −2 ) and wheat grain yield was examined, both in the presence or absence of inoculum of Rhizoctonia solani or the take-all fungus Gaeumannomyces graminis var. tritici (Ggt) . In the absence of R. solani or Ggt inoculum, neither earthworm significantly influenced plant top weight 71 days after sowing. However at harvest, A. trapezoides at an equivalent density of 100 or 300 m −2 significantly increased grain yield (by 56% and 82%, respectively) and plant top weight (by 53% and 76%, respectively). A. rosea at these densities did not significantly influence plant top weight or grain yield. In soil artificially infested with Rhizoctonia solani , there was a significant increase from 0.06 to 1.05 in the Rhizoctonia root disease rating 71 days after sowing, but R. solani inoculum did not significantly influence plant top weight or grain yield at harvest. A. trapezoides and A. rosea did not significantly influence the Rhizoctonia root disease rating and A. trapezoides (at an equivalent density of 300 m −2 ) was associated with a significant increase in grain yield at harvest. In soil artificially infested with Ggt , there was a significant increase from 0.2 to 94% in the length of seminal roots containing take-all lesions 71 days after sowing and plant top weight and grain yield were significantly reduced by Ggt inoculum at harvest. When the effects of the different densities of each earthworm species across all the Ggt treatments were averaged, both A. trapezoides and A. rosea (at an equivalent density of 100 or 300 m −2 ) significantly reduced the Ggt root disease rating. In the presence of Ggt inoculum, A. trapezoides and A. rosea (at an equivalent density of 300 m −2 ) were associated with a significant increase in plant top weight at harvest, but neither earthworm significantly influenced final grain yield. These results demonstrate the potential of A. trapezoides to increase wheat grain yield in the field and that this ability may be influenced by the presence of R. solani and Ggt .

Influence of barley straw and the lumbricid earthworm Aporrectodea trapezoides on Rhizobium meliloti L5-30R, Pseudomonas corrugata 2140R, microbial biomass and microbial activity in a red-brown earth soil

Abstract In greenhouse experiments, the ability of barley straw and the earthworm Aporrectodea trapezoides to influence the persistence of Pseudomonas corrugata 2140R and Rhizobium meliloti L5-30R, previously inoculated separately into soil, was examined. The addition of barley straw (0.62% w/w), significantly increased the numbers of both introduced bacteria ca. 1000- to 3000-fold after 29 d incubation and ca. 25-to 100-fold after 63 d incubation in soil. In the absence of barley straw, there was a significant positive linear relationship between the number of A. trapezoides (at densities equivalent to 0, 105, 315 or 525 m −2 ) and the numbers of both introduced bacteria after 29 d, but not after 63 d incubation. In contrast, in the presence of barley straw, there was a significant negative linear relationship between the number of A. trapezoides and the numbers of both introduced bacteria after 29 and 63 d incubation. By combining data from both sampling times, there was a significant linear relationship between the persistence of both introduced bacteria and changes in microbial biomass only in the presence of added barley straw. This would suggest that A. trapezoides had a selective effect upon the persistence of both introduced bacteria in the absence of barley straw, which was not manifest upon the whole microbial community.