Factors Affecting the Abundance of Earthworms in Soils

Much of the biodiversity of agroecosystems lies in the soil. The functions performed by soil biota have major direct and indirect effects on crop growth and quality, soil and residue-borne pests, diseases incidence, the quality of nutrient cycling and water transfer, and, thus, on the sustainability of crop management systems. Farmers use tillage, consciously or inadvertently, to manage soil biodiversity. Given the importance of soil biota, one of the key challenges in tillage research is understanding and predicting the effects of tillage on soil ecology, not only for assessments of the impact of tillage on soil organisms and functions, but also for the design of tillage systems to make the best use of soil biodiversity, particularly for crop protection. In this paper, we first address the complexity of soil ecosystems, the descriptions of which vary between studies, in terms of the size of organisms, the structure of food webs and functions. We then examine the impact of tillage on various groups of soil biota, outlining, through examples, the crucial effects of tillage on population dynamics and species diversity. Finally, we tackle the question of the design of tillage systems to enhance biological control in cultivated fields. Identification of the optimal tillage system requires a global consideration of soil management, rather than an analysis focusing on tillage alone, taking into account soil ecology. Organic residue management, the prevention of compaction, crop rotation and the timing of cultivation must all be considered together, taking into account their impact on pest populations and on the natural enemies of pests and ecosystem engineers. This approach requires more detailed research and careful experimental design than traditional comparisons of conventional and reduced tillage systems. We propose the development of population modeling in cultivated fields, as the available ecological models rarely include parameters linked to the soil management system.

Tillage and soil ecology: Partners for sustainable agriculture

Intensive agriculture is often criticized for negative impacts on environment and human health. This issue may be solved by a better management of organisms living in crop fields. Here, we review the benefits of earthworms for crops, and we present techniques to increase earthworm abundance. The major points are the following: (1) Earthworms usually improve soil structural stability and soil porosity and reduce runoff. (2) Earthworms modify soil organic matter (SOM) and nutrient cycling. Specifically, earthworms stabilize SOM fractions within their casts, and they also increase the mineralization of organic matter in the short term by altering physical protection within aggregates and enhancing microbial activity. (3) The positive correlation between earthworm abundance and crop production is not systematic, and contrasting effects on yields have been observed. Earthworms induce the production of hormone-like substances that improve plant growth and health. (4) Direct drilling increases earthworm abundance and species diversity, but the beneficial effect of reduced tillage depends upon the species present and tillage intensity. (5) Organic amendments enhance earthworm abundance. (6) Earthworms feeding at soil surface are the most exposed to pesticides and other agrochemicals. Finally, we discuss how to combine management practices, including inoculation, to increase the earthworm services. We conclude that using earthworm services in cropping systems has potential to boost agricultural sustainability.

https://link.springer.com/content/pdf/10.1007%2Fs13593-014-0269-7.pdf

Earthworm services for cropping systems. A review

Many research studies have dealt with the influences of minimum or no-till soil management practices on the major physical, chemical, biological and morphological properties in the soil profile. However little work has been done on the assessment of the rates of changes in pore properties as management practices are converted from conventional to no-till (NT) methods. Short-term changes in soil micromorphology attributed to conversion to no-till from conventionally tilled management are evaluated in this paper. As the number of years in no-till increased there was a decrease in the number pores of 30- to 100-µm diameter in the no-till soils. However, pores from 100- to 500-µm diameter increased in number only after 4 yr of NT. The pores of this size are important for water storage, transmission and root development. The decline in the number of these pores after no-till initiation followed by the increase after 4 yr may explain why crop yields tend to be lower only after the first few years after implemen...

Changes in pore structure in a no-till chronosequence of silt loam soils, southern Ontario

The extent of earthworm injury caused by rotary cultivation followed by ploughing of a meadow fescue and a lucerne ley was estimated. For comparison, parts of the leys were left undisturbed. One year later, earthworm biomasses in the ploughed leys and the undisturbed leys were estimated. The ploughed plots were under barley at the time. Rotary cultivation killed 61–68% of the earthworm biomass. The ploughing that followed increased the mortality by a further estimated 12% and 9% of the original biomass in the meadow fescue and lucerne leys, respectively. One year later, earthworm abundance in the ploughed treatments was similar to that in the undisturbed lucerne ley, while it was lower in the undisturbed meadow fescue ley. The difference in earthworm biomass between the leys was probably due to inferior food quality and drier soil conditions in the grass ley. More large adults of Aporrectodea caliginosa Sav. were found in the ploughed treatments than in the undisturbed leys, and this species also constituted a greater part of the earthworm biomass in the former compared with the latter (i.e. 85% and 60%, respectively). The biomasses of Lumbricus rubellus Hoffm. and juvenile Lumbricus terrestris L. were significantly greater ( P

J.J. Miller

Papers

Impact of ring-billed gull (Larus delawarensis Ord.) foraging on earthworm populations of southwestern Ontario agricultural soils