Over The Horizon

Worms Around the World

Plugs of New Zealand soil, complete with earthworm activity, have been air freighted to France as part of an international study on the environmental effects of agricultural development. Scientists from New Zealand, Australia, Germany, Switzerland and France are working together on how soil structure, developed by earthworms, determines the flows of water, air and solutes through the soil.

The international group is being led by Dr Andr Kretzschmar, director of the INRA Zoology Station at Montfavet, Avignon, France; of 14 team members, three are based in New Zealand. The group is working under than name Cezanne (an anagram of the initials of New Zealand, Australia and the EEC) and much of the laboratory work will be done in the south of France.

Cezanne's first trial is centred on a field experiment run by Dr Jo Springett at AgResearch's Ballantrae Hill Country Research Station near Woodville. In this experiment four different pasture plants (ryegrass, white clover, chicory and lucerne) have been grown in pure swards with one of four different earthworm species, giving a range of different root and earthworm burrow patterns in the soil.

The trial aims to provide an understanding of essential soil fertility processes including how to:

• conserve soil structures responsible for biogeochemical cycles and plant nutrient availability
• ensure optimal "foraging" of soil resources by plant roots
• conserve biodiversity of soil fauna and soil flora.

The study will also examine the effects of agricultural intensification on the ability of plant roots to explore the soil and its consequences for soil erosion, as well as looking at the contribution of soil biological activity to greenhouse gas dynamics.

A set of large cores, 20 centimetres in diameter and 50 centimetres deep, from Ballantrae have been air freighted to Avignon, where they will be CAT scanned and their air and water flow rates measured. They will then be resin impregnated and cut into 5-mm wide serial sections and X-rayed. A second set of smaller soil samples have been sent to Stuttgart, Germany, and will be cut into serial sections on a finer scale.

The analyses of these samples will provide a detailed description of the architecture of the biological and physical components which form soil structure at different scales, from one centimetre down to as far as 10 microns (0.01 centimetres). It will also define the transfer characteristics of water, gas and solutes associated with this structure and with different pasture plants. This will be the first time that a coherent and complete description of the interactions between soil pore and root geometry, and soil transfer properties (water, gas and solute) have been taken from a single, defined set of experimental treatments.

In another first, a model will be developed that creates a theoretical link between pasture management and the physical function of the soil.