Earthworm management in tropical agroecosystems

An ethnological survey of knowledge of earthworms was carried out in four tropical countries (Mexico, Peru, India and Congo). A total of 202 farmers from 20 localities were interviewed to clarify their perception of soil fertility and its relationship to earthworm activity. Four additional farmers' meetings supported the results of these inquiries. In Peru and India, most of the farmers recognized a beneficial effect of earthworms, whereas in Congo and Mexico lack of knowledge predominated. In this last country, sampling was more intensive, covered three different ethnic groups and revealed an interesting inter-ethnic variability. In America, empirical knowledge and myths recognized an important role of earthworms in soil fertility. It is concluded that management practices focused on increasing earthworm populations will be accepted by local farmers. In some situations, however, an educational programme will be necessary. (Résumé d'auteur

Earthworm management in tropical agroecosystems

The effects of earthworms on soil structure and the resulting physical properties in natural or cultivated systems were studied in different sites of the Macrofauna project. Four main results were obtained from these experiments : (1) In kaolinitic soils (Lamto, Manaus, Yurimaguas), irrespective of clay content, andogeic earthworms play a major role in soil structure formation and maintenance, while in smectitic soils (Martinique), the effects of earthworms on soil structure formation and maintenance are not as clear. In the Vertisols of Martinique, the effect of roots and organic materials seem predominant in soil structure development and earthworms play a secondary role. (2) Endogeic earthworm species have different effects on soil properties. Large earthworms such as #Pontoscolex corethrurus or #Millsonia anomala egest large and compact casts. They increase the proportion of large aggregates in soil and the bulk density ; they are called "compacting species". Conversely, small earthworm species such as eudrilid worms feed at least partly on large compact casts and egest smaller and fragile aggregates. They decrease the proportion of large aggregates in soil and the bulk density ; they are called "decompacting species". The effects of "compacting species" on soil structure formation seem to be linked to the presence of organic residues at the soil surface. In agroecosystems of Yurimaguas (Peru), the intense activity of #P. corethrurus$ and the coalescence of surface casts lead to the formation of a compact surfacecrust with impedes water infiltration in the absence of organic residues, but a favourable macroaggregate structure develops in the presence of organic residues and leguminous mulch. (3) The introduction of earthworms in agroecosystems changes soil physical properties and especially water retention and infiltration... (D'après résumé d'auteur

Earthworm management in tropical agroecosystems

In agrosystem field experiments, earthworm inoculation did not impede depletion of soil organic stocks in most cases, in spite of increased carbon inputs through enhanced primary production. Slight evidence of soil organic matter (SOM) protection was found in poorly structured soil, such as a yam plot in Ivory Coast (soil sieved before experimentation), and a pasture plot on Martinique. Aggregation inherited from past earthworm activities probably maintains SOM protection after earthworms have disappeared ; longer term experiments are necessary to observe C dynamics after the disappearance of inherited earthworm structures. In two experiments with maize in Ivory Coast and Peru, the activity of earthworms led to a small increase in the incorporation of organic matter from surface mulch in the SOM. Most of the C incorporated into the SOM originated from root material, and earthworm activities only slightly modified this pattern. Earthworm activity had significant effects on the distribution of C among particle size fractions. The general trend was a depletion of large (greater than 50 micrometers) particles and an accumulation of small (less than 2 micrometers) particles. Nutrient depletion in low-input cropping systems was not impeded by earthworm activities ; at Yurimaguas, some signs of a better conservation of K were noted after 3 years in the traditional rotation. (Résumé d'auteur

Earthworm management in tropical agroecosystems

Collaborative research in the Macrofauna project has enabled development of some techniques that presently are at different stages of advancement, from promising pilot experiments (tomato production and inoculation in plant nursery bags at Yurimaguas and in India) to the fully developed technique of massive worm production and biofertilization of tea gardens in Tamil Nadu (India) (patent deposited). Failures have also helped to gain better insight into the potential feasibility of techniques that had been considered in the objectives of this project. Endogeic earthworms (#Pontoscolex corethrurus$) may be produced in large quantities, i.e.about 12000 worms (1.6-2.8 kg live wt)/m2/year in specific culture beds using either sawdust (Yurimaguas, Peru) or a mixture of high and low quality materials (Tamil Nadu, India) mixed into soil as substrates. Cost of production of 1 kg of earthworm biomass through bed culture is about 3.6 Euro, much lower than the cost of hand collection of worms from pastures/grasslands where these species are abundant (6-125 Euro depending on the cost of labour and earthworm density). The theorical value of an active earthworm community with an average biomass of 400 kg live wt has been estimated at 1400 Euro, the price that it would cost to reintroduce an equivalent biomass produced in our culture units, indicating the cost of land restoration. Direct inoculation of earthworms in the field to improve production may only affect plant growth positively if a large biomass (greater than 30 g live wt/m2) is inoculated from the beginning. An alternative may be to concentrate the inoculum in small areas regularly distributed across the field... (D'après résumé d'auteur

Division S-6-soil and water management and conservation : dynamics of soil physical properties in amazonian agroecosystems inoculated with earthworms

The combined use of earthworm inoculation and organic input is considered an efficient way to improve traditional slash-and-burn agriculture in the humid tropics. This study tests the hypothesis that the resistant macroaggregate structure that results from earthworm activities is likely to promote sustainability by favoring water infiltration and soil aeration. Six successive crops (maize (#Zea mays L.) - rice (#Oryza sativa L.) - cowpea (#Vigna unguiculata (L.) Walp.) - rice - rice - rice) were grown from March 1990 to January 1993 on a fine-sandy, siliceous, isohyperthermic typic paleudult previously covered by forest at Yurimaguas (Peruvian Amazonia). The experimental design included a combination of three organic residue treatments (without residues, with crop residues, and with crop residues plus green manure), with or without earthworm (#Pontoscolex corethrurus) inoculation (36 g fresh weight/m2). Soil physical properties (bulk density, total porosity, infiltration, sorptivity, soil water tension, and aggregate-size distribution) were measured before clearing and after harvesting each crop. The proportion of macroaggregates (> 1 cm) increased from 25.1 to 32.7% in inoculated treatments, whereas the proportion of small aggregates (< 2 cm) decreased from 33.2 to 26.1%, and no change was observed in the intermediate (2-10 mm) category. In the control treatment, no significant changes were observed. Earthworm activities significantly increased bulk density (from 1.12 to 1.23 Mg/m3), and decreased porosity (from 58 to 53%) and sorptivity (from 0.45 to 0.15 cm/s1/2). Soil water tension was also affected by the presence of earthworms through increased water uptake by larger plants and changes in soil structure. Longer term experiments are necessary to confirm that the activity of the earthworm may not eventually have detrimental effects. (Résumé d'auteur

Effect of the endogeic earthworm Pontoscolex corethrurus on soil chemical characteristics and plant growth in a low-input tropical agroecosystem

Low densities of #Pontoscolex corethrurus$ have been introduced into low-input cropping systems at Yurimaguas (Peru) to test their effects on soil fertility under field conditions for six succesive cropping cycles. Earthworm biomass was sustained at 40 g/m2 fw (ca. 3 g ash-free dry mass) on the average with peak values of 80 g at harvests 2 and 3 in treatments receiving an application of legume green manure. At the 6th harvest, earthworm biomass was significantly lower in the treatment with no organic input than in treatments with crop residues and legume green manure. Earthworm activities did not prevent C and nutrient stocks from being significantly depleted although P, K and Ca concentrations tended to be higher than in non-inoculated treatments at the 6th harvest. Plant production was significantly increased by 36% due to earthworm inoculation in a traditional low-input rotation (maize, rice, cowpea, rice, rice, rice) with variation between -43 and +78%, depending on the crop and climatic conditions. In a continuous maize culture that received fertilizers for the last three crops, grain production was increased by 2.45-fold on average, due to earthworm inoculation. These results demonstrate that the maintenance of active earthworm populations was favourable to crop production during the time scale of our experiments (3 y). Longer term experiments are required to test the sustainability of the positive effects observed. (Résumé d'auteur