Successful soil biological management with macro-organisms

Case study A1. Soil fauna and organic fertilizers in tea gardens of Tamil Nadu, India (Giri, 1995; Lavelle et al., 1998; Senapati et al., 1999)

Tea is a high value plantation crop in India with an old history (many estates are >100 years old). In recent years, green tea production has stabilized, despite increasing application of external inputs such as fertilizers and pesticides. The long-term exploitation of soil under the tea gardens has led to important changes in various soil physical, chemical and biological conditions, decreasing organic matter content, cation exchange, water-holding capacity, soil biota (reduced up to 70%) and pH, simultaneously increasing concentrations of toxic aluminium.

In response to these limitations on tea production, a patented technology entitled "Fertilisation Bio-Organique dans les Plantations Arborées" (FBO, for short), was recently developed by Parry Agro Industries Ltd., in association with the French Institute de Recherche pour le Développement (IRD) and Sambalpur University (Orissa, India). This technology aims at improving the physical, chemical and biological soil conditions by inoculating a mixture of low and high quality organic materials (tea prunings and manure) and earthworms into trenches dug in between the rows of tea plants. Measurements performed at two sites, beginning in 1994 have shown that this technique is much more effective than 100% organic or 100% inorganic fertilization alone, increasing yields on average by up to 276% (Figure 1), and profits by an equal percentage (from around US$2,000 ha^-1 using conventional techniques to about US$7,600 ha^-1 using FBO), in the first year of application. This technique has been extended to other countries and is now being used in over 80 ha and over 20 million earthworms are being produced each year. Details on the methodology for its application are described in the patent document (ref. PCT/FR 97/01363).

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Case study A2. Restoring soil structure and plant production in crusted Sahelian soils through organic matter applications and termite activity (Mando, 1997)

The extension of bare and crusted soils in the Sahel has undergone a large increase in recent decades, seriously degrading the landscape and negatively impinging on crop production. In a study performed in northern Burkina Faso (West Africa), when mulch was placed on crusted and bare soil, termites migrating from nearby areas invaded the organic substrate and the topsoil, significantly changing its physical structure. Many burrows were opened to the soil surface reducing surface sealing, and throughout the soil profile, macropores with irregular shapes and sizes were created. As a result, soil compaction was reduced and water infiltration and drainage were increased to a point where crops could again be planted. Furthermore, termites enhanced the decomposition and mineralization of the mulch, releasing nutrients and increasing their availability to plants. In mulched plots where termites were artificially excluded, cowpea yields were more than 100 times lower than where termites were present and active (Table 1). This work demonstrated again that termites, far from being the traditionally held pests in agroecosystems, can also be extremely important in plant production and ecosystem function and that it is possible to manage their activities for human benefit.

Table 1. Effect of termite addition to two different mulch types on cowpea yields and soil properties  in a degraded Sahelian soil (Burkina and Faso) (from Mando 1997)

 *Ksat = saturated hydraulic conductivity

Complete case study with photographs (PDF, 735KB), without photographs (PDF, 294KB)

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Case study A3. Tomatoes grown on vermi- composted sawdust beds in Yurimaguas, Peru (Senapati et al., 1999)

In the Peruvian Amazonian region, thousands of tons of sawdust wastes are produced by the timber industry and left mostly untouched in huge piles many meters tall. A technology developed by Beto Pashanasi and colleagues at the ICRAF (International Centre for Research in Agroforestry) ‘Yurimaguas’ Station, allows the earthworm species Pontoscolex corethrurus to rapidly multiply in a large beds (5m x 1m x 20cm height) containing a mixture of 25% composted sawdust and 75% soil. This technique increases earthworm populations by almost 15 times in 4 months, and in the process the availability of Ca, Mg and K is considerably increased while the high Al toxicity of the substrate decreases. Good quality hybrid variety tomatoes are generally grown far from Yurimaguas, on the Pacific coast of Peru, whereas only native varieties of poor quality and yield are grown locally for household consumption.

The limitations for market gardening in Yurimaguas are the low soil nutrient content, high acidity and Al toxicity, and scarcity of fertilizers. Yields of hybrid tomatoes grown on the earthworm (vermi) composted sawdust beds were twice as high as in control soil, and similar to that obtained with inorganic fertilization. The advantage of this technique is that it uses a wasted resource (sawdust) and a locally unused resource (earthworms) to produce hybrid tomatoes that are much preferred over the traditional varieties and sell at higher prices. Other market gardening crops have been explored as well although the physico-chemical characteristics of the substrate limit its wider applicability.

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