The earthworm is the farmer's friend. Its favorite food, plant matter, nourishes the soil after digestion. In an experiment at ICRISAT-Patancheru, ongoing since 1999, large numbers of earthworms were seen, especially in treatment plots where low-cost inputs, including weeds, glyricidia loppings and other plant materials are used.
How do these creatures survive the temperatures at the height of a summer in the semi-arid tropics (SAT)? About 20 hours after a 36.7mm rainfall, and while assessing soil moisture before sowing, scientists noticed a high number of earthworms, and decided to quantify their population. Samples were taken from six different spots (treated as replications) from each of the four treatments. The highest population of worms was recorded in two treatments that haven't received any agro-chemicals and plowing since 1999 (labeled as Low cost 1 and 2 - LC1, LC2 in Table 1). The number of earthworms was at least 10 times higher than that in the control (Mainstream Agriculture - MA), and indicates the possible negative effects that fertilizers, pesticides and plowing used in the treatment have on earthworm populations.
The treatment ‘MA+Biomass’, which received both agrochemicals (as applied to MA) and biomass (at the rates similar to LC1 or LC2) also had a substantial population of earthworms, but was 38 to 40% lower than that in the LC1-LC2. This indicates that the possible negative effects of the agronomy in the MA were ameliorated by the added biomass.
Two types of full-grown worms (a) 3 to 5 cm long, and (b) 8 to 10 cm long were found. Both types are native to the soil and need to be identified. The big ones seem similar to Eisenia foetida. The small types were 7 to 15 times more in number than the big types. The fact that full-grown worms were observed in the topsoil within 20 hours and quantified within three days after the rain, suggests that large populations survive in depths lower than 60 cm in the soil profile, which may still be moist.
Details about this experiment are in: Rupela OP. 2008. Organic farming: Building on farmers' knowledge with modern science. Pages 28 to 45 in Organic farming in Rainfed Agriculture: Opportunities and Constraints (Venkateswarlu B, Balloli SS and Ramakrishna YS, eds.). Central Research Institute on Dryland Agriculture (CRIDA), Hyderabad.
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