Effect of soil solarization on weeds and nematodes under tropical Indian conditions.
Field trials were conducted on sandy loam at New Delhi in summer 1990 to study the control of weeds and nematodes in soyabean by solar heating of the soil using transparent polyethylene (PE) sheets for 16 and 32 d, with and without irrigation. Data are given on the soil temp. recorded over the 32-d period. PE mulching for 32 d decreased the emergence from seed of the dominant weeds (Dactyloctenium aegyptium, Acrachne racemosa, Trianthema monogyna [Trianthema portulacastrum] and Cyperus rotundus) by >90%. The emergence of C. rotundus from tubers was increased by the mulching treatments. Mulching for 16 d also decreased weed emergence but to a lesser extent than the 32-d treatment. The main solarization effect was restricted to the 0-5 cm layer of soil. Solarization reduced the population of plant-parasitic nematodes (Tylenchus, Heterodera, Xiphinema, Hoplolaimus, Pratylenchus and Rotylenchus spp.) by about 90% and of saprophytic nematodes by about 60% but, after 70 d, the nematode levels had largely recovered. The mean max. soil temp. recorded at 5 cm were higher when mulching followed irrigation. The growth of soyabean was improved and seed yield increased by up to 78% following solarization.