EFFECT OF FARMYARD MANURE AND GREEN MANURE CROPS ON POPULATIONS OF MYCOPHAGOUS SOIL FAUNA AND RHIZOCTONIA STEM CANKER OF POTATO

Effects of organic soil amendments on populations of mycophagous sprin gtails and nematodes and on Rhizoctonia solani stem canker of potato w ere investigated in two field experiments each lasting two years. The organic amendments consisted of three green manure crops (white mustar d, forage rape and oats), and farmyard manure (FYM, alone or in combin ation with white mustard). In Year 1, before the application of soil a mendments, experimental fields were infested with R, solani by growing a potato crop from seed tubers severely infested with black scurf. In the next year potato was grown again as test crop. In Experiment 1, t here was a moderate degree of Rhizoctonia stem infection in the test c rop. Organic amendments reduced the disease severity and increased pop ulations of mycophagous soil organisms. The greatest reduction in dise ase severity was found when FYM application was combined with white mu stard or when oats was grown as green manure crop. In Experiment 2, Rh izoctonia stem infection was so severe that emergence of potatoes in t he test crop was reduced. Again, soil fauna populations were increased by farmyard manure combined with mustard and also when oats was grown as green manure crop. The disease severity was only slightly reduced by the former treatment, and significantly by the latter one. FYM+whit e mustard increased the springtail populations and hed no effect on my cophagous nematodes, whereas oats increased the numbers of mycophagous nematodes tenfold. The results from both experiments support the hypo thesis that stimulating the populations of mycophagous soil mesofauna can contribute to a reduction in Rhizoctonia disease severity in potat o.