Effects of several kinds of organic fertilizer on Renu soil series improvement and super sweet corn yield   Pracha Nakapraves Vanlada Sunanthapongsuk Pitayakon Limtong Siangjeaw Piriyaprin Chaveevan Leaungvutivirog and Kanjana Keeratawatana   ABSTRACT         Study on the effect of organic fertilizers on some properties of Renu soil series and super sweet corn yield was conducted at Land Development Station, Chiangmai Province during 1994 - 1997. The experimental plan was completely randomized block design. There were 6 treaments in 3 replications which consisted of organic fertilizers as compost, animal manure and cooperated rice straw in 3 tons per rai, Cooperated Susbanic green manure in seed rate 5 kgs per rai and added sole chmical fertilizer (15-15-15) 50 kgs per rai. The results indicated in the cooporated rice straw showed contribute highest microbial activities in soil through 75 days of plantation as bacterial actinomycetae and fungal number increased form 7.23, 6.60 and 4.61 to 8.17, 7.94 and 5.37 log no. per gm. Soil plant mutrients, compost application had trended increasing phosphorus, potassium, calcium, magnesium and sulphur from 9.0, 61, 181, 34 and 16 to 14.0, 109, 323, 68 and 38 ppm respectively which had shown significantly statistic when canpared with non-organic fertilizer.. The level of soil pH also raised form 5.7 to 6.2. For the consideration of corn yield, addition compost hed effect increased higher than another applied organic fertilizers as from 101.4 to 440.0 kgs per rai and giving highest net income 3,275 bath per rai. In case animal manure, Sesbanai green manure and coorperated rice straw usage, had given corn yield as 324.4, 215.4 and 346.6 kgs. per rai.         Keywords: organic fertilizers, super sweet corn, Renu soil series