Effect of compost with chemical fertilizer on biological properties in different fertility soil   Chaveevan Leaungvutivirog Vanlada Sunantapongsuk Pitayakon Limtong and Siangjeaw Piriyaprin   ABSTRACT         Effect of compost with chemical fertilizer on biological properties in different fertility soil was carried out in pot experiment at Greenhouse of Organic Matter and Waste Products Sub - division during 1995 - 1998. Completely randomized design was used, with totally 12 treatments and 3 replication, and consisted of no application of compost and chemical fertilizer, compost at 4 ton/rai, chemical fertilizer (15-15-15) at 50 kg/rai, and application of compost 4 ton/rai with chemical fertilizer at 25 kg/rai. Sweet corn was used as plant indicator and three different fertility level of soil was selected namely Rayong soil series was sandy and low level of fertility, Kamphaeng Saen soil series was silty clay loam and medium level of fertility, and Chai Badan soil series was clayey and high level of fertility. This experiment determined effect of compost and chemical fertilizer on changes of soil biological and chemical properties, growth of corn, and response of corn in different fertility level of three soil series. The result showed that each application of compost or chemical fertilizer or compost with chemical fertilizer increased population of total and cellulolytic microorganisms, Azotobacter sp., phosphate solubilizing and nitrogen transformation microorganisms to be higher than no application of compost and chemical fertilizer in all 3 soil series. Moreover, response of population of some specific microbial groups was increased in Kamphaeng Saen soil series and higher than Chai Badan and Rayong soil series. Application of compost with chemical fertilizer clearly increased such microbial population, and higher than each application of compost or chemical fertilizer and microbial population changing had significant different, especially in Rayong soil series. Furthermore, dehydrogenase activity was directly increased to be higher in sole compost or compost with chemical fertilizer application than sole chemical application in all 3 soil series. The highest of dehydrogenase activity was found in Kamphaeng Saen soil series, and average was 121.96 mg/kg of soil in 24 hrs. For studying soil chemical properties found that nitrogen content in all 3 soil series was not changed when applied with sole compost or chemical fertilizer or compost with chemical fertilizer. In contrast, phosphorus and potassium content was increased in Kamphaeng Saen and Chai Badan soil series. In consideration of super sweet corn growth found that no application of fertilizer was the lowest in all 3 soil series. Dry matter and diameter of corn stem in addition of compost or chemical fertilizer or incorporated together nearly increased in Kamphaeng Saen and Chai Badan soil series, which fertility level was medium and high, respectively and clearly increased higher than no application of fertilizer. However, the growth of corn was the highest when applied by compost with chemical fertilizer in Rayong soil series, which fertility level was quite low.         Keywords: Soil fertility, biological property, compost, chemical fetilizer