Cassava (Manihot esculenta Crantz) is an important subsidiary food and industrial raw material in the tropics.
Considering the importance of the crop, an on farm experiment was conducted to study the effect of NPK fertilizer
rate and biocontrol agents (Trichoderma and Pseudomonas fluorescens) and biofertilizers (Azospirillum, AM fungi
and phosphorus solubilising bacteria) on soil chemical, biochemical and microbial biomass carbon in cassava growing
Vertisols of Tamil Nadu during 2008 and 2009. The study was conducted in split plot design with two levels of NPK
fertilizer as main plot treatments and eight microbial inoculations as subplot treatments. Azospirillum with Trichoderma
(170.58 kg/ha), AM fungi with Trichoderma (57.85 kg/ha) and Trichoderma alone (473.70 kg/ha) significantly increased
available nitrogen, phosphorus and exchangeable potassium by reducing the amount of NPK. Pseudomonas fluorescens
with Trichoderma at 50 per cent recommended NPK rate increases the available iron in soil. The AM fungi with
Trichoderma significantly increased available manganese and zinc compared to other inoculations at 50 per cent
recommended NPK rate. Azospirillum with Trichoderma at the recommended NPK rate increased the urease enzyme
activity (835.21 mg urea hydrolysed/g soil/h) compared to other treatments. The soil application of all cultures at 50
per cent recommended NPK rate increased soil dehydrogenase and β glucosidase enzyme activities. Interaction
effect showed significantly higher microbial biomass carbon in AM fungi with Trichoderma at 50 per cent recommended
NPK rate (3792.45 µg/g soil) and was on par with soil application of all cultures at 100 per cent and 50 per cent
recommended rate. In general microbial inoculations at 50 per cent recommended rate gave on par or significantly
higher results compared to uninoculated control at recommended NPK rate.