Mitteilungen der Gesellschaft für Pflanzenbauwissenschaften Band 23

Mitt. Ges. Pflanzenbauwiss. 23: 210 (2011)
Microbial Activities Influencing Growth of Maize and P Uptake
P. B. S. Bhadoria
Agricultural and Food Engineering Department, IIT Kharagpur, India. E-Mail: pbsb@agfe.iitkgp.ernet.in
Objectives
This study was aimed at treatment of field soil with a fungicide (Benomyl) to reduce
arbuscular mycorrhiza (AM) content and subsequent root inoculation capacity of soil;
with observation of plant growth parameters and P uptake of maize. Benomyl
treatment was combined with varying levels of P fertilizer applications to study the
relationship of P stress and abundance with mycorrhizal symbiosis. Soil phosphatase
activity was also monitored to study the extent of microbial mobilization of soil
organic P.
Results and Discussion
Soil from Benomyl – treated plots had almost half the inoculation capacity,
represented by AM spore content per 100 g soil, as compared to untreated plots.
Consequently, root inoculation levels and shoot dry weights were lower in fungicide –
treated plots than in untreated plots. Inoculation by AM additionally decreased due to
higher levels of P application. A trend of overall decreased spore population in both
years were also observed. On untreated soil, AM colonized about 40% of roots at P-0
application, 30% at P-50 and 10% at P-400. These results influenced further
observations including total P uptake efficiency. It is inferred that plants actively
discourage mycorrhizal symbiosis when P is abundant. However, high P levels could
never compensate for the loss of shoot dry weight resulting due to Benomyl
application; which might be due to toxic effects of Benomyl on plant roots.
Soil phosphatase activity was predominantly by acid phosphatases – as expected
for the acid lateritic Kharagpur soil. Benomyl application insignificantly decreased soil
phosphatase activity. The conclusion is that most of the phosphatase enzymes are
prokaryotic in origin and not fungal. Phosphatase activity decreased corresponding to
rising P application levels. It is thus evident that when soil available P is scarce,
microorganisms turn towards organic P content of soil. These findings signify the
potential of biofertilizers as substitute for costly phosphate fertilizers.