Saturday, 15 July 2006

Studies on VA-Mycorrhizal Fungi (VAM ) as a Potential Biofertilizer in an Acid Alfisol of Northwestern Himalayas.

V.K. Suri, Anil K. Choudhary, Girish Chander, and T.S. Verma. CSK HP Ag Univ, Dept of Soil Science, Holta, Opposite HP Housing Board, Palampur, India

In acid soils of Himachal Pradesh (India), phosphorus availability is much limited because of quick fixation of most of the applied soluble P as insoluble phosphate complexes by way of reaction with soil Al and Fe ions. Under such situations, use of VAM may reverse the above process thereby enhancing the availability and uptake of phosphorus by field crops thus economizing the fertilizer phosphorus dose to some extent. In above background, experiments aimed at the development of soil test based and yield target oriented fertilizer recommendations for rainfed maize-wheat and soybean-wheat cropping systems, consisting of combined application of fertilizer NPK, FYM and VAM, were carried out under both controlled as well as field conditions. At first instance, VAM resource survey aimed at screening out efficient local VAM strains was carried out through mycorrhizal analysis of 600 soil samples collected from various crop rhizospheres in wet temperate zone of Himachal Pradesh (India), located in North-Western Himalayas. The crops covered were maize, wheat, oats, berseem, soybean, Frenchbean, onion, potato, garlic, chilies, citrus, apple, pear, peach etc. Maximum spore count(110-185 spores/250 g soil) was recorded under vegetable field soils. In VAM root infectivity studies conducted in green house with selected soils as VAM inoculants, highest infectivity in maize(38%)and soybean (40%) was noticed with use of VAM inoculant from vegetable fields. It is concluded from above that vegetable field soil may be the best inoculant for mycorrhizal biofertilizer. In most soils/crops, Glomus spp. of VAM was found to be predominant. Field experiments(2001-2004)aimed at evolution of VAM biotechnology, comprised of 12 treatments(laid out in RBD with 3 replications) viz. combinations of 3 VAM cultures(TERI,IARI & local) with 2 levels of phosphorus (50 & 75 % of recommended), each culture alone,100 % recommended P2O5 as SSP, farmers' practice and control. Relevant soil test crop response based fertilizer models were used to calculate nutrient (NPK) doses for targets of 25 q in soybean and 30 each in case of maize and wheat per hectare. In above experiments, integrated use of either of the 3 VAM culture(s) and 75% of soil test crop response (STCR) concept/yield target concept based recommended P2O5 dose as single super phosphate (SSP) was almost equal to 100% P2O5 dose as SSP in respect of grain/seed yield and various other supporting parameters. It can be inferred from above that the use of VAM or mycorrhizal biofertilizer can economize soil test based fertilizer phosphorus dose by 25 per cent under the above situation. In above experiments, soil available NPK status and soil organic carbon levels were also at par with that under 100% P2O5 dose as SSP. It is inferred from above study that VAM has the potential to improve crop productivity and soil fertility in P-deficient acid soils. Keywords: maize, wheat, soybean, yield target concept, cropping system, VAM, vesicular arbuscular mycorrhizae, biofertilizer, alfisol.

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