Status of Soil Phosphorus in Context with Phosphate Solubilizing Microorganisms in Different Agricultural Amendments in Kachchh, Gujarat, Western India

Aims: The study was carried out to assess the soil Phosphorus (P) status (available and total) in farms with organic amendments and compared the results to those which practice an integrated amendment system. In conjugation to P status of soil, the soil microbial flora in terms of total microbial count and Phosphate Solubilizing Microorganisms (PSM) was studied. The soil chemical parameters such as pH, electrical conductivity (EC), available nitrogen and potassium were also evaluated.
Study Design: The sites selected for study comprised 8 fields of maize (Zea mays) on two farms (4 fields for A1 and 4 fields for A2).The organic amendment (A1) included farm yard compost (FYC) applied at the rate of 4 ton/Ha, as a basal dose which was applied before sowing. In these fields, after sowing, a five day fermented concoction of cow dung, jaggery, soil, cow urine and gram flour was applied with watering twice, at seven days interval from sowing. In the integrated amendment fields (A2) FYM (farm yard manure) at the rate of 1 ton/Ha) was applied as a basal dose before sowing and DAP (di ammonium phosphate) (40 Kg/Ha) + urea (60 Kg/Ha) was applied at 15-20 days after sowing. The study was carried out for two seasons of crops in the year of 2012, February-May and July-Oct , at three different phases of crop growth (15, 45 and 60 days after sowing).
Place of Study: Different agricultural fields in semi-arid zone of Kachchh, Western India (23º13’48.00’’N, 69º42’35.06’’E) were chosen.
Methodology: Samples were collected from the rhizosphere of the crop upto the depth of 12 cm using standard soil sampling procedure. Four samples were collected per hectare and pooled to form one composite sample. Samples were analyzed in triplicates. Soil samples were divided into two parts, one part of the sample was air dried and sieved through a 2 mm sieve and analyzed for chemical characteristics and another part of soil sample was stored at 4°C for microbiological analysis.
Results: The results demonstrated that although this zone of western India has good amounts of total P, the available P status was statistically significant (P ≤ 0.05, 0.01, 0.001) in organic amended fields than integrated fields. The organic amendments were able to maintain a good microbial count (total as well as PSM) than integrated fields. This confirms that efficient nutrient management in cropping systems could lead to build up of microbial population especially PSM over time which in turn solubilize the fixed P and make it available to plants.
Conclusion: Phosphorous is an important element after nitrogen as a mineral nutrient in terms of quantitative plant requirement. Although abundant in soils, in both organic and inorganic forms, its availability is restricted as it occurs mostly in insoluble forms. PSM play a vital role through solubilisation and mineralization of fixed P. The present study focused on highlighting the beneficial effects of organic farming practices over integrated amendments, especially in the semi-arid tropics.