Studies on Phosphorus Status of Vertisols and Response of Bt Cotton to Phosphatic Fertilizers in Northern Transitional Zone of Karnataka
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Date
2013
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UAS, Dharwad
Abstract
An investigation was carried out to study the available phosphorus status, distribution
of different fractions of phosphorus and response of Bt cotton to applied phosphatic fertilizers
in Vertisols (0-30 cm) having P status below and above 33.50 kg P2O5 per ha in the farmer’s
fields of cluster of villages of Dharwad district viz., Sulla, Byahatti, Kusugal, Hebsur,
Ingalalli, Kiresur, Rottigwad, Siraguppi, Bandiwad and Dattur. Soils were alkaline (7.10 to
8.94), non saline (0.06 to 0.40 dS/m), calcareous (55 to 245 g/kg), low to medium in available
nitrogen (94 to 344 kg/ha), phosphorus (15.5 to 39.50 kg/ha) and sulphur (10.20 to 31.5
kg/ha) and medium to high in potassium (310 to 635 kg/ha).
Among the different inorganic forms of P, Ca-P was the dominant fraction which
ranged from 40.40 to 63.56 ppm and contributed about 9.57 to 24.41 per cent to total–P
whereas, saloid-P was the smallest fraction which ranged from 1.30 to 3.95 ppm contributing
about 0.39 to 1.05 per cent to total-P. The dominance of different P fractions in these soils
followed the order: Ca-P > Red-P > Al-P > Occl-P > Fe-P > Saloid-P. Ca-P had positive and
significant correlation with pH (r=0.928**), EC (r= 0.371**) and calcium carbonate
(r=0.969**). Saloid-P had positive and significant correlation with organic carbon and all the
P forms except Ca-P.
Average P concentration in petiole and whole plant, total P uptake and yield of Bt
cotton obtained in the farmer’s fields of different villages followed the order Bandiwad >
Rottigwad > Kusugal > Hebsur > Dattur > Byahatti > Kiresur > Sulla > Ingalalli > Siraguppi.
Response of Bt cotton (988 kg/ha) to applied phosphatic fertilizer was poor in Vertisols
having P2O5 > 33.50 kg ha-1. However, a good yield (1090 kg/ha) response to applied
fertilizers was observed in low P status soils.