Not AvailableIntegrated use of inorganic fertilizer N and well decomposed cattle manure (CM) or 30–35 days old Parthenium (Parthenium hysterophorus
L.), a weed grown off site as green manure (GM) under repeated applications of fertilizer P and urea N for eight years in
a rice (Oriza sativa L.)–wheat (Triticum estivum L.) sequence was studied on transformation of fertilizer P applied to soil at the
National Research Center for Weed Science, Jabalpur, India. Based on the results, it appeared that, repeated applications of
52 kg super-phosphate P resulted in a marked increase in Olsen P linearly with time. Conjunctive use of urea fertilizer N with
organic manure resulted in a larger increase in Olsen P in the Vertisol. Studies further revealed that the greater accumulation of
fertilizer P applied in excess to crop removal occurred in inorganic P in the plots receiving only fertilizer N. However, plots receiving
fertilizer N along with organic manures led to P accumulation predominantly in organic forms. The study suggests that these two
pools of P acted as a sink when fertilizer P was applied in excess to crop removal and are bio-chemically active. The Olsen P status
after 8 cycles of rice–wheat crops revealed that the average amount of fertilizer P required after adjusting for crop uptake to increase
Olsen P by 1 mg kg 1 soil was 7.2 kg P ha 1 in the plots receiving only fertilizer N. Whereas, application of 5 t FYM or 6 t GM
reduced it to 4.6 kg P ha 1. The plots receiving manure always maintained a greater concentration of Olsen P. The application of
CM or GM with fertilizer N enriched short-term inorganic P as well as long-term organic P fertility. After eight years, larger concentrations
of organic P in the subsurface layer (16–30 cm), compared to initial values, indicates downward movement of P in organic forms.Not Availabl