Abstract:
Field experiments conducted for a period of seven years to study the effect of
continuous application of fertilizer nutrients on the long term productivity of a rice based
cropping system revealed that nitrogen application increased grain yield in all the seasons
for a period of seven years. Both the physical and economic optimum dose of N decreased
@ 4.06 and 3.7% per season, respectively. Nitrogen application @ zero and 120 kg/ha per
season continuously over a period of five years, decreased the grain yield @ 1.47 and 1.28
g/ha/year, respectively. But application of N @ 40 kg/ha during the same period increased
grain yield 6 1.22 q/ha/year. The productivity of plots applied with N @ 80 kg/ha remained
stable. The study clearly revealed the possibility of skipping P for four years and K for
seven years in soils containing medium amounts of these nutrients. Application of N at
optimum dose is important to maintain the long term productivity of a rice based cropping
system involving rice-rice-fallow.
