Abstract:
The organic carbon (OC) status of three continuously cropped permanent manurial ex-
periments, under different cropping systems, over
a period of time is discussed in this pa-
per. The Old Permanent Manurial Experiment (OPME) was originally an irrigated ex-
periment started in 1909 and in 1937, converted
into a rainfed experiment (at this time
the cropping system was converted from two crops per year into a single crop per year).
The New Permanent Manurial
Experiment (NPME) was started in 1925 and was con-
ducted in an irrigated system with one set of treatments receiving 2 t ha
-1
of cattle manure
since its inception. These two experiments
were conducted with different nutrient input
management systems of single inorganic nutrients and their combinations. The effect of
these treatments on the OC status of the soil was evaluated. Along with these, the changes
in the OC status of another irrigated long term fertilization trial which has been con-
ducted since 1972 under the intensive cultivation system with three crops per year were
studied. The results obtained in the three experiments showed that there was a build up in
the OC status of the soil for the balanced app
lication of N, P, and K combined with an or-
ganic manure. Among the inorgan
ic fertilizer treatments, the combined application of all
the three major nutrients (N, P and K) resulte
d in a higher OC status, compared to the
application of single nutrients. This may be
due to better growth and a higher amount of
root residues added after the harvest of each crop, over a period of time. But, in both
OPME and NPME, there was a decline in the OC content after seven years and a build up
has happened in the last nine years. Under th
e intensive cropping system of cultivation,
the soil organic carbon build up occurred in all the treatments, including the unmanured
control, and was the maximum for the combin
ed application of inorganics and organics
(100% NPK + Farm Yard Manure (FYM)). The in
crease in OC is attributed to enhanced
root biomass over a period of 30 years.