Abstract:
A study was conducted at College of Horticulture during the period
1993-95 so as to assess the suitability of Tunisia rockphosphate for direct
application in acid rice soils of Kerala as a source of P compared with single
superphosphate (SSP) diammonium phosphate (DAP) and Mussoorie
rockphosphate (MRP). In addition to above sources a control treatment (with no P
fertilizer) and another treatment with SSP of the rate of 45 kg P2O5 ha-1) given twice
(conventional practice) were also included. The P release from all the sources was
monitored with an incubation experiment. In order to evaluate the residual effect of
fertilizers two continuous pot culture experiments were undertaken using Triveni
variety of rice. The acids soils of Kerala namely Kuttanad alluvium and laterites
were used for the study.
The soils showed variation in pH with submergence irrespective of the
treatments. The different nutrients like N, K, Ca, Mg were higher in Kuttanad soil
compared to laterite soil and was found to decrease with period of incubation. The
available phosphorus content gradually increased with period of incubation and
reached a peak .fit 60 to 90 days for water soluble phosphates and 90th to 120th day
for rockphosphates. Comparing the two extractants, Mathew's triacid extracted
more available P than that of Bray solution in both soil types. In general, Kuttanad
alluvium recorded higher content of available nutrient as compared to laterite. The
extent of fixation of P was higher in Kuttanad soil with Fe-P as dominant fraction
while in laterite soil it was Al-P which was dominated.
While evaluating pot culture experiment the different nutrients showed a
decrease in soil and increase in uptake with the advancement of crop. Of the
different soils Kuttanad alluvium registered a higher yield compared to laterite soil.
It was found that TRP registered a comparable uptake of phosphorus and gave a
comparable yield of grain and straw with other sources in laterite and Kuttanad
alluvium. The residual effectiveness of rockphosphate was found to be higher than
that of water soluble sources and TRP gave the highest. Of the two different type of
soils Kuttanad soil showed a higher residual effectivenes and resulted in higher
yield for 2nd crop while laterite soil registered a lower yield.
