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INVESTIGATIONS ON UTILIZATION OF ACCUMULATED HIGH P OF SOILS TO ECONOMIZE ITS FERTILIZATION FOR RICE CROP IN SELECTED SOILS

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Title INVESTIGATIONS ON UTILIZATION OF ACCUMULATED HIGH P OF SOILS TO ECONOMIZE ITS FERTILIZATION FOR RICE CROP IN SELECTED SOILS
 
Creator RAMESH BABU, L
 
Contributor SURENDRA BABU, P
 
Subject INVESTIGATIONS, UTILIZATION, ACCUMULATED, HIGH P, SOILS, ECONOMIZE, FERTILIZATION, RICE, CROP, SELECTED, SOILS
 
Description Use of supra-optimal and/or indiscriminate amounts of fertilizer P is
leading to accumulation of available P in intensively cultivated areas. In a
study carried out at Radiotracer Laboratory, ANGRAU attempted to
investigate to utilize this accumulated P employing 30 soils belonging to
Vertisol order and with the help of 32P radioisotope. Possibility of reducing
the P fertilization to rice in high P accumulated soils from currently
recommended dose of P, determination of P level requirements to rice in high
P soils, establishment of critical soil test phosphorus values/ranges
corresponding to P requirements, use of low C:P ratio material to augment the
supply of accumulated soil P to crop and evaluation of three different soil P
extractants in high P soils were the objectives under this investigation.
Five levels of P (0, 12.5, 25, 37.5 and 50 kg P2O5 ha-1) corresponding
to 0, 25, 50, 75 and 100% RDP were used to determine soil test values and
corresponding fertilizer requirements to rice. Six soils were separately
employed to study the P contribution from high P soils to rice crop upon using
rice straw, a low C:P material (LCPM) at a constant rate of 5 t ha-1 and with
the same 5 levels of P employed in experiment I. P in experiment I was
tagged with 32P isotope.
The investigation revealed that any attempt to make use of
accumulated high P in soils to reduce currently recommended dose of P
fertilizer to rice should be made cautiously as higher were the yields upto an
initial STPV of 100 kg P2O5 ha-1, beyond which there is a negative response to
applied P. The results indicated that it is possible to save fertilizer from the
currently recommended dose of P even upto 100% in high P accumulated soils
without any compromise in rice yield. The findings related to these aspects
are given below: STPV by Olsen
extractant
(kg P2O5 ha-1)
Optimum P
fertilizer
requirement to rice
within current
RDP (kg P2O5 ha-1)
Best optimum yield
possible with the
recommended P
(mg pot-1)
Percent increase in
yield over that of
soil with STPV
< 50 kg P2O5
100 0 41.0 47
Thus, higher content of available P in P accumulated soils was found to
be beneficial upto an STPV of 100 kg P2O5 ha-1 with increase in yield of rice by
47 per cent when compared with what is possible at STPV < 50 kg P2O5 ha-1.
The ratio of P extraction by Olsen, AB-DTPA and Mehlich-3 was
3.5:1:3.3 and they were found to have good correlations among themselves
(Olsen Vs AB-DTPA r=0.90**, Olsen Vs Mehlich-3 r=0.63** and AB-DTPA
Vs Mehlich-3 r=0.54**) and with Bray’s per cent yield (r=0.67**, r=0.61**
and r=0.52**, respectively). Mehlich-3 extractant was found to have
extracted incorrect amount of soil available P and only 77 per cent of STPVs
could be accommodated in scattered diagram of Cate and Nelson. The values
of STPV by AB-DTPA were low and a small error in analysis can make much
difference for categorizing the soils into different groups and thus Olsen
extractant continues to be the best one for these soils. The critical soil test
phosphorus value (CSTPV) established in high P soils for growing rice was
found to be 70, 20 and 60 kg P2O5 ha-1 by Olsen AB-DTPA and Mehlich-3,
respectively.
Use of rice straw as a low C:P ratio material (LCPM) to utilize
accumulated high P of soils helped in increasing the per cent P derived from
soil (%Pdfs) in rice plants. It was in the range of 92.9 to 79.9 per cent in high
P soils when compared with 88.8 to 77.2 per cent in rice grown on medium P
soils. Increased application of P decreased the per cent Pdfs. The mean per
cent Pdfs in rice plants was lower in medium P group (77.2 per cent) when
compared with that of high P group (84.7 per cent). Use of LCPM in high P
soil was beneficial but could not be quantified for understanding fertilizer
saving as high P in soil resulted in better yields.
The mean per cent P utilization by rice plants was higher or almost
similar with the increasing levels of initial STPVs. It was 22.1 per cent in a
medium P soil with STPV of 33.5 kg P2O5 ha-1 and increased to 30.6 per cent
in plants on a soil having 84.1 kg P2O5 ha-1. But rice plants grown on soils
with highest STPV (158 kg P2O5 ha-1) used in this experiment were found to
contain 26.1 per cent.
The P utilization by rice plants in medium P soils (24 per cent) was
lower than that of high P soils (28.3 per cent) and indicated that applied P was
more efficiently utilized by rice even in high P soils. These results indicated
that plants prefer to take up easily available P from fresh source as and when
available without drawing from the pools already accumulated until a level of
STPV is reached that is to be determined.
Thus, a trade off has to be made while using the accumulated P between
level of yields required within maximum possible limit and the critical level of
STPV to avoid loss from soil surface to water bodies that causes pollution under
natural environmental conditions, whenever such situation occurs.
These experimental findings obtained in this investigation need to be
verified with careful planning under field conditions.
 
Date 2016-08-20T12:10:06Z
2016-08-20T12:10:06Z
2003
 
Type Thesis
 
Identifier ACHARYA N.G. AGRICULTURAL UNIVERSITY RAJENDRA NAGAR, HYDERABAD - 500 03 0
http://krishikosh.egranth.ac.in/handle/1/73150
 
Language en
 
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