STUDIES ON AVAILABLE POTASSIUM IN SOILS OF DIFFERENT CROPPING SYSTEMS IN KURNOOL DISTRICT
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Date
2016
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Acharya N.G. Ranga Agricultural University
Abstract
The present investigation entitled “Studies on available potassium in
soils of different cropping systems in Kurnool district” was conducted with
30 black and red soils belonging to major cropping systems ( rice-rice, maizemaize,
rice-maize/mustard, fallow-bengal gram and groundnut-groundnut) to
study the salient characteristics, different forms of K, potassium release
parameters by 1N HNO3 and Q/I parameters of K. A pot culture experiment was
conducted with above 30 soil samples to know the response of maize crop to
different levels of potassium and to evaluate the relative efficiency of extractants
with reference to dry matter yield and uptake of potassium. Incubation studies
were also carried out to know the potassium release pattern under laboratory
conditions.
The texture of the soils ranged from sandy loam to clay. The pH of the
soils ranged from 6.9 (neutral) to 8.4 (slightly alkaline). The EC ranged from
0.10 to 0.69 dS m-1 indicating that soils were non saline. The organic carbon
content was low (0.21 percent) to medium (0.59 percent). The soils were low to
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medium in available N with the range of 159 to 307 kg ha-1, whereas available
P was high in all villages which were in the range of 68 to 169 kg P2O5 ha-1 and
medium to high in available K with a range of 154 to 2088 kg K2O ha-1.The
Cation Exchange Capacity of the soils varied between 13.03 c mol (p+) kg-1
and 29.91 c mol (p+) kg-1. Base saturation of the soils varied from 62.73 to
88.13 per cent indicating that most of soils were medium fertile in nature.
Mean values of all forms of K in investigated soils were highest in maizemaize
cropping system and lowest in groundnut-groundnut cropping system.
Black soils recorded higher values of all forms of potassium than red soils. The
forms of potassium in the investigated soils was in the order of fixed K > nonexchangeable
K > available K> exchangeable K > water soluble K. Among the
different soil properties pH , organic carbon, CEC , silt and clay percent showed
positive correlation with all forms of potassium indicating that these soil
properties are more influenced by the existence of different forms of potassium.
Extraction of available K by various extractants followed the trend: 1N
HNO3> Mehilich-3 > 1 N NH4OAc > 0.01M CaCl2 > Distilled water. 1N HNO3
extracted the exchangeable, non-exchangeable and also the lattice K to some
extent. All these potassium extractants were positively correlated with each
other, though these extractants removed different quantities of potassium which
indicates that these methods can be used for assessment of availability of
potassium in present investigated soils and also amount of potassium extracted
were comparable.
In this study, potassium release parameters such as step-K and
cumulative-K were the highest in maize-maize cropping system and lowest in
groundnut-groundnut cropping system. However, constant rate K was high in
rice-rice cropping system. The black soils recorded higher cumulative, step and
constant rate K than red soils. All investigated soils recorded less cumulative-K
except two soils under present investigation. Lower cumulative K and
continuous cropping would lead to depletion of soil K reserves and result in K
deficiency.
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The K release parameters were positively correlated with the clay
fraction of soil indicating that potassium was mainly extracted from the clay
fraction in soil.
Mean ARe
K values were highest in groundnut-groundnut cropping
system and lowest in fallow-bengal gram cropping system. Mean labile
potassium of the investigated soils was higher in maize-maize cropping system
whereas mean value of PBCK was higher in fallow-bengal gram cropping
system. Lower mean values of labile potassium and PBCK were recorded in
groundnut-groundnut cropping system. Mean ARe
K values were higher in red
soils than black soils where as labile potassium and PBCK were higher in black
soils than red soils. PBCK and constant rate of-K were low in all investigated
soils indicating low K power supply hence, judicious and frequent application
of potassic fertilizers is required to prevent leaching losses for better crop
production.
Dry matter, K content and K uptake were significantly increased with
increase in each level of potassium from 0 to 90 kg K2O ha-1. There was
abundant increase in above parameters from no K fertilizer application to 30 kg
K2O ha-1 and the increase was gradual with increase in each level of fertilizer
from 30 to 90 kg K2O ha-1. All the above parameters showed significant
difference with soil K status, K levels and their interaction. Percent increase in
K content at 90 kg K2O ha-1 over control in Srinagaram soils was 21 percent
where as in Balapalapalli soils was 59 percent. It indicates that soils having
high initial K status show less response than soils having low initial K status.
These results clearly indicated that even though, soils are having high initial K
status, external application is needed, especially in high K requirement crops.
In incubation studies, irrespective of varying initial soil-K status, water
soluble, available and fixed potassium consistently increased with increase in
level of potassium application over control. Water soluble potassium and
available potassium content increased initially with increasing levels of
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potassium application, later on decreased gradually up to 120 DAI. Unlike
water soluble and available form, fixed potassium gradually increased up to
120 DAI in fertilizer treatments whereas mean fixed form of K in control
decreased gradually from 0 to 120 DAI, indicating the existence of dynamic
equilibrium among themselves so that non exchangeable form decreases and it
becomes available for plant.
Among the 5 extractants tried, 1N HNO3 showed maximum positive
and significant correlation with yield (0.913**) content (0.872**) and uptake
(0.957**) of potassium of maize crop followed by N.N. NH4OAc and Mehilich-
3. Maximum and positive correlation of plant parameters was found with fixed
K. Minimum correlation coefficient with water soluble K and plant parameters.
Thus, it could be concluded that fixed K should be taken into consideration
while giving fertilizer recommendation.
K availability indices i.e. different forms of K, potassium releasing
parameters, step-K, cumulative-K and labile potassium were the highest in
maize-maize cropping system than fallow-bengal gram cropping system even
though fallow-bengal cropping system was grown in black soils which might
be due to lack of K fertilization which results in K depletion over period of
time. These K availability indices were the lowest in groundnut-groundnut
cropping system. Hence, these soils require judicious and frequent application
of potassic fertilizers to prevent leaching losses for better crop production.
Description
D5383
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