ASSESSMENT OF POTASSIUM USE EFFICIENCY IN TRANSPLANTED RICE
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Date
2021
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Abstract
Potassium (K) the third major essential plant nutrient with diverse roles to play
in plant metabolism is required in large amount by crops and is the seventh most
abundant element in the earth crust. The total K reserves are generally large in most
soils but large portion of soil potassium (90 – 98%) remains chemically bound in the
crystal structure of minerals and thus unavailable or slowly available for plant uptake.
Based on availability to plants, potassium is categorized into four groups viz., water
soluble, exchangeable, non-exchangeable/fixed and lattice K. Potassium supply to crop
is a complex phenomenon involving relationships among various K fractions, potassium
fixation and release patterns in soil and quantity-intensity relationships. Moreover, the
net negative balance for K in current agriculture scenario is 69% which is very high as
compared N (19%) and P (12%). This vast difference is partly because of crop removal
where 1.5 times more K is removed than N and the application of potassium through
fertilizer is considerably lower than that of N or P. Keeping these points in view, a study
was carried out on “Assessment of Potassium use efficiency in transplanted rice” in
Nagaon district which is famously known as the 'Rice bowl of Assam'. A series of
laboratory analysis along with field experiments was carried out to assess the potassium
use efficiency in transplanted rice.
The soil of the experimental plot was analysed for salient characteristics such as
texture including mineralogy of sand, silt and clay, pH, EC, OC, CEC, available NPK
contents and various forms of K. An incubation study was conducted upon imposition
of ten different treatments for a period of 150 days to know the availability of various
forms of potassium in the soils at 20, 40, 60 and 90 days after incubation. After
completion of incubation period, soils from various treatments were taken for study the
release pattern of step K, constant rate K and cumulative K and fixation of potassium in
these soils. Along with the incubation study, a field study was also conducted
consecutively for two years with the same ten treatments in rice crop (var. Ranjit) with
three replications in RBD design. Post harvested soils were analyzed for various
physico-chemical characteristics and different K forms. Crop related data were recorded
to study the effect of potassium management on growth and yield of rice.
The texture of the soil of the experimental plot was clay loam with very strongly
acidic pH (= 4.92). Initial status of SOC (0.91%) was high in upper surface (0-15 cm)
and medium (0.65%) in lower surface (15-30cm), available N and P medium and K was
low in upper surface and low available N and K and medium P was found in lower
surface. X-ray diffraction study clearly indicates that clay fraction of this soil contains
minerals like clay mica, mixed-layer minerals, vermiculite, smectite and kaolinite. Sand
fraction is dominated by resistant minerals like quartz, zircon and weatherable minerals
like mica, feldspars and chlorite and silt fraction contains same minerals as that of sand
along with kaolinite. Initial water soluble K (WS-K), exchangeable K (Exch. K), non
exchangeable K (Non Exch. K), lattice K and total K were 9.20, 41.00, 1020.00 8856.00
and 9480.00 mg kg-1 respectively in the upper surface (0-15 cm) of the soil. In the lower
surface the values were 5.40, 28.40, 1454.00, 10222.00 and 10885.00 mg kg-1
respectively for WS-K, Exch. K, Non Exch-K, Lattice K and total K.
In incubation study, where biofertilizers (T2 and T4) and organic manures
(T9 and T10) were applied increase in WS-K was found with progression of the
incubation period and in field study, it was highest with 21.35 mg kg-1 in the plot
receiving T10 = INM Package (50% NP + Full K + 5t/ha Vermicompost) and was the
lowest 8.17 mg kg-1 in the control plot. A perceptibly significant increasing trend of
Exch-K was found, irrespective of the nutrient source except control treatment in
incubated soil. In field condition, Exch. K corresponded to the amount of chemical K
fertilizer applied and also to the INM package including microbial consortia and highest
amount was observed in INM Package (50% NP + Full K + 5t/ha Vermicompost).
Exchangeable K was found to be highly and significantly correlated with available K
(r= 0.993**), non-exchangeable K (r=0.602*), total K (r=0.826*) and lattice K (r=0.
769**). With the increase in incubation time the non exch. K decreased in the
treatments T2 = Microbial consortia (Azospirillum + PSB + KSB) @ 4 kg/ha, T4 =
100% RDF + KSB @ 4 kg/ha and T6 = Potassium nano-fertilizer @ 100 ml/1.2 L.
Lower values of non-exchangeable K were recorded in all the treatments with different
levels of potassium as compared to initial (1.020 mg kg-1) in the field experiment
maximum being found in 100% RDF application. The increase of non exchangeable K
in the control treatment with concurrent decrease in exchangeable K indicates the
existence of dynamic equilibrium among different forms of potassium. Lattice K
content of the treatments varied differently with different treatments but the changes
were statistically insignificant in all the treatments in 40 DAI (Days after incubation) to
60 DAI and the changes was statistically at par in 60 to 90 DAI. Maximum amount of
lattice was recorded in plot receiving 100% K fertilizer along with N & P fertilizers and
INM components while lowest was recorded in plots which did not receive any fertilizer
in field condition. The lattice K was significantly and positively correlated with
available K (r= 0.791*), water soluble K (r=0.801**), exchangeable K (r=0.769*), nonexchangeable
K (r=0.697*) and total K (r=0.865**). Increased levels of fertilizers
brought about significant increase in total K content i.e. in the treatments where
application of full dose of recommended fertilizers were done the total K tended to
increase. In field condition, treatments where 100% K fertilizers were applied alone or
in combination with INM components for 2 years continuously observed an increase in
total K, highest being observed in T10 = 100% NP + Full K + 5 ton/ha Vermicompost)
(11015.50 mg kg-1). Highly significant positive correlation values among various forms
of K implied the existence of dynamic equilibrium. The amount of K released in
successive extraction with boiling 1N HNO3 decreased step wisely in all treatments and
reached to a constant level at 8th number of extraction. Reverse was happened in
cumulative K. K release was higher in INM packages than plots received either organic
or inorganic fertilizer alone. Cumulative K release was significantly correlated to lattice
K (r=0.881**) suggesting that 1.0 mol L−1 HNO3 chiefly extracted K from nonexchangeable
K pool in the soil. The amounts of step K of the treated soils ranged
within a limit of 1837.0 to 3529.0 mg kg-1, which is high and thereby expected to be
nonresponsive to K fertilization for a longer duration to the growing crops. The absolute
amount of K fixed in soil progressively increased while percent K fixation decreased
with increase in level of added K in all the treatments. Least percent K fixation was
observed in T10 and the maximum in control. As this soil contains minerals like mica,
vermiculite and smectite in clay fraction so K fixation is also high in this soil. Grain and
straw yield was significantly affected by various treatments with the highest yield
(= 56.22 q ha-1) in T10 which received 100% NP + Full K + 5 ton /ha vermicompost and
the lowest in control. Yield was always better in INM package plots. Grain yield
exhibited significant positive correlation with NPK uptake (r = 0.891**, 0.946** and
0.970**), water soluble K (r = 0.785**) exchangeable K (r = 0.897**) and available K
(0.867**), suggesting their availability to rice crop. The highest potassium use
efficiency (PUE) of 51.96% was found in the plot receiving 50% NP + Full K + 5 t/ha
Vermicompost (T10) while the lowest of 40.49% in the plot receiving Potassium nanofertilizer
@ 100 ml/1.2 L of water (T6) treatment.
The information generated in the present study related to the status and
distribution of different forms of potassium and its availability, releasing behavior and
fixation evaluated through plant utilizable non-exchangeable K i.e. step K and constant
rate K gave a general idea about the availability of K under the influences of varying
doses of applied K and INM packages.
Finally it can be concluded that INM Packages were found to be better for
maintaining available K status, K release from none available pools and low K fixation
in the soil and the resultant crop yield compared to inorganic treatments.