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Phosphorus and zinc are two important essential elements required by the plants
for various metabolic activities, functions and associated with membrane structure.
Continuous use of phosphatic fertilisers with less zinc, aggravates zinc shortage also
phosphorus applied will be accumulated in the soil leading to formation of zinc phosphate
complex that affect zinc translocation to various plant parts. There are contradictions
regarding phosphorus zinc interaction that is controlled by native P and Zn status.
In this context an investigation entitled “Transformation of zinc in soil and zinc
nutrition in lowland rice under different levels of phosphorus” was conducted. Two
separate experiments were carried out at Regional Agricultural Research Station, Pattambi.
In the first experiment, fractions of Zn under different P levels was studied in Long Term
Fertilizer Experiment (LTFE) with six treatments on rice in RBD with four replications.
The soil samples were taken after the paddy harvest of kharif 2020 and sequential
extraction of Zn (water soluble + extractable, organically bound Zn, amorphous
sesquioxide Zn and crystalline sesquioxide Zn) and P (sol-P, Al-P, Fe-P, sesquioxide
occluded P and Ca-P) were carried out. In the second experiment phosphorus and zinc
interactions was studied using pot culture experiment on rice in factorial CRD with 3
replications. Samples from different locations of Palakkad district having native P <12, 12-
24, >24 kg ha-1
and native Zn <1, 1-3, >3 mg kg-1 were collected. Sixteen treatment
combinations were applied with 4 levels of P (0, 25, 50,100 mg kg-1
) as KH2PO4 and 4
levels of Zn (0, 5, 10, 15 mg kg-1
) as ZnSO4.7H20 through solution for studying the nutrient
uptake and yield.
The results of fractionation study showed that continuous use of inorganic fertilisers
with organic manures in T5 (100% NPK + FYM) increased various Zn fractions except
amorphous sesquioxide Zn fraction which was highest in the control. Even though the
increase in P application increased different P fractions significantly higher content was
observed in 100% NPK+ FYM and these were proved to be beneficial towards increasing
different P fractions. But Ca-P fraction was more in the lime treated plot. Correlation study
concluded that most of the phosphorus fractions have negative impact on different zinc
fractions.
The results of the pot experiment elucidated that P and Zn application increased
number of productive tillers and thousand grain weight but higher zinc application
decreased plant height. Among different soils, soil type S2 (P > 24 kg ha-1
) registered
higher grain and straw yield, P in grain and straw, total P uptake of paddy, but Zn uptake
and Zn in grain and straw were more in soil type S3 (Zn > 3 mg kg-1
). Combined application
of 100 mg kg-1 P and 10 mg kg-1 Zn recorded higher grain (57.27 g pot-1
) and straw yield
(66.82 g pot-1
). Phosphorus application significantly increased the P content in grain and
straw but zinc addition had antagonistic effect on them and treatment combination of
P100Zn0 registered higher P content in grain (0.26%) and straw (0.214%). The Zn in grain
and straw significantly increased by the application of zinc, but phosphorus was having an
adverse effect and treatment combination of P0Zn15 registered higher Zn content in grain
(61.28 mg kg-1
) and straw (44.19 mg kg-1
). Total P and Zn uptake of paddy increased by
the application of both phosphorus and zinc with higher content obtained at P100Zn15 (28.47
mg pot-1
) and P50Zn10 (0.458 mg pot-1
) treatment combination. Correlation study concluded
that phosphorus and zinc application affected P and Zn uptake in high zinc containing soil
(S3) and high P soil (S3), respectively.
In future this work can be used to study the changes in various P and Zn fractions
under continuous crop removal, various management practices to mobilise fixed P in high
phosphorus containing soil and also to study Q/I relationship of both phosphorus and zinc.