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2015 - 201922020 - 20211
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Subject: Soil Sciences × Author: KAU × Start date: 2012 ×
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    ThesisItemOpen Access
    Transformation of zinc in soil and zinc nutrition in lowland rice under different levels of Phosphorus
    (Kerala Agricultural University, 2021) Najiya Rinthas, K; KAU; Moossa, P P
    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 24 kg ha-1 and native Zn 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.
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    ThesisItemOpen Access
    Dynamics and interaction of zinc and boron with phosphorus in ultisol
    (Department of soil science and Agricultural chemistry, College of Horticulture,Vellanikkara, 2015) Semsheer, M; KAU; Sureshkumar, P
    The recent soil fertility assessment of the entire state has revealed that more than 60% of the soils in the state are having high P status due to continuous application of P fertilizers like factomphos and bone meal. It was also established that 15% of the soils are deficient in zinc and about 60% of soils are deficient in boron. Antagonistic interaction of P with zinc has already been well established. However studies on interaction of P with boron are limited. Thepresent study was undertaken in the above background in the Dept. of Soil Science and Agricultural Chemistry during the period from 2013-2015 to understand the chemistry, dynamics and bioavailability of zinc and boron with respect to the P status of the soil, which in turn will help in modifying the fertilizer prescription in terms of quantity and method of application of these nutrients. In order to achieve the objective of elucidating the dynamics of Zn and B as influenced by P status in lateritic soils and to optimize the level of P for balanced nutrition of cowpea with respect to Zn and B, 18 lateritic soil samples (Ultisol), six each coming under low, medium and high P status were identified from an initial 100 soil samples and characterized. A potculture experiment with cowpea as a test crop was conducted in three soils, one each with low, medium and high average P status. Soil and plant samples were collected at flowering and at harvesting stages and analyzedfor nutrient content. The distribution of fractions of inorganic P in the three soils showed that Fe bound P was the dominant fraction contributing to more than 50% of the total inorganic P. The soluble P fraction was about 6% in all the three soils. Fe and Al-P were the main fractions contributing to the available pool initially.Among the fractionsof boron, readily soluble boron recorded the lowest, where as the contribution of residual boron was the highest. Available P status in soils with low and medium P increased due to the application of P while it decreased in soil with high P. The soil with high P soil showed that the application of phosphorus lead to the fixation of phosphorus in to insoluble forms whereas, if P was not applied there was solubilisation of Fe-P and Al- P resulting in increased its availability. Plant adsorbed P from soluble P led to its depletion at the end of vegetative phase. Applied P got transformed into Fe-P and Al- P initially, which along with native occluded P got transformed to calcium bound P which is contributing to the available pool at later stages. Application of Zn was found to reduce Al-P and Fe-P due to the formation of insoluble zinc phosphate. Application of Zn and B reduced the Ca-P, probably due to the formation of zinc phosphate and Calcium borate. In case of zinc fractions, water soluble + exchangeable fraction and organic matter occluded zinc was directly contributing to the available pool. The other Zn fractions except amorphous iron oxide occluded zinc were contributing to the available pool indirectly through water soluble + exchangeable fraction. Application of P reduced the water soluble + exchangeable zinc fraction where as the application of boron enhanced the transformation of zinc into this fraction especially when boron was applied without P. Application of P resulted in adsorption of zinc into specifically adsorbed zinc. With respect to boron fractions, readily soluble boron and oxide bound boron were directly contributing to the available pool where as binding of boron with organic matter as well as its transformation to residual boron reduced boron availability. All the fractions of boron were contributing to available pool indirectly through readily soluble fraction of boron. Application of phosphorus was found to reduce the readily soluble boron due to anion competition. The applied boron either remained in the soluble form or getting transformed to specifically adsorbed, oxide bound, organic matter bund boron. Boron application along with P reduced the readily soluble boron. Application of Zn increased the Zn content in plant. However, the application of P with and without B reduced the Zn content in plants. Application of P and Zn reduced the boron content in plants and application of boron with and without phosphorus recorded the highest boron content. The highest grain yield was recorded in soil with medium P, while the high P status in soil either due to native P or due to applied P reduced the yield resulting from induced lower uptake of zinc and boron. Thus, at high levels of P, enough quantities of soluble zinc should be assured, over and above the quantities of this element precipitated as zinc phosphate, both by optimizing the pH and applying enough quantities of Zn. Similarly H3BO3 and H2BO3 - ions should be enough to overcome competition from H2PO4 - ion at root surface.
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    ThesisItemOpen Access
    Characterisation of soil and water of Palakkad eastern plains in relation to growth and nitrogenase content of Azolla spp.
    (Department of soil science and agricultural chemistry, College of horticulture,Vellanikara, 2015) Bhavyasree, K T; KAU; Jayasree Sankar, S
    A study intended for “Characterization of soil and water of Palakkad eastern plains in relation to growth and nitrogenase content of Azolla spp.” was undertaken in the Department of Soil Science &Agricultural Chemistry, College of Horticulture, KAU, Vellanikkara during 2013-2015. The objectives of the study were to conduct a survey of Azolla spp. in the rice growing tracts of Palakkad eastern plains and to identify soil and water quality parameters congenial for the growth and nitrogenase content of Azolla spp. The preliminary survey conducted in the four block panchayaths of Palakkad eastern plains to identify the prevalence of Azolla revealed two blocks viz. Chittoor and Kollengode to be positive with respect to Azolla and hence, further study was restricted to the grama panchayaths of these blocks. Characterization of soil and water was done in both Azolla growing and non-growing regions. Composition of Azolla collected from different locations was also determined. In order to ascertain the nitrogenase enzyme activity, samples of Azolla collected from five different locations were subjected to Acetylene Reduction Assay (ARA). Among the soil parameters, significant difference was noticed between Azolla growing and non-growing locations with respect to pH , EC, organic carbon, available N, P , total Fe, Mn and Zn in contrast to potassium and copper which did not show any pronounced variation. Soil pH, EC, available P, total Fe, Mn and Zn were comparatively lower in Azolla growing regions. However, available nitrogen in soil was more in Azolla growing locations. Heavy metals like Cd, Cr, Ni and Pb were below the detectable limits in soil. Analysis on flood water quality showed significant effect in the Azolla growing regions on parameters like pH, temperature and dissolved oxygen, Fe, Mn, Zn and Cu. Soil analysis data revealed the pH, EC, soluble Fe, Mn, Zn and Cu to be lower under Azolla growing conditions. Heavy metals like Cd, Cr, Ni and Pb were below the detectable limits. Presence of Azolla decreased the flood water temperature but increased the dissolved oxygen content. On comparison, the composition of Azolla revealed a prominent and significant correlation with location on its content of carbon, nitrogen, phosphorus, potassium and also the C/N ratio. Moisture content varied from 94 to 95 per cent, variation in carbon and nitrogen content was from 22.9 to 39.5 per cent and 2 to 4 per cent respectively among the locations studied. The C/N ratio ranged from 9 to 14. Crude protein content of Azolla registered values between 16 and 22 per cent. The content of phosphorus ranged between 0.20 and 0.23 per cent whereas that of potassium was in the range of 1.2 to 1.5 per cent. Correlation worked out between soil parameters and composition of Azolla disclosed a significant positive effect of soil P on the nitrogen, crude protein and phosphorus content of Azolla. However, soil P was negatively correlated with the C/N ratio of Azolla. Nitrogenase enzyme activity quantified was profoundly affected by the locations. The amount of ethylene produced extended from 192 to 236 nmole ethylene g-1 h-1. It showed a significant negative correlation with soil pH and EC. The study has given valuable information on the influence of soil and flood water quality parameters and locations on Azolla which could be used for further investigations on its nutrient dynamics.