Browsing by Author "Irene Elizabeth John"

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Carbon: nitrogen dynamics in acid sulphate and acid saline rice soils of Kerala
(Department of Soil Science and Agricultural Chemistry, Vellanikkara, 2019) Irene Elizabeth John; Sureshkumar, P
The present study was undertaken to unravel the chemistry of Carbon: Nitrogen dynamics in submerged acid sulphate and acid saline soils, to identify the labile fractions of these elements contributing to soil fertility and to modify the organic carbon based fertility ratings for nitrogen recommendation in Kale lands. Forty-five representative soil samples from 4 different rice growing acid saline and acid sulphate soils of Kerala were collected and characterized for pH, EC, OC, total carbon, total nitrogen, available nutrients (N, P, K, Ca, Mg, S, Fe, Cu, Mn, Zn and B) and microbial biomass carbon. The soil samples were analysed as such after sampling on wet basis and the results were expressed on moisture free basis to have uniformity. The organic carbon status of the soils varied from 0.81 to 7.58 per cent. Soils from Kaipad recorded the lowest and soils from Vechoor Kari of Kuttanad recorded the highest value of organic carbon. The total nitrogen ranged from 0.05 per cent in upper Kuttanad to 0.42 per cent in Vechur Kari. The highest available nitrogen content of281.38 kg ha' was recorded in sample from Vechoor Kari and the lowest of 19.84 kg ha in Purakkad Kari. The C:N ratio varied from 13:1 to 24:1. Widest C:N ratio was recorded in soils of Upper Kuttanad and the lowest in soils from Thrissur Kale. The organic carbon was significantly and positively correlated with total nitrogen and available nitrogen status. Total nitrogen was the single most independent factor explaining 94 per cent variability of organic carbon. Soil samples were subjected to fractionation studies (both physical and chemical) to quantify the carbon and nitrogen that is associated with different inorganic and organic constituents in soil. In physical fractionation, soil carbon and nitrogen preferentially recovered from the sand, silt and clay size fractions were estimated. Of this, carbon recovered from clay size fraction was the dominant independent variable that explained 64.6 per cent variability of organic carbon. The different chemical carbon fractions studied were water soluble carbon (WSC), hot water extractable carbon (HWEC) and permanganate oxidizable carbon (POC). The water soluble carbon being derived from completely decomposed organic matter was not associated with nitrogen in soils. The HWEC being the most labile pool of carbon had significant influence on mineralisation process thereby contributing to total and available nitrogen content. The permanganate oxidizable carbon being a stabilized pool might not undergo further decomposition to release nitrogen and hence, its contribution to available pool was negligible. Among the organic pools of nitrogen, the total hydrolysable nitrogen contributed significantly to mineralizable N. Among the inorganic fractions of nitrogen, ammoniacal nitrogen was contributing more to the available pool of nitrogen than nitrate nitrogen fraction probably because of high solubility and losses of latter by leaching. A field experiment was conducted to investigate the response of rice to different levels of nitrogen in Adattu Kole with an initial C:N ratio of 20:1. The treatments with increased levels of nitrogen based on C:N ratio (treatments Ts-TlO) produced significant effect on plant height, number of productive tillers, number of grains per panicle, straw yield and grain yield. The total nitrogen content both in soil and plant were significantly influenced by higher doses of nitrogen fertilizers prescribed as per the C:N ratio. Among the carbon fractions, hot water extractable carbon contributed more to the mineralizable pool than water soluble carbon. The direct effect of total hydrolysable nitrogen on total and available nitrogen was very high. Ammoniacal nitrogen being a dynamic and time dependent variable, though contributing significantly to available N content, its effect on total nitrogen was negligible. This was in conformity with the results of experiment in characterization of soil samples collected from 45 locations. The maximum grain yield of 8.22 Mg ha" was recorded in the treatment where nitrogen was applied based on C:N ratio (wet analysis). An increase of 1.15 Mg ha of grain yield was recorded over the treatment where soil test based fertilizer recommendation was applied. The highest straw yield of 17.47 Mg ha was recorded in treatment where nitrogen applied was double that of C:N ratio based recommendation. The highest net return was obtained in treatment where nitrogen was applied as per the C:N ratio in soil.
Wet soil analysis for nutrient prescription in paddy soils
(Department of Soil Science and Agricultural Chemistry,College of Horticulture, Vellanikkara, 2014) Irene Elizabeth John; Sureshkumar, P
Three locations from 7 agro ecological units dominated by rice crop were identified namely, Onattukkara sandy soil(AEU 3), Kuttanad(AEU 4), Pokkali(AEU 5), Kole(AEU 6), north central laterite(AEU 10), Palakkad central plains (AEU 22) and Palakkad eastern plains (Black soils )(AEU 23). Geo-referenced soil samples were collected at 3 stages: before cropping season, at active tillering and visual panicle initiation. Plant samples were also collected during the above stages and analyzed for nutrient contents. Initial characterization was done with air dried samples while samples during crop growth period were collected by maintaining the wet anaerobic conditions and analyzed as such as well as after drying. Submergence resulted increase in pH both under wet and dry analysis. The pH on the basis of wet analysis was higher than that by dry analysis. EC decreased during flooding and dry analysis gave higher values than by wet analysis. The (C: N) 1 ratio (based on total carbon and total nitrogen) varied from 9.32 :1 in Onattukarasandy soil to 18:1 in Kuttanad on the basis of wet analysis. Analysis after drying recorded a (C: N) 1 ratio ranging from 10.84 inPalakkad central plains to 22 in Kuttanad. Comparison of wet and dry analysis of other available nutrients indicated that higher values were recorded for P, K, Ca, Mg and Fe in wet analysis while the values for availableS, Mn, Zn and B were higher in dry analysis. Data on analysis after drying, recorded significant negative correlation of pH with organic carbon (0.36**) and available S (-0.37**) due to accumulation of organic acids and SO 42-ions under aerobic condition. Antagonistic interaction of available P with available Ca was attributed to significant negative correlation obtained between them in dry analysis. Wet analysis gave significant positive correlation of pH with available Ca (0.35**) and significant negative correlation with available S (-0.28*). All the C: N ratios computed on the basis of, total carbon and total nitrogen (C: N) 1, total carbon and available nitrogen (C: N) 2, organic carbon and total nitrogen (C: N) 3 and organic carbon and available nitrogen(C: N) 4 were significantly correlated with total and available nitrogen at different stages both under wet and dry analysis. Four soil types namely, Onattukara sandy, Kuttanad, north central laterites and Palakkad eastern plains were used for an incubation study to unravel the pattern of decomposition of added organic matter and to identify the C: N ratio at equilibrium. Changes in pH and redox potential during submergence indicated slight increase in pH after 7 days of submergence and redox potential was constantly decreasing with increasing period of submergence. The (C: N) 1 ratio was found to stabilize at 9.6:1 after 3 months of incubation with organic matter while it was stabilized at 7.6:1 without organic matter in Onattukara soil. In Kuttanad soils it was 18.3:1 and 17:3 respectively. In Chittor soils it stabilized at 10:1. The (C: N) 3 also showed similar trends. However, available nutrient did not give any significant correlationwith the corresponding plant content of the respective nutrient. This focusesto the importance of future studies with more number of samples from eachAEU’s as each of the fertility parameters are highly varying in these units.