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ThesisItem Open Access EVALUATION OF CRITICAL LIMIT OF ZINC AND RESPONSE OF RICE TO ZINC APPLICATION IN SOILS OF ASSAM(AAU, Jorhat, 2014-07) Goswami Kandali, Gayatri; Barua, N. G.Georeferenced and representative soil samples were collected from 14 districts of Assam for assessment of zinc status of soils. Altogether, 4110 numbers of surface (0-0.15m) soil samples were collected from rice growing fields of fourteen districts randomly at an interval of 2 to 2.5 km. using Global Positioning System. Thirty numbers (30) of surface (0-0.15m) soil samples were collected from rice growing fields at block level from each district randomly at an interval of 2 to 2.5 km. Based on DTPA-Zn content , soils were categorized as low, medium and high. Nutrient index and fertility ratings were determined following the procedure of Bajaj & Ramamoorty (1969). The highest Zn deficiency (32.21 %) was observed in Lakhimpur district and the lowest ( 2.66 %) in Dhemaji district. The lowest nutrient index (NI) of 1.38 in Nalbari district and the highest (1.63) in Dibrugarh district were recorded. Deficiency of zinc as a whole in the state of Assam represented by the fourteen districts was 26.22%. Twenty five georeferenced bulk surface soil samples (0-30 cm) with variable zinc status were collected from rice growing areas of Assam representing the major soil orders viz. Inceptisol, Alfisol and Entisol to find out the critical limit of Zn in rice soils. A pot culture experiment was conducted taking these soils with four levels of zinc viz., 0,2,4 and 6 kg Zn/ha to find out the response of rice (cv. Ranjit) to applied zinc and the critical limit of zinc in soils and crop. Dry matter yield of rice in control pots ranged between 7.5 to 21.5 g/pot with a mean value of 13.71g/pot. The mean dry matter yield increased significantly over control with rates of zinc application. The highest was recorded in 4 kg/ha of applied zinc. Bray’s percent yield ranged from 57.18 to 95.7 and the highest Bray’s percent yield of 95.7 was observed in the soil having DTPA-Zn of 0.4mg/kg and the lowest value of 57.18 was observed in the soil with DTPA-Zn 2.49 mg/kg. Higher zinc concentration corresponds to higher dry matter yield and higher zinc uptake. The bulk soil samples were also extracted by different extractants viz., DTPA, 0.5N HCl, 0.1N HCl, Ammonium Acetate, EDTA- Ammonium Carbonate, and Ammonium Bicarbonate-DTPA( AB-DTPA), 0.04M EDTA and 2M MgCl2 solution to find out a suitable extractant / method for available zinc in soil . DTPA showed the highest correlation with all the plant parameters followed by AB-DTPA, 0.05 N HCl and EDTA- Ammonium Carbonate. The critical limits( Cate & Nelson,1965) of DTPA, 0.5N HCl , 0.1N HCl, Ammonium Acetate, EDTA- Ammonium Carbonate, AB-DTPA, 0.04M EDTA and 2M Mgcl2 in soil were found to be 1.24, 1.25, 4.8, 0.9, 2.8, 1.74, 2.8 and 0.37mg/kg respectively. The critical limit of Zn for rice was 35 ppm based on DTPA method. In order to study the distribution of different forms of zinc in rice soils and their relative importance to zinc nutrition of rice , Zn fractions of bulk soil samples were extracted by adopting the sequential extraction procedure of Murthy(1982).Water soluble and exchangeable Zn(WSEX-Zn) fraction in soils ranged from 0.32 to 1.92 ,Complexed Zn (COMP-Zn) from 1.46 to 4.5 , Amorphous Sesquioxide bound Zn from 1.30 to 6.21,Crystalline Sesquioxide bound Zn ( CBD-Zn) from 0.45 to2.25 and Residual Zn(Res-Zn) from 101.79 to285.28 mg kg-1 with mean values of 0.87, 2.71, 2.92, 1.12 and 186.98 mg kg-1, respectively. WSEX-Zn, COMP-Zn, Amorphous Sesquioxide bound Zn, CBD-Zn and Res-Zn constituted 0.45, 1.57, 1.62, 0.63 and 95.70 % of total Zn of soils. WSEX-Zn , COMP-Zn and Amorphous Sesquioxide bound Zn was positively and significantly correlated with clay, OC and CEC of soils. However, CBD-Zn was significantly negatively correlated with pH (-0.522**) and Res-Zn was positively correlated with organic carbon (0.425*) and clay (0.397*) c ontent of the soils. Multiple regression of physico-chemical properties of soil with different Zn-fractions showed the highest R2 value (0.616) with COMP-Zn. Multiple regression of different Zn fractions with plant parameters showed the highest contribution of WSEX-Zn to Zn concentration (76.78%), Zn-uptake ( 63.03 %) and dry matter yield ( 36.15 %) of rice. Path analysis of different Zn-fractions with Zn-concentration in rice showed the highest direct effect (0.5610) of WSEX-Zn on Zn concentration and indirect effect of COMP-Zn (0.3731) and Amorphous Sesquioxide bound Zn (0.2508) via WSEX-Zn. A field experiment was conducted for two seasons (2011 and 2012) in a Zn deficient field of the Instructional cum Research Farm of Assam Agricultural University, Jorhat, to study the response of sali rice (var- Ranjit) to zinc application with six levels of ZnSO4 (0, 5, 10, 15, 20 ,25 and 30 Kg/ha) which corresponds to 0, 1.05, 2.1, 3.15, 4.2, 5.25, and 6.3 Kg Zn ha-1 in a randomised block design with three replications. Addition of 25 kg ZnSO4 ha-1 showed the highest increase in plant height by 3.46 %, total tillers by 42.05%, effective tillers by 46.65%, filled grains by 26.86%, and thousand grain weight by 4.96% over control. The percentage of chaffy grain was also lower by 24.43% over control. The grain yield varied from 26.4 q/ha to 45.9 q/ha and straw yield ranged from 55.1 q/ha to 66.4 q/ha due to zinc application. The highest grain yield (45.9 q/ha) and straw yield (66.4 q/ha) was recorded in 25 kg ZnSO4 ha-1 which was significantly higher than all other treatments. Grain yield varied from 34.47 to 73.86%, while straw yield varied from 3.62 to 20.51 % over control. Maximum mean zinc uptake of 97.57 and 311.75 g ha-1 in grain and straw was recorded in 25 kg ZnSO4 ha-1, respectively. The residual zinc was found to be lower in the second year compared to the first year in all the treatments. The treatment with 25kg ZnSO4/ha registered maximum net returns (Rs.23,198.7) and the highest benefit:cost ratio (2.43)ThesisItem Open Access Bioremediation of iron toxicity in lowland rice ecosystem of Assam(AAU, 2016) Tamuly, Danish; Das, K. N.Two sets of experiment viz., pot (2012-13) and field (2013-14) was carried out to find bioremediation potential to ameliorate iron toxicity in lowland rice ecosystem of Assam. Rice crop was cultivated in Yoshida medium (hydroponic culture) developed specifically for rice. The experimental set up consisted of 6 boxes containing 60 PVC cut pipes each. Two check cultivars namely Mahsuri (sensitive) and Padumoni (tolerant) were tried along with eight test cultivars namely Ranjit, Moniram, Kushal, Pankaj, Luit, Basundhara, Jaymoti and Bahadur. Two weeks old seedlings from sand cultured nursery beds were transplanted into the PVC pipes fixed with half-split foam plugs in such a way that only root was in direct contact with the Yoshida solution. Liquid paraffin oil (low density) was added to each PVC pipe to maintain a 3 mm layer for checking oxidation process. Three bacterial inoculations viz., Control, PSB5w and PSB25w along with four iron levels, 0, 500, 1000 and 1500 mg Fe L-1 were tried in different combinations. Sampling at maximum tillering stage of crop revealed leaf scoring ranging from 0.0 to 4.9 with a mean of 0.3 to 3.7. The highest mean scoring of 3.7 was observed at 1500 mg Fe L-1, which was followed by 1000, 500 and 0 mg Fe L-1 with 2.9, 1.4 and 0.3 scoring respectively. The least scoring of 1.2 was observed in PSB5w followed by PSB25w (2.0) and PSB0 (3.1) inoculated cultivars. Among the rice cultivars the leaf scoring was in the order Mahsuri (1.4) < Joymoti (1.6) < Moniram (1.7) < Prafulla (1.9) < Podumoni (2.0) < Ranjit (2.2) < Luit (2.2) < Kushal (2.3) < Basundhara (2.4). Increasing levels of iron from 0 to 1500 mg Fe L-1 was found to significantly reduce the yield attributing traits of cultivars viz., root length (8.0 to 7.0 cm) and shoot length (22.4 to 17.6 cm). Similar reduction was also observed with N, P and K content in both leaf and stem i.e. leaf N (2.42-0.97%), stem N (1.55-0.90%), leaf P (0.220-0.041%), stem P (0.271-0.039%), leaf K (0.473-0.069%) and stem K (1.420-0.208%). The Fe content in different plant parts viz., leaf, stem and root was found to significantly increase with increased Fe-level. Mean root Fe-plaque was found to significantly increase from 0.19 (Fe0) to 0.94 (Fe1500) mg Fe g-1 root. PSB x Fe-level had significant effect on agronomic growth traits viz., root length and number of leaves and on N, P and K content in both leaf and stem. Both leaf and stem N content was found to be significantly higher with cultivars inoculated with PSB5w. However, P and K content in both stem and leaf were found to be higher in PSB25w inoculated cultivars. PSB5w inoculated cultivars recorded significantly lower leaf Fe, stem Fe and root Fe than control and PSB25w. Significantly, higher root Fe plaque was found in cultivars inoculated with PSB5w than PSB25w and control. Negative and significant correlation exist between scoring with root length, shoot length, number of leaves, leaf N%, stem N%, leaf P%, stem P%, leaf K% and stem K%. However, positive and significant correlation was observed between scoring with leaf Fe, stem Fe, root Fe and Fe plaque. Subsequent validation of results of pot experiment was carried out in the ICR Farm, AAU, Jorhat. Six rice cultivars viz., Mahsuri, Moniram, Joymoti, Prafulla, Podumoni and Ranjit in increasing order of scoring were selected. Following this, the strain PSB5w which showed least scoring was also selected with the highest iron level of 1500 mg Fe L-1. PSB5w inoculated cultivar showed significantly higher root length (21.50 cm), leaf N (2.20%), leaf P (0.313%), stem P (0.277%) and leaf K (0.804%) than non inoculated cultivars. Except for Moniram, all other cultivars showed significantly lower leaf and stem iron content. Significant difference in grain yield was observed with inoculated (1730.70 kg ha-1) and non-inoculated (1644.30 kg ha-1) cultivars. Relatively higher grain yield was achieved in PSB5w inoculated cultivars Mahsuri (2000 kg ha-1) and Prafulla (1850 kg ha-1) as compared to control. Thus the Bacillus sp. PSB5w with suitable carrier material can be used as a bioremediation tool for chronically Fe-toxic lowland rice ecosystem in Assam. Further, a stress encountering bio-package consisting of seedling root dip treatment in PSB5w especially for rice cultivars Mahsuri and Prafulla may be advocated for Fe toxicity affected low land rice ecosystem from the present investigation.