B. SREEKANTHRAHUL CHANDRA2023-11-292023-11-292023-11-29D6394https://krishikosh.egranth.ac.in/handle/1/5810201908The present investigation entitled “Physiological studies on nitrogen assimilation during reproductive stage of ground nut (Arachis hypogaea L.)” was undertaken at Agricultural College Farm, Bapatla during Rabi, 2020. As treatment, 10 kg N ha-1 was applied during four different reproductive growth stages of groundnut viz., at flowering (30 DAS, 50% plants have open flowers), at peg initiation (50 DAS, 50% plants have at least one elongated peg), at pod initiation (60 DAS, 50% plants have an elongated peg with ovary tip beginning to swell to at least twice peg diameter) and at mid pod development stage (72 DAS, a day at the middle of crop maturity and pod initiation) along with an untreated control with only recommended basal application of nitrogen. These treatments were imposed on groundnut cv TAG-24 in a randomized block design. The observations and samples required were collected from 5 random plants from each treatment plots in 4 replications 2 days before every treatment application, starting from flowering stage followed by observations which were made at different reproductive stages and after harvest. Different parameters, both biochemical and physical, were estimated, which are known markers for N uptake and assimilation as well as nodule and root activity in groundnut. At harvest, yield parameters such as number of pods plant-1, pod yield plant-1, seed yield plant-1 and oil content were estimated. Standard methodology was followed in the measurement of all the parameters. From the above investigation, N supplementation was found to positively regulate leaf and shoot dry weights, N supplemented during pod initiation stage was found to maximize shoot and root dry weight, while a negative effect was observed with N supplementation at later reproductive stages particularly on root dry weight. Increment in leaf area, photosynthetic rate and chlorophyll content was observed with N supplementation at different reproductive stages, early reproductive xii stage showed significant response to N supplementation. Maximum increment in leaf area and photosynthetic rate was noticed when N was supplemented at pod initiation stage and significantly higher chlorophyll content was produced by supplementation at pegging stage. No significant effect was observed in nodulation parameters such as nodule dry weight and proportion by mass of active to senescing nodules with N supplementation at any stage, but significantly higher numbers of active nodules were produced when N was supplemented at early reproductive stage (pegging). Ratio by mass of new to old roots were found to be higher when N supplementation was provided at early reproductive stage than when supplementation was done at a later stage. N supplementation positively regulated nitrate reductase content in leaves while leg haemoglobin content was observed to decrease progressively with N application at later growth stages. Significantly higher N content was observed in leaves, shoots, shells, roots and kernels when N was supplemented at early reproductive stages such as pegging and flowering. No effect was observed from N supplementation in peg N content. Yield parameters such as number of pods plant-1, pod yield plant1, seed yield plant-1 and oil content, N supplemented at an early reproductive growing period of plant was found to contribute maximum towards their increment. Maximum response to N supplementation produced by the plant, through increment of yield parameters was from N supplemented at flowering and pegging stage. Correlation analysis performed between root and shoot N assimilation indicators and N content in different plant parts yielded positive correlations between leaf, stem and root N content with NR activity at early reproductive stages. Significant positive correlation was obtained from correlation between root N content and nodule leg haemoglobin content. Correlation performed between the yield parameters (kernel yield and kernel oil yield) and nitrogen assimilation indicators of root nodules and leaves revealed that kernel yield and seed oil content showed a non significant positive correlation when correlated with leaf NR activity, while a non significant negative correlation existed between kernel yield and leg haemoglobin at later stages of reproductive growth. No specific pattern was observed between seed oil content and nodule leg haemoglobin from correlation.EnglishThesis