Study the effect of nitrogen fertilizer management on dry matter remobilization of three cultivars of rice (Oryza sativa L.)

Growth, development and nitrogen uptake efficiency of some sali rice genotypes under delayed dates of sowing

Sali rice which is the major rice crop of Assam faces recurrent floods co-inciding with different phonological stages, especially the seedling stage. Owing to the damage caused to the seedlings, the transplanting also gets delayed. Delayed transplanting results in poor grain yield due to poor biomass accumulation as influenced by prevailing photoperiodic and thermal regimes during that period of the year. From this angle, selection of suitable genotypes appears to be the viable option that can have better early vegetative growth by utilizing available resources and should possess considerable degree of thermo- and photo- insensitivity. Keeping in view the above points, a study was conducted during the sali seasons at the experimental plots of Instructional cum Research (ICR) farm, Assam Agricultural University, Jorhat with already shortlisted seven sali rice genotypes namely, Satya, Luit, Monoharsali, Jaya, Bordhan, Basundhara and Srimanta under delayed dates of sowing using thirty days old seedlings for transplanting laid out in split plot design. Results revealed that as compared to timely sowing, delayed sowing resulted in progressively lower values of various physiological parameters. While comparison was made between timely sowing and the deferred dates of sowing lowest reduction in the values of grain yield were recorded in genotypes of Manoharsali and Srimanta (35.66% and 35.03% with a delay of transplanting by 35 days compared to the recommended date of sowing i.e., 15^th June). These two genotypes recorded better performance in terms of parameters like leaf area index, nitrogen accumulation in biomass and plant biomass etc. The better performing genotypes namely Srimanta and Monoharsali recorded higher values of nitrogen uptake efficiency.

Comparative performance of hybrid and elite inbred rice varieties with respect to their source-sink relationship

Hybrid rice varieties have higher yield potential over inbred varieties. This improvement is not always translated to the grain yield and its physiological causes are still unclear. In order to clarify it, two field experiments were conducted including two popular indica hybrids (BRRI hybrid dhan2 and Heera2) and one elite inbred (BRRI dhan45) rice varieties. Leaf area index, chlorophyll status, and photosynthetic rate of flag leaf, postheading crop growth rate, shoot reserve translocation, source-sink relation and yield, and its attributes of each variety were comprehensively analyzed. Both hybrid varieties outyielded the inbred. However, the hybrids and inbred varieties exhibited statistically identical yield in late planting. Both hybrids accumulated higher amount of biomass before heading and exhibited greater remobilization of assimilates to the grain in early plantings compared to the inbred variety. Filled grain (%) declined significantly at delayed planting in the hybrids compared to elite inbred due to increased temperature impaired-inefficient transport of assimilates. Flag leaf photosynthesis parameters were higher in the hybrid varieties than those of the inbred variety. Results suggest that greater remobilization of shoot reserves to the grain rendered higher yield of hybrid rice varieties.