Integrated nitrogen management in favourable rainfed lowland rice ecosystem

摘要

Field experiments were conducted on integrated nitrogen management (INM) in rice cv. Gayatri grown in a favourable lowland (shallow water) ecosystem for two consecutive wet seasons. The INM practices viz., (i) Dhaincha (Sesbania aculeata) green mannuring (GM) supplemented with deep placement of urea supergranules (USG), (ii) Dhaincha green manuring along with topdressing of prilled urea (PU) at 1:1 ratio-once at 3 weeks after transplanting and again at panicle initiation (PI), (Hi) basal applicationof controlled release N (CRN 6C) fertilizer and PU at 1:1 ratio and (iv) basal application of CRN 6C along with blue green algae (EGA) inoculation and SPAD monitored PU topdressing during the later part of crop growth, were found to be promising and at par with each other in respect of yield and N nutrition of rice. These practices supplying 60 kg N ha~(-1), were equally effective or even better than the treatments receiving PU alone; but were significantly superior to the other INM treatments such as PU + Azospirillum and PU + EGA in terms of yield of grain and straw, N availability in soil, N use efficiency (NUE) and N uptake of rice cv. Gayatri. Averaged over two years, grain yield of rice was in the range of 3.639-3.781 tha~(-1) with GM + USG andGM + PU topdressing as against 3.235 t ha~(-1) with PU basally broadcast applied at 60kg N ha~(-1) and 2.722 t ha~(-1) with 'no N' control. It is therefore, suggested that depending upon the feasibility, any of the above said promising INM practices maybe adopted in favourable lowland rice ecosystem. It was also observed that mineralization of Dhaincha green manure-N incorporated into soil in submerged uncropped field, was faster than that of Azolla-N and BGA-N. The apparent net mineralization of N during the period of 45 days after incorporation (DAI) was also consistently higher in case of Dhaincha green manure than in other two bio-fertilizers. During the first 8 DAI as much as 22.1% of Dhaincha N was apparently mineralized as against only 5.7% ofBGA-N and 5.5% of Azolla-N.