Abstract
Nine experiments were conducted at the Agronomy Field Laboratory, Bangladesh Agricultural University, Mymensingh during the three years period from 1 April 2001 to 31 May 2004 to observe the effect of green manures and levels of nitrogen on transplant Aman rice and their residual effect on succeeding Boro rice. Three experiments were conducted with seven green manure species viz. Sesbania rostrata, Sesbania aculeata, Crotalaria juncea, Vigna unguiculata, Vigna radiata, Phaseolus mungo, and Glycine max and three rates for each of seed, phosphorus and nitrogen to select suitable green manure species in terms of biomass production and nodulation. Two other experiments were conducted to evaluate the effect of seven green manure species and three levels of nitrogen viz. 0, 40 and 80 kg ha1 on the yield of transplant Aman rice and their residual effect along with three levels of nitrogen viz. 0, 60 and 120 kg ha1 on succeeding Boro rice in order to select suitable green manure species. Two of the remaining four experiments were conducted with four selected green manure species viz. S. rostrata, S. aculeata, C. juncea and P. mungo and four levels of nitrogen viz. 0, 40, 60 and 80 kg ha' along with one seasonal fallow as control treatment to observe the performance of transplant Aman rice and the residual effect of green manures on the succeeding Boro rice along with four levels of nitrogen viz. 0, 40, 80 and 120 kg ha'. These experiments were repeated for the next cycle. All the experiments were conducted in randomized complete block design with three replications.
Among the green manure species, S. rostrata, S. aculeata, C. juncea and P. mungo occupied the first, second, third and fourth position, respectively in terms of biomass yield and S. aculeata occupied the the first position in terms of number of nodules plant'. Seed rate had significant influence on biomass yield and nodulation of green manure species. The highest seed rate produced the highest biomass yield and the lowest number of nodules plant'. While phosphorus rate had significant influence on nodulation but had no significant influence on biomass yield. The highest P rate produced the highest number of nodules plant'. Nitrogen rate had significant influence on biomass yield but had no significant influence on nodulation. The highest N rate produced the highest biomass yield. In terms of grain yield of transplant Aman rice and residual effect on grain yield of Boro rice, S. rostrata occupied the first position followed in order by S. aculeata, C. juncea and P. mungo, respectively. Thus these four green manure species were selected for further experimentation. In transplant Aman rice, the highest plant height, number of tillers hill', dry matter, LAI, CGR, NAR, LAD, number of effective tillers hill', grains panicle', grain yield and straw yield were observed with 80 kg N ha'. However, 60 and 40 kg N ha exhibited similar behaviour as 80 kg N ha regarding the aforesaid parameters. It was observed that 40 kg N ha' (ie, 50% of the recommended dose) in combination with green manures produced similar grain yield as that of 80 kg N ha'. Yield and yield contributing parameters of succeeding Boro rice were not significantly influenced by the residual effect of green manures but were influenced by N rates. The highest values of the aforesaid parameters were observed when the crop was fertilized with 80 kg N ha'. Grain yield of Boro rice was not significantly affected by the interaction between residual effect of green manure and levels of N. But numerically higher grain yield compared to control plots indicated some sorts of residual effect of green manures though not statistically significant. Soil nutrient status viz. N, P, K, S and organic matter increased due to green manuring which was observed after the harvest of transplant Aman rice.