Abstract
Four sets of experiments were conducted at the Agronomy Field Laboratory, Bangladesh Agricultural University, Mymensingh to see the rice productivity and soil fertility through in situ and in vitro application of biomass under irrigated and rainfed ecosystems during July 1996 to December 1999. Against the farmers' predominant cropping pattern Boro rice- Fallow-T.aman rice (I1), five patterns were designed by accommodating green manuring crops and they have been tested under irrigated ecosystem. The designed patterns were Boro /rice + Azolla-Fallow-T.aman rice + Azolla (12), Boro rice-Sesbania rostrata-T.aman rice (13), Boro rice-Mungbean-T.aman rice (14), Boro rice-Fallow-T.aman rice + Blackgram (Is), and Boro rice-Fallow-T.aman rice + Grasspea (16). During three years study, the highest grain yields were obtained in I2 and I3 in boro seasons and T.aman seasons, respectively. The designed five patterns performed better than that of farmers' pattern in respect of rice productivity, apparent nutrient balance and soil fertility. In rainfed ecosystem, five patterns were designed against Fallow-Direct seeded Aus rice-T.aman rice (R1) - a predominant pattern practiced by the farmers through inclusion of legumes as intercrop(s) for green manuring. The patterns were Fallow-Direct seeded Aus rice + Mungbean-T.aman rice (R2), Direct seeded Aus rice-T.aman rice + Grasspea (R3), Direct seeded Aus rice-T.aman rice + Blackgram (R4), Direct seeded Aus rice + Mungbean-T.aman rice + Grasspea (Rs), and Direct seeded Aus rice + Mungbean-T.aman rice + Blackgram (R6). Yield and yield contributing characters of rice were significantly affected by green manuring crops. The highest rice productivity, NPKS uptake by rice plants and organic matter content of soil were recorded either in Rs or R6. All legume containing rice based patterns performed better in respect of rice productivity and soil fertility. For in vitro biomass application, nine treatments viz. NPKS, NPKS + Azolla (compost), NPKS + Azolla (fresh), NPKS + S. rostrata (compost), NPKS + S. aculeata (compost), NPKS + Ash, NPKS + Cowdung, NPKS + Compost, NPKS + Poultry manure were tried both under irrigated and rainfed ecosystems. In irrigated ecosystem, the highest grain yields were obtained due to poultry manure or Azolla compost in boro seasons, and for S. rostrata compost in T.aman seasons. The highest rice productivity was found for S. rostrata compost application in 1997, and by application of Azolla compost in rest of the years. Total NPKS uptakes by rice plants were significantly higher due to biomass treatments) The highest organic matter contents were observed by Azolla compost treatment. Under rainfed ecosystem, yield and yield contributing characters of rice varied significantly and showed increasing trend due to biomass application. The highest productivity was found for poultry manure, S. rostrata, and Cowdung in 1997, 1998 and 1999, respectively. Nutrient uptakes by rice plants and organic matter contents of soils were higher due to biomass application. In situ and in vitro application of biomass from different sources showed positive results in respect of rice productivity and soil fertility. Farmers may opt for any designed pattern(s)/treatment(s) as mentioned above depending upon their choice and preferences for sustaining rice productivity and soil fertility.