Abstract
A study was made to examine the mineralization pattern of N, P, K and S from different sources of organic matter and their suitability for integrated use with inorganic fertilizers to increase crop productivity and sustain soil fertility. Mineralization was studied by an incubation experiment with FYM, dhaincha (Sesbania aculeata) and mungbean (Vigna radiata) residues (MBR) applied at two rates (2.5 and 5 t ha⁻¹) under saturated soil and field capacity conditions over 12 weeks at 30°C. Two soils, one from BAU farm, Mymensingh and the other from OFRD farm, Rangpur, were used in this study. The release of N, P, K and S from the amended soils increased progressively and attained a peak within 4 to 7 weeks of incubation at both soil moisture conditions. The amount of 64-91% N, 33-75% P, 44-75% K and 48-82% S were released depending on the types of manure, rates and moisture level. In both soils, mineralization potentials for N, P, K and S were higher for saturated soil compared to the field capacity. Field experiments were conducted over three years during 2001-2002 to 2003-2004 at BAU farm, Mymensingh and during 2002-2003 to 2004-2005 at OFRD farm, Rangpur using FYM, dhaincha (Sesbania) and mungbean residue along with inorganic fertilizers. For the first crop (maize), there were five treatments. Each year, FYM was applied to maize crop and GM/MBR was applied before transplanting of T. aman rice. Integrated use of manure and inorganic fertilizers (IPNS basis) produced comparable seed yield of maize with the chemical fertilizers alone irrespective of moderate or high, yield goal basis (MYG or HYG) in both locations. After harvest of maize, mungbean and dhaincha (Sesbania) seeds were sown as per treatments. For T. aman rice (third crop), each of the treatments T₂ and T₃ plots were subdivided into six, so there were altogether 15 treatments. At both locations, the incorporation of Sesbania biomass and mungbean residue along with inorganic fertilizers for MYG gave identical grain yields of T. aman rice with the fertilizers alone applied for HYG. The balance for N and K was negative and that of P, S and Zn was found positive, generally. Considering gross margin and marginal benefit-cost ratio (MBCR), legume residue incorporation along with inorganic fertilizers (IPNS basis) was found to be the best treatment. After three years of cropping, the nutrient status of soils in control, fallow and mungbean residue removal plots showed a decreasing trend while incorporation of Sesbania biomass and mungbean residue had a positive effect on soil fertility. From this study it may be concluded that addition of mungbean residues or Sesbania biomass to the fertilizer schedule may ensure higher crop productivity and sustain soil fertility over a long-term.