Abstract
Soils of varying K status were selected from BAU farm, Mymensingh and BADC farm, Madhupur for conducting laboratory, pot and field experiments to see the dynamics of potassium in wet land rice soils. The soils were BAU-1(0.087 cmol K kg soil), BAU-2 (0.146 cmol K kg1 soil), Madhupur-1 (0.097 cmol K kg1 soil) and Madhupur-2 (0.706 cmol K kg1 soil). Almost neutral silt loam soils (Sonatola series) of BAU farm developed on the recent alluvial deposits of Old Brahmaputra Flood Plain and the acidic clayey soils (Noadda and Kalma series) of BADC farm developed on Madhupur clay. The Laboratory experiments conducted were on; forms of potassium, potassium release capacity of soils, Q/I relationships of potassium, changes in solution and exchangeable potassium under continuously flooded and alternately flooded soils, hydraulic conductivity and mineralogical composition. Response of T. aman and Boro rice to potassium application was studied under pot and field conditions with different levels of K (0, 30, 60, 90, 120 and 150 kg K ha ̈1). Soil solutions were collected from treated plots/pots for the determination of K. Rain and irrigation waters were also collected and analyzed for K. Results of the experiments showed that BADC farm soils released more K than BAU farm soils. The Q/I relationship showed that the equilibrium exchangeable K (EKO) and labile K (KL) of Madhupur-2 soil were higher than other soils. The potential buffering capacity (PBC) was higher in BAU-2 (5.19±0.12 cmol kg/ (mol L-1)/2) soil followed by BAU-1 (4.07±0.09 cmol kg/ (mol L-1)/2) and then Madhupur-2 soil (2.23±0.04 cmol kg/ (mol L-12). BAU farm soils adsorbed 55 to 60% of added K in nonexchangeable form while it was 33 to 39% in BADC farm soils. Soil solution K and exchangeable K increased due to alternately flooding and drying over continuously flooded soils. The exchangeable K increased with added K but decreased with time in pot experiment. Rice grown under pot and field conditions responded positively to K in three K deficient soils. Considering the MBCR and net marginal return of 60 and 90 kg K ha1 was found economically viable for rice. In pot and field experiments, the soil solution K increased with increasing levels of K but decreased gradually with time. The decrease of solution K was drastic between 45 and 60 DAT. Afterward, it maintained almost a stable level upto 90 DAT. The solution K of Madhupur-2 soil also decreased upto 105 DAT but the concentration was higher than other soils. In field condition, the leaching loss due to rain and irrigation water was much higher than their addition. The crop uptake was again higher than leaching loss of K. As a consequence, the balance of K was negative ranging from -31.97 to - 284.95 kg ha1 irrespective of soils and seasons. The negative K balance reduced to some extent with increasing levels of K in K deficient soils because of lower K use efficiency mainly.