Abstract
Lime requirement of acid soils was determined in the laboratory through calcium carbonate incubation, SMP-single buffer and NuMaSS methods, and verified in the field through crop response to lime application. Laboratory determination was made on 72 soils collected from high and medium high lands of 36 upazilas across 21 districts of Bangladesh. The field test was made for crop response to added lime on six sites under three districts in the wheat - T. aman rice and maize - T. aman rice cropping systems. For estimating lime requirement (LR) through calcium carbonate incubation, 2 months' incubation was adequate. Four soil properties such as pH, ECEC, %Al saturation and %OM were found to be the controlling factors for estimating lime requirement of soils. Estimation of lime requirement by calcium carbonate incubation method was equally dependent on pH, ECEC, %OM and %Al saturation. The NuMass method estimated lime depending mostly on the %Al saturation and the SMP-single buffer method estimated lime depending on the % Al saturation and %OM content. Generally, SMP-single buffer and NuMass methods had lower LR estimation compared to the soil-lime incubation method. However, relationship between LR by different methods was highly significant. Addition of dolomite increased soil pH and this increment was sustained over 2 years' period indicating that liming had substantial residual effect on soil pH. Application of lime increased crop yields. Addition of 1 t lime ha1 provided yield benefit of wheat by 35% as direct effect and 31% as residual effect over no lime application (control). The yield benefit for maize due to 1 t lime ha was 38% and 35% as direct and residual effects, respectively. On an average (over the patterns, seasons and sites) 1 t lime ha1 as residual effect gave 14% yield advantage of rice compared to control. It is evident that one year lime addition may benefit the crops for at least two years. In general, the lime rate of 1 t ha applied once prior to the 1st crop was found to be the best for most of the strongly acid soils of this country for growing crops over two years. After liming, soil pH had increased, the Al, Fe and Mn toxicity had reduced and the availability of P and Mo had increased which resulted in increased yield of wheat and maize. Among the three methods of lime estimation, NuMaSS method with 30% Al saturation estimated lime requirement quite satisfactorily.