II Soil Acidity

Acid soils are found mainly in the eastern part of the Indo-Gangetic Plain, i.e. in West Bengal, Bangladesh and the mid-hills region of Nepal, where cropping is intensive and monsoonal precipitation is high. In many of these soils, organic matter is also quite low, resulting in poor buffering capacity and low nutrient contents. In a previous experiment at Dinajpur, application of 3 t lime/ha can increased wheat yields by 33%, most likely because of increased P availability at higher pH’s. However, micronutrient availability (B, Zn, Cu, Mn) will be reduced at higher pH, potentially inducing micronutrient deficiencies. For example we demonstrated that liming increased sterility and reduced wheat yields by exacerbating an existing soil B deficiency at Sipaghat in Nepal. Given that the micronutrient status of many soils in the Dinajpur area is poor, research was initiated to investigate the effect of liming soil on the productivity of rice and wheat and to determine whether there are interactions between liming and and micronutrient availability.

Lime and Micronutrient Interactions

One farmer and one on-station experiment were initiated in Dinajpur district, Bangladesh in the 1999 rice season. The soils at these sites range in pH from 4.9 to 5.1 and lime was added at 1.1 t/ha to raise soil pH to 5.6-5.8. Lime was applied prior to rice to ensure adequate reaction time prior to wheat. Flooding during the rice season causes the pH to rise to about 7, so lime is not really necessary for rice growth. An "overliming" treatment at 2.2 t/ha was also included to determine whether this would induce any micronutrient deficiencies. Zinc availability is known to be marginal in the area and we have previously identified Zn deficiency in wheat on farms in this region. A split-plot experiment with treatments of: NK, NPK and NPK+ Mg was implemented on the farmer plot to determine changes in macronutrient availability with liming. On station ± micronutrient treatments were also added in split-split plots. BR-32 rice, which is susceptible to micronutrient deficiencies, was transplanted in these experiments and Kanchan will be the wheat variety used.