Over the past decade, West Bengal has maintained a very favorable nutrient use ratio which is very close to the ideal ratio of 4:2:1 of N, P2O5 and K2O. However, while maintaining such an ideal ratio of NPK consumption in the state there still exists a considerable gap between nutrient removal by crops and nutrient replenished through external sources. Potassium constitutes the major portion of this gap. This questions the very basis of deciding the ideal ratio of nutrient use. Alarming statistics of K mining from soil is coming out in different reports and an estimated deficit of nearly 18 million tonnes of potash is expected in 2020. The strikingly low use of potash is mainly due to the reluctance of farmers to use potash presumably on the common belief that the soils of the state are potash rich. With the projected demands of food crop, cultivation without or little potash will denude the soils of their K reserve. Moreover, the latter would go largely unnoticed as per the conventional soil test for plant-available K (which excludes the non- exchangeable K reserve of soil) and hence may prove alarming. Broadly speaking, the available K status of the soils of West Bengal is variable. It is low in the red and lateritic belt (covering 27% of the geographical area), low to medium in the hill and terai soil ( covering 17% of the geographical area), low or medium to high in the alluvial soils (covering 42% of the geographical area) and the coastal soils (covering 14% of the geographical area). The long-term experiments have shown that when exchangeable K is not quickly replenished, the crop starts drawing K from the non-exchangeable K pools, leading to depletion of soil K reserves. It is quite natural that different types of soils have different K buffering capacity under a continuous crop removal regime and may require different rates of K replenishment through external sources. This might also be true for similar type of soils but with varying K supplying capacity.
Alluvial soils is the major soil group in West Bengal and they are an important component for food security in the state. The vast area under alluvial soils currently have a blanket K recommendation for individual crops despite having different K reserves or supplying powers. This project aims to look at the K dynamics in different types of alluvial soils of West Bengal and fine tune K fertilizer recommendations for soils according to K supplying power to improve yield and profit in important cropping sequences.