Soil potassium fertility and management strategies in South Asian agriculture

Almost one-fourth of the global population live in South Asia (SA) countries with 14% of cultivable land. Most of the countries in the South Asian region are facing multiple challenges like high population growth, declining farm land area, and low productivity in primary and secondary sectors leading to limited employment opportunities. Consequently, both availability and access to food are adversely affected. Regions exposed to natural disasters, tribal and the hilly regions of SA are amongst the most vulnerable in terms of food security. Accelerated efforts are required to ensure that conflicts do not exacerbate the already fragile food situation in SA. Despite recent strong gains in economic growth and agricultural productivity, food and nutritional security remains a major concern in SA. The region has the largest concentration of poverty and hunger in the world, with nearly 40% of the world's impoverished and 45% of the world's undernourished people. The enormity of malnutrition in SA can be gauged from the fact that it is the home to nearly two-thirds of the world's undernourished children. More than 56% of the world's low-birth-weight babies are born in SA. Furthermore, food and nutrition security remain major challenges with a large proportion of the world's poor living here and global hunger index (GHI) at 30.9. Overcoming these twin challenges require actions both at the national and regional level. Among production constraints and yield gaps, imbalanced nutrient use is a critical issue in many of the SA countries, with nutrient application focused mainly on nitrogen (N), leaving the possibility for other plant nutrient deficiencies including phosphorus (P) and potassium (K). In some cases, the use efficiency of N may be low due to losses in the form of N₂O emissions, a potent greenhouse gas (GHG), or via leaching with the undesirable offsite effects. Among the primary nutrients, K is an essential nutrient for productivity, food quality and numerous functions in the plant system. It plays a major role in activating ∼60 enzymes, regulating stomatal functions, controlling water relations especially under rainfed crop production, influencing the water balance of plant systems, and underpinning agronomic productivity and sustainability. Negative K balance in soil under intensive cropping is reported because of low external input and large crop removal, leading to large scale K mining in soils. Declining yield trends were observed in several fertilizer experiments 30–40 years long with continuous application of either N alone or NP without K under both irrigated and rainfed crop production systems in the region. Recent K fertility analysis indicates widespread K deficiency in light-textured alluvial soils, red and lateritic soils beside acid soil types in India, Bangladesh, Sri Lanka, and Pakistan. The countries in SA depend largely on imported K fertilizers. Such imported fertilizer should be utilized most efficiently in the light of limited global K mineral reserves and 93% of world total K exports are from five countries viz. Canada (37.12%) followed by the Russian Federation, Belarus, Germany and Israel. Therefore, the current review addresses issues related to the K supplying capacity of soils in various crop production systems in SA, crop K responses, soil test methods followed, emerging issues in soil K fertility, K balance in major cropping systems and rationalizing K recommendations among crops, soil types and agro-ecological regions. The role of K in balanced nutrition, farm productivity, food and nutritional security in these countries is examined. The review also covers the critical role of K in climate change adaptation, mitigation of nitrous oxide (N₂O) emissions and improving overall nitrogen use efficiency (NUE) in the SA region.