Soil Potassium Fertility in South Asia

Could potassium fertilizer be the key to sustainable agriculture and food sustainability in South Asia? There are indications that it could certainly be part of the solution according to a recent article published in the scientific journal Advances in Agronomy. The conditions encountered in South Asia demonstrate the significance of potassium fertilizers for crops, both in this region and elsewhere around the world.

South Asia Geography

South Asia is a densely populated region that is home to almost 25% of the global population, and yet it only has 14% of the global cultivatable land. This imbalance alone would indicate a significant challenge for food security in the region. However, this is only one facet of the food security situation. Many parts of the region also achieve low levels of agricultural productivity. These issues of high population density, limited agricultural land, and low productivity contribute to the region’s fragile food security situation. Despite strong gains in economic growth and agricultural productivity in some parts of South Asia, the area still has the world’s highest concentration of poverty and hunger. South Asia has almost 40% of the world’s impoverished and 45% of the world’s undernourished people. The region is also home to nearly two-thirds of the world’s undernourished children. These are staggering figures for a region with just 25% of the global population.

South Asia Crop Productivity

In many South Asian countries, imbalanced nutrient use appears to be one of the major production constraints limiting crop yield. Focusing on nitrogen application leads to nutrient imbalances which can result in potential potassium and phosphorus deficiencies. This can, in turn, reduce nitrogen use efficiency. Low nitrogen use efficiency means growers spend money on nitrogen that is not utilized fully by crops. This unutilized nitrogen is, instead, lost to the environment, either in emissions of the greenhouse gas N₂O or through nitrogen leaching, which can lead to other undesirable environmental side effects.

Why is Potassium so Important?

Potassium is one of the three macro-nutrients crops require, along with phosphorus and nitrogen. In plants, potassium is involved in activating around 60 enzymes, as well as regulating stomatal functions and controlling plant water use. Potassium is involved in the transport, within plants, of organic compounds such as sugars, amino acids, and starch. Potassium also increases root growth and improves the drought resistance of crops.

In many ways, potassium underpins agricultural productivity and sustainability.

What Causes Potassium Nutrient Imbalance in South Asia?

Farmers often underestimate the importance of potassium. Crops can be seen to respond relatively quickly when applying nitrogen and phosphorus, which encourages their use. Potassium is different. The benefits of potassium application are generally only seen as crops mature. This can lead to a lack of awareness among farmers about the importance of potassium for the yield and quality of crops. When combined with poorly designed policies and poor access to correct guidelines on the correct use of fertilizers, this can lead to the adoption of imbalanced fertilizer practices. Some parts of South Asia have suffered from years of low, imbalanced levels of external inputs. This continued imbalance between the nutrients applied to the crop, and the nutrients removed from the field at crop harvest, has led to large-scale soil potassium mining.

Soil Potassium Mining

With each crop harvest, potassium is removed from the field. If potassium fertilizer has not been applied, then any potassium removed with the crop will have originated in the soil. This has been demonstrated in the region in multiple long-term crop fertilizer experiments.

Potassium deficiency in plants manifests as chlorosis (yellowing) of leaves, leaf burning, and weak stems. These symptoms are common in crops grown in K-deficient soils, such as red and lateritic soils, acidic soils, and other problematic soils. Crops like tuber crops and quality crops that require high amounts of K per unit time are particularly susceptible to K deficiency.

Potassium analysis in India, Bangladesh, Sri Lanka, and Pakistan has revealed the extent of the soil potassium deficiency. In India, for example, it is calculated that 6.2 Mt of potassium is lost from the soil each year. This continued potassium loss is having a significant impact on crop production and, in turn, on food security in the region.

Potassium Management Strategies

The article “Soil Potassium Fertility and Management Strategies in South Asian Agriculture”, published in the Advances in Agronomy journal, covers all these aspects in great detail. There is an in-depth exploration of the role of potassium in crop production and the current nutrient situation throughout the South Asia region. Effective potassium management strategies are essential for different cropping systems and ecosystems:

• Irrigated Ecosystems: In irrigated ecosystems, potassium management is vital for sustaining high crop yields. The rice-wheat and rice-maize cropping systems, predominant in the Indo-Gangetic Plains, require adequate potassium application to maintain soil fertility and enhance crop productivity. The study highlights that balanced fertilization, including potassium, can significantly improve yields and prevent soil nutrient depletion. For example, in the rice-wheat system, potassium application has been shown to increase grain yield by 25-30% in Bangladesh. Similarly, split application of potassium in maize enhances grain yield and improves soil potassium content. These practices not only boost crop yields but also contribute to long-term soil health.
• Rainfed Ecosystems: Rainfed agriculture, which relies on natural rainfall, is highly susceptible to climate variability and water stress. Potassium plays a crucial role in enhancing drought tolerance and improving water-use efficiency in rainfed crops. Foliar application of potassium in crops like maize and pulses can mitigate the effects of drought and enhance yield. In maize-based systems, foliar potassium application has been shown to increase grain yield by up to 79% in Bangladesh. Additionally, potassium improves the nutritional quality of crops, making them more resilient to environmental stresses.
• Horticulture: Potassium is often referred to as the “quality element” for horticultural crops due to its significant impact on fruit and vegetable quality. Adequate potassium nutrition enhances the shelf life, taste, and nutritional value of horticultural produce. The study underscores the importance of potassium in improving the quality and marketability of high-value crops like bananas, tomatoes, and grapes. For instance, potassium application in banana cultivation increases fruit size, sugar content, and overall yield. In tomato crops, potassium improves fruit firmness and reduces post-harvest losses. These benefits highlight the need for targeted potassium management in horticulture to maximize both yield and quality.

Recommendations for Future

With an increased understanding of the issues growers face and the potential benefits that balanced potassium use can bring to the region, the authors suggest following key steps which might be useful for future potassium management to improve potassium use where it is most needed and where potassium application will have the greatest benefit.

1. Considerate K management: Efficient use of imported K fertilizers is crucial due to their high cost. Farmers should be educated on the importance of balanced nutrient application, including adequate K.
2. Soil Testing: Strengthen soil testing laboratories and develop digitized GIS maps for precise K management. This will help in identifying K-deficient areas and tailoring fertilizer recommendations accordingly.
3. Tailored Recommendations: Develop K recommendations based on specific cropping systems and soil types. This approach will ensure that K application is optimized for different agricultural contexts.
4. Non-Exchangeable K: Include non-exchangeable K in soil test-based recommendations. This will provide a more accurate assessment of soil K status and help in developing effective fertilization strategies.
5. Residue Recycling: Promote crop residue recycling to maintain soil K balance. Crop residues contain significant amounts of K, which can be returned to the soil through proper management practices.
6. Conservation Agriculture: Implementing conservation agriculture practices to enhance soil K status and crop productivity even in rainfed systems where 40–70% K requirement can be met through efficient residue management.

By implementing these strategies and prioritizing soil potassium fertility, South Asian countries can improve agricultural productivity, helping to ensure food security and foster resilience to climate change. Collaboration among stakeholders, including farmers, researchers, and policymakers and the adoption of balanced fertilization practices, efficient use of resources, and innovative management techniques will not only improve yields but also contribute to long-term food security and economic stability in the region.