Potassium limits productivity in intensive cereal cropping systems in Southeast Asia

Potassium (K) has received little attention as a potential yield-limiting factor in cropping systems. Here we investigated the K status in intensive cereal cropping systems in Indonesia, which are representative of many other Southeast Asian countries. Our analysis included nutrient input–output balance, leaf nutrient status, long- and short-term fertilizer trials, and farmer surveys. We revealed that soil K levels alone are insufficient to meet plant requirements, and current fertilizer applications are inadequate to prevent K deficiencies and large negative annual soil K balances in farmer fields (average −62 kgK ha−1). On-farm fertilizer trials indicated that nearly 80% of rice crops and 70% of maize crops achieved higher yields with the application of K fertilizer. Addressing K limitations will require an enhanced capacity to predict crop responses to K fertilizer, together with long-term, flexible fertilizer and crop residue management strategies. Furthermore, similar K limitations have probably emerged in other regions globally due to intensive cropping with insufficient K replenishment, which must be addressed to close yield gaps on existing farmland. Future yield improvements will require a closer examination of specific production factors and their interactions. This study quantifies potassium (K) limitations in Indonesia’s intensive cereal cropping systems and reveals that current soil K levels and fertilizer applications are inadequate to meet crop needs, exacerbating the existing yield gap in rice–maize systems in Indonesia and other countries in Southeast Asia.