Rice in the tropics and subtropics is typically produced on small landholdings, which can vary across short distances in management practices, availability of irrigation water, and yield. These variations influence constraints at the field level and affect the needs of rice for fertilizer. Fertilizer and crop management guidelines customized to field-specific conditions could markedly improve productivity and profitability of rice farming in such small landholdings. Research has resulted in science-based principles for site-specific nutrient management (SSNM) and integrated crop management (ICM) in rice-growing environments. Extension workers, crop advisors, and farmers now need simple tools, which use the principles of SSNM and ICM to rapidly indicate the best management practices customized for specific fields and rice-growing conditions. Internet and mobile phone based tools are being developed to rapidly acquire essential information from farmers and then calculate and deliver to farmers a customized guideline for their field. The acquisition of information from farmers requires answers through mobile phone or Internet to 10 to 15 easy-to-answer questions regarding historical rice yields, rice variety, crop residue management, water supply, crop rotation, and landscape position. The answers are then used by country and region-specific ‘Nutrient Manager for Rice’ and ‘Rice Crop Manager’ software to calculate and deliver to farmers a customized guideline in their local language. Applications of ‘Nutrient Manager for Rice’ using the Internet, interactive voice response (IVR) with mobile phones, and Smartphones are available in the Philippines. As of April 2011, Internet applications of ‘Nutrient Manager for Rice’ were also released in local languages in Indonesia and Guangdong Province, China. Internet applications are under development in Bangladesh, West Africa, India, and Vietnam. Initiatives are underway to integrate nutrient and crop management guidelines obtained through mobile phone applications with other services for farmers including mobile banking, crop insurance, and improved access to input providers.