Long-term field experiments have provided important information for guiding agricultural development and are valuable for determining yield change over time, for assessing soil nutrient status and system sustainability as well as for predicting soil-carrying capacity. In China, rice (Oryza sativa L.), wheat (Triticum aestivum L.) and maize (Zea mays L.) are the main crops grown on an area of 31.7, 28.9 and 25.9 million hectares, respectively.
