Abstract: Science and Technology Backyard (STB) is an integrated platform for technology innovation, knowledge transfer, people training and agricultural transformation towards sustainable intensification. STB professors, graduate students and extension workers lived and worked together with smallholder farmers in rural areas. They identified the problems that limit sustainable agriculture and provided smallholder farmers systematic, integrated and holistic solutions without time lags, limitation, fees and distances. Many people, including farmers, graduate students, extension workers, have been trained via more than 100 STBs during the last decade (Zhang et al. 2016). 

The bottom-up approach has been developed and broadly used in the STBs to study the “field-farm-agriculture” ecosystem and the “Three Rural Issues”, and to explore possible measures for achieving the three major pillars of sustainable intensification: food security, resource conservation and environmental sustainability. With the involvement of various stakeholders, e.g., government, industry, university and farmer, a series of single and integrated technologies have been developed and tested in farmers’ fields. Based on the results, the major limiting factors of crop production were identified, key technologies and models for realizing sustainable crop production have been developed. 

In this special focus, we systematically summarize the methods of technology innovation in the STBs, especially focus on identifying the problems in agricultural production and give suggestions for achieving sustainable intensification (Jiao et al. 2019). For example, we have identified that low planting density is the major limiting factor for maize production in North China, followed by inappropriate nutrient management approach, based on the data collected from 235 farmer plots in three villages in the North China Plain (Chen et al. 2019). Maize yield could be improved by 20%, and partial factor productivity (kg of grain produced per kg N applied) could be improved by 30%, by integrated soil-crop system management and improving plant density in smallholder farmers’ plots in North China Plain (Chen et al. 2019). Similar results were obtained in other crops and places, such as in wheat production of North China Plain and Northeast China Plain (Cao et al. 2019; Huang et al. 2019; Zhao et al. 2019). 

For cash crops, e.g., mango, inappropriate nutrient management and low plant density were the major limiting factors, based on data collected from 103 farmers’ field plots. By improving plant density and nutrient management, mango yield could be improved by 50%, and 20% chemical N could be saved (Zhang et al. 2019b). This has provided important value and great significance for mango production. Similar results were obtained on apple production in Shaanxi Province (Zhang et al. 2019a). In this special focus, we present seven papers about the methodology of conducting technology innovation in the STBs. We hope to improve our understanding of research approach of STBs and provide guidance for countries facing similar challenges worldwide.