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.

China’s grain yield increased from 1 t ha^–1 in 1961 to 6 t ha^–1 in 2015, while successfully feeding not only its large population but also supplying agricultural products all over the world.  These achievements were greatly supported by modern technology and distinct governmental policy.  However, China’s grain production has been causing a number of problems mainly related to declining natural resources and a lack of environmental protection.  Due to the growing population and changing dietary requirements, increasing food production must be achieved by increasing resource use efficiency while minimizing environmental costs.  We propose two novel development pathways that can potentially sustain agricultural crop production in the next few decades: (i) enhancing nutrient use efficiency with zero increase in chemical fertilizer input until 2020 and (ii) concurrently increasing grain yield and nutrient use efficiency for sustainable intensification with integrated nutrient management after 2020.  This paper provides a perspective on further agricultural developments and challenges, and useful knowledge of our valuable experiences for other developing countries.

China is in a dominant position in apple production globally with both the largest apple growing area and the largest export of fresh apple fruits. However, the annual productivity of China’s apple is significantly lower than that of other dominant apple producing countries. In addition, apple production is based on excessive application of chemical fertilizers and the nutrient use efficiency (especially nitrogen) is therefore low and the nutrient emissions to the environment are high. Apple production in China is considerably contributes to farmers’ incomes and is important as export product. There is an urgent need to enhance apple productivity and improve nutrient use efficiencies in intensive apple production systems in the country. These can be attained by improved understanding of production potential, yield gaps, nutrient use and best management in apple orchards. To the end, priorities in research on apple production systems and required political support are described which may lead to more sustainable and environmental-friendly intensification of apple production in China.

Wheat is an important source of essential minerals for human body. Breeding wheat with high grain mineral concentration thus benefits human health. The objective of present study was to identify quantitative trait loci (QTLs) controlling grain mineral concentration and to evaluate the relation between nitrogen (N) and other essential minerals in winter wheat. Wheat grains were harvested from field experiment which conducted in China and analyzed for this purpose. Forty-three QTLs controlling grain mineral concentration and nitrogen-related traits were detected by using a double haploid (DH) population derived from winter wheat varieties Hanxuan 10 and Lumai 14. Chromosomes 4D and 5A might be very important in controlling mineral status in wheat grains. Significant positive correlations were found between grain nitrogen concentration (GNC) and nutrients Fe, Mn, Cu, Mg concentrations (FeGC, MnGC, CuGC, MgGC). Flag leaf N concentration at anthesis (FLNC) significantly and positively correlated with GNC, FeGC, MnGC, and CuGC. The study extended our knowledge on minerals in wheat grains and suggested which interactions between minerals should be considered in future breeding program.

Maize plants adapt to low phosphorus (P) stress by increasing root growth. It is of importance to know the extent to which genetic improvement of root growth can enhance P acquisiton. In the present study, the contribution of root growth improvement to efficient P acquisition was evaluated in two soils using T149 and T222, a pair of near isogenic maize testcrosses which were derived from a backcross BC4F3 population. T149 and T222 showed no difference in shoot biomass and leaf area under normal growth conditions, but differed greatly in root growth. T149 had longer lateral roots and a larger root surface area compared to T222. In calcareous soil, when P was insufficient, i.e., when P was either supplied as KH2PO4 at a concentration of 50 mg P kg-1 soil, or in the form of Phy-P, Ca3-P or Ca10-P, a 43% increase in root length in T149 compared to T222 resulted in an increase in P uptake by 53%, and shoot biomass by 48%. In acid soil, however, when P supply was insufficient, i.e., when P was supplied as KH2PO4 at a concentration of 100 mg P kg-1 soil, or in the form of Phy-P, Fe-P or Al-P, a 32% increase in root length in T149 compared to T222 resulted in an increase in P uptake by only 12%, and shoot biomass by 7%. No significant differences in the exudation of organic acids and APase activity were found between the two genotypes. It is concluded that genetic improvement of root growth can efficiently increase P acquisition in calcareous soils. In acid soils, however, improvements in the physiological traits of roots, in addition to their size, seem to be required for efficient P acquisition.

Chemical fertilizer plays an important role in increasing food production in China. Nevertheless, excessive nitrogen fertilizer use in China has resulted in severe environmental problems. The goal of this paper is to examine the impacts of an improved nitrogen management (INM) training experiment on farmers’ chemical nitrogen (N) use behaviors in maize production in China. Based on household data collected from 813 maize farmers in Shandong, China, this study finds that while INM training can significantly reduce farmers’ N fertilizer use, an INM training is not sufficient to change farmer’s practices significantly, and farmers only partially adopted the recommended INM. This study reveals that China faces challenges to transform its agriculture to a low-carbon one. The research also sheds light on China’s extension system and future technologies in meeting the objectives of reducing the excessive nitrogen fertilizer use in agricultural production.

Aerobic rice has the advantage of saving water. Most published work has focused on improving its yield, while few reported on its micronutrient status. In fact, Fe deficiency is a common nutritional problem in the production of aerobic rice. Shortterm hydroponic culture experiments were conducted to study the response of aerobic rice to Fe deficiency and the effect of root exudates from Fe-deficient wheat on its Fe uptake ability. The results indicate that the amount of phytosiderophores (PS) released from aerobic rice did not increase under Fe deficient conditions. The Fe(III) reducing capacity of Fe-deficient aerobic rice did not increase and the solution pH did not decrease significantly. What’s more, no obvious swelling was observed in the root tips. Aerobic rice did not show special responses to improve their Fe nutrition under Fe deficiency as both strategy I and II plants though they were very sensitive to Fe deficiency. This may be a reason which causes Fe deficiency problem in aerobic rice. However, root exudates from Fe-deficient wheat (PSw) could improve its Fe nutrition in the presence of insoluble Fe(OH)3. This suggests that aerobic rice could utilize Fe activated by PSw.