COMMENTS Comments on “ Adaptation of Chinese and German maize- based food-feed-energy systems to limited phosphate resources—a new Sino-German international research training group” Antje SCHWALB (✉) Institute of Geosystems and Bioindication, Technische Universität Braunschweig, D-38106 Braunschweig, Germany Of all nutritional elements essential for plants, phosphorus is one of the most limited elements worldwide. Recent estimates that consider a continued high consumption level and compare this with the available phosphate rock reserves for the production of fertilizer and feed phosphates suggest that the available phosphorous reserves have a life expectancy of less than 300 years. In addition, the world phosphate resources are unevenly distributed with more than 70% located in Morocco and the Western Sahara where access might be at risk in the long term. In China, reserves are estimated to run out in less than 25 years, based on the current consumption, and Germany does not have any phosphate resources of its own at all. Taking these limitations into account it seems to be a paradox that overfertilization with phosphate continues, even though it causes environmental problems in water bodies, particularly in areas with high life stock densities and intensive cropping. Furthermore, phosphate is lost through the pathways of human waste and waste water, leading to additional environmental risks. Another problem is that phosphate resources may be contaminated with heavy metals such as cadmium and uranium. To extend the life of the existing phosphate reserves, the situation calls for closing of the phosphate cycles and increasing the phosphate fertilizer and feed additive utilization efficiencies. The paper by Müller and Zhang (https://doi.org/10.15302/J-FASE-2019282) thoroughly reviews the state of the art of science and current shortcomings within this context and highlight the fields of research where additional work is needed. As the authors argue, “it is virtually unknown how the steps within the phosphate cycle will react and interact if phosphate input is increasingly reduced or even limited and demand pressure can be expected to rapidly impact on prices”. The complexity of this issue calls for an interdisciplinary, if not holistic, approach to achieve solutions towards sustainability. The second part of the paper introduces the new International Research Training Group (IRTG) “Adaptation of Chinese and German maize-based food-feed-energy systems to limited phosphate resources (AMAIZE-P)”, jointly carried out by China Agricultural University (CAU, Beijing, China) and the University of Hohenheim (UHOH, Stuttgart, Germany). Maize-based cropping systems were chosen because maize is one of the most important crops world-wide, with a high phosphate demand, particularly in the early stages of growth. In addition, maize is a multi- purpose crop, providing different elements in human nutrition, animal feeding and bio-energy/biomass production. China and Germany together cover most aspects of the multi-purpose crop maize under a wide range of different climate conditions. In this uniquely interdisciplinary and international research and training program for early career scientists, the vision of a closed phosphate cycle is the driving force for science tackled by four consecutive research areas that address genetic potential, management at field and farm level, nutrition and recovery as well as economic evaluation and synthesis. Each subject area is further subdivided into two to four research subjects each, with a total of 13 Received September 15, 2019 Correspondence: antje.schwalb@tu-braunschweig.de Front. Agr. Sci. Eng. 2019, 6(4): 443–444 https://doi.org/10.15302/J-FASE-2019288 Available online at http://journal.hep.com.cn/fase © The Author(s) 2019. Published by Higher Education Press. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0)