Research Subject 2.3 “Detecting phosphate status in soil and in maize canopies by non-invasive methods” within the International Research Training Group "Adaptation of maize-based food-feed-energy systems to limited phosphate resources”

The fate of phosphate in the environment equals an open cycle. Phosphate is supplied by mining and fertilizer production, followed by different steps of phosphate utilisation, including primary production, animal feed, human food and conversion of biomass to energy and raw materials, with accumulation in soils, little return and in particular severe environmental losses. Most importantly, phosphate is a limited essential nutrient (350 years lifetime). It is unknown how the steps within the cycle will react and interact, if phosphate is increasingly limited and economic pressure escalates as a result. Closing cycles and reducing primary phosphate consumption are fundamental future challenges.

Globally, maize is one of the most important crops, with high phosphate sensitivity, therefore, ideal for studying the consequences of phosphate limitation. China and Germany together cover the whole variation of maize production systems in food-feed-energy supply chains and a wide range of climatic conditions.

Research is driven by the hypothesis that under phosphate limited conditions, high productivity and high phosphate use efficiency can be achieved simultaneously by adapting phosphate cycling and availability (sources) to the multipurpose phosphate demands (sinks) in maize based food-feed-energy systems.

In an interdisciplinary system oriented approach, twelve complementary research groups at the China Agricultural University (Beijing) and at the University of Hohenheim investigate (1) the genetic potential of maize populations and mechanisms of their ability to adapt to limited phosphate supply, (2) maize cultivation under limited phosphate supply at field scale, (3) mechanistic interactions of related products with their utilization in human and animal nutrition, and phosphate recovery by biomass conversion. (4) An economic evaluation will be done at plot, farm, region and sector levels, taking market effects into consideration. Joint field experiments in China and Germany allow for complementary and comparative analyses. Genetic and molecular approaches, modern spectroscopic methods, economic surveys and modelling approaches at different scales will be used.

Phosphate status differs both, spatially and temporally in the soil and in the crop canopy during plant growth. Due to high expenditure of time and costs of standard chemical analyses, phosphate patterns in soils are typically monitored in a large grid size of about one sample per ha once per year, which is far to coarse at given variability. Encouraged by the successful example of optical nitrogen sensors for on-the-go measurement in plant canopies, the research idea of RS 2.3 is the investigation of the spectral absorbance behaviour of phosphate in soil and plant tissues in visible, near infrared and mid infrared (VIS-NIR-MIR) wavelengths range as basis for the development of optical measurement systems for non-invasive, quasi-continuous detection of phosphate status.