Understanding the nitrogen balance in barley from integrated sensing;Creating a nitrogen balance for barley crops using sensing methods

By Thijs Seubring

Abstract
With an ever-increasing population, the demand for food will rise over the coming decades. Therefore, increasing food security whilst at the same time decreasing its impact on the environment is essential. Nitrogen is one of the main inhibitors of plant growth, and ample supply is critical in growing enough food. However, providing crops with too much nitrogen, or at the wrong moment, proves to be disastrous for the environment. This is when cover crops come into play, as they leave legacy effects which can be used by the subsequent crop reducing the need for fertilizing. The concept of a plant benefitting from legacy effects left by a previous crop is called plant-soil feedback (PSF).

In this study, the effects of cover crops on the nitrogen balance of barley (Hordeum vulgare L.) were studied. The objective was to understand the nitrogen balance within an experimental agricultural parcel of barley crops by using (remote) sensing based methods. Several data sources were used to construct nitrogen balances for barley. UAV imagery was used to assess nitrogen uptake and resin bags for leaching. Moreover, literature research was done to find information about volatilization, denitrification, mineralization, and deposition.

One of the focal points of this research was to assess plant N-uptake from UAV imagery. We did this with the help of several different vegetation indices (VIs). Chlorophyll content was used as a proxy for nitrogen uptake, and Area under the curve (AUC) was used to assess the estimation. Cl_red emerged as the best estimator of nitrogen uptake compared to lab measurements of total nitrogen in the harvested crop (R2=0,65).

To create the nitrogen balances, many assumptions were made. This reduced the accuracy and precision of the balances. Therefore, the quality of the results and conclusions cannot be checked, but a proof of concept has been shown. We found that the fallow cover crop treatment generally resulted in the lowest nitrogen uptake and the highest volatilization and denitrification. On the other hand, the oat-radish and vetch-radish treatment resulted in more uptake and more leaching.

Future research might look into different ways of assessing nitrogen uptake by using different VIs or by looking into different plant properties like protein content. Furthermore, the effect of spatial variability on the nitrogen balance could also be looked into.