Analysis of site-specific N balances in heterogeneous croplands using digital methods

In this study, the spatial variability of nitrogen (N) balances were determined on heterogeneous arable fields in southern Germany using digital methods (combine yield sensing system, tractor mounted multispectral sensor and satellite data, vegetation indices, and models). The aim of this study is to precisely localize N surplus and nitrogen loss potentials through a high spatial resolution. The spatial variability of plant properties (yield, N uptake) were determined in order to calculate the N balances. The spatial variability of soil properties (soil organic carbon content, soil total nitrogen content, available water capacity) were determined to identify the causes of high or low N surplus on sub fields. N surplus, yield, and N uptake determined using different digital methods showed similar spatial variability. N surplus determined in test plots correlated best with N surplus calculated using tractor mounted multispectral sensor data (up to r = 0.67). Site-specific N balancing identified zones with high N loss potential (N surplus up to over 100 kg ha⁻¹), even if, on average, N inputs and N outputs are almost balanced (N surplus = 0). Soil properties showed considerable spatial variation within the fields. Soil organic carbon and soil total nitrogen content was closely correlated in all fields (up to r = 0.97) and were most closely positively correlated with yield and N uptake (up to r = 0.62) and negatively correlated with N surplus (up to r = − 0.62). The combine yield sensor data showed weaker correlations with soil parameters than tractor mounted multispectral sensor and satellite data. Based on these results, digital technologies are suitable for the calculation of site-specific N surplus. However, their accuracy must be further improved before they can be used to make precise management decisions. Site-specific N balancing using digital methods makes it possible to identify N loss potentials at a sub field scale.