S13 - Session P3 - Genotypic differences in N response, N efficiency traits and spectral reflectance behavior among six common broccoli varieties

Authors: Felix Besand *, Bianca Mausolf, Kai-Uwe Katroschan

Selection of N efficient varieties, quantitative knowledge about their N demand and a close match of fertilizer N supply with crop demand are critical issues for decreasing the crop-inherent high N budget surplus of broccoli. Two field experiments including six varieties and different N supply levels were conducted in 2020 and 2021 under northern German climate conditions to investigate genotypic differences in broccoli N use efficiency. Nitrogen supply levels (SMN at planting date plus total N of added fertilizer) amounted to 230, 310 (SMN target value for broccoli) and 390 kg N ha 1 . To evaluate the potential of different vegetation indices (NDVI, GLI, NDYI, CCCI) for increasing the precision of split N fertilizer application rates, plots were nadir-scanned in 2020 24 days after planting (DAP) and before beginning of harvest 49 DAP with a 5-channel multispectral camera (MicaSense RedEdge MX) mounted on a quadcopter drone. Depending on variety, N level and experimental year, total fresh matter yield varied between 19.3 and 28.1 Mg ha -1 , while N budget surplus ranged from about 130 to 330 kg N ha -1 . In 2020, N uptake efficiency was positively related to crop duration, particularly at the high N level. In most but not in all cases, N utilization efficiency was found to be positively related to dry matter harvest index. The fraction of broccoli heads greater 500 g increased with N fertilization also at an N supply level above the officially recommended SMN target value of 310 kg N ha -1 , exemplarily pointing out the impact of retailer standards on practical N fertilization decisions. All studied vegetation indices were affected by broccoli variety. Shortly prior to harvest the effect of N level exceeded the varietal effect only on GLI.