Interaction between burial depth and N source in drip-fertigated maize: Agronomic performance and correlation with spectral indices

Abstract

Increasing drought severity and evaporative demand in Mediterranean areas makes it necessary to implement irrigation systems with high water and nutrient supply efficiency. The combined management of drip irrigation burial depth and different nitrogen (N) sources, thus far unexplored, predicting these effects using proximal and spectral vegetation indices. A 2-year field experiment was conducted comparing maize yield and N uptake from four N fertilization treatments: ammonium sulfate (AS), AS with the nitrification inhibitor DMPP (AS+INH), calcium nitrate (CN) and a control without N fertilization combined with surface or subsurface (30 cm depth) drip fertigation. Multispectral data were collected to calculate various vegetation indices, while the chlorophyll content was measured with a soil plant analysis development (SPAD) sensor in the second year. Subsurface drip and AS+INH increased maize grain yields compared to surface drip and AS-only (by 12 % and 18 %, respectively, P < 0.05). However, this was observed only in the second season, as were increases in grain N content. The results show that the use of CN performed better in surface drip, while the use of NH₄⁺-N-based fertilizers were recommended for subsurface irrigation. Regarding the spectral data, at the flowering-milky kernel and dent kernel phenological stages Normalized Difference Red Edge (NDRE) and the canopy chlorophyll content index (CCCI) were the two vegetation indices that best estimated agronomical parameters and were able to discriminate the phenological differences between irrigation systems. This study highlights the potential for (i) predicting yield and N uptake using proximal and multispectral sensors in drip-fertigated maize and (ii) optimizing crop performance by combining drip burial depth and N source (DMPP combined with subsurface irrigation), with relevant implications for climate change adaptation (i.e., potential improvements in crop phenology and water saving).