Combined effect of different irrigation and fertilization scenarios on wheat and barley development and their C-band radar response in a semi-arid region

Irrigation and fertilization are the two most important inputs determining high crop biomass production. Several in situ and remote sensing studies have investigated these drivers’ individual effects on yield. However, their combined effects on vegetation development throughout the season, as well as on their microwave response, remain to be explored. In this study, the combined effect of three irrigation and four fertilization scenarios is examined in depth over an extensive and unique database collected over fifteen wheat and barley fields in a semi-arid plain in Morocco. The database includes several in situ vegetation and soil variables, collected at near-weekly to daily intervals, as well as various variables derived from Sentinel-1 and Sentinel-2 data. The results reveal that irrigation is the main factor determining vegetation development throughout the season in the semi-arid region, with a correlation of 0.86 (p < 0.001) between the seasonal irrigation amount and the final yield. Fertilization increases the percentage of straw (13–22%) for all irrigation scenarios. Applying 25% of the recommended amount of fertilizer results in a 26% decrease in yield. Analysis of remote sensing data shows that the backscattering coefficient ( σ VV 0 and σ VH 0 ), is more sensitive to vegetation growth differences between fields than interferometric coherence and NDVI. In particular, a period of stress resulted in a decrease of 1.81 dB in σ VV 0 and 2.82 dB in σ VH 0 . This analytical study shows the importance of irrigation and fertilization for a semi-arid region and highlights promising potential applications of radar data for monitoring crop growth and water status.