Assessment of phenology of winter wheat using Sentinel 2 multispectral data for varying sowing dates

Wheat is one most widely grown and consumed crops globally. Region-wise, the north Indian plains are one of the largest producers of wheat in the world. However, there remains a substantial variation in the sowing dates and thus the phenology of wheat grown in the area owing to variation in cropping patterns, soil type and agricultural practices. In this study, field data including the extent of wheat crops along with their sowing and harvest dates were collected in the Gautam Buddha Nagar district of Uttar Pradesh, India during the 2022-23 crop season. The study region is then classified into croplands and further into wheat and non-wheat areas using the random forest classifier in the Google Earth Engine. On the basis of the sowing dates, the study region is divided into early sowing (sowing date before 10 November 2022) and late sowing (sowing date after 25 November 2022) areas. The phenology of the wheat agricultural fields is analyzed using the normalized difference vegetation index (NDVI) derived using the Sentinel 2 surface reflectance data product available in the Google Earth Engine. Results showed that the early sowing wheat has the largest period (6 to 7 weeks) in which canopy cover was near maximum. The same period for late sown wheat was found as 4 to 5 weeks for late sown wheat. In general, the peak vegetation density for the crop season decreased as the sowing time of the wheat was delayed. The average value of peak normalized difference red-edge index (NDRE) was found as 0.67 (in second week of February 2023) and 0.62 (in first week of March 2023) for the early and late sown wheat, respectively. The lengths of the crop seasons of the early and late sown wheat were found as 140 and 120 days, respectively. The findings of the present study can be extrapolated to understand the phenology as well as the yield patterns of the wheat in one largest wheat producing regions in the world.