Image-based tracking of ripening in wheat cultivar mixtures: A quantifying approach parallel to the conventional phenology

Abstract

Developing the quantitative methods independent of the conventional qualitative phenology is a vital necessity for evaluating the temporal trends in the crop growth cycle, particularly in the heterogeneous canopies of cultivar mixtures. A digital camera was used to take ground-based nadir images during two years (2014–15 and 2015–16) of a field experiment conducted at the School of Agriculture, Shiraz University, Iran, for monitoring and quantifying the ripening trends in wheat cultivar mixtures with different ripening patterns grown under two irrigation conditions. The experimental treatments consisted of 4 early- to middle-ripening wheat cultivars and their 10 mixtures, under post-well- and deficit-irrigated conditions, arranged in a randomized complete block design with 3 replicates. Then the images were processed and three image-derived indices including CC (canopy cover), GR [(G-R)/G; RGB color system], and CCGR (CC × GR) were used as the quantifying criteria. The declining trends of these indices during ripening showed strong fits to binomial equations, based on which simple prediction models were suggested and validated. Furthermore, the split linear trends and their slopes were estimated to assess the short-term variations. Some agronomic aspects were also evidenced using the mixtures-monoculture diversions, and the relationship between CC and GR. The frameworks evaluated appear to provide reliable and simple solutions for quantifying the crop temporal trends parallel to the conventional phenology.