Combining Fractional Cover Images with One-Class Classifiers Enables Near Real-Time Monitoring of Fallows in the Northern Grains Region of Australia

Abstract

Fallows are widespread in dryland cropping systems. However, timely information about their spatial extent and location remains scarce. To overcome this lack of information, we propose to classify fractional cover data from Sentinel-2 with biased support vector machines. Fractional cover images describe the land surface in intuitive, biophysical terms, which reduces the spectral variability within the fallow class. Biased support vector machines are a type of one-class classifiers that require labelled data for the class of interest and unlabelled data for the other classes. They allow us to extrapolate in-situ observations collected during flowering to the rest of the growing season to generate large training data sets, thereby reducing the data collection requirements. We tested this approach to monitor fallows in the northern grains region of Australia and showed that the seasonal fallow extent can be mapped with >92% accuracy both during the summer and winter seasons. The summer fallow extent can be accurately mapped as early as mid-December (1-4 months before harvest). The winter fallow extent can be accurately mapped from mid-August (2-4 months before harvest). Our method also detected emergence dates successfully, indicating the near real-time accuracy of our method. We estimated that the extent of fallow fields across the northern grains region of Australia ranged between 50% in winter 2017 and 85% in winter 2019. Our method is scalable, sensor independent and economical to run. As such, it lays the foundations for reconstructing and monitoring the cropping dynamics in Australia.

Natural afforestation of the fallows in the Western Polissya

“…Bilous [16; 17] investigated afforestation of fallows and the influence of grass vegetation on them, plant growth on poor old arable land, and L. Boletus [18] -the role of fallows in preserving the rare fauna that inhabits them. Interesting are the studies by L.P. Lysohor et al [19][20][21], who proposed ways to attract fallows as renewable elements of the eco-network, and researchers [22][23][24], which found recovery sites characterised by significant cenotic diversity [25] and the presence of sozologically valuable species [26][27][28], and the influence of afforestation of agricultural soils and the species composition of trees on changes in the physical characteristics of the soil [29].…”