Divergent climate feedbacks on winter wheat growing and dormancy periods as affected by sowing date in the North China Plain

Abstract

Abstract. Crop phenology exerts measurable impacts on soil surface\nproperties, biophysical processes and climate feedbacks, particularly at\nlocal or regional scales. Nevertheless, the response of surface biophysical\nprocesses to climate feedbacks as affected by sowing date in winter wheat\ncroplands has been overlooked, especially during winter dormancy. The\ndynamics of leaf area index (LAI), surface energy balance and canopy\ntemperature ( Tc ) were simulated by a modified SiBcrop (Simple Biosphere) model under two\nsowing date scenarios (early sowing, EP; late sowing, LP) at 10\xa0stations in\nthe North China Plain. The results showed that the SiBcrop model with a modified\ncrop phenology scheme well simulated the seasonal dynamic of LAI, Tc ,\nphenology and surface heat fluxes. An earlier sowing date had a higher LAI with\nearlier development than a later sowing date. But the response of Tc to\nthe sowing date exhibited opposite patterns during the dormancy and active-growth periods: EP led to higher Tc (0.05\u2009K) than LP in the dormancy\nperiod and lower Tc ( −0.2 \u2009K) in the growth period. The highest difference\n(0.6\u2009K) between EP and LP happened at the time when wheat was sown in EP but\nwas not in LP. The higher LAI captured more net radiation with a warming\neffect but partitioned more energy into latent heat flux with cooling. The\nclimate feedback of the sowing date, which was more obvious in winter in the\nnorthern areas and in the growing period in the southern areas, was\ndetermined by the relative contributions of the albedo radiative process and\npartitioning non-radiative process. The study highlights the surface\nbiophysical process of land management in modulating climate.