Yield and water use efficiency of wheat in the Loess Plateau: Responses to root pruning and defoliation

- Root pruning increased wheat yield at high seeding rate condition in a dry year.
- Defoliation reduced wheat grain yield and water use efficiency in a wet year.
- The dual-purpose use of winter wheat needs further studies in the region.

Improved crop yield and water use efficiency (yield per unit evapotranspiration) is important for food security in semiarid areas including the Loess Plateau of China, the focus of this study. We investigated the responses of winter wheat yield, evapotranspiration and water use efficiency to management practices aimed at modulating water use. Six treatments resulted from the factorial combination of practices, i.e. root pruning, defoliation and untreated control, and two seeding rates (15-19, 19-23 g m−2). Crops were grown under straw mulching over two seasons; the drier season had 341 mm in-fallow rain and 160 mm in-season rain compared with the wetter season which had 392 and 252 mm, respectively.Yield ranged from 2748 to 6669 kg ha−1 and responded to both management and the interaction between management and seeding rate. Relative to controls, root pruning increased grain yield by 28% in the dry season and by 8% in the wet season at high seeding rate; root pruning did not affect yield at low seeding rate. Seasonal evapotranspiration did not respond to any of the experimental sources of variation. Higher yield thus lead to increased water use efficiency of root-pruned crops in the dry season at high seeding rate. Defoliation did not affect yield in the dry season, but decreased biomass and grain yield in the wet season compared to the control. Water use efficiency was lower under defoliation at high seeding rate in the wet year. It is concluded that that root pruning could improve wheat yield and water use efficiency in dry conditions of winter wheat under stubble mulching. Considering forage from defoliation, the dual-purpose use of winter wheat may be possible without effect on grain yield in dry seasons but would reduce grain yield under the prevalent conditions of the Loess Plateau.