Can mulching of maize straw complement deficit irrigation to improve water use efficiency and productivity of winter wheat in North China Plain?

Improving resource-use efficiency is vital for sustainable agricultural production and food security in water-scarce regions such as North China Plain. The aim of this study was to assess the effects of irrigation and straw-mulch on accumulated intercepted photosynthetically active radiation (AIPAR), radiation-use efficiency (RUE) and water-use efficiency (WUE) of wheat. A two-factorial field experiment was carried out at Luancheng Research Station (China) during 2015-16 and 2016-17. The factors included three irrigation levels - full (FI), deficit (DI) and partial root-zone drying (PRD), which besides rainfall received 200, 100 and 100 mm of irrigation, respectively, and two mulching strategies - mulch and no-mulch: similar to 8 and 0 Mg ha(-1), respectively. The results showed that mulch reduced AIPAR (6-11%) and increased RUE for total aboveground dry biomass (3-9%). Mulch affected intercepted photosynthetically active radiation (IPAR) between the tillering and anthesis stages, largely because of reduced soil surface temperature (0.8-1.5 degrees C), which led to delayed growth/development and impaired light interception. No significant difference was observed between DI and PRD for grain yield; however, effects on WUE varied during the two seasons. DI led to higher WUE during season I compared to PRD, while PRD resulted in highest WUE during season II. AIPAR was reduced under DI and PRD; however, RUE remained unaffected for irrigation treatments. The complementary effects of mulch were observed only under DI where WUE was increased by 4-6%. The results imply that the PRD irrigation under field conditions is not as effective as it has been anticipated, especially in soils with high clay content. Mulch induced reduction in growth/development tends to nullify its positive effects through water conservation. Taken together, these results reiterate the need to further optimize mulching and PRD irrigation practices before recommending their use under field conditions, especially for small grain cereals.