Incorporating root distribution factor to evaluate soil water status for winter wheat

• RASW is easily calculated but takes the soil water availability to crops equally.
• Relative root length abundance factor was introduced into the RASW (RASWr).
• RASWr improved the correlation of RASW with crop performance.
• Root factor can be simulated by a form parameter and maximum rooting depth.

Many indicators have been developed to determine when and how much to irrigate to improve the irrigation efficiency. The relative available soil water (RASW) is an indicator that can be easily calculated but takes the availability of soil water to crops equally throughout the root zone profile without considering the soil water uptake ability as related to the root distribution. This study introduced a root parameter related to the relative root length abundance at different soil depth into RASW to evaluate the soil moisture conditions on crop performance (simplified as RASWr). The field study was carried out in the North China Plain (NCP) from 2010 to 2014 for four growing seasons of winter wheat (Triticum aestivum L.) under six irrigation treatments to create different soil moisture conditions. The results showed that RASWr was more closely related than RASW to the leaf water potential and stomatal conductance, and it was less affected by daily weather fluctuations as compared to crop water stress index (CWSI). Compared to the fraction of transpirable soil water (FTSW), RASWr was more easily obtained. The simple RASW indicator was improved by incorporating the relative root abundance factor which can be simulated by a form parameter of root distribution and maximum rooting depth at different growth stages of the crop.