Plant roots play a significant role in plant growth by exploiting soil resources via the uptake of water and nutrients. Root traits such as fine root diameter, specific root length, specific root area, root angle, and root length density are considered useful traits for improving plant productivity under drought conditions. Therefore, understanding interactions between roots and their surrounding soil environment is important, which can be improved through root phenotyping. With the advancement in technologies, many tools have been developed for root phenotyping. Canopy temperature depression (CTD) has been considered a good technique for field phenotyping of crops under drought and is used to estimate crop yield as well as root traits in relation to drought tolerance. Both laboratory and field-based methods for phenotyping root traits have been developed including soil sampling, mini-rhizotron, rhizotrons, thermography and non-soil techniques. Recently, a non-invasive approach of X-ray computed tomography (CT) has provided a break-through to study the root architecture in three dimensions (3-D). This review summarizes methods for root phenotyping. On the basis of this review, it can be concluded that root traits are useful characters to be included in future breeding programs and for selecting better cultivars to increase crop yield under water-limited environments.

Drought is the most important factor limiting winter wheat yield in the North China Plain (NCP). Choosing high-yielding cultivars is an important measure to minimize the negative effects of drought stress. Field studies were conducted with 10 cultivars in the 2020–2022 seasons under three irrigation treatments (I0, without irrigation; I1, irrigated at jointing stage; I2, irrigated at jointing and anthesis stages) in the NCP to examine the water use strategies and root and shoot traits of high-yielding cultivars under different water supply conditions. The results showed that yield variation among cultivars was 21.2–24.6%, 23.7–25.9% and 11.6–15.3% for the I0, I1 and I2 treatments, respectively. Under water deficit conditions (I0 and I1), high-yielding cultivars reduced water use during vegetative stages and increased soil water use during reproductive stages, especially water use from deeper soil layers. Those cultivars with higher root length density (RLD) in deep soil layers exhibited higher water uptake. Each additional millimeter of water used after anthesis from the 100–200 cm soil layers increased grain yield by 23.6–29.6 kg/ha and 16.4–28.5 kg/ha under I0 and I1, respectively. This water use strategy enhanced dry matter accumulation after anthesis, decreased canopy temperature (CT) and increased relative leaf water contents (RLWC), which ultimately improved grain yield. For winter wheat grown under I2, cultivars that decreased water use after anthesis had higher water productivity (WP). Root length (RL), root weight (RW) and root:shoot ratio were each negatively correlated with grain yield, while above-ground biomass was positively correlated with grain yield. Therefore, higher dry matter accumulation and smaller root systems are two important traits of high-yielding cultivars under sufficient water supply conditions (I2) in the NCP.

This study aims to elucidate the effects of split-topdressed nitrogen (N) via micro-sprinkling fertigation on grain filling and N translocation and overcome the bottleneck in the synchronous enhancement of yield-quality under traditional border irrigation with broadcast N application. Using Gaoyou 2018 (strong gluten) and Heng 4399 (medium gluten), four treatments were established: conventional border irrigation with N at jointing (I1), micro-sprinkler irrigation with N at jointing (I2), micro-sprinkler irrigation with N at jointing and anthesis (1:1; I3), and micro-sprinkler irrigation with N at jointing, anthesis, and 12 days after anthesis (DAA) (5:3:2; I4). Results showed that I4 achieved the highest grain yield (10,578.6 kg·ha⁻¹; +9.6% average), primarily attributed to significantly increased thousand-kernel weight (TKW; +1.7–4.2 g). I4 accelerated mid-to-late filling, extended the active filling period, and increased final grain mass by 1.5–4.6 g. I4 promoted post-anthesis N uptake and its remobilization to grains, improving nitrogen uptake efficiency (NUpE). I4 elevated grain protein content (gliadin-to-glutenin ratio +6.0%), improved gluten characteristics, and enhanced bread-baking quality, with these advantages being more pronounced in the strong-gluten cultivar. Overall, I4 synergistically enhances grain yield and quality by optimizing grain filling and N translocation. This study provides a theoretical basis for mitigating N leaching and ammonia volatilization while implementing high-yielding, high-quality cultivation practices.