Stable soil moisture cuts water use while lifting tomato output and quality, study finds

A research paper published in Engineering, outlines how mitigating soil moisture fluctuations (SMFs) via regulated slow wetting irrigation delivers coordinated gains in water conservation, crop yield and fruit nutritional quality, based on greenhouse tomato trials conducted by researchers from China Agricultural University alongside overseas collaborators.

Global agricultural water shortages have created persistent trade-offs between food production, nutritional quality and water conservation, as conventional irrigation creates repeated drying-rewetting cycles that destabilize rhizosphere microbial communities and trigger plant stress signaling pathways. The research set three irrigation treatments defined by distinct wetting processes: fast wetting (FW), medium wetting (MW) and slow wetting (SW), quantified by average quantity per time-volume (AQTV), an indicator measuring irrigation intensity per unit wetted soil volume. Lower AQTV values correspond to gentler infiltration and smaller SMFs, while the study standardized planned wet soil depth and irrigation upper and lower limits across all groups to eliminate baseline differences in average soil water content and wetted soil volume.

Field sampling and multiomics profiling were deployed to unpack the underlying mechanisms. Rhizosphere soil 16S rRNA amplicon sequencing tracked bacterial community shifts, fruit RNA-seq transcriptomics captured gene expression patterns, and untargeted LC-MS metabolomics recorded metabolite variations linked to tomato quality traits. Sequencing data revealed that slowed wetting elevated soil bacterial alpha diversity; phylum-level profiling showed rising relative abundance of Myxococcota and Chloroflexi alongside reduced Actinobacteria abundance, particularly the antagonistic genus Streptomyces. Functional prediction via FAPROTAX indicated suppressed aerobic chemoheterotrophy and enhanced nitrate reduction under reduced SMFs, accompanied by consistent improvements in soil organic carbon, organic matter, total nitrogen, available nitrogen and available phosphorus concentrations.

Transcriptome and metabolome joint analysis pinpointed core functional genes regulating tomato nutrient accumulation. The ascorbic acid biosynthesis gene GME and regeneration gene DHAR displayed upregulated expression under SW treatment, supporting vitamin C retention, while inhibited IDH1 and SDBH expression in the TCA cycle restrained organic acid synthesis. Genes crtB and crtH, coding rate-limiting enzymes in lycopene biosynthesis, were significantly upregulated with milder moisture variation, limiting lycopene breakdown into abscisic acid precursors. Structural equation modeling (SEM) validated a cascading pathway: stabilized soil moisture directly raises microbial diversity and soil fertility, which activates transcriptional programs for nutrient assimilation and antioxidant production, while reduced SMFs also exert direct regulatory effects on fruit metabolic pathways shaping yield and quality.

The paper notes that slow wetting irrigation achieves a 30%–35% reduction in total irrigation quota while lifting tomato yield, vitamin C and lycopene concentrations. The research departs from conventional perceptions of irrigation dry-wet cycles and offers a low-complexity precision irrigation framework suitable for water-scarce agricultural zones, without the intricate management demands of regulated deficit irrigation. The authors state that follow-up work will separate SMF amplitude and frequency to clarify their independent microbial impacts and conduct field validation across diverse soil textures and crop varieties to expand practical application scope.

The paper “Reducing Soil Moisture Fluctuations Significantly Improves Crop Yield and Quality: Insight into Multiomics in Soil–Plant Systems,” is authored by Weijie Chen, Naikun Kuang, Christoph Martin, Akshit Puri, Bin Liu, Jing He, Yunpeng Zhou, Yunkai Li. Full text of the open access paper: https://doi.org/10.1016/j.eng.2025.10.038. For more information about Engineering, visit the website at https://www.sciencedirect.com/journal/engineering.