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Soil drying and re-wetting effects on phosphorus availability and plant yields

Research output: ThesisDoctoral Thesis

Published
Publication date2018
Number of pages238
QualificationPhD
Awarding Institution
Supervisors/Advisors
  • Dodd, Ian, Supervisor
  • Blackwell, Martin S. A., Supervisor, External person
Thesis sponsors
  • BBSRC
Publisher
  • Lancaster University
Original languageEnglish

Abstract

Water and phosphorus (P) are essential resources for crop production, yet both are increasingly limited, threatening global food security. Soil drying and re-wetting (DRW) has reportedly increased P availability in numerous soils, whilst intermittent irrigation that applies less water than conventional full irrigation can maintain crop yields. To test the hypothesis that DRW could release P at soil water potentials (SWPs) that can support plant growth, thereby increasing crop P use efficiency and yields, experiments at different scales aimed to evaluate P release and plant uptake. Laboratory studies using three low-P UK soils determined that available P (sodium bicarbonate extractable P) significantly increased (by 4-7 mg kg-1) as SWP decreased (to a minimum of -212 MPa). A significant change point (releasing 2 mg P kg-1) occurred at -2.9 MPa. A pot study showed that surface soil drying to this change point did not increase P availability over one or two DRW cycles, suggesting laboratory results could not be scaled up spatially and temporally. Initially air-drying (to -38 MPa) and re-wetting soil prior to planting Brachypodium distachyon in pots significantly increased available P at transplanting (by 1 mg kg-1) and doubled grain yields independent of P fertiliser application. In a field trial in central Madagascar in low-P, highly P-fixing soil, applying alternate wetting and drying (AWD) or post-anthesis soil drying to Oryza sativa hardly altered P uptake or yields. Thus, DRW increased P availability and yields in pots, but plants did not benefit during a cropping cycle in the field. Applying P fertiliser (10 or 25 kg ha-1) had a greater effect than AWD, with optimal harvest index (HI) and P use efficiency (PUE) at the intermediate rate. Further research to determine locally-relevant management techniques, stimulating P release at appropriate spatial and temporal scales to allow plant uptake, is urgently required.