Interaction between contrasting rice genotypes and soil physical conditions induced by hydraulic stresses typical of alternate wetting and drying irrigation of soil

Huan Fang,Gareth J. Norton,Paul D. Hallett,Sacha J. Mooney,Xinhua Peng,Annette C. Raffan,Hu Zhou,Adam H. Price

doi:10.1007/s11104-018-3715-5

Abstract

Background and aimsAlternate wetting and drying (AWD) saves water in paddy rice production but could influence soil physical conditions and root growth. This study investigated the interaction between contrasting rice genotypes, soil structure and mechanical impedance influenced by hydraulic stresses typical of AWD.MethodsContrasting rice genotypes, IR64 and deeper-rooting Black Gora were grown in various soil conditions for 2 weeks. For the AWD treatments the soil was either maintained in a puddled state, equilibrated to −5 kPa (WET), or dried to −50 kPa and then rewetted at the water potential of −5 kPa (DRY-WET). There was an additional manipulated macropore structure treatment, i.e. the soil was broken into aggregates, packed into cores and equilibrated to −5 kPa (REPACKED). A flooded treatment (puddled soil remained flooded until harvest) was set as a control (FLOODED). Soil bulk density, penetration resistance and X-ray Computed Tomography (CT) derived macropore structure were measured. Total root length, root surface area, root volume, average diameter, and tip number were determined by WinRhizo.ResultsAWD induced formation of macropores and slightly increased soil mechanical impedance. The total root length of the AWD and REPACKED treatments were 1.7–2.2 and 3.5–4.2 times greater than that of the FLOODED treatment. There was no significant difference between WET and DRY-WET treatments. The differences between genotypes were minimal.ConclusionsAWD influenced soil physical properties and some root characteristics of rice seedlings, but drying soil initially to −50 kPa versus −5 kPa had no impact. Macropores formed intentionally from repacking caused a large change in root characteristics.

Highlights

Rice (Oryza sativa L.) is the staple food for over half of the world’s population (Chen et al 2014)
This was reflected in the calculated total porosity, but when separated into air-filled porosity at −5 kPa, the equivalent of 60 μm macropores, the REPACKED cores were very different to the FLOODED ones
The water potentials during the growing period were the same for the treatments, except for the FLOODED treatment, the water contents were different because their different soil structures affected their water holding capacity (Table 1)

Summary

Introduction

Rice (Oryza sativa L.) is the staple food for over half of the world’s population (Chen et al 2014). AWD is likely to produce different soil physical conditions for rice growth than a flooded system, potentially influencing cultivar choice to maximise plant performance. Drying and wetting cycles from AWD have been shown to affect paddy soil structure compared to flooded systems (Zhang et al 2003) and it has been demonstrated that AWD irreversibly increases soil strength at least in the top 12 cm of the soil (Norton et al 2017). Yoshida and Hallett (2008) found drying of paddy soils to −50 kPa water potential increased mechanical strength considerably, and that this strength did not decrease with subsequent wetting. Alternate wetting and drying (AWD) saves water in paddy rice production but could influence soil physical conditions and root growth. This study investigated the interaction between contrasting rice genotypes, soil structure and mechanical impedance influenced by hydraulic stresses typical of AWD.

Objectives

Methods

Results

Discussion

Conclusion