Abstract
AimsCracks and biopores in compacted soil such as plough pans could aid deep rooting, mitigating constraints to seasonal upland use of paddy fields for rice production. This research investigated how soil macropores through a simulated plough pan affects root growth of contrasting deep and shallow rooting rice genotypes.MethodsDeep rooting Black Gora and shallow rooting IR64 rice varieties were grown in packed cores of unsaturated soil in a controlled greenhouse. Simulated biopores and cracks (macropores) were inserted through the plough pan to form treatments with no macropores, biopores, cracks, and combined cracks and biopores. Different root parameters such as root length density (RLD), root volume, root diameter, number of root tips and branches were measured. The number of roots was calculated manually, including the number of roots growing through macropores in the plough pan layer.ResultsPlough pans with macropores had 25–32% more roots than with no macropores. RLD was 55% greater in the plough pan layer if cracks were present compared to biopores. Conversely, RLD was 26% less in subsoil if the plough pan had cracks compared to biopores. Different root parameters were greatly influenced by the presence of macropores in the plough pan, and deep-rooted Black Gora produced 81% greater RLD, 30% more root numbers and 103% more branching than the shallow rooted rice genotype IR64 within the plough pan layer.ConclusionsMacropores greatly improve rice root growth through plough pans for a deep rooting but not a shallow rooting rice variety. Whereas cracks produce a greater number of roots in the plough pan, biopores result in greater root branching and root numbers deeper in subsoil.
Highlights
Rice is one of the main food crops in the world and around 90% of rice is produced and consumed in Asia (Coats 2003)
About 8–32% greater shoot dry weight was recorded for Black Gora than IR64 (Table 2)
Root length density in the plough pan layer differed between genotypes and soil structure treatments (Fig. 2b)
Summary
Rice is one of the main food crops in the world and around 90% of rice is produced and consumed in Asia (Coats 2003). The sustainability of flooded rice production is threatened by fresh water scarcity, labour shortages, and higher irrigation cost that affect the farmer (Bouman and Tuong 2001; Godfray et al 2010) These impacts are exacerbated by climate change, with methane emission from flooded paddy systems thought to contribute 12% of the global emissions of this greenhouse gas. A conversion from continuously flooded rice paddy systems to either upland rice that is continuously drained or to alternate wetting and drying (AWD) irrigation offers solutions to help tackle water scarcity and decrease methane emissions. These new approaches can produce more rice with less water and more efficient fertiliser capture (Bouman 2001).
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