Impact of soil puddling intensity on the root system architecture of rice (Oryza sativa L.) seedlings

Puddling of rice paddies is undertaken to create a soft soil bed for easy transplanting of rice seedlings, to control weeds and reduce water and nutrient leaching. There is a drive for less intense puddling because of its physical disturbance of soil, energy inputs and labour requirements, which may produce different soil physical conditions for root growth. The objective of this study was to investigate the influence of puddling intensity on soil structure and the subsequent impact on the growth of rice seedling roots. Three treatments with different puddling in-tensities were established: (1) No puddling; (2) Low and (3) High intensity puddling. The rice genotype, Nipponbare was grown in soil columns for 18 days. Soil bulk density, aggregate size distribution and three-dimensional (3D) macropore structure were measured. Two-dimensional root traits were determined by WinRhizo and 3D root traits were determined by X-ray Computed Tomography (CT). Our results show the percentage of large macroaggregates (> 2 mm) decreased by 69.6% (P < 0.05) for low intensity puddling and by 95.7% (P < 0.05) for high intensity puddling compared with that of no puddling. The macroporosity (> 0.03 mm) of no puddling was 2.3 times greater than low intensity puddling and 3.5 times greater than high intensity puddling. The total root lengths of no and low intensity puddling were 1.56-1.86 times greater than that of high intensity puddling. Large roots, including radicle and crown roots, were the same length regardless of puddling intensity. Our study demonstrates that intensive puddling can degrade soil structure, which consequently limits rice root growth.