An effective method for estimation of rice (Oryza sativa L.) crown root numbers at the heading stage in saline-sodic soils of Northeast China

Saline-sodic stress is a major abiotic constraint responsible for rice (Oryza sativa L.) yield reductions in Northeast China. The rice root system is crucial for yield development, and it is usually recognized as the key for improving future crop productivity. However, most of the saline-sodic soils in these areas contain high levels of soluble Na2CO3 and NaHCO3, which results in a high pH (>8.5), clay dispersion, soil swelling, and overall poor soil physical properties. Isolation, washing and measurement of the rice crown roots is highly time-demanding in this kind of soil. Our aim was to explore whether differences in shoot characters could be reliable indicators, and a low cost and easy method for estimating crown root numbers in rice. In this study, 97 randomly selected field-grown rice hill plants, with 728 stem samples, of three genotypes at the heading stage were used in saline-sodic soils. Results gave a reliable estimation of values for crown root numbers as indicated by high positive correlations with number of stems (0.788***) and tillers (0.801***); diameter of long (0.545***), short (0.555***), and mean stems (0.586**), and hill (i.e., equal to 5 plants) circumference (0.796***) and mean hill diameter (0.366***) (P