Alterations in soybean root development due to cultural practices: A review

The heterogeneous nature of the soil of the root zone will produce wide variations in soybean (Glycine max (L.) Merrill) root development. The effects of management practices on root development are not as well understood as are the effects of cultural practices on shoot development. General descriptions of soybean root system production are presented in the literature. Evidence has also been presented in support of the concept that soybean root development is a dynamic, self regulated process, controlled, in part, by the root zone environment. Numerous quantitative and qualitative techniques have been used to characterize field rooting patterns, and significant differences in root production and distribution have been observed among soybean cultivars. The effect of planting date on soybean root production is primarily a combination of the effects of temperature, moisture, and photoperiod. Root growth appears to have a lower optimum temperature than shoot growth. Soybean possesses a great water uptake potential and roots tend to proliferate in moist soils. Soybean root production is more concentrated in the upper soil horizons under irrigated than nonirrigated production. The response in root distribution to flooded soil conditions changes during different phases of crop development. Soybean root growth is hindered under short day length or low Insolation conditions. The effect of tillage on a given soil's physical properties can alter soybean root growth through changes in soil bulk density, porosity, and nutrient distribution throughout the root zone. Root development is limited by increased bulk density, increased penetration resistance, reduced porosity, and smaller mean pore diameters. Reduced soil aeration and lower oxygen diffusion rates will also inhibit root development. Soil fertility status can influence total soybean root production and root distribution throughout the profile. Rooting responses to N and P availability are similar and synergistic. These two nutrients tend to promote increased root length and root surface area. The effect of K availability on soybean root development is not clear, but root surface area has been shown to increase under low K conditions. Low soil pH may inhibit soybean root growth through Ca deficiencies and/or Al toxicities.