Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/21/2007
Publication Date: 7/1/2007
Citation: Myers, D.B., Kitchen, N.R., Sudduth, K.A., Miles, R.J., Sharp, R.E. 2007. Soybean root distribution related to claypan soil properties and apparent soil electrical conductivity. Crop Science. 47:1498-1509.
Interpretive Summary: Soybean yields vary within fields mainly because of differences in soil properties within the root zone. As the root environment changes across the soil landscape, the suitability of the soil for growth and development of roots is altered, affecting overall plant performance. Because of the difficulties in sampling and studying roots, very few studies have measured soybean root distribution in the field, or tried to explain how soil properties affect root distribution. Studying soybean root variability is particularly important in the claypan soils found in northern Missouri and south-central Illinois. These soils have a specific arrangement of soil layers (called “soil horizons”) including a layer with a high percentage of clay (called the claypan). The depth of the claypan horizon varies systematically across landscapes, from 12 inches on hilltops, to 4 inches on eroded hillsides, and up to 40 inches at the bottom of slopes. We found this systematic soil variation to be an important influence on soybean root growth and distribution in the soil. The quantity of soybean roots and root diameter were greatest near the surface, decreased to very few just above the claypan, and increased again just below the claypan. Several chemical and physical soil properties were believed to be responsible for these effects. We also found that the amount of roots and root diameter could be predicted with soil electrical conductivity, a measurement that can be obtained with commercially-available on-the-go sensors. Because soybeans account for more than 60% of crop production on claypan soils, understanding and predicting yield variability on these soils is important for developing efficient and sustainable cropping systems. The results of this field study provide an important picture of the “hidden half” of soybeans on claypan soils. This information will be useful for researchers developing new soybean varieties and for those modeling crop yield to learn how to grow food efficiently. As new, higher-yielding soybean varieties are developed using these findings, farmers may benefit economically. Growing crops that are resilient to changing soil conditions can help provide a safe food supply to the general population.
Technical Abstract: Soybean [Glycine max (L.)] yield in claypan soils varies as a result of systematic relationships with soil properties and landscape position. This variability is likely caused by soil-landscape interactions with soybean roots. While much data exists on the landscape variability of yield, field observations of soybean root distribution are needed for elucidating the influence of root distribution on yield variability. This study was conducted to examine profile distributions of soybean root length density (RLD) and average root diameter (ARD) as a function of landscape position, depth to claypan (DTC), apparent soil electrical conductivity (ECa), clay-maximum translated depth (Dt), and other chemical and physical soil properties. A landscape of claypan and associated depositional soils was sampled post-harvest at two sites near Centralia, MO, in 2001. Roots were extracted from soil cores in 15-cm layers (15-120 cm) via hydropneumatic elutriation, and measured with image analysis techniques. RLD and ARD were significantly related to landscape position, DTC, Dt, and ECa. Predictions of the root measurements were best from 15 to 60 cm, corresponding to the profile depths with the greatest influence from claypan soil morphology. Soil property distributions within the profile were found to match root density profile distributions, particularly base cations, P, and pH. In general, soybean root growth was inhibited in the eluviated zone above the claypan and stimulated 20 to 40 cm below the claypan upper boundary. Soybean roots growing below the claypan had about 20 to 30 % reduction in average diameter. We conclude that DTC and rapid estimators of claypan morphology, such as ECa, can be implemented to successfully predict soybean root distribution in claypan soil landscapes.