Soybean and Corn Rooting in Southwestern Minnesota: II. Root Distributions and Related Water Inflow

Abstract

Root length density (RLD) of corn (Zea mays L.) and two isolines (determinate and indeterminate) of Harosoy soybean (Glycine max. L. Merr.) in a Nicollet soil were measured from 1 July to 15 Aug. 1971. These measurements, along with water uptake sinks in these vertically developing root systems, were used to evaluate water relations of these three crops.Both soybean isolines had about 0.2 cm/cm3 RLD in the Ap layer with values < 0.1 below the Ap layer. This RLD distribution persisted with depth as the root system expanded vertically. Corn RLD were about 0.3 initially in the Ap layer, and as the root system expanded vertically, maximum RLD of about 0.3 was produced even to the 100‐cm depth on 9 Aug. Vertical extension rates of corn after 1 July were 1.3 cm/day as compared with 1.7 for soybeans, but maximum rooting depths on 9 Aug. were 145 and 120 cm, respectively.Modal specific water inflows were 0.03 cm3/cm root per day—maximal values for soybeans were 0.2; maximal values for corn were about 0.05. Maximum soybean rooting depths coincided with maximum depth of water uptake sink, but corn rooting depths ranged 15 to 30 cm deeper than the water uptake sink.Specific water inflow generally increased as soil hydraulic conductivity increased and RLD decreased, which agrees with models for steady‐state water flow into single roots. At low RLD, specific water inflows were either constant or increased as hydraulic conductivity decreased. This increased root resistance to water flow at the lower fringes of rooting may have resulted from low soil temperatures. Soybean root conductivities decreased with decreasing soil water potential. Corn root conductivities were largest at about −700 mbars and decreased as soil water potential decreased. Decreases of corn root conductivity resulted from potentials > −700 mbars when soil temperatures were low.

Incorporation of crop phenology in Simple Biosphere Model (SiBcrop) to improve land-atmosphere carbon exchanges from croplands

“…The estimated average root:shoot ratio soybean at harvest was 0.18. This ratio fell within the range (of 0.14-0.19) observed by Allmaras et al (1975), and it was slightly higher than the value of 0.15 observed by Silvius et al (1977) for non-stressed plants, and the highest value (i.e. 0.126), among the values reported by Taylor et al (1982).…”

Nitrogen fertilizer effects on soil carbon balances in Midwestern U.S. agricultural systems

“…They can also differ over time, as evidenced by Buyanovsky and Wagner's (1998) estimate that the total net annual production of corn and its post-harvest residues have more than tripled since 1950. Root production can vary widely among sites and cultivars (Prince et al 2001), yet estimates of root : shoot ratios are typically based on a few published ratios (Allmaras et al 1975, Anderson 1988. To assess the effect of these differences in allometries on estimates of NPP from yield data, Prince et al (2001) conducted sensitivity analyses, based on published ranges of these ratios, and found the limit of accuracy to be ;1 MgÁha À1 Áyr À1 .…”

Water uptake and transport of soybeans as a function of rooting patterns

“…Most of the values were in the range of 5 X 10 ^ to 0.2 cm^ H20/cm roof day. The results from this experiment were similar to those of Allmaras et al (1975) in several ways. The uptake rate, q^, increased with depth except in the early growing season when the young roots expanded rapidly in the top 15 cm layer but then q^ decreased as plant age increased-Apparently, the proportion of the more permeable young roots to the older and more suberized roots was greater in the deep soil than the soil of the upper layers, and this pro portion decreased as the plant aged.…”