The largest detriment to crop productivity in many environments is available water. Biomass accumulation is proportional to water moving through the plant, i.e., transpiration. The supply of water for crop biomass accumulation is provided from the soil reservoir by the root system. Our objective was to quantify peanut (Arachis hypogaea L.) root growth over time by depth and lateral spread in the soil profile. By soil coring techniques, we determined the growth of roots, in response to irrigation treatments imposed under field conditions, of two virginia-, runner-type peanut cultivars over time. Root length density (RLD) and root weight density (RWD) in the soil profile were not significantly different between cultivars or among irrigation treatments. However, significant year differences were observed. Following crop establishment under similar environmental conditions in both years, 1988 was hotter and drier than 1989. Also, postplant rainfall through 45 DAP was less in 1988 than 1989 and total water received by the crop was less in 1988 than 1989. Under these conditions, there was nearly twice and three times as much RLD and RWD in 1988 than 1989. Root length density and RWD significantly increased at each depth increment with days after planting (DAP) until 80 DAP. At 40 to 45 DAP, roots had penetrated to a depth of 120 cm and spread laterally to at least 46 cm (mid-furrow). The 15-cm depth increment had the highest mean RLD, which increased to a maximum at 2.1 and 1.7 cm cm-3 at 80 and 93 DAP in 1988 and 1989, respectively. However, over the same time period there was also a simultaneous increase in RLD at depths below 15 cm. Thus, peanut roots were established both deeply and laterally in the soil profile early in the growing season. This could prove advantageous in a drought environment and the knowledge useful for water management of the crop. July 20, 19931.
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