Impact of planting pattern and root system on comparative drought resistance of a soybean plant introduction under field conditions

The most reasonable and profitable solution to soybean (Glycine max (L.) Merr.) drought problems is to develop stress tolerant varieties. Researchers at NC State University have found that soybean Plant Introduction (PI) 416937 has an unusually extensive root system, and appears to be unique in its ability to maintain turgidity under water-stressed(w-s) conditions. The objectives of this study were to investigate (1) the effects of planting pattern on the response of this PI, in contrast with 'Forrest', to water deficit stress during podfill, and (2) the relative importance of this PI's root system in drought resistance.;A genotypic difference was found in response to water stress, with PI 416937's yield relatively less affected than Forrest's. Reciprocal grafting showed PI's drought resistance appeared to be attributable to the shoot system, and that PI's yield potential could be improved under well-watered(w-w) conditions without compromising its performance under water-stressed conditions. PI had higher leaf water potentials, which appeared not to be directly associated with water absorption by the roots. PI's roots tended to extract more water from the subsoil profile under w-w conditions, but not under w-s conditions. PI maintained a higher leaf area index (LAI) during podfill when water stress was imposed. Pod growth rate of PI was less affected by water stress than was that of Forrest. There were no consistent differences in specific leaf area between the two genotypes and their responses to water stress. Water stress did not necessarily reduce individual seed weight.;Planting pattern changed leaf distribution and pod setting patterns on the main stem and branches without impact on total LAI and final total pod number. Planting pattern did not affect leaf water status, pod growth rate, individual seed weight, specific leaf area (SLA), and total above-ground dry matter. Narrowing row spacing enabled water in the interrow region to be more thoroughly used. Narrow rows yielded the same as, or better than, wide rows under w-w conditions, while they yielded equally under w-s conditions.;The differential response in seed yield of PI and Forrest to water stress was not affected by changing planting pattern. The effect of water treatment on growth, leaf water status, and soil water absorption of PI and Forrest was not changed differentially by planting pattern.