Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 28, 2011
Publication Date: May 9, 2011
Repository URL: http://handle.nal.usda.gov/10113/58333
Citation: Russelle, M.P., Lamb, J.F. 2011. Divergent alfalfa root system architecture is maintained across environment and nutrient supply. Agronomy Journal. 103(4):1115-1123. Interpretive Summary: Roots are the anchors of plants and they also provide water and nutrients to the stems and leaves. Roots need to grow where the nutrients and water are available. Plants have evolved to take advantage of these resources in their natural habitats, but when we grow plants in farming systems, not all plants are genetically programmed to use resources efficiently. Using conventional plant breeding techniques, we developed alfalfas that had either more or fewer branch roots in the topsoil. The first type should be able to better absorb nutrients from fertilizer and manure, whereas the second type should be able to capture water and chemicals that have moved deep into the soil. This research showed that the root system architectures of these new alfalfas were preserved, regardless of soil type (sandy or silty) or nutrient availability. This means that farmers will be able to count on new varieties to have the desired root system architecture. In addition, new varieties may be selected from these to improve alfalfa's role in agriculture or to remove contaminants from the soil.
Technical Abstract: Plant root system architecture can alter and be altered by soil fertility and other environmental conditions. In soils with suboptimal fertility, plant root length often is correlated with P and K uptake because these nutrients are supplied by diffusion. We developed alfalfa (Medicago sativa L.) populations selected for tap- or branch-rooted architectures and determined responses of these selections to P supply and K placement in field experiments. In Experiment 1, populations representing the parental composite and the progeny from the first and second cycles of divergent selection were seeded on soils testing low to medium for plant available P and K, a sandy loam soil (Becker, MN) and a silt loam soil (Rosemount, MN). Experiment 2, at Becker, included only second-cycle progeny. In both experiments, P was added to one-half of the plots by injection of potassium phosphate (monobasic) at 224 kg P/ha into the uppermost 30 to 40 cm of soil. Added P did not affect herbage dry mass in the first and second years following stand establishment but increased herbage P concentration and uptake. There was no effect of K placement, but the tap-rooted germplasm had lower K concentration in herbage than the parent. Although progeny did not differ in total root mass, the relative proportion of thickened to total root mass was larger below 30 cm for the tap-rooted selection, which also produced more fine roots. There were no differences in P or K uptake between alfalfa populations with different root system architectures. Selected root system architecture characteristics were expressed under, and apparently not modified by, growing conditions that covered three site-years on two contrasting soils with differential P supply and K placement.