Field-based Selection Method Creates Alfalfa Populations That Differ in Nitrate Nitrogen Uptake
2008
Lamb, JoAnn F. S. | Russelle, Michael P. | Fenton, Diana M.
Sustainable agricultural systems could benefit from alfalfa (Medicago sativa L.) germplasm that reduce N losses to the ground water and decrease N fertilizer inputs. With the goal of producing alfalfa populations with altered nitrate N uptake, our objectives were to develop, assess, and refine an inexpensive selection method using Br⁻ as an analog for nitrate under field conditions. Two selection schemes using divergent herbage Br⁻ concentration and/or divergent herbage Br⁻ uptake, both in combination with high herbage N content, produced two Cycle 1 and four Cycle 2 alfalfa populations. We evaluated these populations for both Br⁻ uptake and nitrate N uptake (estimated by N derived from fertilizer, Ndff [¹⁵N-labeled]) for one regrowth period in two locations in each of 2 yr. Weak associations between Br⁻ uptake and Ndff were found during the establishment year, but strong correlations were found between Br⁻ concentration and fraction of Ndff (fNdff) (r = 0.83) and between Br⁻ uptake and Ndff (r = 0.85 to 0.90) when populations were evaluated during the first production year. Populations selected for high Br⁻ concentration or uptake had greater Br⁻ concentration and uptake, fNdff, and Ndff than populations selected for low Br⁻ Our method of selecting alfalfa plants for differences in herbage Br⁻ concentration or uptake in combination with high herbage N content is the first to successfully produce alfalfa populations that differ in nitrate N uptake in a field environment.
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