Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 1, 1996
Publication Date: N/A
Interpretive Summary: Nitrogen is important for all forms of life, because it is required for growth and reproduction. Fertilizer nitrogen and manures are used as nitrogen sources for cereal crops, like wheat and corn. Excess nitrogen can move downward through the soil as nitrate, causing pollution of groundwater. No methods are currently available for removing nitrate from deep soils (> 6 feet) or from groundwater. One solution would be to use deeply rooted crops, like alfalfa, to intercept and absorb nitrate. Our research project has been breeding alfalfa with superior root traits for nitrate cleanup. This report describes a new technique for identifying rate and depth of alfalfa root growth. The technique includes placing a chemical called fluridone in the soil at a particular depth. Alfalfa is seeded and observed until leaves begin to turn white. This indicates that the plant roots have reached the fluridone. Those plants that show the symptoms first have the fastest growth. The method is reliable and it has shown large differences among individual plants for root growth rate. We are using this new technique to develop specialized kinds of alfalfa that can help clean up the environment and also provide farmers with a valuable crop.
Technical Abstract: Alfalfa (Medicago sativa L.) is a deep rooted perennial that may be able to remove nitrate from subsoil beneath the rooting zone of annual crops. Alfalfa cultivars with rapid and deep root elongation would be beneficial for reducing future nitrate contamination of ground water supplies. The objectives of this research were to (i) develop a protocol using the herbicide fluridone (1-methyl-3-phenyl-5-[3-(trifluromethyl)phenyl]-4(1H)- pyridinone) as a marker for indicating alfalfa root penetration in soil, and (ii) determine the variability in rate of geotropic root elongation within and among diverse alfalfa germplasms. Fluridone caused rapid, distinctive bleaching of alfalfa leaves at a rate of 25 mg a.i. kg/ha soil, without being fatal. When transplanted after onset of fluridone symptoms, alfalfa recovered and resumed normal growth and flowering. Alfalfa populations did not differ in sensitivity to fluridone. Decomposition of roots from a fluridone-treated plant did not cause symptom development in other plants. Individual plants within alfalfa germplasms differed by 56 d in onset of symptoms, indicating a similar difference in root activity at 80 cm depth in soil. Mean geotropic root elongation rate for 12 diverse germplasms ranged from 1.12 to 1.40 cm/d. Populations selected for unique root morphological traits were significantly faster in geotropic root elongation rate than their unselected parental populations. Our method permits in situ identification of plants with rapid geotropic root elongation rates within heterogeneous populations and has proven useful in germplasm selection.