Metabolic Responses Induced by Serial Harvesting of Alfalfa Pasture Established on Amended Acid Soil

Abstract

Alfalfa pasture has not been sustainable on the coastal plain of the United States because of its intolerance to soil acidity. This study examined the responses of alfalfa metabolism to differential amendments of acid soil and to serial harvesting. The soil was spatially amended with different quantities of flue gas desulfurization sludge and gypsum after liming to pH 7. The serial harvests oscillated the RNA synthetic activity of glutamate dehydrogenase (GDH) from an oxidized to a reduced state irrespective of the soil amendments. The amplitudes of the redox cycles changed from one harvest to the next, thus demonstrating improved regrowth persistence. The chlorophyll, hexose, nucleotide, and protein contents, and the fructose‐1, 6‐bisphosphatase activity, decreased and fluctuated inconsistently in the successive cuttings. Consideration of the metabolic responses per harvest showed that the alfalfa had optimized saccharide metabolism in the first harvest, optimized RNA metabolism in the second harvest, optimized saccharide and RNA metabolism in the third harvest, and depressed saccharide metabolism in the fourth harvest, thereby optimizing the regrowth potential of the alfalfa pasture. Sustainability of the pasture was conferred by the coordinate compensatory regulation of metabolism in response to the synergistic interaction between the differential amendments and the nitrogen (N) nutrient excreted by the alfalfa into the soil.