Date of Award
Program or Major
Doctor of Philosophy
A series of field, greenhouse and laboratory experiments were conducted to examine the influence of soil acidity and liming on the growth of Rhizobium and the nodulation, nitrogen fixation, and yield of alfalfa and red clover.
In the greenhouse, from soil pH 5.0 to 5.6, nitrogen fixation was shown to be more correlated to Al saturation than pH or available P. Once Al saturation was reduced to less than 5 percent by liming, the application of P was more beneficial to yield and nodulation than further application of lime. Lime pelleted alfalfa seed sown at a soil pH of 5.0 increased nodule weight and number but did not improve nitrogen fixation or yield. Increasing the soil pH by soil-incorporation of lime eliminated the advantage of pelleting. The growth response of red clover to liming was less than for alfalfa. Work with ('32)P in hydroponics showed that red clover was capable of mobilizing P under acidic conditions in the presence of Al to a greater degree than alfalfa. The ratio of Al/P in the nodules was significantly less in red clover than alfalfa as measured by electron dispersive analysis by X-ray.
Using an aeroponic culture, nitrogen fixation by red clover was more tolerant than alfalfa to Al stress at pH 5.0. The addition of nitrogen, however, reduced nitrogen fixation in both legumes by over 90 percent after four weeks. Nitrate reductase activity in red clover was shown to be four to five times that in alfalfa when the plants were grown at pH 5.6. The addition of fertilizer nitrogen to the soil increased nitrate reductase activity in both legumes with a compensatory decrease in nitrogen fixation such that yields were not affected.
The growth of Rhizobium meliloti in acidic media was shown to be influenced by Al. At pH 5.0, the addition of the element severely reduced growth in the three strains tested. At pH 5.5, there was an increase in growth lag, but the strains demonstrated a differential adaptation to the toxicity. In order to test the effectiveness of these strains in soil, three alfalfa varieties were inoculated and seeded into sterile soil at pH 5.0, 5.5, and 6.0. No single combination of strain-variety gave the highest yield, nodule number, or nitrogen fixation for all three soil pH's.
Two field experiments were established to study the influence of banded/broadcast lime and phosphorus on the growth of alfalfa and red clover established by minimum tillage in an acidic soil. In the Harmony Hill experiment, lime rate from 4.6 to 13.8 t/ha had no influence in the soil pH of the top 5 cm of the profile. At greater depths, the higher lime rates raised pH and significantly increased yields. Banded lime did not improve yields, percent legume, or stand persistence. One year after establishment, red clover averaged less than 25 percent of the stand; inspection indicated severe internal breakdown and secondary infection by Fusarium solani. The effects of low P and high Al saturation in the subsoil on alfalfa stand persistance is not known.
In the Demerit experiment, hydrated lime increased the soil pH from 5.6 to over 6.5 in the top 5 cm of the soil one month after liming but actually reduced yield and nodulation of the legume. The application of broadcast P decreased the Al saturation in the unlimed plots in the top 5 cm of the soil to levels comparable to the dolomitic and hydrated lime plots. The yields of alfalfa in the unlimed plots equaled those in the limed plots when both sites received a single addition of banded monoammonium phosphate. These higher yields in the banded plots occurred in the first spring harvest following the August 1978 seeding and may have resulted from the presence of both N and P in the band.
Results from the two field experiments indicated that good yields of alfalfa can be achieved in the year following establishment in the acidity is reduced in the top 10 cm of the soil profile and adequate P is present; longevity of the stand remains undetermined.
ROBERTS, DANIEL STEWART THOMAS, "GROWTH, NODULATION AND NITROGEN FIXATION OF ALFALFA (MEDICAGO SATIVA L) AND RED CLOVER (TRIFOLIUM PRATENSE L) AS INFLUENCED BY SOIL ACIDITY AND LIMING" (1979). Doctoral Dissertations. 1272.