PHYSIOLOGY AND PERSISTENCE OF ALFALFA WITH CHANGES IN SOIL CHEMISTRY
The influence of liming on soil chemical changes and on nodulation, nitrogen fixation and yield of alfalfa was investigated. In the field, increasing rates of lime improved alfalfa dry matter yield at the Kingman Farm. Optimum dry matter yield was obtained with 3.5 tons lime/ha. A quadratic response curve showed that liming accounted for about 70 percent of the yield variation in alfalfa. Herbage N, P and Mg increased in response to liming six years after establishment. The simple correlations between dry matter yield and plant N, plant P and Plant Mg were positive and significant. Plant Al and Mn showed negative influences on plant P, N and Mg as well as on dry matter yield. Total nitrogen accumulation and protein yields were significantly increased with liming. Nitrogen content was strongly associated with the yield of alfalfa. Depletion of soil N appeared to be the main cause for the improvement in the response of N(,2) fixation and yield to liming, especially in the last two years (1980-1981). The relation between herbage composition and alfalfa yield was studied with regression analysis. In 1981 optimum alfalfa dry matter of 14.9 tons/ha was obtained with a herbage composition of 0.33% P, 1.0% Ca, 0.33% Mg, 4.7% N and 2.4% K. This optimum yield was 143% of the control yield. In the greenhouse, exchangeable Al was found to be a better indicator of crop response to lime application than soil pH. The relationship of improved yield to reduced Al saturation was far more pronounced than the relationship between yield and soil pH. Top and root dry weights were shown to be more correlated to Al saturation than pH or available P. Work with radioactive phosphorus in the soil showed that liming caused a precipitation of the applied ('32)P. The ('32)P was reverted and so less ('32)P was mobilized to plant roots when lime was applied to the soil. The ratio of Al/P in 'Iroquois' roots was reduced through liming.
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