Influence of calcium:magnesium ratio in limestone on nodulation, dry matter yield and mineral composition of alfalfa

This study evaluated the effect of different Ca:Mg ratios on dry matter yield, mineral composition of alfalfa, and nodulation. A dystrophic Dark-Red Latosol (Oxisol) soil was used in the experiment. A randomized design was adapted with five Ca:Mg ratios(1:0; 1:1; 2:1, 3:1 and 4:1)at a recommended limestone dosage of 3.9 t ha(-1). An additional treatment was included at a ratio of 3:1 with the dosage of 7.8 t ha(-1). All treatments had four replicates in six cutting times. The analyzed variables were dry matter production, concentrations (g kg(-1)) of N, P, K, Ca, Mg and S in dry matter and weights of fresh and dry nodules. The changes in the ratios of Ca:Mg at the recommended limestone rate did not affect the dry matter production. The highest dry matter yield was obtained in the treatment that used twice the recommended dosage. The concentrations of Ca and Mg in the aerial dry matter were directly proportional to their availability in the soil, while the K concentrations were inversely proportional to the rate Ca applied. No treatment influenced the concentration of P in the aerial dry matter. The concentration of S was influenced by the ratio of Ca:Mg and diminished with increases in Ca. The 4:1 treatment showed the highest concentration of N in the dry matter. The N fixation enhanced as the Ca rate in the soil increased.