The effect of increasing levels of lime, magnesium, manganese and boron on the growth and nitrogen fixation of Stylosanthes guyanensis

Abstract

Four greenhouse experiments were carried out to study the negative effect of liming found previously when tropical forage legumes, especially Stylosanthes are grown in a red-yellow podzolic soil frequently occurring on the hill pastures of Rio de Janeiro State. Five levels each of magnesium, manganese and boron were studied with five levels of lime in incomplete factorial designs. None of the elements completely eliminated the decreases in yield observed when the pH was increased from 4.8 to 6.5, however manganase and boron lessened the effect. In young plants (during the first 50 days) liming to pH 6.8 reduced both nodulation and yield by half. Older plants (after 70 days) were less sensitive and yield decreases were less than 30%. However, nodulation and nitrogen fixation increased with liming up to pH 6.2. These conflicting results show the importance of seperating the nutrition of plant growth and legume-Rhizobium symbiosis.