Effects of phosphorus, soil temperature and soil humidity on nodulation and development of two varieties of perennial soybean (Glycine javanica L.)

Abstract

A greenhouse experiment was carried out with two varieties of perennial soybean (Glycine javanica L.) to study effects and interactions of phosphorus and soil humidity on the establishment of the Rhizobium symbiosis and on forage production. Fertilization with superphosphate increased considerably nodulation, nitrogen fixation and forage yield, demonstrating high phosphorus requirements already at the initial stabe of plant growth. Daily maximal temperatures of the soil between 34 and 43°C reduced nodulation, nitrogen fixation, forage yield and its protein content, when cornpared with daily maxima between 29 and 32°C. High soil temperature effects were less pronounced at high phosphorus levels. The variety SP-1 was more sensitive to high temperature and low phosphorus injuries, than the variety Tinaroo. There were also differences between the two varieties in relation to soil humidity at the two soil temperatures. The variety SP-1 at the cooler soil temperature grew better at the lowest soil humidity (evaporation until two times the humidity of the wilting point), but in hotter pots growth was best at intermediate humidity. The variety Tinaroo preferred intermediate soil humidity (evaporation until 70% of field capacity), at both soil temperatures. The variety Tinaroo was superior in nodulation, nitrogen fixation and forage yield in all treatments and less sensitive to environmental effects.