ABSTRACT
Toxic levels of Al and/or Mn are often the main cause of low crop yields in the tropics. The effect of soil acidity factors on soybean were determined in a series of field experiments on 2 Ultisols and 1 Oxisol. The term "nodulation" embraces all the events and processes leading to effective N2 fixation in root nodules. Nutritional variables can influence nodulation in two ways, sometimes difficult to distinguish. The variable may affect nodulation directly, with resulting effect on N2 fixation. Glasshouse and field observations have implicated temperature in the development of manganese toxicity symptoms in some species. The average soybean yield in Thailand has remained consistently low for many years, although high yielding local varieties have been adopted for cultivation. Soybeans are being grown on a small scale under dryland conditions in N.S.W. These experiments were undertaken to obtain a preliminary assessment of the effect of water stress on the response of soybeans to applied phosphate.
