EMERGENCE AND GROWTH OF 2 NONNODULATED SOYBEAN GENOTYPES (GLYCINE-MAX(L) MERR) IN RESPONSE TO SOIL ACIDITY

Toxic levels of extractable soil Al limit production of important crop s in many areas of the world. The nature of the limitation in soybeans is not completely understood. Our objectives were to investigate the cause of acid-soil-induced delays in seedling emergence, the effect of acidity on productivity in non-nodulated soybeans and further test th e Al tolerance of PI 416,937 compared to a sensitive control, Essex. G rowth characteristics of the two genotypes through the flowering stage were measured on a Corozal clay (Aquic Tropudult) in Puerto Rico whic h had been differentially limed to provide a wide range of soil Al. Ea rly growth was also studied in the laboratory using soil from the fiel d experiment. Highly acidic soil conditions, coupled with high Al leve ls, reduced growth in both Essex and PI 416,937. The principal factor responsible for delayed emergence in the high Al soil was not delayed radicle initiation, but delayed initiation of hypocotyl elongation. Hy pocotyl initiation was highly associated with rate of tap root growth, with the former possibly determined by the latter, because a minimum tap root length of 60 mm was required in both high and low Al soils be fore hypocotyl initiation commenced. In seedlings, the high acidity re duced root more than shoot growth. By 44 days after planting (DAP), ho wever, soil acidity had reduced shoot growth greatly. Although the soy bean plants were not nodulated, foliar N levels and shoot growth were decreased by high Al levels, indicating that interference with N fixat ion may not be the sole mechanism by which nitrogen accumulation and p lant growth is reduced in the field.