Various hypotheses have been proposed to explain the fruit-induced monocarpic senescence in soybeans. Among these are the depletion of needed minerals in the leaves and the theory of hormonal control. To test these hypotheses, foliar sprays of (alpha)-naphthaleneacetic acid (NAA), 6-benzylaminopurine (BA), and foliar fertilizer (FF) were applied in a factorial combination on field-grown soybeans. The chemicals delayed monocarpic senescence (as measured by leaf yellowing) and plant maturity, but did not affect seed yield. The delay in leaf yellowing was mainly due to the effect of BA but in the absence of the later NAA and FF had some minor effects on leaf color and plant maturity;In a second experiment, the effect of ethylene production inhbitors on leaf abscission and other agronomic attributes of field-grown soybeans was tested. Foliar applications of Ethrel were used to increase ethylene levels in the leaves in a factorial combination with the inhibitors cobalt chloride and sodium benzoate. Ethrel enhanced leaf abscission significantly, which caused significant reductions in seed yield and 100-seed weight. The inhibitors did not reverse the effect of Ethrel for any of the variables measured;In a third experiment, the effects of foliar applications of BTS44584, a potentially useful plant growth regulator, on some morphological and physiological characteristics of two soybean cultivars were tested. When applied at R1 with a rate of 1.0 kg/ha, BTS44584 produced a 30% increase in seed yield of Wayne in 1979 and 1980. Harcor was not as responsive to chemical treatment as Wayne. The data suggested that the effect on Wayne was due to a significant decrease in plant height accompanied by an increase in the number of of pods and seed yield on branches. Both field and greenhouse measurements showed no effect of BTS44584 on nodule number and fresh weight, acetylene reduction or specific activity of the nodules in all cultivars used.