Effect of Humic Acids on Soybean Seedling Growth under Polyethylene-Glycol-6000-Induced Drought Stress

Humic substances (HS) are the most important natural biostimulant of plants. However, relationship between their structure and biological activity in plants is still not well recognized. The objective this paper was to assess influence molecular fractions humic acids (HA) (HA < 30 kDa HA > kDa) on reducing negative effects drought stress soybean (Glycine max (L.) Merr.) seedlings Progres Nawiko cultivars. Drought induced laboratory conditions by addition polyethylene glycol 6000 (PEG 6000) make a water potential ?0.5 MPa. were extracted according International Substances Society procedure, then separated into two membrane filtration. following physiological biometric parameters determined: chlorophyll content, photosynthesis activity, electrical conductivity, fresh dry mass overground roots, plant length. enzyme ion contents also measured. Differences response with or Hoagland’s solution observed among studied caused decrease increase peroxidase case both results measurements showed that cultivar appears have better tolerance stress. significant deficit macroelement content matter leaves cultivars observed, while its effect microelement uptake concluded. In cultivar, leaves, whereas there increase. KDa features varied. fraction up-regulated antioxidant defense system. Unfortunately, no either macro- micronutrients system observed.