THE EFFECT OF PLANT-INDUCED CHANGES OF PH UPON THE ADSORPTION AND PHYTOTOXICITY OF S-TRIAZINE HERBICIDES

The effect of plant‐induced changes of soluiion pH upon the adsorpiion of s‐lriazme herbicides in either K‐monimorillonite or Na ‐ bentonite ciay‐nutrieni suspensions and iheir phyioioxi‐ city in soil was studied. ln clay‐NO3− suspensions (wiih NO3‐ as the nitrogen source) maize planls (Zea may L.) caused a marked rise in solution pH and this resulted in a rapid descrp‐ tion of bound atrazine or simazine. in clay‐NHa + suspensions (with NH4 + as the nitrogen source) the lowering of solution pH through plant aclivity resulted in jnereased adsorption of these herbicides. In soil, changes of rhizosphere pH were also found when either KNO3 or (NH4) 2SO4 were supplied as fertilizers, bul it was nol established whether ihis had a direct effeci upon the significant increase in weight of (NH4)2SO4 treated wheat (Tri‐ ticum aestivum L.) planls at low herbicide concentrations compared with KNO3 treated wheat plants. Copyright © 1979, Wiley Blackwell. All rights reserved