The relationships between selected soil properties and the bioactivity of atrazine (2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine) were investigated in field trials. Bioactivity was determined periodically for up to twelve months on a variety of soil types using oats (A vena sativa L.) as the test plant. The initial bioactivity of atrazine which was assessed 35 days after application was best correlated with the organic matter content (% C) and P reversion characteristics of the soils. Clay content and CEC were also important but at lower levels of significance. Six months after herbicide application, % C, soil pH and P reversion were important predictors of atrazine persistence, whilst both CEC and clay content were poor criteria. Persistence was negatively correlated with % C, but positively with both soil pH and P reversion. Since the dissipation of atrazine in most of the soils was virtually complete after twelve months, the prediction of persistence by the soil properties was poor at that stage. Differences in persistence between trials in close proximity suggest that persistence of the herbicide was more closely linked to soil characteristics than to climatic conditions. Results suggest that current waiting periods, which are recommended for specific crops, can be refined by distinguishing between soils on the basis of soil characteristics that affect adsorption and degradation of atrazine.Die verwantskappe tussen geselekteerde grondeienskappe en die bio-aktiwiteit van atrasien (2-chloro-4-(etielamino)-6-(isopropielamino)-s-triasien) is in.veldproewe ondersoek. Bio-aktiwiteit is periodiek tot op twaalf maande op 'n verskeidenheid van grondtipes met hawer (A vena sativa L.) as toetsplant bestudeer. Die bioaktiwiteit van atrasien was 35 dae na toediening die beste met die grondeienskappe organiese materiaalinhoud (% C) en P-reversie gekorreleerd. Klei-inhoud en KUV was ook belangrik, maar by laer vlakke van betekenisvolheid. Organiese materiaalinhoud, grond pH and P-reversie was ses maande na onkruiddodertoediening belangrike voorspellers van nawerking, terwyl beide klei-inhoud en KUV swak kriteria was. Nawerking was negatief gekorreleerd met % C, maar positief met beide grond pH en P-reversie. Na verloop van 'n verdere ses maande was die voorspelling van atrasiennawerking deur die grondeienskappe swak as gevolg van die verlies van die onkruiddoder uit meeste van die gronde. Verskille in nawerking tussen nabygelee proewe dui daarop dat nawerking van atrasien sterker verband gehou het met grondeienskappe as met klimatologiese toestande. Resultate dui daarop dat huidige wagperiodes wat vir bepaalde gewasse aanbeveel word, verfyn kan word deur tussen gronde te onderskei op basis van grondeienskappe wat adsorpsie en afbraak van atrasien beinvloed.

No abstract