The effect of thermal time and soil water on emergence of Ranunculus repens

The effect of temperature and soil available water (AW) on the emergence of Ranunculus repens L. was examined in artificial media in growth chambers. Two seed populations, 'arable type' and 'wild type', were investigated. Moi sture levels were 20%, 40%, 60% and 80% AW, and temperatures were 10/5 degr ees C, 15/7 degrees C, 20/10 degrees C and 25/15 degrees C. Time to onset o f emergence varied from 11 to 28 days for both seed populations, primarily as a result of mean temperature. Mean thermal time (TT) required for the on set of emergence of both populations was 251 +/- 45 TT. Total emergence of the 'arable type' R. repens varied from 3% at 10/5 degrees C and 20% AW to 30% at 25/15 degrees C and 60% AW. Total emergence of the 'wild type' was g reater, ranging from 4% at 10/5 degrees C and 20% AW to 57% at 25/15 degree s C and 80% AW. Temperature and AW significantly affected total emergence. A logistic response was displayed for the cumulative emergence of both popu lations. Seedling emergence models based on TT were: developed for both pop ulations at each of the four levels of AW.