Thermal time approach to predicting seedling emergence dates of red clover, white clover and lucerne in farm fields

Abstract

A practical method for predicting seedling emergence dates of red and white clovers, and lucerne is proposed. The germination response at seven different constant temperatures ranging from 5 to 35°C was examined. Germination rate, which is a reciprocal of the duration for 50% germination of seeds, was linearly regressed against temperature to calculate the base temperature and thermal constant of seed germination. The calculated values were 3AE9°C and 15AE8 degree days for red clover, 4AE2°C and 13AE6 degree days for white clover, and 2AE9°C and 17AE7 degree days for lucerne. Using the base temperatures, thermal constants, and the daily mean air temperatures at the study site, the seedling emergence dates of the three forage legumes were predicted. At the same time, in an outdoor pot experiment, seeds of these legumes were sown approximately every 3 weeks and seedling emergence dates were determined. The predicted dates of seedling emergence generally fitted the observed dates. Another prediction was attempted using the base temperatures, thermal constants, and normal daily mean air temperatures recorded over more than 30 years in the study site. This prediction showed that the seedlings of the three forage legumes began to emerge at the beginning of April and could continue to emerge until the beginning of November when their non-dormant seeds were present in the site, and that when the seeds were sown from mid-November of one year to late March of the next year, the emergence of seedlings was delayed until the beginning of April.

Species Diversity and Botanical Composition of Permanent Grassland as a Response to Different Grazing Management Practices

“…In organic cropping systems symbiotically fi xed N 2 is the most important external source of nitrogen (Lüchner et al, 2012). Because legumes fi x nitrogen, which is done by symbiotic bacteria, the savings in nitrogen fertilizer and their superior nutritional value make them valuable components of most forage systems (Sakanoue, 2010). However, when large amounts of nitrogen are applied, legumes slow down or shut down the nitrogen fi xation process.…”

Assessment of daily heat pulse regimes on the germination of six Amaranthus species

“…This approach is based on the estimation of base temperature (T b ), that is, the threshold below which germination rate is zero (Steinmaus et al, 2000), and on the calculation of the heat sum (d°C) required for a given percentile of seed population to germinate (Larsen & Bibby, 2005). Several models aiming to predict the time-course of germination in field crops or in weed dynamics models are based on the combined evaluation of T b and thermal time or heat sum (Gardarin et al, 2010(Gardarin et al, , 2011Sakanoue, 2010). They are frequently adopted to quantify heat unit accumulation on daily basis (Cesaraccio et al, 2001) or to compare germination patterns among different species, climates and locations (Wagenvoort & Bierhuizen, 1977;Moot et al, 2000).…”

Seed emergence of lucerne varieties under different soil conditions

“…Lucerne seed emergence was widely investigated in relation to temperature (Sakanoue 2010), moisture (Wang et al 1996), salinity (Al Doss 2011), seed size (Steppuhn et al 2009), sowing depth (Townseed 1992) or light level (Wu et al 2011). Nevertheless, there is a lack of information about lucerne seed emergence in different soils.…”

“…Hrušková (1991) reported lower emergence of hard seeds, but in our experiments the content of hard seeds was not significantly different between the groups of varieties, which could be connected with a lower occurrence of hard seeds -up to 13%. It should be noted that seed emergence in the field is also related to actual field conditions such as temperature (Sakanoue 2010) or soil moisture (Wang et al 1996). A detrimental effect of the higher content of clay was indicated by significantly lower emergence in Chernozem in comparison with Luvisol at the same pH value, but at higher clay content.…”