Emergence of field pennycress (Thlaspi arvense L.): Comparison of two accessions and modelling

• We compared field emergence of two Thlaspi arvense accessions in Spain and USA.
• Emergence differed for accessions suggesting some are more suitable for cropping.
• Two different emergence models successfully predicted T. arvense emergence.
• Adding photoperiod to a hydrothermal time model improved its prediction accuracy.

Many weed species are becoming rare due to intense agricultural management, which leads to a decrease of biodiversity in agroecosystems. Cultivating some of these species for their oilseed content may help preserve them while profiting agronomically. Thlaspi arvense is one of these species with potential as an industrial crop. The aim of this work was to develop a model to describe the emergence of this species, and that can help to make decisions for its management, whether for conservation or production purposes. The emergence of two accessions of T. arvense, one from Spain and the other from USA, sown in Spain (Almenar) and USA (Morris), over two seasons (2011–12 and 2012–13) and in Riga (Latvia) over one season (2012), was followed to compare patterns and extent, as well as to develop emergence prediction models based on hydrothermal time (HTT) and photohydrothermal time (PhHTT). For the USA accession, the percentage of seeds that emerged was significantly higher than that of the Spanish accession. Both accessions presented two emergence peaks (autumn–winter and spring) in both localities, but while these peaks could be considered as two different flushes in Almenar – for both accessions –, they appeared to be a single flush disrupted by low winter temperatures in Morris. An HTT-based model was applicable for both accessions with less precision than the PhHTT-based one, which was more accurate in most cases but failed in certain circumstances for the USA accession. The differences in emergence percentage among accessions suggest that some accessions might be more amenable to being used as a crop. The two models developed in this work predicted the emergence of both accessions of T. arvense quite accurately. The inclusion of photoperiod in the hydrothermal time equation, creating a new unit that we have called photohydrothermal time, offers a possibility to obtain more accurate models.