Modelling seedling emergence in chickpea as influenced by temperature and sowing depth

Quantitative information about temperature and sowing depth effects on seedling emergence in chickpea (Cicer arietinum L.) is scarce. The main objective of this study was to develop a seedling emergence model for chickpea. To do this, a field experiment with a range of sowing dates and a pot experiment were conducted to determine cardinal temperatures and physiological days (i.e., number of days under optimum temperatures) required for seedling emergence, and to quantify the response of seedling emergence to sowing depth. In the field experiment, four chickpea cultivars were sown at 11 dates and time to emergence and emergence percentage were evaluated. Sowing depth was 5 cm. Several linear and non-linear functions were used to describe the relationship between emergence rate and temperature. The pot experiment was conducted in a controlled-temperature room (21 ± 1 °C) using five sowing depths (2.5–14 cm). Results showed that the response of chickpea emergence to temperature is best described by a dent-like function with cardinal temperatures of 4.5 °C for base, 20.2 °C for lower optimum, 29.3 °C for upper optimum and 40 °C for ceiling temperature. Six physiological days (equivalent to a thermal time of 94 °C days) was required from sowing to emergence at a sowing depth of 5 cm. The physiological days requirement increased by 0.9 days for each centimetre increase in sowing depth. Based on the results from the field and pot experiments, a seedling emergence model was constructed. This model successfully simulated emergence date (range 4–140 days) in spring, winter and ‘dormant’ sowing dates across Iran. Using an example for North West Iran, it was shown how this model could be used to optimise sowing management, including the local ‘dormant sowing’ practice, whereby the crop is sown prior to winter for early emergence in the following spring.