Abstract
Developing new cropping strategies (very early sowing, crop expansion at higher latitudes, double cropping) to improve soybean production in Europe under climate change needs a good prediction of phenology under different temperature and photoperiod conditions. For that purpose, a simple phenology algorithm (SPA) was developed and parameterized for 10 contrasting soybean cultivars (maturity group 000 to II). Two experiments were carried out at INRA Toulouse (France) for parameterization: 1) Phenological monitoring of plants in pots on an outdoor platform with 6 planting dates. 2) Response of seed germination to temperature in controlled conditions. Multi-location field trials including 5 sites, 4 years, 2 sowing dates, and 10 cultivars were used to evaluate the SPA phenology predictions. Mean cardinal temperatures (minimum, optimum, and maximum) for germination were ca. 2, 30, and 40°C, respectively with significant differences among cultivars. The photoperiod sensitivity coefficient varied among cultivars when fixing Popt and Pcrt, optimal and critical photoperiods respectively, by maturity group. The parameterized algorithm showed an RMSE of less than 6 days for the prediction of crop cycle duration (i.e. cotyledons stage to physiological maturity) in the field trials including 75 data points. Flowering (R1 stage), and beginning of grain filling (R5 stage) dates were satisfactorily predicted with RMSEs of 8.2 and 9.4 days respectively. Because SPA can be also parameterized using data from field experiments, it can be useful as a plant selection tool across environments. The algorithm can be readily applied to species other than soybean, and its incorporation into cropping systems models would enhance the assessment of the performance of crop cultivars under climate change scenarios.
Highlights
EU-28 needs to import about 40 million tons of soybean for feeding livestock, and humans to a lesser extent
Phenotyping was divided into two complementary protocols to determine a) cardinal temperatures (EXP1) and b) development response to temperature and photoperiod (EXP2). Data produced in these experiments were used to parameterize simple phenology algorithm (SPA) (Simple Phenology Algorithm), which was evaluated with independent data from field experiments
We showed in this study that with a planting date around 20th July (D5), a cultivar from maturity groups (MGs) I could reach beginning maturity (R7) at the same cumulative thermal time than a cultivar from MG 000 (Table 8)
Summary
EU-28 needs to import about 40 million tons of soybean (seed equivalent) for feeding livestock, and humans to a lesser extent. Three cropping strategies could be proposed to grow soybean under these conditions: (i) early sowing to use less irrigation water in summer as escaping strategy (Maury et al, 2015); (ii) northward cultivation of the crop to extend its cropping area toward regions becoming more suitable with increasing temperatures (Olesen et al, 2011); or (iii) double cropping after cereals under late sowing to fully use the thermal time window (Seifert and Lobell, 2015) These new crop management systems using either early or late sowing and new cultivation areas will expose the crop to a wider range of thermal and photoperiodic conditions under higher latitudes (from 43° to 52° N). Optimum temperature has been reported between 22 and 32°C depending on the studies (Grimm et al, 1993; Boote et al, 1998a; Setiyono et al, 2007; Boote, 2011; Parent and Tardieu, 2012) while maximum temperature has been less explored, with reported values between 40 and 47°C (Salem et al, 2007; Setiyono et al, 2007)
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