Speaker
Description
Introducing new crops that can thrive under changing climate conditions is crucial for sustainable agriculture. Sorghum (Sorghum bicolor L.) shows promise as a C4 crop due to its high heat and drought stress tolerance. Its deep root system may contribute to increased soil organic carbon, supporting climate change mitigation. However, one of the challenges in expanding sorghum production in higher latitudes and altitudes, such as Germany, is its low tolerance to chilling stress and the risk of low temperatures, especially during early and late seasons. There is limited information about sorghum production potential in different regions of Germany and its role in climate change mitigation. Achieving optimal crop yield depends on matching available thermal units with the cultivar's requirements. This study aims to develop an algorithm to determine optimal sowing dates, growing season length, and suitable maturity groups for sorghum cultivars and assess the climatic water balance in various regions of Germany.
To reduce this knowledge gap, a spatiotemporal analysis was performed on 13,785 grid cells (5kmx5km) all over Germany. This analysis incorporated a dataset spanning 30 years of historical weather data, as well as projections of climate change based on 12 distinct climate scenarios for the time period between 2031 and 2060. Temperature and rainfall thresholds were employed to create weather indices (WIs) and develop the algorithm. The growing season starts after the last freezing temperature, provided that there is sufficient rainfall (>20 mm) to ensure emergence and the average temperature of five consecutive days is above 15°C. Later, the growing season ends after the first cold temperature happens, provided there is not enough GDD (<20°C) to recover from cold stress and/or complete seed ripening in the next two weeks. Finally, the cumulative thermal units between the start and end dates were calculated using a three-segmented function. This calculation aimed to quantify the duration of the growing season for different maturity groups of cultivars. The cardinal temperatures utilized in the function were obtained by fitting a thermal-time model to the data obtained from an extensive germination test on new cold-tolerant sorghum hybrids tailored for German conditions in constant temperatures ranging from 10 to 40°C with 5°C intervals.
By the middle of the century, better growing conditions are projected to be available for sorghum cultivation, as a longer growing period with more heat can be used for growth and yield formation (Figure 1). This is due to the warming in the main growth phase, particularly in lower altitudes caused by climate change, and at the same time, to the possibility of earlier sowing and later harvesting. While experimental sorghum cultivation has so far been limited primarily to southern Germany, the analyses show that parts of North Rhine-Westphalia and Brandenburg already offer suitable growing conditions. In the future, suitability for cultivation will increase significantly in most regions, and it is expected that varieties with later maturity and correspondingly higher yield potential can also be cultivated with a lower productivity risk.
Further analyses will investigate sorghum's potential cultivation advantage, particularly in regions with an increased risk of drought stress, using phenology models and degree-days as a stress index. Sorghum has demonstrated higher yield stability and levels than maize in trials conducted in dry locations and years with low precipitation, including in 2022 in the Bavarian State Research Center for Agriculture (LfL) field trials in the dry region of Lower Franconia at the Schwarzenau site. These findings highlight sorghum's suitability for cultivation in regions prone to drought stress.
Additionally, the ongoing climate chamber assessment at the Julius Kühn-Institut, Kleinmachnow, aims to quantify the effects of different temperature regimes. This assessment focuses on physiological and morphological development in the early sorghum growth stages. Finally, the research aims to parametrize a process-based crop model through wide north-south gradient field trials and run a comprehensive simulation to provide Germany-wide insights into the yield and stability of sorghum versus maize, identify promising regions for sorghum cultivation in Germany, and understand its complex responses to climate, soil, and water balance.
Figure 1. Germany-wide available thermal units (TU, °C) of the growing season of sorghum under historical (1976-2005 (left)) and future climate conditions (2031-2060, RCP4.5 (center) and RCP8.5 (right)). The growing season is not fixed in different scenarios.
| Keywords | Sustainable agriculture; Crop modeling; Thermal units; Chilling stress; Drought stress |
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