Evaluation of Yield and Crop Water Requirement in Response to Change of Planting Date under Climate Change Conditions in Kermanshah Province

APSIM model was used to investigate yield and water requirement of maize in different planting dates under two emission scenarios (RCP4.5 and RCP8.5) at the three locations of Kermanshah province (Kermanshah, Kangavar and Eslamabad-Gharb). Climatic parameters were predicted using the AgMIP methodology. Results of this study indicated that in the future, average maize grain yield will be reduced in all locations, scenarios and planting dates (70 percent) compare to the baseline. Reasons for yield loss are increasing temperature over growing season (15.7%), decreasing length of growing season (4.7%) and is likely to concurrency time of flowering with extreme temperature. In addition, maize water requirement, on average, will be increased 14 percent is comparison to the baseline in all locations, scenarios and planting dates mainly due to rising temperature. In conventional planting date (4 May), crop water requirement of maize on average increased 12 percent under two emission scenarios compared with the baseline while on earlier and later planting dates, crop water requirement increased 15 and 7 percent, respectively. Due to the amount of higher cumulative rainfall during the growing season (54.27) on earlier planting dates (4 and 19 April) as well as lower yield loss compare to other planting dates (56 percent), earlier planting dates can be explained as adaptation strategy in order to achieve appropriate yield. The results also showed that among study locations, Eslamabad-Gharb and Kermanshah were the most suitable areas in terms of grain yield (4221.8 Kg.ha-1) and water requirement (1489.2 mm), respectively

An Investigation into Germination Patterns of Common Lambsquarters (Chenopodium album) in Reaction to Temperature, Salinity and Waterlogging Stress

Gaining insights into the germination and emergence patterns of weeds as well as the factors which have an impact on these patterns is beneficial for weeds management programs. In order to investigate the effect of temperature, waterlogging and salinity on germination and emergence of common lambsquarters, three separate experiments were conducted, adopting a completely randomized design with four replications. The results of the temperature experiment showed that the highest germination percentages, which were 87, 93 and 88%, were obtained in the temperature range of 15, 20 and 25°C, respectively. Maximum values of germination rate, radicle length, plumule length, and seedling dry weight were obtained at 20°C. In addition, optimum seed vigor index of 796.29 was observed at 20°C. The results of the Regression Model showed that germination percentage decreased with an increase in waterlogging duration and halted after 8 and 10 days of consecutive waterlogging. Mean comparisons revealed that radicle and plumule length, seedling dry weight and vigor index decreased significantly by increasing the period of waterlogging. Salinity adversely affected germination percentage, germination rate and seedling dry weight of common lambsquarters. These factors were at their highest amounts in the control and 50 mM NaCl treatments. A downward trend was observed in these factors as NaCl concentrations increased and finally the germination process stopped in concentrations ranging from 300 to 400 mM NaCl. Radicle and plumule length also decreased from 10.51 and 9.23 cm in the control treatment to 3.57 and 2.47 cm at 250 mM NaCl. Overall, the results revealed that the maximum seed vigor index of 851.84 was obtained in the control treatment and seed vigor halted when the salinity level increased to more than 250 mM NaCl. Finally, the results showed that optimum temperature for germination of common lamsquarters was 20 °C and the existence of salinity and waterlogging stress can decrease growth indices of this weed at germination and seedling stages

Risk assessment of frost damage to sugar beet simulated under cold and semi-arid environments

In the semi-arid climatic conditions, water shortage is a key factor to generate crop production. Planting in autumn and winter and using precipitation can help cope with the problem. But in the semi-arid areas with cold winter, frost is another limited factor affecting crop production. For this purpose, in the present study, a simple and universal crop growth simulator (SUCROS) model was used to estimate the potential yield of sugar beets and frost damage from 1993 to 2009 for four autumn sowing dates (2 October, 17 October, 1 November, and 16 November) and two spring dates (6 March and 6 May) in eight locations (Birjand, Bojnord, Ghaen, Mashhad, Torbat-e Heydarieh, Neyshabor, Torbat-e Jam, and Ghochan) of the Khorasan province in northeastern Iran as a semi-arid and cold area. There was a large variability between locations and years in terms of frost damage. The crop failure from frost for the autumn sowing dates ranged from 62.5 to 100% at Neyshabor and Ghochan, respectively. Although autumn sowing dates performed better than spring sowing dates in terms of fresh storage organ yield (~ 109.9\ua0t\ua0ha vs. ~ 78.4\ua0t\ua0ha ), the risk of frost stress under autumn sowing dates was high at all studied locations. To maximize potential yield and minimize frost risk, sugar beet farmers under semi-arid and frost-prone conditions in the world such as Khorasan province should choose optimum sowing dates outside the high frost risk period to avoid crop damage. The last frost day under these areas normally happened between the 15th and 28th of February, after which no frost events occurred. Accordingly, it is recommended to farmers to sow sugar beet after the period during which no frost risk for sugar beet occurred

Modelling Germination Pattern of Two Pigweed Ecotypes in Response to Temperature

Introduction: Seed germination is an important stage in the life history of plant affecting seedling development, survival, and population dynamics. Germination begins with seed, water uptake and terminates with the elongation of the embryonic axis from the seed coat. Germination and seedling emergence are the most important phonological development stages in pigweed and have a vital role in its establishment. Accordingly, predicting the phenological stages would be resulted in improvement of crop management as the number and time of pigweed emergence could be quantified. Sigmoidal curves, also known as growth models, have wide application in agricultural research and can be evaluated by means of nonlinear models, which operates through data modelling by a nonlinear combination of parameters depending on one or more independent variables. This study was conducted to evaluate various regression models to describe the response of germination rate to temperature range in two pigweed ecotypes (Alborz and Fars). Materials and Methods: A glasshouse experiment was carried out as a completely randomized design with four replicates. The seeds were sterilized by soaking in a 3% solution of hypochlorite sodium for 30 seconds. After the treatment, the seeds were washed several times with distilled water. 25 seeds were put in each Petri dish (with 9 cm diameter). The petri dish is monitored on a daily basis and afterwards germinated seeds (according to exit of radicles to the size of 2 mm) were measured and recorded daily in each Petri dish. Six regression models were applied to quantify the germination patterns of two pigweed ecotypes (Alborz and Fars) under a range of temperature between 5 to 35 °C. For both regions, during spring and summer, the range of temperatures was selected in order to simulate the temperature changes. The models were included Weibull, Lognormal, Logistic, Gompertz, Sigmoidal and Chapman. Some criteria were used to describe the goodness of fits of the models, including coefficient of determination (R2), root mean square of error (RMSE) and Akaike index (AIC). Moreover, a simple program called Germin was used to calculate D10, D50 and D90 (the time interval to maximum 10, 50 and 90% of germination, respectively). Results and Discussion: Results showed that Weibull four-parameter and logistic models were the best for describing the germination rate in Alborz and Fars ecotypes, respectively compared to the other models. The difference between ecotypes could be attributed to their base temperatures and thermal time requirements at each developmental stage. Therefore, it can be concluded weed germination during different seasons is not a random phenomenon. However, the germination and emergence of a clear pattern over time follows the pattern of different environmental conditions is subject to change. Results also indicated that the time to D90 was only 4 and 5 days in Alborz and Fars ecotypes, respectively meaning that with increasing temperature during early spring, this weed would germinate much sooner than spring crops and consequently resulted in crop damage. The results showed that the in Alborz population, with increases temperature from 10 to 30 °C, germination percentage linearly increased and with increasing temperature to the desired temperature, it decreased. However, germination in Fars ecotype showed that, in temperatures 10, 15 and 20 °C respectively, the germination was 36, 56 and 84 percent, while, with an increase in temperature from 25 to 35 °C, this component was always a constant process. Germination rate increased with increasing temperature from 10 to 35 °C which was higher in Alborz ecotype compared to Fars. At lower temperatures, the main reason for less germination rate could be decrement of water imbibition and enzyme activity in biochemical processes of germination. Conclusion: Increasing public awareness and concern about the impacts of herbicides on the environment, development of herbicide-resistant weeds, and the high economic cost of herbicides have increased the need to reduce the amount of herbicides used in agriculture. Prediction of weed emergence timing would help reduce herbicide use through the optimization of the timing of weed control. It was concluded that Weibull four-parameter and logistic models could be used as decision making tools in Alborz and Fars, respectively, to predict seed emergence of pigweed which in turn resulted in efficient management as well as reduction of herbicides usage. Future research should be addressed to determine a wider validation of the models, which could be valuable tools for farmers and practitioners for adequate timing of control in pigweed weed

Large-scale characterization of drought pattern: a continent-wide modelling approach applied to the Australian wheatbelt – spatial and temporal trends

* Plant response to drought is complex, so that traits adapted to a specific drought type can confer disadvantage in another drought type. Understanding which type(s) of drought to target is of prime importance for crop improvement. * Modelling was used to quantify seasonal drought patterns for a check variety across the Australian wheatbelt, using 123 yr of weather data for representative locations and managements. Two other genotypes were used to simulate the impact of maturity on drought pattern. * Four major environment types summarized the variability in drought pattern over time and space. Severe stress beginning before flowering was common (44% of occurrences), with (24%) or without (20%) relief during grain filling. High variability occurred from year to year, differing with geographical region. With few exceptions, all four environment types occurred in most seasons, for each location, management system and genotype. * Applications of such environment characterization are proposed to assist breeding and research to focus on germplasm, traits and genes of interest for target environments. The method was applied at a continental scale to highly variable environments and could be extended to other crops, to other drought-prone regions around the world, and to quantify potential changes in drought patterns under future climates

Future climate change could reduce irrigated and rainfed wheat water footprint in arid environments

The concept of water footprint (WF) has been used to manage freshwater resources for the past two decades and is considered as indicator of the sustainability of agricultural systems. Accordingly, the current study aimed to quantify WF and its components in the future climate for rainfed and irrigated wheat agro-ecosystems in 17 provinces of Iran located in arid or semi-arid environments. The provinces were divided into five climate classes. The simulations were conducted under current (1980–2010) and future climate (2040–2070) using the Agricultural Production Systems sIMulator (APSIM) crop model, following the Agricultural Model Intercomparison and Improvement Project (AgMIP) protocol. Baseline simulations indicated that the total WF, averaged across all climate classes, was 1148 m3 t−1 for irrigated and 1155 m3 t−1 for rainfed wheat. WF was projected to decline in the future compared to baseline in both irrigated and rainfed systems mostly because of increases in yield of +9% in rainfed systems and 3.5% in irrigated systems, and decreases in water consumption by −5.4% and −10.1%, respectively. However, the share of gray water footprint (WFgray) was projected to increase in the near future for both rainfed (+5.4%) and irrigated (+6.9%) systems. These findings suggest that cleaner and more sustainable production (i.e. obtaining grain yield under optimal water and nitrogen consumption) could be achieved in irrigated and rainfed wheat ago-ecosystems if optimal N fertilizer management is adopted. Additionally, rainfed cultivation can be further expanded in some areas which is expected to result in a substantial reduction in blue water (i.e. less irrigation), especially in sub-humid and semi-arid cool areas

An optimal combination of sowing date and cultivar could mitigate the impact of simultaneous heat and drought on rainfed wheat in arid regions

Drought and heat stress are the most important limiting factors for crop production. Simultaneous impacts of drought and heat stress during crop's sensitive growth phases could be more harmful than their individual impacts. Accordingly, we investigated several management practices including 4 sowing dates, 3 cultivars in combination with 4 initial soil water contents to investigate the simultaneous impact of drought and heat stress on rainfed wheat grain yield in different climates (57 locations) across Iran from 1980 to 2016. A modified version of the wheat module of the Agricultural Production Systems sIMulator (APSIM) modelling framework was adopted. Historical temporal trends showed that grain yield has increased by + 10 kg ha-1 y-1 in cold regions and decreased by 14.5 kg ha-1 y-1 in mild and hot regions since 1980 for Azar-2 (as common cultivar). Long-term simulations indicated that grain yields of 3.3 t ha-1 could be obtained in rainfed agro-ecosystems under only-drought growth conditions. By adding the impact of heat stress, however, average grain yield further declined to 2.9 t ha-1 indicating a reduction of 0.4 t ha-1 owing to heat stress per se for the common cultivar. The results also showed that the long-term impact of drought and heat stress could be diminished with an optimal combination of sowing date, cultivar, and initial soil water depending upon climate classes. A combination of an early-maturity cultivar (“Azar-2”) with early sowing date (07-Oct) was recognized as the best management practice for cold and mild regions while the interaction of a mid-maturity cultivar (MMC), and an intermediate sowing date (20-Oct) was the best management practice for hot climates

Impact of Heat Stress on Rainfed Wheat Growth and Yield Under Semi-arid, Semi-humid and Mediterranean Climates in Iran Condition

peer reviewedAssessing crop yield in response to heat and drought stress is important in implementing the best adaptation strategies to mitigate the effects of climate change. For this aim, observations from 105 agricultural/meteorological experiments in the semi-arid (Maragheh, Qamlou and Sararoud), Mediterranean (Hashem Abad and Oltan) and semi-humid (Gharakhil) regions of Iran were used to investigate the response of the reproductive growing duration (RGD) and grain yield of rainfed winter wheat to certain climatic and agro-climatic indices consisted of precipitation (mm), growing degree days (GDDs), and cumulative extreme temperatures above wheat tolerance threshold level of ≥ 34 °C (TAT). Accordingly, multiple linear regression was applied under baseline (1998–2012) and future increasing temperature (by 1 °C and 2 °C). Results indicated that the average of wheat RGD and yield were 37.2 ± 0.71 d and 2.3 ± 0.05 t ha−1 in semi-arid, 25.7 ± 0.8 d and 2.9 ± 0.11 t ha−1 in semi-humid, and 21.7 ± 0.59 d and 5.25 ± 0.17 t ha−1 in Mediterranean regions, respectively. The main findings showed that, on average during 1998–2012, wheat RGD and yield changed by − 0.26 d yr−1 and − 0.93% (0.02 t ha−1 yr−1) in semi-arid, + 0.25 d yr−1 and − 1.27% (0.04 t ha−1 yr−1) in semi-humid, and − 0.01 d yr−1 and − 0.27% (0.01 t ha−1 yr−1) in Mediterranean regions, respectively. Precipitation and TAT had substantial positive and negative impacts on RGD by + 0.1 d yr−1 and − 0.03 d yr−1, and crop yield by + 0.04% and − 1.14% in all study locations. An increase in GDDs, however, significantly shortened RGD (− 0.06 d yr−1) and consequently reduced grain yield (− 0.04%) in semi-arid regions, while in semi-humid and Mediterranean regions, increasing GDDs had a positive impact on RGD (+ 0.07 d yr−1) and yield (+ 0.19%). Among the indices, TAT showed significantly greater detrimental effects on RGD and grain yield particularly when accompanied by less precipitation (i.e. drought stress). Our results highlighted that any increase in temperatures even by 1 °C or 2 °C would lead to drastic increases in TAT and GDDs in all study regions, most especially in semi-arid regions. Under these conditions, any benefits from precipitation would be neutralized by the negative impacts of increased GDDs and TAT in all study locations. The insights into crop response to weather variations and climate extremes provide excellent evidence and a basis for reducing crop yield damage by designing for improved heat tolerance for the future