The consequences of change in management practices on maize yield under climate warming in Iran

The potential impacts of climate warming on grain yield, water, and nitrogen consumptions of maize have been repeatedly assessed across different regions of the world. However, to date, there is no comprehensive, large-scale evaluation on the effects of climate warming on the cropping systems of Iran. The objective of the current study was to quantify the effects of climate warming on the length of the growing period and grain yield of maize. We also tested the potential of changes in irrigation, nitrogen application rate, and using late maturity cultivars of maize to offset the negative impact of climate warming in order to maintain the current levels of grain yield (4 to 10tha(-1) depending upon the province) in Iran. The crop modeling framework SIMPLACE was used to evaluate the effects of the warming temperatures, nitrogen application rate, and changes in thermal requirements of the cultivar scenario combinations on grain yield of maize in Iran. The climate, soil, and management inputs of the crop model were obtained from global datasets as grid cells at 0.5 degrees x0.5 degrees resolution, and the outputs of the crop model were aggregated to the province level. Results of the grain yield projections showed a decline (-0.1 to -22%) in maize, especially in the Southern provinces (Khuzestan, Fars, and Kerman) under different warming scenarios by +0.5 to +2 degrees C, an increase from the baseline. The grain yield decline appeared to be mainly driven by a shortening of the length of the growing season and extreme heat stress during anthesis, the most sensitive period of crop growth. Increasing temperatures during the growing season lead to a marginal increase of absolute irrigation requirements over the maize growing areas. For all provinces, application of 10-25% more nitrogen than the current rate (170kgN/ha(-1)) was able to offset the negative effects of higher temperatures (+0.5 and +1.0 degrees C) during the growing season. However, the increased nitrogen application rates were not able to maintain the baseline level of grain yield under the +1.5 and +2.0 degrees C warming scenarios. Introducing late maturity cultivars, which required 20% more temperature sum than current cultivars to reach maturity, improved the grain yield in the cooler provinces by up to 10%. In conclusion, the grain yield baseline level may not be maintained under the highest magnitude of warming by increasing nitrogen application rates or using late maturity cultivars. Furthermore, more water is needed to produce a unit of grain under a warming climate. This study also suggests that combined adaptation strategies should be considered by policymakers in order to mitigate the negative impact of climate warming on the cropping systems of Iran.