Radiation is down up to June 1 according the latest FACTS extrapolations.
The springtime decreases in radiation—especially in May—could have caused yellowing corn leaves and slowed down leaf appearance rates (radiation and moisture play a role in phenology, even though temperature is the main driver). The cooler temperatures means lower soil N mineralization, slower plant growth and lower soil water evaporation.
This indicates that the benefit of very early planting has somewhat disappeared by the unfavorable cold and cloudy May weather, yet crops still have a high yield potential.
Key Observations for May and March–April–May periods across IA, IL, IN, NE:
- Number of cloudy days (defined as a day with radiation < 10 MJ/m2/d):
- Increasing over the last 10 years. Same trends for IN, IL, IA, NE and for both the month of May or March through May time period.
- 3 more cloudy days this May compared to 20-yr average (68% increase)
- 5 more cloudy days this March-April-May compared to 20-yr (26% increase)
- Number of sunny days (defined as a day with radiation > 20 MJ/m2/d):
- Decreasing over the last 10 years. Same trends for IN, IL, IA, NE and for both the month of May or March through May; 5 less sunny days this May in IA compared to 20-yr average (28% decrease)
- 3 less sunny days this May in NE compared to 20-yr average (17% decrease)
- Over the March-April-May period there was a decrease in sunny days (3.5 less days or 10% decrease) in IA, IL and IN but not NE
- Radiation amount (MJ/m2, Fig 1):
- Decreasing pattern since 2010 in all 4 states and both time periods
- Across states, there is 7% reduction in radiation in May and 4.5% reduction in March-April-May period
- Thermal time accumulation (GDD, base = 50 oF):
- Getting colder over the last 3-years in all states
- Across states, May 2020 was 20% colder than 20-yr average
- Across states, March-April-May 2020 was 24% colder than 20-yr average
- Getting wetter over time
- May 2020 in IA was drier than normal, other states wetter than normal
- March-April-May in IA and NE drier than normal, IL and IN wetter than normal
The methods included using gridded weather data (from Iowa Environmental Mesonet and NASA POWER), which drive APSIM model simulations used in the FACTS project. The weather data has been checked with local data for accuracy. In this article, the gridded weather data was integrated to state level.