Commments on "Making crops climate ready" by Tracy Hmielowski

Authors: Kiniry, James

Submitted to: Agronomy Journal
Publication Type: Other
Publication Acceptance Date: 6/21/2019
Publication Date: N/A
Citation: N/A

Interpretive Summary: A recent article brought up the idea of improved heat tolerance in maize. In a 1987 experiment station publication, we investigated how much high temperature is a factor in restricting maize yields as you move south out of the Midwestern Corn Belt. We compared temperatures from planting to silking, at silking, and for the 40 days following silking (representing approximate grain filling). We analyzed data from 6 diverse sites where maize is grown in the U.S. The mean temperatures from planting to silking did not show a tendency for higher temperatures in the southern locations. At silking, mean temperature is range was 4 C for all six locations, and the two Texas locations differed from central Iowa by only 1 C. The greatest temperature differences were for the 40 days following silking. Thus, high temperatures before silking and at silking are not a factor for yield differences with latitude within the U.S. Farmers at all latitudes tend to plant as soon as the soil is warm enough, and the patterns of air temperature increase until silking are similar across several latitudes. Because of the temperature differences during the 40 days following silking, it is only during this “grain filling” period that latitudinal differences become obvious. Thus, any “hybrid adaptation” targeting southern locations only needs to consider the grain filling interval. An obvious exception to this is when hot dry winds occur at silking at a site, causing loss of pollen by tassel blasting.

Technical Abstract: A recent article brought up the idea of improved heat tolerance in maize. In a 1987 experiment station publication, we investigated how much high temperature is a factor in restricting maize yields as you move south out of the Midwestern Corn Belt. We compared temperatures from planting to silking, at silking, and for the 40 days following silking (representing approximate grain filling). We analyzed data from 6 sites in: 1. Southern Michigan (representing an extreme northern site for growing maize for grain), 2. the High Plains of Texas, 3. Central Texas, 4. Central Iowa, 5. Central Missouri, and 6. the Panhandle of Florida. The mean temperatures from planting to silking only differed by 3 C and did not show a tendency for higher temperatures in the southern locations. At silking, this range was 4 C for all six locations, and the two Texas locations differed from central Iowa by only 1 C. The greatest temperature differences were for the 40 days following silking. Thus, high temperatures before silking and at silking are not a factor for yield differences with latitude within the U.S. Farmers at all latitudes tend to plant as soon as the soil is warm enough, and the patterns of air temperature increase until silking are similar across several latitudes. Because of the temperature differences during the 40 days following silking, it is only during this “grain filling” period that latitudinal differences become obvious. Thus, any “hybrid adaptation” targeting southern locations only needs to consider the grain filling interval. An obvious exception to this is when hot dry winds occur at silking at a site, causing loss of pollen by tassel blasting.