Feb. 2, 2011

Seeds require optimum soil temperatures to initiate germination and sustain early development, irrespective of the climate zone or year. Farmers who plant before the soil reaches optimum temperatures assume a higher risk of yield loss. This could be due to such factors as seed death, poor germination, or limited initial growth.

Knowing when, on average, an area reaches the minimum soil temperature for plant germination can aid in scheduling planting.

Maps of Optimum Soil Temperatures for Planting

Figure 1 shows the general distribution of when soil temperatures first reach a minimum temperature each season, based on average soil temperatures over the last 10 years. For example, much of the state reaches the 55°F soil temperature during the first to third week of April. Since field corn requires a minimum soil temperature of 55⁰F to germinate, the average earliest time to plant field corn would be in the second or third week of April. For other crops use Table 1 to determine the minimum soil temperatures required for germination and use Figure 1 to view the average time when a location reaches a given temperature.

It is important to understand that the soil temperature maps in Figure 1 provide an average trend using data from the last 10 years to provide generalized results. When making planting decisions, also consider year to year variations in soil temperature. Daily and weekly soil temperature records and maps are available in the Weather section of CropWatch during the crop production season or on the High Plains Regional Climate Center website.at http://www.hprcc.unl.edu/awdn/maps/.

Analysis Indicates a Warming Trend

Soil temperature analysis shows minimum planting dates are occurring earlier in the season than they used to due to a warming trend of the last decade. Advantages of this change include a longer growing season, increased yield, and possibly minimized fall freeze risk for some crops. In continued study, we are identifying the shift in dates from the last decade to this decade when soil temperatures reach optimum levels.

Tapan Pathak
Extension Educator in Climate Variability