“Early planting” has taken on a new definition for many farmers this spring as unusually warm, dry weather allowed them to finish planting corn in record time. It’s also causing some farmers to question how early to plant soybeans.

Benefits of early planted soybeans, defined as late April or early May planting, have shown to outweigh potential risks in some university studies. Research by Iowa State University shows the optimal planting dates for soybeans – if soil conditions are suitable – in the southern 2/3 of the state is the last week of April and the first week of May for the northern 1/3 of Iowa. Seventy-nine percent of the time planting in late April or early May resulted in higher yields than soybeans planted around May 20.

When determining how early to plant, the potential benefit of yield gain must be weighed against the potential risks. Planting seeds in cool soils can delay emergence and predispose soybean plants to seedling diseases. The ideal soil temperatures for soybeans is 77 degrees Fahrenheit; germination may be delayed by three weeks if the soil temperature at two inches is about 50 degrees. Cool soil temperatures may also slow root development and make seedlings more susceptible to root rotting pathogens that can cause “damping off”.

Early planting may also predispose soybean plants to infection by Sudden Death Syndrome (SDS). To reduce the risk of SDS infection, choose soybean varieties with good tolerance to that disease. Also be aware of whether the field in which the soybeans will be planted has a history of SDS.

Recent conversation on Farmers for the Future centered around a very good question: just how early is too early to plant corn?

Since the 1970s, the time for planting corn in the spring has moved up 10 to 14 days. The ability to plant earlier is mainly attributed to advances in plant breeding and seed treatments, and perhaps, changes in climate.

A recent article in “Top Crop Manager” states that planting dates vary from April 15-24 across the Corn Belt, depending on soil conditions. Although breeding and seed treatments have allowed for earlier planting, it’s still a good idea to watch the weather. Seed is most vulnerable during its first few days in the soil, so you certainly don’t want to put it in unfavorable conditions early on.

One tip included in this article involves grabbing a clump of soil and watching how easily it crumbles. If the soil stays in a ball, conditions are not right for planting. If it crumbles easily, the soil is fit for planting.

It’s also very important to look at farm insurance policies as they relate to planting dates. Make sure you have looked at the specifications for the “do not plant before” dates — if you plant outside those dates, your insurance coverage could be jeopardized.

In the end, when you plant is truly is a judgment call based on weather and soil conditions. You know your fields better than anyone. And as the article states, it’s very rare that judgment leads a farmer too far beyond the limits.

To read more of the “Top Crop Manager” article, click here. For a helpful table provided by the University of Nebraska Extension on planting dates, click here.

Despite the trend of farmers planting earlier and earlier, research results recently released by Iowa State University Extension agronomists show that farmers have nearly a month-long window to plant their crops and still realize 95 percent of the crop’s yield potential. The optimal start dates to begin planting corn, according to this study, range from April 11 in southern Iowa to April 15 in northwest Iowa.

ISU agronomists conducted research on seven sites for three years – 2006, 2007 and 2008 – for a total of 21 site-years. Based on yield data obtained, recommendations have been developed to achieve maximum yield possible in relation to planting date for each of three regions across the state. Each region had a different window of time that optimized the yield, on average. A summary of these windows, as published in Integrated Crop News, follows:

Northeast region (red):
This region has the narrowest planting window due to the need to maximize the length of the available growing season. Grain yields begin to drop off more significantly here than the rest of the state if plantings are too late. We recommend planting between April 12 and May 2 (95-100 percent yield window) or between April 12 and 30 (98-100 percent yield window). The dataset is limited for plantings before April 12 in this region, hindering our ability to make recommendations prior to this date.

Northwest and central region (yellow):
This region has a flatter yield response to planting date than the other regions. In other words, planting date does not appear as important of a management practice here as in other parts of the state. We recommend planting between April 15 and May 18 (95-100 percent yield window) or between April 15 and May 9 (98-100 percent yield window). Again, information for this dataset is limited for plantings before April 15 in this region, diminishing our ability to make recommendations prior to this date.

Southern region (blue):
The yield response in this part of the state is presumably related more closely to rainfall patterns and soil moisture than the length of the growing season since this typically is not a limitation as it is in the northern part of the state. We recommend planting between April 11 and May 13 (95-100 percent yield window) or between April 17 and May 8 (98-100 percent yield window).

An expanded article, with more detail specifically on the methods behind this project and the development of recommendations can be found on the ISU Corn Production website.