For many Iowa farmers, spring brings the beginning of a new crop year. Before any seed hits the ground, farmers have to make a lot of important decisions regarding the planting season. In Iowa, many farmers are planting corn and soybeans right now; some might even be done with planting already. However, getting the seed in the ground isn’t as easy as it looks! Among other things, farmers have to decide what crops they want to plant in which fields, and then try to decide when the optimal time to get the seed in the ground is while managing the weather and the calendar.
What to plant?
First and foremost, farmers have to choose what crops to plant on which fields. A lot of variables influence this choice.
Overall, farmers have to choose a crop mix for that year. If the markets are looking good for soybeans, a farmer might choose to plant more acres of soybeans than they usually do; if corn looks profitable, a farmer might incorporate more of that. This often comes down to economics and the relative profitability of the crops. Farmers also need to consider the soil types of their fields and the other aspects of their farm. For example, a farmer who raises cattle may plant corn continuously and use the manure as fertilizer. Corn and soybeans are by far the most common, but some Iowa farmers plant hay, straw or silage crops such as alfalfa, wheat or rye.
Rotating crops each year can help control diseases and insects. Farmers have to consider their rotation and what was planted on their fields the previous crop year. Some farmers use traditional corn-soybean rotations, where corn and soybeans are planted alternately each year. Corn often has higher yields following soybeans due to nitrogen from the breakdown of soybean residue. Because of a symbiotic relationship with a nitrogen-fixing soil bacteria, soybean residue is very high in nitrogen. However, rotation has become slightly less effective as some pests, like the European corn borer, have adapted to the rotation.
Some farmers choose to plant corn for several consecutive years, too. This requires slightly more management (potentially more tillage and fertilizer) than a corn-soybean rotation. Other farmers might choose to plant wheat or oats, depending on the relative profitability of the crop that year. Most farmers don’t plant soybeans continuously because they are more susceptible to soil-borne diseases. Personal preference often influences this choice; some farmers like raising one crop more than another, and that will impact their decision making as well.
When choosing which crop to plant in a specific field, farmers have to look at known diseases and fungus problems. If they know a specific field has a problem with Northern Corn Leaf Blight, they would choose a resistant variety of corn to plant in that field or plant soybeans. Through plant genetic improvement and breeding, there are many different hybrids of common Iowa crops that are resistant to many of the most damaging crop diseases. Farmers may also choose different seed treatments for protection of the seeds from known insects and fungi. Using resistant varieties and seed treatments on fields with known pest problems can greatly improve yield.
For selecting specific varieties of corn and soybeans, farmers can look at the yield trials of that hybrid or consult with an agronomist. Farmers have many varieties from several companies to choose from, so they can select ones they feel are best suited for each field.
When to plant?
After farmers have selected a crop and variety for each field, they have to wait for just the right time to plant. Choosing when to get into the fields with a planter can be a balancing act between weather and the calendar date, based on the farmer’s personal risk tolerance. Planting early gives the crop more time to mature, but is also more risky.
The most important factors in the readiness of a field for planting are the soil temperature and moisture. For corn and soybeans, the soil must be 50 degrees and rising; planting when it is too cold will prevent seeds from emerging. If the soil is too wet, the plant roots will grow poorly, due to compaction of the soil. Without proper root structures, corn becomes very susceptible to damage from wind. If the soil is too dry, the seeds will sit in the soil and won’t be able to germinate until they get enough moisture.
There are also optimal planting dates for corn and soybeans which indicate the dates in which yield potential for the crop is maximized. In general, corn is planted before soybeans because soybeans have less of a yield reduction for later planting. Most corn is planted in early to late April, and soybeans are planted from the end of April through May.
Yield is strongly correlated with planting date, and planting after the optimal planting date can reduce yields. The strong yield advantage may outweigh the risks of planting early. This yield advantage can be attributed to faster canopy closure (the leaves of the plant cover the soil between rows), a longer reproductive period, pollination occurring at a more favorable temperature and moisture, and allowing the grain to dry faster when it is still in the field.
The weather and the optimal planting dates have to be balanced, and farmers spend a lot of time worrying about Mother Nature and watching the calendar. Weather can drastically change the field conditions before or after seeds are in the ground and damage yield potential. In April, snowstorms and cold rains are not unheard of and can negatively impact the germination of the seeds. In some cases, planted fields that have gotten too cold must be planted again, because the first seeds won’t germinate. On the other hand, waiting until it is very warm in May to plant reduces the risk of the weather damaging crops, but also reduces yield. Many farmers choose to take on more risk as it gets closer and closer to the end of the optimal planting window.
On a day like today in early May, farmers can be seen all over Iowa keeping a close eye on the weather channel and trying to make the best planting decisions they can. The choices made before and during planting season directly impact the success of the crop through the entire growing season. It can be a stressful time of year, but there is nothing more rewarding than seeing those little green plants popping up in rows. In a way, this time of year is the most hopeful too.