Early Season - Setting the Stage for Soybeans
Because soybeans flower for a long period of time and have the ability to branch under low populations, they are quite resilient to stress. However, in order to maximize yield, farmers need to ensure early season establishment and manage stress during critical pod-setting and pod-filling stages. This article will discuss 3 early season management strategies.
Early Season Strategy 1 – Seed Treatment
The recent trend in early planted, high-yielding soybeans has increased the importance and need for a strong seed treatment package. When soybeans are planted in cool soil conditions, emergence delays are expected as well as some stand loss. Young seedlings are exposed to insects and disease for a longer period of time during the emergence process when they are planted early. Seed treatments can provide protection against insects, nematodes and diseases, including Fusarium, Pythium, Phythopthora and Rhizoctonia.
Early Season Strategy 2 – Nodulation
It might be surprising to learn that soybeans require more nitrogen than corn on both a per bushel and per acre basis (Table 1). Luckily, soybeans cooperate with microbes in the soil to supply a large portion of this nutrient requirement. Soon after germination, soybean plants use root exudates to lure distinct types of soil rhizobia bacteria to their roots. These bacteria infect root hairs causing them to develop into nodules. Inside the nodule, the bacteria convert atmospheric N2 to plant-available nitrogen. In exchange, the soybean plants provide the bacteria with carbohydrates. Depending on environmental conditions, it takes a few weeks for nodules to become fully functional, leaving soybeans a little yellow and starved for nitrogen. But by V2 or V3 (second or third trifoliate), nodules are visible to the unaided eye and provide nitrogen to the soybeans. Aided with this boost, soybeans at V5 are ready to enter their fastest growth period. When evaluating nodulation, you should look for 5-8 large nodules during the early season. Nodules on the main tap root are likely from the inoculant used during planting. Nodules on lateral roots are likely from existing soil rhizobium populations. Rhizobia employ an enzyme with an iron hemoglobin cofactor similar to blood hemoglobin to convert gaseous nitrogen to plant-available nitrogen. Therefore, healthy nodules are pink on the inside. Poor nodulation can be due to extreme pH (below 5.7 or above 7.3), high soil nitrogen typically from too much manure, saturated soil, new soybean fields, drought or compaction.
Early Season Strategy 3 – Nutrition
Last year, many of our Extractor® soybean tissue samples were taken early in the season. We saw some interesting deficiencies showing up in these results (Table 2).
The table shows that most of the samples were low in boron and copper. In the past, boron, sulfur and manganese have shown up most deficient. It appears that sulfur and manganese deficiencies are getting better; however, boron continues to be problematic. Unfortunately, low and deficient results for copper are as common as boron in early soybean tissue samples.
Soybeans have a small root system early in their growth, which can often prevent the crop from taking up some of the nutrients it needs during accelerated growth. Foliar nutrients can help to rectify these deficiencies in the crop. It is always best to take an early tissue sample to make sure the soybean crop is not lacking an important nutrient, and really, all of them are important.
We often recommend taking an Extractor tissue sample about a week before spraying a post herbicide on the crop. This will tell you if there is a nutrient deficiency, and gives you an opportunity to add that nutrient, or nutrients, to the spray solution. It is also best to sample each field, as one field’s nutrient needs may be quite different than another field.
- Written by Division Agronomists: Ryan Lee, Ben Wilson, Randy Simonson