According to the latest USDA-NASS Report, South Dakota soybean planting progress is 63% complete and 20% emerged compared to the average 71 planted and 33 emerged. Long-term research done at the SDSU Southeast Research Farm near Beresford shows that a 0.4-0.5 bushel per acre loss per day in early to mid-June can be expected (Figure 1). What management practice can be done to maximize yield with June-planted soybeans? Should you consider having some of your acres custom planted?
Soybean yield is determined by amount of photosynthates (products of photosynthesis) supplied or sourced to the reproductive sinks during reproduction. A concept often referred to as the source-sink relationship in crop science. The goal of managing a soybean crop is to have fields canopied as soon as possible to increase sunlight interception and yield potential. Early planted soybeans flower earlier, have a longer period of time during yield formation (R1 to R6), greater node production, and have greater seasonal canopy photosynthesis. Also, soybeans planted later tend to be shorter and pods are set low on the stem, which reduces the harvestable yield.
Soybean yield components in fields are determined by the number of plants per acre, pod(s) per plant (nodes per plant and pods per node), seeds per pod, and seed size. The diverse components of soybean yield provide a high level of compensation when one component is high or low.
In any operation, seeding rate, row-spacing, and relative maturity changes (variety selection) are practices that can be used to improve performance of June-planted soybean. Ideally, seeding rates should be increased by 10 to 15% and planted in narrow rows as we move into June to compensate for other yield components that can decrease (nodes per plant, pods per plant). It is worth considering having some of your soybeans custom seeded with a narrow-row planter and too hasten completion of planting. At yield losses of 0.4-0.5 bushels/acre/day (Figure 1), this becomes a strong financial consideration.
The maturity rating is a general indication of when that soybean variety is able to start flowering based on the night length, since soybeans are photoperiod sensitive. Moving a group 0 too far south (where nights are longer in the midsummer) may limit yield potential. Selecting an appropriate maturity that utilizes the full growing season provides the best chance to achieve the highest yield. Yield data from SDSU variety performance trials and from your own experience often provide a good approach to determine the most appropriate range of maturity groups to plant in your region. It is recommended to reduce the maturity rating, from what is normally planted as a full-season soybean in your area, when planting is delayed past mid-June. The final planting date for full insurance coverage is June 10 in South Dakota with delayed planting coverage until July 5. Consider reducing the maturity rating by 0.5 from normal as planting is delayed past mid-June and by as much as 1.0 if planting into early July to minimize the risk of frost damage during seed fill.