InsiGHts
Shattering caused by excessively dry pods is a primary source of physical soybean harvest yield loss.
Yield reductions from pod shattering and grain shrinkage reduced maximum gross revenue by 4% for every 1% decrease in harvest moisture below the suboptimal range.
Harvesting at moistures at or above optimal moistures and proper combine settings and speed can minimize harvest-associated yield losses.
Introduction
Soybean yield losses and subsequent reduced profitability from improper harvest management can easily be underestimated. This is probably because these yield losses aren’t as visually apparent as in-season factors like weed or disease pressure. However, because of more emphasis placed on soybean management, and subsequent increases in input costs, maximizing the amount of grain delivered to the elevator is critical.
Yield losses at harvest are most often associated with pod shattering. Once physiological maturity is reached, the seam along of the edge of pod begins its degradation. Continued drying beyond optimum harvest moistures weakens its strength of the bond, thus making it more susceptible to break. Wetting and drying cycles from precipitation also further its degradation. Other abiotic (drought, fertility) and biotic factors (disease, insect damage) can also increase the potential and magnitude of loss from pod shattering.
Although it is known that yield losses occur when soybeans are harvested at suboptimum moistures, the magnitude of those losses is not well quantified, which may also factor into why the importance of proper harvest management could be overlooked.
Soybean Harvest Timing Trial
Graph 1. Relationship between % of maximum soybean yield and harvest moistureTo quantify yield and gross profitability losses associated with delayed harvest timing, field trials were established at two Agronomy in Action research sites (Slater, IA, and Waterloo, NE). Two Golden Harvest® soybean varieties with similar pod shattering resistance ratings, GH2505E3 and GH2610E3 brands, were planted at all sites. Harvest timing treatments were applied according to target moistures:
- Optimal (~14%)
- 2% moisture loss (12%)
- 4% moisture loss (10%)
- 6% moisture loss (8%)
Yield Response to Suboptimal Harvest Moisture
Graph 2. Relationship between shatter loss and harvest moisture at Waterloo, NE. Dashed lines identify minimum moisture where shatter loss was minimized and the amount at that moisture.To account for variability in harvest timings across locations, a regression analysis between the percent of maximum yield (PMY) and harvest moisture was used. It found that PMY decreased quadratically as harvest moisture declined (Graph 1). For example, the regression predicted that PMY would decrease by 3.3, 9.0, and 17.2% when harvest moisture decreased from an optimum of 14% to 12, 10, and 8%, respectively. This translates to yields of 67.7, 63.7, and 55.9 bu/ac at 12,10, and 8% harvest moistures compared to 70.0 bu/ac at 14%.
The relationship between shatter loss and harvest moisture was also evaluated via regression analysis. The analysis found that shatter loss increased quadratically as harvest moisture decreased (Graph 2). Based on the regression, yield losses from shattering increased 0.2, 1.2, and 3.3 bu/ac at 12, 10, and 8% harvest moisture, respectively, over the optimum 14% moisture. The regression also predicted shatter loss would be minimized at a moisture of 13.1% or greater. However, it still predicted a harvest loss of 1.3 bu/ac at that moisture. All combined-specific variables (concave/sieve settings, harvest speed, real speed) were all adjusted accordingly to maximize harvest efficiency in the trial, suggesting that eliminating harvest loss at the header is not practically attainable (Figure 1).
Relationship Between Gross Revenue and Harvest Moisture
Figure 1. Harvesting at optimum moisture with proper combine harvest settings and speed still does not eliminate harvest loss. Approximately 0.5 bu/ac loss is depicted.Harvesting at suboptimal moistures carries risk for decreased gross revenue due to lower soybean yield from pod shattering and/or shrink. Shrink refers to the weight of grain below an elevator’s base moisture content (typically 13%) that is unaccounted for when the grain is sold, resulting in less bushels paid. Graph 3 shows the relationship between gross revenue and harvest moisture in this trial and found a linear decrease in the percent of maximum gross revenue (MGR) and harvest moisture. Specifically, the relationship predicted that MGR would decrease 4% for every 1% decrease in harvest moisture below the suboptimal range.
Graph 3. Relationship between % maximum gross revenue and harvest moisture. The magnitude of gross revenue loss due to suboptimal harvest moistures in a dryland and irrigated environment (based on predicted yields from the regression equation in Graph 1) is further shown in Table 1. In this example, harvesting soybeans at 11.5% would result in a loss of $38.80 and $52.65 per acre in a 60 bu/ac dryland and 80 bu/ac irrigated environment, respectively. Of that value, $12.20 and $16.25/ac, respectively, or the value of nearly a bushel of soybeans, would be attributed to shrink alone, which represents 31% of total revenue loss. Revenue loss became more extreme as harvest moisture continued to decrease below the optimal range. For example, harvesting at 8.5% moisture would decrease gross revenue by 18% ($147.43 and $197.47/ac for the dryland and irrigated environment, respectively). Although shrink now accounted for 22% of the loss, it was still predicted to be $32.63 and $43.47/ac respectively. In comparison, gross revenue loss at this moisture due to agronomic reasons was $114.80 and $154.00/acre for dryland and irrigated, respectively. These results show that revenue loss through improper harvest management can be substantial.
Summary
Yield and subsequent profit losses from improper harvest management of soybeans can easily be underestimated, and the results from this trial underscore its true importance, as even slight moisture reductions (e.g., 1.5%) from the optimum moisture range can decrease overall profitability. Unfortunately, soybean moisture can decrease over a very short time when conditions are favorable (e.g., high temperatures, low humidity, windy conditions), meaning some profitability loss due to suboptimal harvest moistures is sometimes inevitable. However, proper planning, field prioritization, and combine harvest settings and speed can help reduce these potential losses. Also, results from this study suggest that any moisture dockage associated with soybeans delivered above 13% far outweighs the agronomic (pod shatter) + shrink revenue losses from soybeans harvested at suboptimal moistures.
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