RESEARCH 22 The results reflected what Earl regularly sees in the field: the belief that a single input or practice can unlock yield gains. “Growers are sometimes looking for some sort of silver bullet,” he says. “Part of the value of a project like this is to combat that silver-bullet thinking.” With that said, Earl noted that growers can realize yield gains by addressing nutrient deficiencies. “In the absence of such an identified problem, just throwing inputs at a soybean crop is not likely to produce impressive results,” he says. A DIFFERENT PATHWAY Earl also discovered that management-driven yield increases worked through a completely different pathway than those driven by environment. Environment mostly increased yield by boosting seed number; intensive nitrogen treatments advanced yield mainly by increasing seed size. Earl believes those extra nitrogen applications kept the plants green longer at the end of the season. Under normal circumstances, soybeans draw nutrients from their leaves to fill seed, which shortens the seed-fill period, he says. With extra nitrogen available, that process was delayed, allowing the plants to stay active longer and produce larger seeds. This distinction - environment influencing seed number, and added nitrogen influencing seed size - is one of the clearest findings in the study. It shows that even when both environment and management increase yield, they may do so for fundamentally different reasons. Earl and his colleagues noticed a second pattern in the data that raised questions. Growth measurements taken earlier in the season suggested that the crop’s performance around R2.5 to R3 - before any seeds had formed - might be linked to final seed size. This is earlier than expected; seed size is usually thought to be determined much later. Earl stressed that this signal needs more investigation, but said it may point to an additional window of development that contributes to how soybeans build yield. EXPLORING BIOLOGICAL CEILINGS To explore how far soybean yields might go under ideal conditions, the team also grew soybeans in pots using a sand-peat mix and daily fertigation. These plants shared the same above-ground environment as field plots, but the environment below ground was completely optimized. The pot system produced very large plants and suggested potential yields exceeding 100 bushels per acre; however, disease issues prevented clear results. Earl says that while the results were inconclusive, they are still informative. They suggest that agricultural soils may have fundamental physical limitations that cannot be overcome solely with added fertilizer or irrigation. Understanding those limitations may become an important research direction. Taken together, the project’s results are not intended to guide best management practice recommendations for farmers, but they do offer value for soybean breeders. Understanding the stages when yield is formed, and the conditions that support it, could help breeders shape future genetics that perform more consistently across Ontario’s fields. “Understanding the physiology of yield formation in our environment is key for developing regionally adaptive varieties,” Earl says. • continued from page 21 ONTARIO GRAIN FARMER
RkJQdWJsaXNoZXIy MTQzODE4