Dordt University



Yield Response to Soybean Planting DatesDordt College2016 Growing SeasonAuthor: Jordan Van MaanenIntroduction Deciding when to plant soybeans is one of the most important management decisions that impacts yield. The optimal date for planting soybeans in Northern Iowa is the first week of May (Soybean Planting Date). Some of the benefits of planting soybeans early include higher yield and profitability, shorter plants with less lodging, and more vegetative nodes, which can result in more pods per plant. Some of the disadvantages of planting soybeans early include soil crusting, late spring frost, and sudden death syndrome. Planting soybeans early can increase the chance of having to replant. In this study we wanted to look to see if there would be a yield difference between soybeans that are planted early and soybeans that are planted late. Materials and MethodsAn early and a late soybean variety were each tested in this trial. The early variety, Pioneer P18T85R, and the late variety, Pioneer P27T03R were both planted on 30 inch rows. The trial was conducted at the Dordt College Agricultural Stewardship Center in Sioux County, Iowa. Both varieties were planted at an early date, May 5 and at a later date, May 21. Each variety was randomized in a complete block design and replicated three times each throughout the field. The plots were managed throughout the growing season to minimize any variables such as weed and disease pressure. During this trail, this soybean field got sprayed twice with Warrant Ultra? due to an applicator error. Once the grain had matured and dried down, the grain was machine harvested. Each strip was weighed and measured to determine moisture. Yield was then calculated using the moisture corrected yield formula. Results and DiscussionThe AVOVA for these data showed a significant effect of planting date on soybean yield (P=.00000016). Soybeans planted on May 5 yielded an average of 80.58 bu/acre and the May 21 planted soybeans averaged 74.94 bu/acre over both planting soybean varieties. The average yield difference was 5.64 bu/per acre. There was also a significant effect of the maturation variety on soybean yield (p=.000000027). The early maturity soybean, P18T85R, averaged 80.85 bu/acre compared to the average of 74.67 bu/acre for the later maturity soybean, P27TO3R. The average yield difference was 6.18 bu/acre across both planting dates.The yield differences were consistent across treatments since the interaction between the soybean variety and planting date was not statistically significant (p=.28) as determined by the ANOVA.The results from one year suggest that soybeans planted earlier in the season will have a higher yield than soybeans planted later for both maturity varieties used in this trial. The data also indicate that an early maturity soybean will yield more than a late maturing soybean at either planting date. The yield of the early maturing soybean planted at the later date was similar to the yield of the late maturing soybean planted at the early date. Variety and planting dates were important variables affecting soybean yield for this year. The trial should be repeated over multiple years with different growing seasons to determine if these result would be consistent.AcknowledgementsMike Schouten- Agricultural Stewardship Center ManagerIowa State University Extension- Soybean Planting Date by Palle Pederson ................
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