Soybean Yield Response to Nitrogen Applied at Different Growth Stages
There are confounding results in previous research of application of nitrogen (N) fertilizer in soybean (Glycine max L. Merr). The application of N fertilizer may induce to a trade-off in which N fixation could have a negative impact, but production of biomass and grain could favor by the energy savings. The objective of this experiment was to determine the effect of N fertilizer/timing on soybean yield, yield components. Field experiments were conducted on 2015 and 2016 in central Iowa to determine the effect of the application of different rates of Ammonium-Nitrate (34%) and application times. The experiment was set up as randomized complete block design, with four levels of nitrogen fertilizer rates (0, 40, 80 and 120 lb N/acre), and three application times (planting, R1/R2, R3/R4). Plant samples were collected at maturity for dry matter yield, grain yield and N determination in each plant organ from aboveground biomass. Preliminary results of this experiment show us that there is a significant effect by the interaction of N rate x timing only in 2016, supported by a high number of plants/m2. Moreover, N fertilization affected the fruit-to-plant ratio only on 2016. However, the average of seed-to-fruit ratio did not change in both years with an average of two to three seeds per fruit. Biomass dry weight was only significant on 2016 in which application of 120lb N/acre at planting, results were higher than in 2015. Results of this experiment suggest that farmers should not consider N fertilization in soybeans in Central Iowa as a method to increase grain yield or yield components.