In 2019 we established plots at the Russell E Larson Agricultural Research Center to demonstrate the effectiveness of different sulfur containing fertilizers in corn. We applied S at a rate of 40 lbs per acre using gypsum, ammonium sulfate (AMS), elemental sulfur and poultry litter and maintained two unfertilized check plots. During the 2019 corn growing season, we took monthly soil samples to monitor S availability in the top 8” of soil and soil acidity in the top 2”. Sulfur was extracted from soil samples using a Mehlich III extraction method and extractants were analyzed using an ICP at the Penn State Agricultural Analytical Services Lab. After corn harvest, we took soil cores to a depth of 32” (separated in 8” segments) to determine whether the S had moved downward through the soil profile in each of the treatments. While S concentrations were similar in the top 8” of soil in the treatment plots and check plots, there was greater S deep in the soil profile in the treatment plots. We will use this same set of plots with soybeans in 2020.

Prior to soybean planting in the spring of 2020, we will collect soil cores to 32” again to determine whether the S that was in the soil profile in the fall of 2019 has leached out of the soil profile or whether it remains adsorbed in the clay rich subsoil. Our hypothesis is that there will be S remaining in the soil profile of the gypsum, AMS, poultry litter and elemental S treatments that could be accessed by the soybeans, but this S may be too deep in the soil profile to be initially utilized by seedling plants with shallow root systems. After soybean planting, we will apply gypsum, ammonium sulfate and urea to the plots which did not receive any S in 2019 and maintain one untreated control plot. The fertilizers will be surface applied at a rate of 40 lbs S per acre and should be readily available in the top soil for the seedling soybean plants and continue to supply S throughout the growing season. The urea will be applied at a rate to match the N supplied in the AMS treatment. By applying AMS, gypsum and urea alone, we should be able to make some conclusions about whether yield increases are due to the added S or added N if we observe any yield increases in these treatments.

Following the establishment of the plots, we will collect soil samples to a depth of 8” at monthly intervals after fertilization until physiological maturity of the soybean crop to monitor S availability. We will also take soil cores to 32” in order to monitor the depth to which the soybean plants have rooted. These cores will be collected at monthly intervals after soybean planting. Because of the destructive nature of the root coring from equipment traffic in the plots, root cores will be taken from additional plots on the edge of the experiment, not directly from the fertilizer response plots. The rooting depth data will be compared to the depth distribution of S in preseason soil core data to estimate when the plants can access any S deep in the soil profile.

Plant tissue samples will be collected at the V2/V3 and R1 stages of development. These samples will be analyzed for S content at the Penn State Agricultural Analytical Services Lab. Current Penn State recommendations are that soybean plant tissue be in the range of 0.16-0.41 % S on a dry weight basis to be considered normal. Using these results, we will be able to determine if plants are accessing sufficient S and if there is any increase in S uptake by the soybean plants in response to the various S treatments compared to the no S control. Our hypothesis is that treatments which received S in 2019 but not 2020 will be S deficient at the early sampling date, but after developing a root system which can reach the S in the subsoil, will be sufficient at the later sampling date.

We will measure soybean yield from each of the treatments at harvest using a small plot combine. At the time of harvest we will also collect soybean grain samples from each of the treatments. We will submit these grain samples to a laboratory for analysis of total S content and crude protein, to quantify what effect the different treatments had on grain S uptake and grain protein. We will also have the samples analyzed for concentrations of the amino acids cysteine and methionine to quantify any effect the treatments had on sulfur containing amino acid content.

Updated April 4, 2021:
Please see uploaded final report.

View uploaded report

In this experiment we hypothesized that soybean yield and quality would respond positively to sulfur (S) fertilization. We tested S fertilizers applied at 40 lbs/ac S applied to corn in the year before soybean production (2019) to S fertilizers applied in the soybean production year (2020). Our results indicated that there was not an effect of S fertilization on grain yield or crude protein concentration, however, grain S concentration increased as well as the concentration of the S-containing amino acids cysteine and methionine. This suggests that in cases where S doesn’t limit yield, there are still some effects of the addition of S, especially if producers are concerned about the amino acid concentration of their grain. We also sought to describe the depth distribution of S in the soil profile after S application, and did so at three time points: after corn harvest in 2019, prior to soybean planting in 2020, and after soybean harvest in 2020. We found that even after two seasons of crop production, subsoil S content was higher in after soybean harvest in treatments which had received S in 2019 than treatments which received no S in either year. This is an important finding because it illustrates the fact that the subsoil can act as a reservoir to hold S for use by multiple cropping cycles. In addition, our soybean plant rooting depth data and plant tissue testing data indicated that once roots reached the deeper soil layers containing S, plants readily took it up and assimilated it into their tissues. Finally, when considering the potential interaction between N and S, our plant tissue, soil testing, and grain analyses all indicated that gypsum and ammonium sulfate performed equally well. There was no difference in S content between the two treatments at either plant tissue sampling date, there were no differences in yield, and both treatments resulted in increased grain S, methionine, and cysteine concentrations when compared to the control. Therefore, if a producer’s intends to add S to their soybean crop, the cheaper of these two products should be selected, since the results so far indicate similar crop performance. It also appears that if S is added during the corn year of the rotation, producers should be able to rely on excess S stored in clayey subsoils.