Farmers in southeastern South Dakota, southwestern Minnesota, northwestern Iowa and northeastern Nebraska produce corn and soybeans in rotation under various tillage conditions. The land is flat in some places but gently to steeply rolling in other places. The soils in this region were formed from loess, a silt size material transported by wind from the Wisconsin period glacial outwash. The main soil series for region is the Nora/Crofton association. Erosion is commonplace along the shoulders of some of the hills and this has reduced crop yield goals. It was observed that nutrient deficiency symptoms (strong yellow interveinal striping of the upper corn leaves) occurred in for plants growing on these eroded sites. No differences in leaf color were observed for the soybeans. To alleviate this problem, we applied a solution of ammonium sulfate with a watering can down the center of two rows during the growing season in 1998. The sulfur treatment alleviated the striping somewhat, but increased yields at least 10 bu/a. Sulfur deficiency was identified for corn in this eroded landscape. It would be important to determine if other forms of sulfur would also be as affective in alleviating the S deficiency of these soils and increase yields.

Separate research sites were selected for the corn and soybeans project in established no-till fields near Garretson SD. The fields exhibited soil erosion and depositional areas. These experiments were conducted by including them within the plot plans of another experiment. Treatment plots were randomized within four replications and established on the footslope (no erosion) and repeated at the shoulder landscape (moderately eroded) positions. Dekalb corn hybrid DK521 was planted on April 30, 1999 at 26,500 seeds/a. Dekalb soybean variety CS232 was planted on May 20, 1999 at 200,000 seeds/a. Adequate levels of N,P, K, and Zn fertilizer were applied to the corn to meet the yield goal of 140 bu/a. Fertilizer P was also applied at the same time as planting the soybeans enough to meet the yield goal of 45 bu/a. Soil cores were removed from each plot on May 18, 1999 to a depth of 12 inches. Samples were dried and ground for chemical analysis. Weed control was managed by the farmer and was very adequate. Elemental sulfur treatments of either 30 and 60 lb. S/a rate as TIGER 90 CR were surface broadcast-applied on May 25, 1999 for both the corn and soybeans. The material was hand-applied across the entire plot area. Check plots without sulfur were also included. Corn plant samples at the V-6 and ear leaf growth stage were removed on June 11 and July 28, 1999, respectively. V-6 growth stage samples were taken from 5 foot of row adjacent to grain harvest area. Ear leaf samples were taken from 16 plants within each plot soon after pollination. Soybean plant samples were taken from each plot as upper trifoliate leaves during pod set growth stages on August 16, 1999. Plots were harvested on October 4 and 19, 1999 from the soybean and corn experiments, respectively. Soybean grain oil and protein concentrations were measured with NIR techniques. Belmond Labs of Belmond, IA completed soil sample analysis. Midwest Labs of Omaha, NE completed plant sample nutrient analysis. Dependent variable analysis was completed with SAS.

Results and Discussion

There was a difference in landscape position for pH and organic matter (Table 1). Generally, the shoulder (more eroded position) had higher pH and lower organic matter than the footslope (no erosion) landscape position. We believe that the higher organic matter of the footslope supplies more adequate levels of S to crops through organic matter mineralization. Corn plant tissue analysis revealed that there was a slight increase in the shoot tissue S concentration sampled at the V6 stage when comparing the check plots with the S treated plots (Table 2). The same increase was not apparent in the ear leaf plant tissue. There was also a slight increase in the grain yield at the shoulder (eroded) landscape position after either 30 or 60 lb. S/a rate was applied compared to the check plots. The 30 lb./a rate seemed to be adequate to supply the corn crop with the S level it needed. The 60 lb./a rate did not increase yield incrementally over the 30 lb./a rate. It would not be necessary to increase the application rate over the 30 lb./a rate to effectively increase yield. A yield increase for S applications in the footslope was not observed nor was it expected. In addition, the overall yields of corn growing in the footslope was higher than that growing in the shoulder position as expected. The soils in the footslope are very deep and nutrient rich and probably have a somewhat greater water holding capacity than soils growing on the shoulder position. The footslope presents a better crop growing environment with less stress potential than corn growing in the shoulder position.

There was a difference in landscape position for pH and organic matter (Table 3). Generally, the shoulder (more eroded position) had higher pH and lower organic matter than the footslope (no erosion) landscape position as in the corn site. Plant tissue analysis revealed that there was a slight increase in the shoot tissue S concentration sampled at the early pod-fill stage when comparing the check plots with the S treated plots (Table 4). There was also a slight increase in the grain yield at the shoulder (eroded) landscape position after either 30 or 60 lbs. S/a rate was applied compared to the check plots. No differences in oil or protein were observed for the S treatments. As in the corn plots, the 30 lb. S/a rate seemed to be adequate to supply the soybean crop with the S level it needed. It would not be necessary to increase the application rate over the 30 lb. S/a rate to effectively increase yield. A yield increase for S applications in the footslope was not observed nor was it expected. In addition, the overall yield of soybeans growing in the footslope was higher than that growing in the shoulder position as expected.

A 30 lb. S/a treatment of Tiger 90 CR elemental S slightly increased the grain yield of corn and soybeans when applied on shoulder position of the landscape. We would like to continue this study for another year to continue to document the efficacy of Tiger 90 CR in increasing yields of corn and soybeans. Another site will be chosen to contrast the expected affects on the different landscape positions.