Sulfur and nitrogen impacts on a wheat, double crop soybean rotation in southwest Indiana

Stephen Maloney, Purdue University

Abstract

Sulfur (S) is often an overlooked secondary nutrient in today's agronomic cropping systems, especially for cool season crops. The objective of this study was to determine optimum rates of nitrogen (N) and S in a field low in S. A field experiment was conducted near Vincennes, Indiana from fall 2009 through fall 2011 on an Ade loamy fine sand (Coarse-loamy, mixed, superactive, mesic Lamellic Argiudoll). The first year of the study was initiated with winter wheat (Pioneer 25R54) in the 2009-10 growing season followed by double-crop soybean (Pioneer 94Y06) in 2010. Experimental design was a 4 x 5 factorial with 4 replications. Treatments were arranged in a randomized complete block design with 4 S rates of 0, 17, 34, and 50 kg S ha-1 and 5 N rates of 0, 45, 78, 112, and 146 kg N ha-1. Fertilizer was applied on March14, 2010 when wheat broke dormancy. In year two, winter wheat (Pioneer 25R54) was planted in 2010-11 growing season, followed by double crop soybean (Pioneer 94Y06). The second year was to investigate the residual impact of S applied in 2010 versus a second application in 2011. The second study year used a similar experimental design of split plot 4 x 5 factorial with 4 replications in a randomized complete block design in the same treatment plots as the first study year. The same treatments of N were applied to the whole plot as the first year, however S was only applied to half of each respective plot on March 18, 2011. This site in Vincennes, IN was severely S deficient in the early spring 2010 growing season, which was confirmed through visual observations and tissue N:S ratios greater than 16:1 for the 0 kg S ha-1 application rate at wheat Feekes growth stage 6. However, as the growing season progressed disease development and lodging limited response to S application. Greater S availability from atmospheric deposition and S mineralization as the season progressed may have also contributed to recovery from S deficiency. The 2010 double crop soybean crop responded to S fertilization with increased tissue S, although grain yield and biomass at harvest did not increase with S fertilization. Approximately 70% of the SO4-S applied in spring of 2010 was leached from the soil profile during the 2010-11 winter months following double crop soybeans. A majority of the SO4-S remaining in the profile was below 60 cm depth, providing little residual benefit to the next wheat crop. Heavy rainfall and flooding in the spring of 2011 prevented almost all data collection for 2011 wheat; except for harvested grain collection for elemental analysis. Despite weather conditions, only about half the SO 4-S applied in March 2011 was lost from the 90 cm soil sampling depth. Though soil SO4-S in the 0 kg S ha-1 treatment where S was applied in 2010 was extremely low (< 2 mg kg-1 throughout the upper 60 cm) in June 2011, there was no soybean yield or biomass benefit of S fertilization. Even when the 2011 soybean leaf tissue S concentration at flowering was considered low (N:S > 16) without S fertilization there was no yield decrease. In conclusion application of S had no benefit for yield in wheat or soybean in 2010 or in 2011. However early in the 2010 growing season S was deficient, which was shown in wheat tissue samples. Plus application of S increased plant S accumulation especially in soybeans. The application of S increased soil SO4-S, but soil SO4-S decreased rapidly during winter rainfall with little residual SO4-S in the soil profile in 2011 from the 2010 S application.

Degree

M.S.

Advisors

Casteel, Purdue University.

Subject Area

Agronomy

COinS