Sulphur (S) is an essential nutrient necessary for plant growth. In the past it was assumed that soil sulphur supplies were adequate to meet soybeans full yield potential. Since air-borne sulphur emissions have been drastically reduced in the Great Lakes Basin, is it now necessary to feed soybeans sulphur?
The simple answer
In 2023 three trials compared a pre-plant application of 87 lb/ac urea and a 110 lb/ac urea/AMS blend to untreated soybeans. There was no significant yield increase to the application of S on these clay loam and silt loam soils. These results agree with 15 trials conducted in 2018-19 which also showed no yield gain to S. There was a small yield gain (2.7 bu/ac) to the pre-plant urea but only on 30” rows in a late planting window. It should be noted that while we did not observe a benefit on the clay loam soils tested, S has been shown to provide yield gains on course texted (sandy) soils in other Ontario trials.
A little more information
Much like nitrogen (N), sulphur moves quickly in the soil and can be depleted rapidly even if soil levels were adequate just a few years previously. One major challenge in assessing the need for S fertilizer is that soil tests for S are unreliable. S deficiency symptoms are also not obvious in soybeans. Soybeans are known to remove relatively little S compared to other crops such as canola or corn. An average soybean crop will remove 5 lb/ac of S while canola will remove 15 lb/ac of S and corn will remove 10 lb/ac of S.
The full story
Three replicated trials were conducted in 2023 in both 15” and 30” rows and at two planting dates to assess the possible yield benefits of a small amount of pre-plant urea or a urea/AMS blend applied to soybeans. Trial sites were located near Stratford, Elora and Winchester. The soil at Stratford is classified as a clay loam, Elora as a silt loam and Winchester as a clay loam. The variety used was Viper R2X. When comparing N to the untreated control in the same row width, only the 30” rows showed a yield gain at the late planting date (2.7 bu/ac). This gain could be caused by a faster canopy closure, especially beneficial in a late planting window. The addition of the S in the urea/AMS blend did not provide any additional yield over the straight urea application, see Table 1.
