SuperCal SO4 was applied to a high pH 7.5 field with corn at Cedar Falls, Iowa in 2002. Four replications of six treatments were arranged in a randomized complete block design. This was an excellent year for corn and good yields were noted throughout the area. A moisture stress period was noted in midsummer, but timely rains contributed to good yields.
Yields increased from 207.6 bu/A for control to 221.8 bu/A with 300 lbs/A SuperCal SO4 applied at planting. A base rate of 140 lbs/A nitrogen (N) was applied as anhydrous ammonia to soybean ground, considering a rough credit 50 lbs. N/A for the contribution of soybeans in the rotation. However, the addition of 80 lbs N/A at sidedress time resulted in only a 2.1 bu/A yield increase over the 140 lbs N/A areas. One could speculate that the maximum nitrogen response rate had been reached with 140 + 50 + 80 = 270 lbs/A N with soybean credits. Yields did not increase with 300 lbs/A SuperCal SO4 plus 80 lbs N/A at sidedress time, and it is speculated the plants may have grown too much prior to the moisture stress period. Early application of SuperCal SO4 at planting may have contributed to promoting plant growth at the right time, and resulted in increased partitioning of photosynthates into the kernel.