Interpretive Summaries:

In 2003/04, six sites were planted to corn (rotation corn-wheat/soybeans), and five sites to wheat/soybean (rotation corn-soybean-wheat/soybean).

Corn: Significant responses to N were found at four sites, and to PS at all sites. Soil nitrate-N availability at planting explained 49% of corn yield for the 19 experiments during the three growing seasons. Similarly, low soil Bray P (less than 15 to 16 parts per million [ppm]), and low sulfate-S (less than 10 ppm, 0 to 20 cm depth) availability at planting were significantly related to P and S response, respectively. The average yield response to NPS across all six sites was 3,857 kg/ha, a 58% increment over the check.

Wheat: Excellent climatic conditions allowed for high yields and responses to crop fertilization. Average yield responses were: 995, 1,339, 268, and 456 kg/ha to N, P, S, and other nutrients (KMgBCuZn), respectively. Responses to N and P were significant at four of five sites. Two of five sites showed significant responses to S and other nutrients. Grain yield responses to N and P were related to soil nitrate-N and Bray P availability at planting, but there was no relationship between soil sulfate-S availability and crop response to S. The average yield response to NPS for the five sites was 2,392 kg/ha, a 108% increase over the check.

Soybean: Four of the five sites showed significant responses to PS applied to the previous wheat crop. Application of PS for wheat increased doublecropped soybean yields by 363 kg/ha, a 14% increase compared to the check. Data from the 16 experiments conducted over the last three growing seasons indicate that a critical Bray P-1 level of 14 to 16 ppm (at wheat planting) is required to produce doublecrop soybean yields near 3,500 kg/ha., Soybean responses to S are prevalent with sulfate-S concentrations of 10 ppm or less at wheat planting. Argentina-12