Establishing a Plant Nutrition Network for the CREA Region in Southern Santa Fé

The Regional Consortium of Agricultural Experimentation (CREA), a farmers' organization based in Southern Santa Fe, has established a network of field experiments with the objectives of: 1) determining direct and residual responses to nitrogen (N), phosphorus (P), sulfur (S), and where indicated, to potassium (K), magnesium (Mg), boron (B), copper (Cu), and zinc (Zn), 2) evaluating recommendation methods for N, P, and S fertilization, 3) identifying the degree of deficiency and potential response to nutrients other than N, P, and S, and 4) evaluating the evolution of soil quality under contrasting nutrient management practices. In 2015/16, the two sites under corn-wheat/soybean (C-W/S) rotation were planted to wheat and double-cropped soybean, and the three sites under corn-soybean-wheat/soybean (C-S-W/S) rotation were planted to corn.

Excessive precipitation in the 2015/16 season affected some of the experimental sites, with temporary flooding occurring at three of the sites (Balducchi, La Blanca, and La Hansa sites). Wheat grain yield responses were significant to NPS at Balducchi and to P at San Alfredo. Responses to NPS averaged 2.5 t/ha (+145%) for both sites. Double-cropped soybean, planted after wheat, reached record yields at Balducchi (+4,700 kg/ha) but were low at San Alfredo because of diseases (3,100 kg/ha). Average responses to PS and NPS were of 1,250 (+61%) and 1,810 kg/ha (+88%), respectively. Corn grain yield responses were significant to applications of NPS at La Blanca and La Hansa and to NP at Lambare. Average grain yield response to NPS at the three sites was 2,990 kg/ha (+42%). There were no significant responses to other nutrients (K, Mg, B, Cu, and Zn) at any of the sites and crops evaluated this 2015/16 season.

Responses to N were related to available N at planting (soil + fertilizer N) for corn and wheat. Corn yields of 10 to 12 t/ha might be reached with 166 to 231 kg N/ha; while wheat yields of 4 t/ha would be reached with 140 kg N/ha. Significant relationships were observed between Bray P-1 soil P concentrations and P responses, with critical P concentrations ranging between 11 and 16 ppm Bray P-1 for the three crops. Below these critical levels, P responses are highly probable. Responses to S were related to pre-plant soil sulfate-S concentrations (0-20 cm), with a critical level of 6 to 10 ppm for corn, wheat and double-cropped soybean.

For the 2016/17, sites will be cropped to corn under the C-W/S rotation, and to full season soybean under the C-S-W/S rotation.