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 N, P, S, and where indicated, to K, Mg, B, Cu, and Zn), 2) evaluating recommendation methods for N, P and S fertilization, 3) identifying the level 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 2011-12, all five remaining sites of the network were planted to wheat/double cropped soybean, with two sites under corn-wheat/soybean (C-W/S) rotation and three sites under corn-soybean-wheat/soybean (C-S-W/S) rotation. Favorable climatic conditions at most of the experimental sites allowed for high yields for wheat. Grain yield responses to N, P and S were significant at all sites (average of 2,730 kg/ha, +113%), but for nutrients other than NPS, responses were significant only at the La Hansa site (407 kg/ha, +9%). Dry conditions affected double cropped soybean yields, which averaged from 1,300 to 3,300 kg/ha in the five experiments. Responses to N, P and S were significant at four sites, with average responses of 404 and 852 kg/ha for C-W/S and C-S-W/S rotations, respectively.

Considering the 12 seasons with 40 sites under corn, 38 sites under wheat, 57 sites under full-season and double cropped soybean, significant relationships were observed between Bray P-1 and P responses, with critical levels ranging between 12 and 20 ppm for the three crops. Below these critical levels, P responses are highly probable. Also, significant relationships were observed between grain yields of corn and wheat and soil N supply as predicted by soil nitrate-N measured at sowing + fertilizer N rate. The analysis of the first 12 years of the nutrition network has shown that adequate NPS management increased grain yields, contributed to improved water use efficiency, tended to increase soil organic matter, decreased soil pH, and allowed for soil P build-up. Return on investment (ROI) estimates were better for the W/S rotation than for the S-W/S rotation. For both rotations, ROI values averaged 2.7 and 0.6 US$/US$ N for corn and wheat, respectively, 2.1, 1.8 and 1.9 kg US$/US$ P for corn, wheat and soybean, respectively, and 4.4, 1.6 and 7.5 US$/US$ S for corn, wheat and soybean, respectively. During the 2012-13 season, sites will be planted to corn crop in both rotations. Argentina-12.