Soil test correlation and calibration trials

Soybean response to fertilizer-phosphorus (P) fertilization experiments were conducted at 39 sites in Arkansas from 2004-2018 with the main objective of developing data to correlate and calibrate fertilizer-P rate recommendations for irrigated soybean [Glycine max (L.) Merr.] in Arkansas. The dataset includes information for 39 site-years representing eight eastern Arkansas counties including Arkansas (4), Clay (1), Cross (3), Desha (2), Lee (4), Poinsett (9), St. Francis (15), and Woodruff (1). Most of the fields where trials were located are poorly drained and have had some land-forming (e.g., precision leveling) done to aid surface drainage of water and are periodically used for flood-irrigated rice (Oryza sativa L.) production. The crop planted before soybean varied among the trials, but the previous summer crop grown was either fallow, grain sorghum (Sorghum bicolor), flood-irrigated rice, or soybean.

The size of the individual plots within each experiment was uniform but plot size varied among trials due to the planting/irrigation system used. Trials that were planted on beds (or ridges) having row widths ≥76.2 cm were four beds wide, furrow irrigated, and the middle two rows were used for collecting soil, samples, plant tissues, and harvest. Sites with row widths ≤76.2 cm were typically 2-3 m wide, planted into a flat seedbed, flood irrigated, and rows within the middle 1.3-1.5 m of each plot were harvested. The dimensions listed in the data are the harvested area in each plot. Irrigation and pest management were performed as needed by the cooperating producer or experiment station staff.

Each experiment included three (2 sites), four (1 site), or five (36 sites) fertilizer-P rates ranging from 0-59 (site no. 1 & 2), 0-73 (site no. 3), or 0-78 (site no. 4-39) kg P ha-1, respectively. Triple superphosphate (TSP, 200 g P kg-1) was the lone fertilizer-P source used in 31 trials with each trial being a randomized complete block design of five fertilizer-P rates. The other eight trials were randomized complete block designs with a factorial treatment structure. Site no. 3 compared four fertilizer-P rates applied as monoammonium phosphate (MAP) or MAP treated with AVAIL (treated fertilizer was provided by the manufacturer; Chien et al., 2014). Site no. 33-39 compared TSP and MESZ (120 g N, 175 g P, 100 g S, 10 g Zn kg-1; The Mosaic Company) each applied at five fertilizer-P rates. For the eight TSP-MESZ trials the N, S, and Zn included in the MESZ were not balanced in the TSP treatments (only TSP was applied). Site 39 had an extra treatment of each source applied at 39 kg P ha-1 at the R3 growth stage. The fertilizer-P treatments were pre-weighed and broadcast applied to the soil surface with a small-plot cone-type fertilizer distributor or by hand. Each trial had 4 to 7 blocks where each treatment was represented. The dates of soil sample collection, fertilizer application, planting and harvest are, when available, provided for each site. The time of fertilizer application in relation to planting for each site is described as preplant, pre-emerge, or post-emerge.

Each trial received a blanket application of 90-120 kg K ha-1 as muriate of potash (500 g K kg-1) and most sites with pH > 7.0 also received either granular B fertilizer at the time of plot establishment (1 kg B ha-1) or a postemergence foliar application of B (0.25 kg B ha-1).

Soil samples were collected from the 39 field experiments before fertilizer application using a homemade stainless-steel soil probe (~2.5 cm outer diameter) with a 10-cm wide washer welded at the 10-cm depth mark to ensure that the soil was collected only from the 0-10 cm depth. A composite soil sample was collected from the no-P control plot in each block with each composite sample comprised of six soil cores. Soil samples were oven-dried at 65°C for 72 hours (APHIS requirement for fire ant control), placed through a soil grinder (Dynacrush soil crusher, Custom Laboratory), passed through a 2-mm sieve, and stored at room temperature until analysis was completed. Each sample was analyzed for soil pH (1:2 v/v soil to water ratio, Sikora & Kissel, 2014) and Mehlich-3 extractable P, K, and other nutrient concentrations (10:1 v/v solution to soil ratio; Zhang et al., 2014) as determined by inductively coupled plasma atomic emission spectroscopy (ICP–AES). Soil organic matter was determined on most samples using the weight-loss-on-ignition method (Combs & Nathan, 2015).

The dates of tissue sample collection and harvest were included for most sites where these data were collected and are included in the dataset. Tissue samples were collected from all but three trials (Sites 2, 28, & 39) from all or selected treatments. At or near the R2 growth stage, a mature trifoliolate leaflet (no petiole) from one of the top three nodes was taken from twelve plants in each plot to assess soybean nutritional status. The date of first bloom, R1 development, as predicted by the SoyMap program (Popp et al., 2016; https://agribusiness.uark.edu/decision-support-software.php) is listed in the dataset as a standard reference of plant development when tissue was collected. The SoyMap predictions are based on the planting date, maturity group, and geographic location, which was input as Marianna, Arkansas for all sites except the trials in Desha County, which used Rohwer, Arkansas as the site in SoyMap. The time between R1 development and tissue sample collection is identified as days after R1.Trifoliolate leaf samples were placed in paper bags, oven-dried to constant moisture at 60°C, ground to pass a 2-mm sieve, digested in concentrated HNO3 and 30% H2O2 (Jones & Case, 1990), and the nutrient concentrations were determined by ICP–AES.

At maturity, 7 to 10.5 m2 of soybean from the interior rows of each plot were harvested with a small-plot combine. The harvested grain was weighed and analyzed for moisture content. Yields were calculated after grain weights were adjusted to uniform moisture of 130 g kg-1.

The soybean trials were funded by the Arkansas Soybean Checkoff funds administered by the Arkansas Soybean Promotion Board, Arkansas Fertilizer Tonnage Fees administered by the Arkansas Soil Test Review Board, the University of Arkansas System Division of Agriculture – Agriculture Experiment Station, and Agricultural Experiment
Station funding related to Hatch Project 2570.

References

Chien, S. H., Edmeades, D., McBride, R., & Sahrawat, K. L. (2014). Review of maleic–itaconic acid copolymer purported as urease inhibitor and phosphorus enhancer in soils. Agronomy Journal, 106(2), 423-430. https://doi.org/10.2134/agronj2013.0214

Combs, S. M., & Nathan, M. V. (2015). Soil organic matter. In M. V. Nathan & R. Gelderman Eds., Recommended chemical soil test procedures for the North Central region (pp. 12.1–12.6). North Central Regional Publ. 221 (revised). Univ. of Missouri.

Jones, J. B., & Case, V. W. (1990). Sampling, handling, and analyzing plant tissue samples. In R. L. Westerman (Ed.), Soil testing and plant analysis (3rd ed., pp. 389–428). Madison, WI: SSSA.

Popp, M., Purcell, L. C., & Salmerón, M. (2016). Decision support software for soybean growers: Analyzing maturity group and planting date tradeoffs for the US midsouth. Crop, Forage, & Turfgrass Management, 2: 1-9 cftm2016.04.0028. https://doi.org/10.2134/cftm2016.04.0028

Sikora, F. J., & Kissel, D. E. (2014). Soil pH. In F. J. Sikora & K. P. Moore (Eds.), Soil test methods from the southeastern United States (pp. 48–53). Southern Cooperative Series Bulletin 419. Athens, GA: University of Georgia. Retrieved from https://aesl.ces.uga.edu/sera6/PUB/MethodsManualFinalSERA6.pdf

Zhang, H., Hardy, D. H., Mylavarapu, R., & Wang, J. J. (2014). Mehlich-3. In F. J. Sikora & K. P. Moore (Eds.), Soil test methods from the southeastern United States (pp. 101–110). Southern Cooperative Series Bulletin 419. Athens, GA: University of Georgia. Retrieved from https://aesl.ces.uga.edu/sera6/PUB/MethodsManualFinalSERA6.pdf