Legacy Phosphorus and Potassium Correlation Experiments: Qulin, Missouri

Correlation experiments for P and K were conducted from 1968 through 1973 at a research farm in Qulin, Missouri to better define the relationships between soil tests, crop yields, and fertilizer treatments. Three crop rotations each were conducted for P and K trials (ranges C, D, E, F, G, and H), and included corn (Zea mays L.), soybean [Glycine max (L.) Merr.], wheat (Triticum aestivum L.), cotton (Gossypium hirsutum L.), and sorghum [Sorghum bicolor (L.) Moench]. Crop rotation order was wheat, soybean, cotton, and corn for ranges C through F, with wheat grown first (established fall 1968) in ranges C and D and cotton first (established spring 1969) in E and F. Ranges G and H had sorghum grown in 1969 followed by the normal rotation starting with wheat (established fall 1969). The main objective of these studies was to learn what crop yield levels were associated with given soil test values for phosphorus and potassium. A second objective was to learn how the soil tests change following annual P and K fertilizer applications. Two additional studies on liming were conducted at this location but are not included in these results. The experiments consisted of a series of plots ranging from low to high in P and K fertility.

For the P trials: Fertilizer treatments consisted of six initial broadcast plow-down treatments (0, 50, 100, 200, 400, and 800 lbs P2O5/acre) and three annual banded treatments superimposed on each of the initial broadcast treatments (0, 25, and 50 lbs P2O5/acre). An initial application of 400 lbs K2O/acre was broadcast to all plots and plowed under (split into two applications of 200 lbs K-2O/acre to avoid potentially harmful salt and/or chloride effects). Annual rates of 50 lbs K2O/acre were applied via broadcast to all plots to meet crop needs.

For the K trials: Fertilizer treatments consisted of six initial broadcast plow-down treatments (0, 50, 100, 200, 400, and 800 lbs K¬2O/acre) and three annual banded treatments superimposed on each of the broadcast treatments (0, 25, and 50 lbs K¬2O/acre). Potassium was applied in the form of KCl. An initial application of 400 lbs P2O5/acre was broadcast to all plots and plowed under. Annual rates of 50 lbs P2O5/acre were applied via broadcast to all plots to meet crop needs. Because of possible danger of salt and/or chloride effects from the heavy KCl treatments, the higher rates were applied in split applications. For the 400 and 800 lbs K2O/acre applications, 200 lbs K2O/acre were applied followed by disc and plowing. Potassium was applied in 200 lbs K2O/acre increments until the 400 or 800 lbs K2O/acre treatment rates were reached.

For both P and K trials: Dolomitic lime was applied to all plots as indicated by soil tests, and 50% of the lime should pass through a 40-mesh screen and 100% should pass through an 8-mesh screen. If these requirements were not met, corrections were made accordingly. Half of the lime application was disked into the surface and plowed under, while the remaining 50% was disked into the surface after plowing. The following rates of N were annually applied to each crop: 50 lbs N/acre for wheat, 0 lbs N/acre for soybean, 100 lbs N/acre for cotton, and 150 lbs N/acre for corn. Recommended practices for insect and weed control were followed. All plots were irrigated and harvested with conventional machine methods.

Soil samples were collected before the trial began (either late September or mid-May) as well as each summer. The initial soil samples were taken at both 0-6 inches (topsoil; all plots) and 6-12 inches (subsoil; every third plot). Annual soil samples were taken from the topsoil only. Both Bray-1 and -2 were used to measure soil test P, and ammonium acetate was used to measure soil test K, Ca, and Mg. Laboratory methods for pH and soil organic matter as well as other specific details about laboratory methods were not found.

As much metadata as possible was determined from the materials available, however there are some pieces of information missing such as dates of some field activities.

• Resource Title: Fisher et al., 2021 Data.

  File Name: Fisher et al., 2021 Data.xlsx

  Resource Software Recommended: Microsoft Excel,url: https://www.microsoft.com/en-us/microsoft-365/excel