Potassium Recommendations for Corn in North Dakota

1. Problem and Opportunity Statement-Importance of this project for North Dakota corn producers

Potassium recommendations for corn in North Dakota were developed nearly forty years ago. Potassium (K) soil test levels were commonly above 400 ppm at this time, good corn yields were edging towards 100 bushels per acre and the primary rotations within the state were small-grain driven, with little K removed from the soil. Today, soil K levels are commonly around 150 ppm in the eastern part of the state where soybeans in particular have been grown in some cases continuously for over twenty years. Corn yields commonly approach and sometimes exceed 200 bushels per acre. The demand for K is higher today for corn than it was when our published recommendations were last considered. Establishing modern K soil test levels and revisiting our soil sampling and testing procedures will enable North Dakota corn growers to be more profitable and efficient into the future.

2. The objectives of the project are:

• Build a modern K rate data base in corn to enable revision of our current K fertilizer recommendations and soil test critical levels.
• Investigate seasonality of soil test K for the purpose of better diagnosis of potential K fertilizer needs and to better track soil test K trends over time.
• Investigate alternative laboratory methods for determining soil test K- field moist vs dried soil.

3. Methods/Procedures:

At least twelve sites will be selected for K rate studies in North Dakota. Previous soil testing from the N recalibration study for corn in North Dakota will provide some guidance for areas that are between 50 ppm and 200 ppm K. Most of these sites will be located in farmer fields. Each site will have N and P applied uniformly as needed. Potassium rates from 0 to 150 lb K₂0 per acre will be applied randomly within each plot, organized as a randomized complete block design with 6 treatments and 4 replications. Soil samples obtained prior to treatment application will serve as a soil test foundation for the experiment, and periodic sampling of the check plots at each location will provide information regarding the seasonality of the K soil test. All soil tests will be analyzed from a field-moist sample and a dried soil sample.

Plots will be taken to yield and harvested with a plot combine, or in case of severe wetness they will be hand-harvested and then shelled on campus.

The data base will be used to construct an economic production function model with soil test vs probability of profitable K response. Also, an economic return to K model will be developed to predict rates that would be most profitable for growers at different beginning soil test K levels.

The predictability of the dry soil sample compared to field moist will be compared and presented. The seasonality of the soil test K level will also be investigated and recommendations to growers and their consultant partners will be developed to best select timing of soil test K sampling dates and procedures.

4. Impacts of the research:

Potassium deficiencies are becoming increasingly common in North Dakota, particularly in drier growing seasons. Our data base for potassium response is not large and our recommendations are based mostly on southern MN and southern SD data, Iowa, Illinois and other cornbelt states. The inadvertent K mining of soils through continuous soybean production and movement from a small grains cropping system to corn and soybean rotations have depleted our native K supplies greatly. This research will establish critical soil test K levels for direct use by North Dakota growers.

5. This project is best described as a soil fertility study evaluating response of corn to K soil test and K fertilization and determining methods that maximize soil testing as a diagnostic tool for determining North Dakota K status. The study is mostly is mostly field work, with a laboratory component.

6. Similar work has been conducted in southern Minnesota. Iowa has conducted the greatest body of work on this subject within the last 10 years (Antonia Mallarino). No one has conducted work on K in North Dakota for forty years, with the exception of Dr. Chatterjee’s limited number of sites in 2013.

Reference:
Franzen, D.W. 2011. Variability of soil test potassium in space and time. pp. 74-82. Proceedings of the 2011 North Central Extension-Industry Soil Fertility Conference, Des Moines, IA. November 16-17, 2011. IPNI, Brookings, SD.
Barbagelta, P.A. and A.P. Mallarino. 2012. Field correlation of potassium soil test methods based on dried and field-moist soil samples for corn and soybean. Soil Science Society of America Journal 77:318-327.