In the last decade, soybean has become a popular crop choice for farmers in northwest MN. The USDA National Agricultural Statistics Service (NASS) details an 11 county area of northwest MN as District 10. District 10 includes the following MN counties: Becker, Clearwater, Clay, Kittson, Mahnomen, Marshall, Norman, Polk, Pennington, Red Lake and Roseau. According to the USDA, soybean acres in District 10 were 1,106,000 in 2007 and had risen to 1,813,000 in 2017. This is an increase of 707,000 acres of soybean during this ten year period. In this same time frame, spring wheat acres have ranged from a high of 1,284,000 in 2008 to a low of 944, 000 in 2017. This data would indicate a spring wheat-soybean crop rotation is now a common cropping sequence for farmers in District 10 of northwest MN.
In the last ten years (2007-2017), USDA NASS data indicates spring wheat yields have ranged from a low of 47.8 in 2011 to a high of 68.5 bu/acre in 2017. That’s a wheat yield increase of 20.7 bu/acre from low-to-high during the last decade. However, reported soybean yields have been relatively flat during this same ten year time frame. As an example, soybean yields were 35.7 in 2007 and 34.1 bu/acre in 2017.
Agvise Laboratories, conducts a soil survey each year in their trade area. In 2017, the area that roughly corresponds to USDA District 10 had 67% of soil samples with a Phosphorus (Olsen Test) level of less than 10 ppm. Further, 39% of submitted the soil samples had Potassium levels less than 150 ppm. This soil survey data suggests that over 2/3 of the fields sampled for P and over 1/3 sampled for K, may not have adequate nutrients for the production of high yield soybean and wheat. With the recent increase in wheat yield and the potential increase in soybean yield, the soil levels of P and K may be a limiting factor for plant growth, development and yield.
Methods and Timetables:
Objective 1
The objective of this research is to establish two small plot replicated research sites and five on-farm locations in 2019 and continue for four years. These sites will serve as in-field laboratories to determine if P and K levels are limiting crop production in a spring wheat-soybean rotation. A complete analysis will be conducted on collected soil and tissue samples to determine potential nutrient interaction with elevated applied levels of P & K. Previous research suggests elevated levels of P can interact with zinc. Further, high levels of K can have a negative impact on the uptake of calcium, nitrogen and magnesium. All sites will include an alternating spring wheat-soybean rotation for at least four years. The on-farm cooperators will be selected with input from the MN Wheat OFRN. Farmer cooperators will agree to have this site in a wheat-soybean rotation for at least four years and will follow best management practices. Wheat and soybean varieties will be selected from varieties in the upper 25% of yield trials for the geography near the small plot or on-farm research location.
Objective 2
Conduct small plot replicated research to determine the influence of elevated levels of P and K on wheat and soybean growth, development and yield. The nutrient sources will be 11-52-0 and 0-0-60 and will be applied broadcast and incorporated prior to seeding. Experimental design will be a RCB with a factorial arrangement of treatments. Broadcast fertility treatments will be blended and applied by hand. Individual plot size will be 6 x 15 feet This small plot fertility trial will have 5 fertility rates for P, 5 for K and the combination of each plus a no treatment (no added P &K). Total number of treatments will be 15 plus a control = 16 treatments replicated 4 times for a total of 64 individual plots. Proposed treatments:
• 11-52-0 @ 20 units; 0-0-60 @ 20 units; 11-52-0 + 0-0-60 @ 20 units of each
• 11-52-0 @ 40 units; 0-0-60 @ 40 units; 11-52-0 + 0-0-60 @ 40 units of each
• 11-52-0 @ 60 units; 0-0-60 @ 60 units; 11-52-0 + 0-0-60 @ 60 units of each
• 11-52-0 @ 80 units; 0-0-60 @ 80 units; 11-52-0 + 0-0-60 @ 80 units of each
• 11-52-0 @ 100 units; 0-0-60 @ 100 units; 11-52-0 + 0-0-60 @ 100 units of each
• Untreated control
These small plots will be managed for a yield goal of 80 bu/acre for spring wheat and 50 bu/acre for soybeans. Individual plots will be harvested with a small plot combine for yield with a sub-sample collected from each plot for seed quality assessments. Soil samples will be taken prior to seeding in the spring of 2019. Annual soil samples will be taken after each crop harvest to determine soil residual levels of P & K. In-season tissue samples will be collected at early tillering and again at early heading in wheat and at the second to third trifoliate stage and at early bloom in soybeans. Crop vigor 30 days after planting, a relative chlorophyll index (RCI), and plant height will be collected for each plot.
Objective 3
The large on-farm trials will be conducted at various locations in USDA District 10. A goal is to have five field locations for this long term wheat-soybean rotation project. The trial design will be a randomized complete block with four replications. The farmer cooperators selected to participate in these research trials will strive for high yield wheat 80 and soybeans 50 bu/acre. Farmer cooperators will agree to utilize best management practices in each year of this project. Each site will have two treatments replicated four times (eight strips). All sites will have a standard farmer practice (FP) P & K rate (treatment 1) and an enhanced P & K strip (treatment 2).
• Treatment 1: FP - The current P & K fertility program
• Treatment 2: Enhanced P & K fertility program = FP P & K rate + an additional 50 units of P and K
Plot size will be one or two passes of the application equipment (70 or 140 feet) wide by the length of the field to accommodate the cooperator’s production practices and equipment. Commercial equipment will be used in all facets of the on-farm trials with a weigh wagon and/or combine yield map to determine wheat and soybean yield. Northland College Aerospace will conduct a mid-season unmanned aerial flight UAS at each location. Other data to be collected include: Crop vigor and color 30 days after planting, plant tissue samples at the same timing as small plot trials, plant height at physiological maturity, and soil samples from each strip after harvest. If aerial imagery or combine yield data suggests pockets of low or high yields, these areas will be marked for intensive soil sampling and analysis to determine the cause for this variable yield response. Soil cores will be taken from the same location within each strip for each year of this project.