By James DeDecker
Sulfur and zinc are essential plant nutrients that must be maintained at critical levels to optimize dry edible bean yield and quality. Dry beans remove approximately 0.52 pound of sulfur per bushel, or around 17.5 pounds per acre for an average 20 hundredweight (cwt) crop. In years past, sulfur deficiencies were uncommon in Michigan dry beans. Mineralization of organic sulfur and deposition of atmospheric sulfur dioxide easily fulfilled the crop’s sulfur requirement in most fields.
However, the recent decline in atmospheric sulfur deposition is making sulfur deficiency increasingly common, particularly where soil organic sulfur and mineralization capacity are limited. Research by Michigan State University Extension trialing various sources of sulfur in soybeans has produced mixed results. Gypsum increased soybean yield in only one year of three, and only on very poor soil where significant sulfur deficiency was observed.
Dry beans are known to be sensitive to even minor zinc deficiency, which can delay crop maturity. Damage to dry bean roots or anything that limits their association with mycorrhizal fungi can indirectly cause zinc deficiency by limiting uptake. MSU generally recommends 1 pound per acre of zinc for dry beans in the absence of a soil test. However, an average 20 cwt crop generally removes less than 0.5 pound per acre. Gypsum products with micronutrients like boron or zinc added offer a potential advantage to those producing a responsive crop like dry edible beans.
Presque Isle County MSU Extension conducted research in 2017 investigating the potential of two Sul4R PLUS gypsum products from Charah, Inc. as sources of supplemental sulfur and zinc for dry edible beans.
Materials and methods
A commercial black bean field near Rogers City, Michigan, was selected for this trial based on preliminary soil analysis showing the need for supplemental sulfur and zinc (Appendix A). The field consisted of Iosco and Cheboygan loamy sands with 0-12 percent slope. One hundred pounds per acre of 0-0-60 potash was top-dressed across the entire trial area to address any possible potassium limitations. Plots 60 feet wide by 500 feet long, running north-south, were established at the site in June 2017.
Two different treatments of SUL4R-PLUS FGD gypsum were broadcast pre-plant on June 14 using a calibrated fertilizer spreader. The first treatment consisted of SUL4R-PLUS gypsum (21% Ca, 17% S) applied at a rate of 147 pounds per acre. Treatment two was SUL4R-PLUS B+Z gypsum (18% Ca, 16% S, 0.50% B, 1.5% Zn) applied at a rate of 147 pounds per acre. Remaining plots served as an untreated control.
Each treatment was replicated four times in a completely randomized design. Zenith black beans were no-till planted on June 21 at a rate of 133,000 seeds per acre.
Soil and dry bean tissue samples were collected from each plot Sept. 4. New trifoliates were collected from 40 plants per plot and submitted to A&L Great Lakes lab for the PT2 tissue analysis package (total nitrogen, phosphorus, potassium, magnesium, calcium, sulfur, sodium, iron, aluminum, manganese, boron, copper and zinc). Soil samples were submitted to A&L Great Lakes for the S1 and S6 analysis packages (organic matter, available phosphorus, exchangeable potassium, magnesium, calcium, soil ph, buffer ph, cation exchange capacity, percent base saturation of cation elements, sulfur, zinc, manganese, boron).
Our dry bean plots were harvested Nov. 6 using the cooperating grower’s combine. Plot yield was measured using a weigh wagon, and adjusted for grain moisture content.
Results and discussion
Dry bean yield was not significantly different between the treatments (Table 1). Average yield was highest in the control treatment (31.24 cwt per acre), similar in the SUL4R-PLUS treatment (30.98 cwt per acre) and lowest in the SUL4R-PLUS B+Z treatment (26.72 cwt per acre). Dry bean yield was significantly correlated with tissue sulfur, zinc and boron status (yield cwt = 8.94 + 59.03 S + 0.474 ZN – 0.396 B + E; R2 = 0.40, P = 0.07) (Table 2). However, soil and tissue nutrient status showed little discernable relationship to our gypsum treatments (Table 3).
Only soil boron concentration was significantly affected by treatment (R2 =0.62, P=0.005), but tissue boron concentrations were not correlated with soil boron status. Instead, tissue nutrient status was significantly correlated with soil organic matter concentration (sulfur: R2 =0.54, P=0.01; zinc: R2 =0.52, P=0.02; and boron: R2 =0.31, P=0.03).
This suggests a gradient in soil quality at our site, which likely overwhelmed any treatment effects. While not evident in the soil survey or our initial scouting of the site, this west-to-east gradient in plant biomass is visible in satellite imagery of the site from 2017.
We hypothesize that differences in soil quality likely influenced nutrient uptake indirectly through effects on root growth or mycorrhizal associations. This would explain the apparent decoupling of soil nutrient status and tissue nutrient concentrations in this case. However, we are left questioning why our gypsum treatments apparently failed to significantly increase soil sulfur and zinc concentrations.
Table 1. Dry bean yield by treatment.
Table 2. Dry bean tissue nutrients by treatment.
Tissue S (%)
Tissue B (ppm)
Tissue Zn (ppm)
Table 3. Soil nutrients by treatment.
Soil S (ppm)
Soil B (ppm)
Soil Zn (ppm)
The authors with to thank Charah, Inc. for supporting this research and Jim Delekta for his time and energy in carrying out the study.