Low Soil Phosphorus and Potassium Limit Soybean Grain Yield
Aaron P. Brooker, Laura E. Lindsey, Steven W. Culman, Sakthi K. Subburayalu, and Peter R. Thomison
A soil survey was conducted in Ohio with the following objectives: (i) to assess the status of soil fertility; (ii) to examine soybean grain yield in areas with fertility levels in the build-up range, where soil test levels were less than the critical level (CL); the maintenance range, where soil test levels were between the CL and maintenance range; and the drawdown range, where soil test levels were greater than the ML; and (iii) to determine if the soil test and yield data collected support the state-established fertility recommendations. Soil sampling was conducted from 2013 through 2015 resulting in 593 total samples. Soil phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg); pH; organic matter (OM); and cation exchange capacity (CEC) were measured. Soil grain yield was also collected from the sampling areas.
- 21% of the soil samples collected were within the build-up range for P where P is likely limiting.
- 23% of the soil samples collected were within the build-up range for K where K is likely limiting.
- On average, grain yield was 7 bu/acre lower in sampling areas associated with soil P levels in the build-up range.
- On average, grain yield was 4 bu/acre lower in sampling areas associated with soil K in the build-up range.
- In sampling areas, there was no difference in grain yield associated with soil P and K levels within the maintenance and drawdrown range.
- Our data suggest that soil test levels within the build-up range were associated with lower soybean grain yields.
Methods. In Ohio, a survey to assess the status of soil fertility and associated soybean grain yield was conducted annually from 2013 through 2015. Farmers volunteered to participate and selected fields that they manage to be used in the survey. In total, 199 fields were sampled by Ohio State University Extension educators and graduate students using a common protocol (Lindsey et al., 2014). Soil samples were collected from three sampling areas within each field and GPS coordinates of each area recorded. There were 593 soil samples collected in total. Soil samples were collected in the spring just prior to soybean planting. Each soil sample consisted of 10-15 homogenized 1-inch-diamter by 8-inch deep soil cores in a zig-zag pattern within each sampling area as recommended.
The soil-test nutrient level from each sampling area was assigned to one of three categories: build-up range, maintenance range, or drawdown range as shown in Figure 1 (Vitosh et al., 1995). The build-up range, maintenance range, and drawdown ranges are shown in Table 1. (Note: Original Bray-P and ammonium acetate extraction values have been converted to Mehlich-3.)
Soybean grain yield data were collected from the soil sampling areas using the recorded GPS coordinates by either weigh wagon or using calibrated yield monitors. Yield was reported at 13% moisture content. Yield information was obtained from 35% of the sampling areas (n = 219).
Soil fertility results. In Ohio, 21% and 23% of the soil samples collected were within the build-up range for P and K, respectively. Thirty-five percent and 44% of the soil samples were within the drawdown range for P and K, respectively. There were no soil samples within the build-up range for Ca and only three soil samples within the build-up range for Mg. Nineteen percent of the soil samples had a pH less than 6.0, 59% were within the recommended range for soybean production of 6.0-6.8, and 23% were higher than 6.8. Organic matter levels ranged from 1.1 to 33.7%, with an average of 3.2%. The soil CEC ranged from 4.4 to 38.3 meq/100 g with a mean of 14.4 meq/100 g.
|Soil nutrients||Build-up range||Maintenance range||Drawdown range|
|CEC 5 meq/100 g||<88||88-140||>140|
|CEC 10 meq/100 g||<100||100-150||>150|
|CEC 20 meq/100 g||<125||125-175||>175|
|CEC 30 meq/100 g||<150||150-200||>200|
Of the fields sampled, 65% had at least one area of the field that had a soil P level within the build-up or maintenance range, for which fertilizer application would be recommended. Fifty-eight percent of the fields had at least one area of the field where soil K level was within the build-up range or maintenance range, for which fertilizer application would be recommended. Nineteen percent of the soybean fields had at least one area with soil pH less than 6.0, for which lime application would be recommended. These data indicate that many fields in Ohio have at least one area where P fertilizer, K fertilizer, or lime application would be recommended. Soil sampling and precise fertilization and soil amendment application may help reduce the risk of yield loss in specific areas of a field.
Association between soil fertility factors and soybean grain yield. Grain yield ranged from 22 to 82 bu/acre, and the average yield was 56 bu/acre. Sixty-nine percent of the sampling areas with soil P in the build-up range were below the average yield. No sampling area had a yield greater than 63 bu/acre when soil P was within the build-up range. A grain yield reduction of 7.4 bu/acre was associated with soil P levels within the build-up range. Sampling areas with soil P within the maintenance range yielded 56 bu/acre compared with those above the maintenance range, which yielded 59 bu/acre, but this difference was not statistically significant.
Fifty-eight percent of the sampling areas with soil K in the build-up range were below the average yield. A grain yield reduction of 4.0 bu/acre was associated with K levels within the build-up range. Sampling areas with soil K within the maintenance range yielded 56 bu/acre compared to those above the maintenance range, which yielded 57 bu/acre, but the difference was not statistically significant.
Recommendations. Data in this survey support the Tri-State Fertility Recommendations. We recommend soil sampling and applying fertilizer to maintain soil test levels within the established state guidelines.
Lindsey, L.E., S. Prochaska, H.D. Watters, and G.A. LaBarge. 2014. Identifying soybean yield-limiting factors in Ohio. J. Extension. Vol. 52. http://www.joe.org/joe/2014october/iw9.php (accessed 14 Aug. 2017).
Vitosh, M.L., J.W. Johnson, and D.B. Mengel. 1995. Tri-state fertilizer recommendations for corn, soybeans, wheat, and alfalfa. Ext. Bull. E-2567. Ohio State Univ. Ext. Ser., Columbus.
- Research funded by Ohio Soybean Council.
- Salary and research support provided in part by state and federal funds appropriated to the Ohio Agricultural Research and Development Center (OARDC) and Ohio State University.
- Thanks to Ohio State University Extension educators for assistance with sampling and data collection as well as the many farmer-cooperators who participated in this study.
Originally published: Brooker, A.P., L.E. Lindsey, S.W. Culman, S.K. Subburayalu, and P.R. Thomison. 2017. Low soil phosphorus and potassium limit soybean grain yield in Ohio. Crop, Forage, and Turfgrass Management. 3:1-5.