Principal Investigators: Peter Scharf, John Lory, Manjula Nathan, and Bill Wiebold Agronomy Department, University of Missouri

Objectives:

1. Test the performance of current University of Missouri soil test recommendations for predicting soybean response to P, K, S, and B in a statewide network of experiments.
2. Explore the possibility that subsoil test values, soil type, or soil region could be used to improve our fertilizer recommendations and make them more site-specific.
3. Test soybean response to N at planting or at early pod fill in a statewide network of experiments.

Methods:

• Experiments were added to an existing statewide network of 20 soybean variety trials conducted by the University of Missouri. Variety testing personnel planted, and harvested the experiments, as well as controlling weeds.
• Five experiments were located in northern Missouri, 5 in central Missouri, 5 in southwest Missouri, and 5 in southeast Missouri.
• N, P, K, S, and B fertilizers were hand-applied to separate plots at rates of 25 lb N, 80 lb P2O5, 120 lb K2O, 20 lb S, and 1 lb B/acre. These rates should be high enough to produce full yield response. Two separate N timings were applied: at planting and at early pod fill.
• Two unfertilized check plots were used in each replication.
• Five replications were used.
• Soil samples were taken at depths of 0 to 6, 6 to 12, 12 to 24, and 24 to 36 inches in each experiment and analyzed for pH, NO3-, NH4+, P, K, S, and B.
• One well-adapted variety was used at each location.
• A few of the variety test locations may receive P and K applications by cooperating producers (3 of the 20 locations in 1999). Either these locations will not be used, or the P and K treatments will be omitted at these locations.
• All experiments are in rotation.
• 2001 experiments are in different fields than 2000 experiments.

2000 EXPERIMENTAL SITES

LOCATION	COUNTY	SOIL SERIES
Corning	Atchison/Holt	Salix Silty Clay Loam
Albany	Gentry	Grundy Silt Loam
Osborn	DeKalb	Grundy Silt Loam
Novelty	Knox	Putnam Silt Loam
LaGrange	Lewis	Westerville Silt Loam
Henrietta	Ray	Aholt Clay
Grand Pass	Saline	Haynie Silt Loam
Columbia	Boone	Mexico Silt Loam
Truxton	Montgomery	Mexico Silt Loam
Annada	Pike	Tice Silt Loam
Garden City	Cass	Haig Silt Loam
Butler	Bates	Kenoma Silt Loam
Urich	Henry	Hartwell Silt Loam
Nevada	Vernon	Barden Silt Loam
Lamar	Barton	Parsons Silt Loam
Oran	Scott	Commerce Silt Loam
Wyatt	Mississippi	Commerce Silt Loam
Morehouse	Stoddard	Sharkey Clay
Portageville	Pemiscott	Portageville Clay
Portageville	Pemiscott	Dundee Silt Loam

Results for 2000:

1. Experiments were carried out alongside an existing statewide network of 20 soybean variety trials as planned.
2. Average yield across all 20 locations was 45 bu/acre.
3. Yield response to fertilizer treatments was not statistically significant at any of the 20 individual locations.
4. However, when analyzed over all locations, the difference between the yield of K-treated plots and control plots was related to soil test K. This result was statistically significant with 95% confidence.
5. Average yield response was only 1.5 bu/ac for the six locations with soil test K less than 200 lb/ac in the top six inches, and less at locations testing higher.
6. A six-inch sample depth was as good as or better than deeper samples; subsoil K levels did not appear to affect yield response to K fertilizer.
7. Early-season drought in 2000 resulted in many reports of K deficiency symptoms in Missouri and may have been a factor in the response to K. Also, soybean grain contains large amounts of K and soybean is thought of as being more responsive to K than to P or other nutrients.
8. Analyzed over all locations, soil test was not related to apparent response for any of the other nutrients tested (planting N, N at early pod, P, S, and B).
9. Nine locations tested medium for K, and 11 were high. Eleven locations tested medium for P, and nine were high. The interpretation of the medium category is that there is a moderate probability of yield response to fertilizer, so we would have expected several of the medium-testing sites to respond. The minimal responses observed means that University of Missouri soil test interpretations were adequate to insure nutrient sufficiency for soybeans across Missouri in 2000.

2001 EXPERIMENTAL SOYBEAN SITES

LOCATION	COUNTY	SOIL SERIES
Grand Pass	Saline	Haynie Silt Loam
Truxton	Montgomery	Mexico Silt Loam
Corning	Atchison	Salix Silty Clay Loam
Albany	Gentry	Grundy Silt Loam
Henrietta	Ray	Haynie Silt Loam
LaGrange	Lewis	Westerville Silt Loam
Annada	Pike	Tice Silt Loam
Novelty	Knox	Putnam Silt Loam
Oran	Scott	Sharkey Silty Clay
Lamar	Barton	Barden Silt Loam
Garden City	Cass	Haig Silt Loam
Urich	Henry	Hartwell Silt Loam
Butler	Bates	Kenoma Silt Loam
Osborn	DeKalb	Grundy Silt Loam
Nevada	Vernon	Parson Silt Loam
Morehouse	New Madrid	Sharkey Clay
Columbia	Boone	Mexico Silt Loam
Portageville	Pemiscot	Portageville Clay
Portageville	Pemiscot	Tipton Silt Loam
Wyatt	Mississippi	Commerce Silty Clay Loam

Error processing SSI file