SOYBEAN PROFITABILITY

Soybean is an extremely important crop to the rural economy and the producers who grow soybean in NW Minnesota.  Approximately 1 million acres of soybean were grown in 2002 in northwestern Minnesota with a farm value of $160 million. Average production has been about 32 bushels per acre over the past several years.  Fertilizer use is a key management practice for growers who seek to maximize profit from their soybean acres. Statewide, the Minnesota Ag Statistics indicate 13% of soybean acres in Minnesota are fertilized with an average of 34 pounds of P₂O₅ per acre.  Previous research on soybean phosphorus fertility in NW Minnesota had not shown a positive yield response with band or broadcast applications.  New soybean cultivars with higher yield potentials have been developed for the region over the past ten years and this prompted the idea to conduct a phosphorus rate study to determine if the phosphorus nutritional needs of the crop were still being met from residual phosphorus in the soil.

Evaluation of Phosphorus Rates on Soybean as a Tool to increase Yield and Protein

Soybean phosphorous rate experiments were conducted at four locations on soils testing low to medium for P₂O₅ to determine if the significant results obtained in 2002 effecting yield and protein concentration could be repeated.  The treatments consisted of five rates of P₂O₅ and a control plot replicated four times in a randomized complete block design.  P₂O₅ rates were 0, 20, 40, 60, 80 and 100 pounds per acre.  Data collected includes, yield, protein concentration and oil percentage.  The phosphorus trials were located at Crookston, Ada, Rindal, and Rothsay.  A summer field day was held at each location.

Crookston site – Peterson Farm:

The Crookston site statistical design included 0 or 100 lb. potassium rates with the five phosphorus rates in a complete factorial design.  The variety, planting and harvest dates and soil test data is included in table 1.

Table 1. Crookston site information.

Table 2 list the analysis for yield, protein and oil percent for each individual treatment.  The treatment with 50P 100K was the only treatment significantly different from the 0P 0K treatment with respect to yield.  There was no significant difference in protein percent or oil percent when compared to the 0P 0K treatments. 

Table 2. Treatment means for Yield, Protein% and Oil%.

Figure 1 shows a graphic representation of the soybean grain yields with 0K and P₂O₅ rates from 0 – 100 pounds per acre in increments of 25 pounds.  No statistical yield differences are evident. 

Figure 1.  Soybean grain yield with 0K and 0 to 100 P rates.

Figure 2 shows a graphic representation of the soybean protein percent with 0K and P₂O₅ rates from 0 – 100 pounds per acre in increments of 25 pounds.  Protein percent increased in a linear relationship with phosphorus rate from 32.1% with no added phosphorus to 32.8% with 100 pounds of P205 added. This trend in protein increase was not statistically significant. 

Figure 2.  Soybean protein percent with 0K and 0 to 100 P rates.

Figure 3 shows the soybean yield relationship of phosphorus rates with 100 pounds of K₂O added to all plots. There was about a 2 bushel increase in soybean yield which was not statistically significant. 

Figure 3.  Soybean grain yield with 100K and 0 to 100 P rates.

Figure 4 shows the protein percent relationship of phosphorus rates with 100 pounds of K₂O added to all plots. There was virtually no protein rate response at this site when 100 pounds of K₂O was added to the soil.

Figure 4.  Soybean protein percent with 0K and 0 to 100 P rates.

Ada site – Nelson Farm:

The Ada site statistical design included phosphorus rates from 0 to 100 pounds of P₂O₅ per acre in 20 pound increments in a randomized complete block design.  The variety, planting date, harvest dates and soil test data is included in table 3.  This site had the greatest carbonate % measured in the spring soil test.

Table 3. Ada site information.

Table 4 list the analysis for yield, protein and oil percent for each individual treatment.  There was no significant difference in yield, protein percent or oil percent at this location.

Table 4.  Treatment means for Yield, Protein% and Oil%.

Figures 5 and 6 show the graphic relationships of yield and protein to phosphorus fertilizer rates.

Figure 5.  Soybean grain yield at five phosphorus rates.

Figure 6.  Soybean protein percent at five phosphorus rates.

Rindal site – Black Bros. Farm:

The Rindal site statistical design included phosphorus rates from 0 to 100 pounds of P₂O₅ per acre in 20 pound increments in a randomized complete block design.  The variety, planting date, harvest dates and soil test data is included in table 5.  This site had a low phosphorus soil test and a medium carbonate level.  Soybeans yielded quite well for the later planting date.

Table 5. Rindal site information.

Table 6 list the analysis for yield, protein and oil percent for each individual treatment.  There was no significant difference in yield, protein percent or oil percent at this location.

Table 6.  Treatment means for Yield, Protein% and Oil%.

Figures 7 and 8 show the graphic relationships of yield and protein to phosphorus fertilizer rates.  There was a 1.3% increase in protein percent however it was not statistically significant.

Figure 7. Soybean grain yield at five phosphorus rates.

Figure 8.  Soybean protein percent at five phosphorus rates.

Rothsay site – Nordick Farm:

The Rothsay site statistical design included phosphorus rates from 0 to 100 pounds of P₂O₅ per acre in 20 pound increments in a randomized complete block design.  The variety, planting date, harvest dates and soil test data is included in table 7.  This site had the lowest phosphorus, carbonates and soluble salt soil test level.  Environmental conditions were not normal at this site with 15 inches of rain recorded early in the growing season.  A second experiment at this site with high carbonates and high soluble salts was abandoned due to excessive water damage. The variety, planting date, harvest dates and soil test data is included in table 7.  This site had a low phosphorus soil test, low carbonate and low soluble salt level. 

Table 7. Rothsay site information.

Table 8 lists the treatment means for yield, protein percent and oil percent.  There were no significant differences for soybean yield, protein concentration or oil concentration at this site.

Table 8.  Treatment means for Yield, Protein% and Oil%.

Figure 9. Soybean grain yield at five phosphorus rates.

Evaluation of Phosphorus Application Method to increase Yield and Protein

A phosphorus application method experiment was conducted to determine if phosphorus can safely be applied with an air-seeder at planting time to reduce input costs associated with broadcast application and incorporation prior to planting.  The treatments consist of three phosphorus sources (DAP) diammonium phosphate, (MAP) monoammonium phosphate and (TSP) triple super phosphate air-seeder applied at four rates of P₂O₅ and a control plot replicated four times in a complete factorial design.  P₂O₅ rates were 0, 23, 46, 69 and 92 pounds per acre.  Nitrogen was broadcast to appropriate plots to equalize the total amount on nitrogen added to each plot from each source.  Data collected included population, yield, protein concentration and oil percentage. The phosphorus trial was located at the Gerald Nordick farm near Rothsay. Table 9 lists the soybean grain yields with the three phosphorus sources and five rates.  There were no significant differences with respect to grain yield.   Figure 10 shows the graphic relationships of yield with the three phosphorus sources at the five application rates.

Table 9.  Soybean grain yield of phosphorus sources and rates.

Figure 10.  Soybean grain yields at phosphorus sources and rates.

Table 10 lists the soybean populations with the three phosphorus sources and five rates.  There were no significant differences with respect to population.

Table 10.  Soybean populations at phosphorus sources and rates.

Table 11 lists the soybean protein concentration with the three phosphorus sources and five rates.  Protein concentration was significant at the p=.07 level when averaged across sources.  There were no significant differences in protein concentration between sources.   Figure 11 shows the graphic relationships of protein concentration with the three phosphorus sources at the five application rates. There was a linear trend to increase protein concentration with increased P₂O₅ application rate equaling a 1% protein concentration increase.

Table 11.  Soybean protein concentration at phosphorus sources and rates.

Figure 11.  Soybean protrin concentration at phosphorus sources and rates.

Table 12 lists the soybean oil concentration with the three phosphorus sources and five rates.  Protein concentration decrease was significant at the p=.06 level when averaged across sources.  There were no significant differences in oil concentration between sources.   Figure 12 shows the graphic relationships of oil concentration with the three phosphorus sources at the five application rates. There was a linear trend to decrease oil concentration with increased P₂O₅ application rate equaling a 1/2% oil concentration decrease.

Table 12.  Soybean oil concentration at phosphorus sources and rates.

Figure 12 Soybean oil concentrations at phosphorus sources and rates.

The variety, planting date, harvest dates and soil test data is included in table 13.  Environmental conditions were not normal at this site with 15 inches of rain recorded early in the growing season.

Table 13. Rothsay site information.