Cooperative Extension Service
|Boron deficient soybean (stunted plants and dark leave color) between the previous years rice levees in Poinsett County.|
When do boron deficiency symptoms appear and what do they look like?
Symptoms of boron deficiency on soybean have been observed from shortly after emergence (V1 stage) through maturity. Boron deficiency is most commonly observed when soil moisture is limited. One of the most common times symptoms are observed is after the first irrigation – plants in some areas of the field respond to irrigation with vigorous growth whereas boron deficient soybean plants will not grow and tend to have darker colored leaves. The importance of soil moisture in boron uptake by plants cannot be stressed enough. The most diagnostic symptom of boron deficiency is death of the growing point. Other symptoms will include misshapen leaves, cupped leaves, short internodes, swollen nodes, and thick leathery leaves.
|Close-up of healthy soybean leaf (new growth) and boron deficient soybean plants. Note leaf cupping, leathery appearance, and overall dark color of boron deficient plants. Photos courtesy of University of Arkansas Soil Fertility Program|
What are the best boron fertilization strategies?
There are several options for supplying boron fertilizer to soybean. The first option is to blend granular B (1 lb B/acre) with P and K that will be applied preplant. This option usually works best when the blended fertilizer is applied in advance of planting and incorporated. Granular B may not dissolve when left on top of the soil when rainfall is limited making early application advisable. Boron may also be applied after soybean emergence. For foliar application, early is definitely better than late application. A soluble boron fertilizer or a liquid boron formulation can be mixed with an early herbicide application (check for compatibility before mixing) at rates as low as 0.20 to 0.33 lb B/acre. The amount of foliar burn, which is cosmetic and should not harm yield potential, will increase as the B application rate increases. Boron should be applied by the time soybean begins to bloom (R1 stage). In field trials, where B was yield limiting, waiting until the R1-R2 stage to apply B resulted in a yield loss compared to preplant granular application or foliar application at the V2-V4 stage. Waiting to apply boron until the R1 to R2 stage is risky in that boron deficiency could occur before the boron is applied. The best approach is to apply boron early and go with the most economical and convenient option (granular or soluble) or the one that best fits your management system.
|Boron deficient soybean plant with a dead growing point.|
Give Soybeans Nutrients for High
Yields - Preseason Phosphorus and Potassium Applications
Nathan Slaton, Professor & Director of Soil Testing
University of Arkansas Division of Agriculture
The nutritional needs of soybean must be satisfied to produce high soybean yields. Conventional soybean fertilization practices in Arkansas usually focus on phosphorus (P) and potassium (K) fertilization, which is the topic of this discussion arranged in a question and answer format.
How accurate are soil test results in predicting whether soybean yields will be increased by P fertilization?
Over the past eight years, we have had about 40 trials evaluating
soybean response to P fertilization, most of them on loamy soils. We
have found that the Mehlich 3 soil test does a good job of
identifying soils that do not require P fertilization. This simply
means that we have high confidence (nearly 100%) that soybean grown
on soils with ‘Optimum’
or ‘Above Optimum’ soil test P levels (>35 ppm or 70 lb/acre) will show no yield increase from P fertilization. We are equally confident that soybean will seldom respond to P fertilization in what we call the ‘Medium’ soil test level (26-35 ppm or 52 to 70 lb/acre). By definition we expect soybean yields to be increased from P fertilization on soils that test below optimum in P [‘Low’ (16-25 ppm or 32 to 50 lb/acre) or ‘Very Low’ (<16 ppm or 32 lb/acre)]. Unfortunately, soybean does not always respond to P fertilization when soil test results are Low or Very Low. Our research shows that soybean yields are increased on about one-fourth of our soils that test Low in P with yields increased by 5 to 10%. For soils testing Very Low in P, soybean yields are increased on about one-half of these soils with increases ranging from 10 to 25%. The likelihood of soybean yield being increased by P fertilization increases considerably as soil test P drops to <10 ppm (or <20 lb/acre).
Were phosphorus fertilizer recommendations for soybean changed for the 2011 cropping season?
Yes, as of January 1, 2011 we reduced the amount of P recommended in the Very Low, Low, and Medium categories by 20 lb P2O5/acre. Although we do not expect a significant yield increase from P fertilization on soils having a Medium soil test P level, some fertilizer is still recommended to help replace a portion of the P that will be removed by the harvested crop.
|Soil Test P Availability Index||Recommended P Fertilizer Rate||Equivalent amount of
|(ppm)||lb P2O5/acre)||(lb 0-46-0/acre)|
Soil P was extracted with the Mehlich-3 soil test method
How accurate are soil test results in predicting whether soybean yields will be increased by K fertilization?
In contrast to soil test P, the Mehlich 3 soil test method does an excellent job of assessing soil K availability for soybean. Research trials conducted in silt loam soils having Low (61-90 ppm or 122 to 180 lb/acre) or Very Low (<61 ppm or <122 lb/acre) soil test K levels showed soybean yields were increased at 94% of these sites with yield increases from optimal K fertilization averaging 35 to 60% above the yield of soybean receiving no K. Soybean yields were increased at 46% of the sites having a Medium soil test K level (91-130 ppm or 182 to 260 lb/acre) with the average increase being about 10% above the yield of unfertilized soybean. For soils having an ‘Optimum’ (131 to 175 ppm or 262 to 350 lb/acre) or ‘Above Optimum’ soil test K level, we expect no significant yield increase from K fertilization. However, the University of Arkansas does recommend that 50 lb K2O/acre be applied on soils having an Optimum soil test K level. This recommendation serves two purposes. First, for fields that are soil sampled using the field average approach (one or two composite soil samples per field) it reduces the risk of yield loss from K deficiency in field areas that may test below optimum. Secondly, this recommendation serves to replace a portion of the K that will be removed by the harvested soybean, helping to maintain the soils K fertility. Understanding how K fertilizer rates change from one level to another and properly interpreting the expectation of returns from fertilization will aid in making the appropriate decision for each field.
How much P and K are removed by each bushel of harvested soybean?
The most common average values of P and K removal per bushel of harvested soybean are 1.4 lb K2O and 0.8 lb P2O5. These values are equivalent to 2.3 lb 0-0-60 fertilizer and 1.7 lb 0-46-0 fertilizer that are removed for each bushel of harvested soybean. Arkansas research has shown that these average values are appropriate.
How much P and K total uptake is needed to produce each bushel of soybean?
The aboveground portion of the soybean plant must accumulate the equivalent of about 5.0 lb N, 1.0 lb P2O5, and 3.8 lb K2O to produce one bushel of soybean.
I applied my P and K fertilizer in late fall of last year. Is it still available or do I need to add more?
Over the last three years (when fall weather allowed), we have established several trials evaluating crop nutrient uptake and yield response to the time and rate of P and K application. The limited amount of data that we have shows that fertilizer application rate is more important than the time of application. This is consistent with what most of the published literature shows. Our primary concern with fall application is that we have observed both P and K deficiencies in fields that had fertilizer applied before planting, which suggests that some soils have the capacity to rapidly fix P or K into unavailable forms, the P and K could be lost (sandy soils), or that the applied fertilizer rate was simply insufficient. That said, there are some good guidelines to follow in determining whether to apply P and K in the fall or spring. Factors including the soil test level, soil texture, rate of fertilizer to be applied, winter field management (will the field be flooded for waterfowl habitat), how responsive the following crop is to fertilization, and whether the field has had nutrient deficiency problems in the past should be considered.
This market economics component looks at cash market & forward pricing quotes from selected markets as reported to National Agricultural Statistics Service in Arkansas.
Arkansas soybean markets had a shortened trading week due to the President’s Day holiday on Monday. The Arkansas cash market opened on Tuesday at $12.85, a full 70 cent decline from the previous Friday closing mark (Figure 1). The market recovered well through the remainder of the week with gains each trading day to a Friday closing price of $13.54. After all of the price movement, the closing price left cash beans just one cent under the previous Friday closing mark. High individual market daily average for the week was $13.76 at both West Memphis and Old Town/Elaine on Friday. Helena was two cents behind at $13.74 on the same day. The top individual market price was 39 cents under the high of the previous week. The lowest individual market daily average was found on Tuesday with $12.62 reported at both Jonesboro and Wheatley.
Forward booking prices for 2011 crop beans fell similar to the cash market over the holiday weekend and recovery was not as steady through the remainder of the week. Over the long weekend, the forward market lost 68 cents to open at $12.59 on Tuesday (Figure 2). New crop bean prices wavered through the midweek before moving sharply higher on Friday, finally reaching a close of $13.14. The final mark represented a 13 cent decline from the previous Friday closing price. West Memphis again posted the top daily price of the week with $13.36 on Friday. Helena at $13.30 and Old Town/Elaine with $13.25 followed on the same day. The lowest price of the week was $12.34 at Wynne on Tuesday, the only sub-$12.40 price at any market. All markets ended the week above the $12.90 level. The shrinking price margin between cash market old crop beans and new crop booking prices paused as the difference actually rose to 40 cents, a 12 cent widening from the previous week.
(Market average prices stated in this report are unweighted averages of the state markets surveyed by NASS. Price data was based on USDA LR GR111 Arkansas Daily Grain Reports.)
Please contact your local County extension agent in Arkansas or the author(s) if you have questions or comments regarding the newsletter. You may also contact Jeremy Ross, Extension Agronomist for Soybeans at firstname.lastname@example.org or (501) 944-0621.
University of Arkansas • Division of Agriculture