Volume 11, Issue 6 - July 2021

David Moseley, Foster, Matthew, Parvej, Md Rasel, Towles, Tyler, Brown, Sebe, Salassi, Michael, Deliberto, Michael, Tubana, Brenda S., Dodla, Syam

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Cotton In-Season Nitrogen Management

Rasel Parvej, Brenda Tubana, and Dr. Syam Dodla, LSU AgCenter Soil Scientists

Cotton in-season nitrogen (N) status can easily be tracked by different methods such as crop sensing (vegetation indices), measurement of leaf chlorophyll content, and petiole (leaf stalk that connects the leaf blade to the main-stem) testing for nitrate-N (NO3-N) concentration. Monitoring petiole nitrate-N concentration is the best tool for tracking in-season N status in cotton. This tool allows producers and crop consultants to predict the yield potential dictated by soil nutrition and environmental conditions and adjust in-season N supply, if needed, to help achieve the highest potential yield. In addition, it helps motivate producers not to apply excessive amount of N at planting and hope for the best, which often causes environmental concerns. Also, excessive N results in continuous vegetative plant growth that delays maturity, increases pest problems, and decreases harvest-aid effectiveness. Cotton petiole nitrate-N concentration typically indicates in-season N need 7-10 days prior to the onset of N deficiency stress.

A successful petiole nitrate-N monitoring program consists of several weekly petiole samplings starting one week prior to first bloom and continuing for 4 to 5 weeks after first bloom. At each sampling time, at least 20 uppermost recently mature leaves with petioles on the vegetative stem should be collected. These leaves are usually the 3rd to 5th leaf from the terminal (a quarter-sized main-stem leaf at the top of the plant should be counted as the 1st leaf). The petiole of each sampled leaf should be separated from the leaf blade, placed in a labeled paper bag, and sent immediately to the plant diagnostic lab for nitrate-N, total phosphorus (P), and total potassium (K) concentrations. The total N concentration in leaf blade at first bloom is also important in interpreting petiole nitrate-N concentration. Therefore, the leaf blade (without petiole) of the collected sample at first bloom should also be analyzed separately for total N concentration. Leaf blade testing is not required at other sampling times. The K concentration in the petiole is also valuable in monitoring in-season K nutritional stress since K is one of the key nutrients in cotton production.

Cotton petiole nitrate-N concentration across the blooming period can be interpreted using the nitrate-N concentration in Table 1 and 2. Table 1 consists of Arkansas interpretations and Table 2 consists of Georgia interpretations. The Arkansas interpretation offers higher sufficiency ranges of nitrate-N concentration than the Georgia interpretation and should be used for cotton production in Louisiana. Petiole nitrate-N concentration in both interpretations peaks before blooming and then gradually declines towards boll maturation. In the Arkansas interpretation (Table 1), the sufficient petiole nitrate-N concentration range from 10,000 to 35,000 ppm (1 to 3.5%) at first bloom and 1,000 to 5,000 ppm (0.1 to 0.5%) 6-wk after first bloom and the sufficient leaf blade N concentration range from 3 to 4.5% N at first bloom stage. It is very important to note that these sufficiency ranges of petiole nitrate-N concentration across the blooming stages are not the critical levels, but desirable ranges, and nitrate-N concentrations below or above these desirable ranges do not directly indicate N deficiency or sufficiency because petiole nitrate-N concentration is greatly influenced by plant stress caused by several abiotic and biotic factors. However, these sufficiency ranges may indicate in-season N status and incipient problems. Along with nitrate-N concentration, P concentration in petiole during the blooming period is very important in understanding environmental or physiological stress that can influence petiole nitrate-N concentration and hence the interpretation. For example, petiole P concentration at first bloom should be >800 ppm (>0.08%) and a decrease of >300 ppm (>0.03%) petiole P concentration from the previous week during blooming period is a good indicator of water stress and in-season N fertilization decision should be delayed until the next sampling results are received. For proper interpretation of petiole nitrate-N concentration, it is very important to make sure that the observed petiole nitrate-N concentrations have not been influenced by any stress during the growing season. Therefore, petiole nitrate-N concentration should be interpreted and in-season N fertilization decisions should be made based on physiological, environmental, and nutritional conditions including crop growth stage, soil moisture status, irrigation events, seasonal rainfall amount, fertilization history, leaf blade N concentration at first bloom, petiole P concentration trend during blooming period, fruiting load, internode length, number of nodes above the white flower, pest damage, heat units, cloud cover, etc.

Overall, monitoring in-season petiole nitrate-N concentration is simply a tool that, in combination with other stress indicators, can help make better in-season N management decisions and maximize cotton yield and profitability. This tool is best suited for high yielding cotton fields with irrigation or in high rainfall areas where water does not limit yield. Care should be taken in making in-season N fertilization decisions for fields with a potential for late-season N mineralization from organic materials.

Table 1. Sufficiency ranges of nitrate-N (NO3-N) concentration in cotton petiole during blooming period in Arkansas.

Time of sampling

Sufficiency ranges of nitrate-N concentration (ppm) in cotton petiole Minimum

Sufficiency ranges of nitrate-N concentration (ppm) in cotton petiole Maximum

Week of 1st bloom

10,000

35,000

Bloom + 1 week

9,000

30,000

Bloom + 2 week

7,000

25,000

Bloom + 3 week

5,000

20,000

Bloom + 4 week

3,000

13,000

Bloom + 5 week

2,000

8,000

Bloom + 6 week

1,000

5,000

Source: Mitchell C.C., and W.H. Baker. 1997. Plant nutrient sufficiency levels and critical values for cotton in the southeastern U.S. Proceedings of the Beltwide Cotton Conference, National Cotton Council, Memphis, TN. 1:606-609.

Table 2. Sufficiency ranges of nitrate-N (NO3-N) concentration in cotton petiole during blooming period in Georgia.

Time of sampling

Sufficiency ranges of nitrate-N concentration (ppm) in cotton petiole Minimum

Sufficiency ranges of nitrate-N concentration (ppm) in cotton petiole Maximum

1 week before 1st bloom

7,000

13,000

Week of 1st bloom

4,500

12,500

Bloom + 1 week

3,500

11,000

Bloom + 2 week

2,500

9,500

Bloom + 3 week

1,500

7,500

Bloom + 4 week

1,000

7,000

Bloom + 5 week

1,000

6,000

Bloom + 6 week

500

4,000

Source: Mitchell C.C., and W.H. Baker. 1997. Plant nutrient sufficiency levels and critical values for cotton in the southeastern U.S. Proceedings of the Beltwide Cotton Conference, National Cotton Council, Memphis, TN. 1:606-609.

Entomology Update for Louisiana – July 2021

Tyler Towles and Sebe Brown: LSU AgCenter Entomologists

Cotton

Trap catches in Central and South Louisiana have plateaued over the last few weeks but are beginning to increase in numbers. Reports from the field indicate substantial tarnished plant bug adult migration out of corn into cotton. Cotton fields adjacent to corn are experiencing the largest increases.

Bollworm numbers are unusually low for this time of year. This may be caused by the lateness of this year’s crop and lack of worms in corn, specifically in Northeast Louisiana.

In 2 gene cotton varieties such as Bollgard II and TwinLink, it is especially important to scout cotton for eggs. The LSU AgCenter recommends applications be made on a 20% egg lay in the 2 gene cotton varieties. However, insecticide applications based on percent egg lay on the newer 3 protein expressing cotton varieties (Bollgard 3, WideStrike 3, TwinLink +) are not recommended. This gives the Bt proteins a chance to work on bollworm neonates. Fruit injury thresholds for both 2 and 3 protein expressing cotton varieties are 6% fruit injury of any kind. Once bollworms move into fruiting structures, such as bolls, they are typically shielded from an insecticide application. If applications are necessary, whether on eggs or live larvae, recommended insecticides are Vantacor at 1.71 oz/acre or Besiege at 10.0 oz/acre. Also, Prevathon is no longer being sold or produced by FMC. Its replacement is Vantacor, which has the same active ingredient as Prevathon only at a much lower use rate. A conversion chart is included below.

Tarnished plant bug numbers are variable around Louisiana with larger numbers found in fields adjacent to corn. Threshold in blooming cotton is 2 to 3 plant bugs per 5 foot of row. Numerous insecticides are available for plant bug control. However, keep in mind that Diamond is an insect growth regulator therefore it will only have activity on nymphs. If broad-spectrum insecticides (pyrethroids, organophosphates) are being used for plant bug control, remember that both can flare spider mites.

Soybean

Redbanded stink bugs are beginning to trickle into soybeans in Northeast Louisiana, while a small number of fields in Central and South Louisiana have received at least one application for stink bugs.Numbers of green and brown stink bugs are increasing around much of Louisiana as well. Redbanded stinkbug thresholds are 16 per 100 sweeps or 1 per 6 row foot with a drop cloth. While green and brown thresholds are 9 per 25 sweeps or 1 per 6 row feet with a drop cloth.

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Estimating Combine Harvesting Costs

Michael Deliberto and Michael Salassi, LSU AgCenter economist

For most farming operations, harvesting equipment accounts as a major production expense. This report presents information on estimating combine harvest cost. Using representative farm data from the LSU AgCenter, procedures for determining combine performance rate, capital cost, and operating cost are presented in this report.

The concept of combine performance rate is defined as the time required to cover a field distance based upon factors including machine speed traversing a field, machine/implement width being used, and the field efficiency of the operation being conducted. Field speed of grain combines typically range from 2 to 5 miles per hour, depending upon field conditions. Typical combine header sizes include 25 ft. and 30 ft. headers. Field efficiency is a percentage value which specifies, of the total time a combine is running and what percent of that time is being spent actually cutting the crop. Reasons for this field efficiency value to be less than 100% include idling time, traveling or waiting to unload or time spent traveling to another field. Field efficiency can vary drastically from farm to farm, with typical values in the 65% to 80% range (American Society of Agricultural and Biological Engineering Standards).

Acres per Hour = (Field Speed*Machine Width*Field Efficiency)/8.25

Hours per Acre= 1/(Acres per Hour)

For example, a combine with a 30 ft. header, traveling across the field at 3.0 miles per hour, operating at 65% field efficiency would cover 7.09 acres per hour. Harvest time required per acre would be estimated at 0.141 hours per acre of harvested crop. These performance rates are then used in determining operating or variable costs per harvested acre, influencing primarily fuel and labor harvest expenses.

Capital costs, also referred to as ownership costs, are expenses associated with combine ownership (e.g., interest and depreciation). Producers incur these ownership costs regardless of the hours that the combine is being used during the course of a year. Other ownership expenses may include taxes, insurance and housing. Calculation of combine depreciation and interest costs are presented here.

Depreciation is a noncash expense that reflects a loss on value of the combine due to age, wear and obsolescence. Depreciation is an economic accounting cost which serves the purpose of charging for the use of the machine over its entire useful life. Annual depreciation using the straight-line method would be estimated as follows:

Depreciation = ((Purchase Price-Salvage Value))/(Useful Life)

The amount of machine value which is depreciable (purchase price – salvage value) divided by the estimated years over which the machine will be used (useful life) gives the annual depreciation expense for that machine for each year of use. This value divided by hours of annual use would give an estimate of depreciation cost per hour of machine use.

Capital that is invested in a combine cannot be used for other purposes. Therefore, there is an opportunity cost associated with not having that capital available for other uses. To gauge this opportunity cost accurately, any estimate should reflect the expected return from the use of that capital in its next best alternative investment. This opportunity cost is calculated as an annual interest cost on the average value of the investment. Annual interest on investment cost can be calculated as follows:

Average Machine Value = ((Purchase Price+Salvage Value))/2

Interest = Average Machine Value*Interest Rate

An alternative to determining depreciation and interest costs separately is to calculate the capital recovery charge or cost. Capital recovery cost includes both depreciation and interest. The capital recovery factor and annual capital recovery cost for a machine, using the interest rate (i) and years of useful life (n), is estimated as follows:

Capital Recovery (Amortization)Factor= 〖i*(1+i)〗^n/(〖(1+i)〗^n-1)

Capital Recovery Cost=[Capital Recovery Factor*(Purchase Price-Salvage Value)]+(Interest Rate*Salvage Value)

Total annual combine capital or ownership cost would be calculated as the sum of depreciation and interest costs, plus any applicable charges such as taxes, insurance and housing. Capital cost estimates in this report only include charges for depreciation and interest.

Operating or variable costs for a combine include charges for fuel, labor and repairs. Diesel fuel consumption is primarily a function of horsepower size. Diesel engines consume, on average, 0.044 gallons of diesel per horsepower-hour per PTO horsepower. Harvest fuel cost per acre can be calculated by multiplying the fuel consumption rate per hour times the estimated combine performance rate (in hours per acre) times the price of diesel fuel as show in:

Fuel Consumption per Hour (gallons per hour)=0.044 gallons per HP HR*Machine HP

Fuel Cost per Acre=Diesel Price per gal*Gallons per Hour*Hours per Acre

Harvest combine labor cost is a function of the hourly labor rate charged and the harvest performance rate. Actual hours of labor usually exceed the machine hours by 10% to 20%, due to travel time, time required to lubricant and service the machine and other factors. In this example, the combine harvest labor cost is estimated using a labor multiplier of 1.1 (10%) as shown below:

Labor Cost per Acre=Labor Rate*Performance Rate*1.1

Combine repair and maintenance cost is also an important operating cost to include in the estimation of harvest cost. Repair and maintenance costs for agricultural equipment is usually expressed as a percent of the machine purchase price. The repair and maintenance factor (RMF) is a variable that can be defined as the total repair and maintenance expense of a machine over its entire useful life expressed as a percentage of its original purchase price. This cost is then allocated to actual use on a repair cost per hour of operation basis. RMFs for combines are typically in the 40% to 70% range, depending on age and use. Estimated repair cost per hour of operation multiplied by the harvest performance rate of the combine will give an estimate of allocated repair and maintenance cost for the machine on a per harvested acre basis.

Repair Cost per Hour= (Purchase Price*RMF)/(Estimated Life*Hours of Annual Use)

Repair Cost per Acre=Repair Cost per Hour*Performance Rate

Total combine harvest cost would be the sum of all capital and operating costs associated with the ownership and use of the machine. Total fixed cost per acre would be equal to the capital recovery cost divided by annual acres harvested. Total variable (or direct) harvest costs per acre would be the sum of fuel, labor and repair costs per acre.

Fixed Cost per Acre= (Capital Recovery Cost)/(Acres Harvested Annually)

Variable Cost per Acre=Fuel Cost per Acre+Labor Cost per Acre+Repair Cost per Acre

Total Combine Harvest Cost per Acre=Fixed Cost per Acre+Variable Cost per Acre

The data parameters contained in Table 1 are used to provide an estimate of combine harvesting cost, subject to economic information contained in the LSU AgCenter Projected Costs and Returns for Corn document (2021).

Table 1. Data parameters needs to calculate performance rate, capital costs, and operating cost for a combine.

Parameter

Unit

Value

Combine Purchase Price

dollars

$375,000

Repair and Maintenance Factor

percent

60%

Hours of Annual Use

hours

300

Years of Useful Life

years

8

Salvage Value (at the end of useful life)

percent

20%

Interest Rate (amortization)

percent

4.5%

Acres Harvested Annually

acres

1,000

Combine Field Speed

mph

3.0

Combine Machine Width

feet

30

Field Efficiency

percent

65%

Labor Cost

dollars per hour

$15.30

Combine Engine Size

HP

300

Fuel Consumption

gallons per HP-hour

0.044

Diesel Fuel Price

dollars per gallon

$1.73


Performance Rate Equations:

Acres per Hour= (3.0 mph*30 feet*65%)/8.25=7.09 acres harvested per hour

Hours per Acre= 1/7.09=0.141 hours per harvested acre

Capital Cost Equations:

Capital Recovery (Amortization)Factor= 〖4.5%*(1+4.5%)〗^8/(〖(1+4.5%)〗^8-1)=0.1516 CRF

Capital Recovery Cost=[0.1516*($375,000-$75,000)]+(4.5%*$75,000)=$48,858 per year

Fixed Cost per Acre= $48,858/1,000=$48.86 per acre

Operating Cost Equations:

Fuel Consumption per Hour (gallons per hour)=0.044 gallons per HP HR*300=13.2 gallons per hour

Fuel Cost per Acre=$1.73*13.2*0.141=$3.22 per acre

Labor Cost per Acre=$15.30*0.141*1.1=$2.37 per acre

Repair Cost per Hour= ($375,000*60%)/(8*300)=$93.75 per hour

Repair Cost per Acre=$93.75*0.141=$13.22 per acre

Variable Cost per Acre=$3.22+$2.37+$13.22=$18.81 per acre

Total Cost Equation:

Total Combine Harvest Cost per Acre=$48.86+$18.81=$67.67 per acre

The variable harvest cost, which include charges for fuel, labor and repairs, can vary widely due to a variety of factors. Some of the more important factors influencing variable harvest cost include the harvest speed of the combine travelling through the field, the field efficiency of the harvest operation (i.e., of the total time the combine is running, what percent of that time is it actually cutting/harvesting a crop, and the price of diesel fuel. Estimates of the impact of alternative harvest speeds, field efficiency and fuel price on total variable corn harvest costs per acre for the example illustration above are shown in Tables 2 and 3.

Table 2. Variable cost comparison per harvested corn acre for alternative field efficiencies and combine field speeds.

Field Efficiency

Field Speed 1.0 mph

Field Speed 2.0 mph

Field Speed 3.0 mph

55%

$66.71

$33.35

$22.24

60%

$61.15

$30.57

$20.38

65%

$56.45

$28.22

$18.82

70%

$52.41

$26.21

$17.47

75%

$48.92

$24.46

$16.31

Table 3. Variable cost comparison per harvested corn acre for alternative field efficiencies and diesel fuel prices.

Field Efficiency

$2.00 Diesel Price

$2.30 Diesel Price

$2.60 Diesel Price

55%

$22.83

$23.49

$24.15

60%

$20.93

$21.53

$22.14

65%

$19.32

$19.88

$20.43

70%

$17.94

$18.46

$18.98

75%

$16.74

$17.23

17.71

This research is funded in-part by the Louisiana Rice Research Board, the Louisiana Soybean and Feed Grain Research and Promotion Board, and the Louisiana State Support Committee of Cotton Incorporated.

Late-Season Nitrogen Application in Soybean: Does It Work?

Rasel Parvej and David Moseley, LSU AgCenter Scientists

Nitrogen (N) is the most yield limiting nutrient for any row crop including soybean. Since soybean, like other legume crops, can fix atmospheric N symbiotically through Rhizobium bacteria (Bradyrhizobia japonicum), the crop usually does not require any supplemental N. However, symbiotic N fixation only supplies 20 to 80% of the total N requirement to the soybean plant (depending on soil types, soil N concentration, cultivars, and management practices.) When discussing N fixation in soybean, a common question is usually asked: Does soybean need supplemental N to maximize yield? Unfortunately, there is no straight answer for this question. Researchers have studied soybean response to N fertilization over 200 environments across the United States, but the results are mixed: either no response or an increase or decrease in yield.

The reason for decreased yield or no response is mostly because supplemental N can suppress symbiotic N fixation through poor nodulation. High residual soil N also can decrease nodule production and reduce N fixation. Most researchers that found soybean yield decline or had no response to N fertilization applied their N fertilizer treatments at planting or a few days after planting. Therefore, it is almost certain that under ideal conditions any supplemental N at or a little after planting would not give any yield benefit unless there is a deficiency in N fixation caused by ineffective Rhizobium populations or other soil and environmental conditions (e.g. high residual soil N concentration, drought, waterlogged soils, etc). However, soybean will respond to preplant N fertilization if the symbiotic N source is completely replaced the by inorganic N fertilizer. This often happens in yield contest fields where producers try to yield >100 bushels soybean per acre partially by applying an abundance of N (500 pounds or more) and do not rely on any N from the N fixation process. However, this is not an economically viable soybean production practice.

Researchers who found a soybean yield benefit from supplemental N, applied their N fertilizer treatments during the reproductive stages at or after R3 (pod set) for high yielding irrigated soybean. The reason for a soybean yield increase from late-season N application is partly due to the inadequate supply of N from symbiotic N fixation (inactive nodules). A soybean plant N demand peaks from the R3 to R6 stages when soybean requires N from both soils and the nitrogen fixation process: especially in high yielding irrigated fields. Does N fixation supply enough N during these reproductive stages to maximize soybean yield under high yielding conditions? Again, researchers have mixed opinions for this question. One of the strong opinions is N demand during pod-set to seed-filling periods may be greater than N supply from symbiotic N fixation under high yielding irrigated conditions and supplemental N is required to maximize soybean yield. Note that soybean can produce around 80 bushels per acre by utilizing symbiotically fixed N under high yielding irrigated conditions. A supplemental N may be needed to produce more than 80 bushels per acre. Considering this possible yield limitation with only utilizing the N fixation process, we are evaluating soybean response to late-season N application across different environments. The results will be shared at the end of this growing season. Although the LSU AgCenter currently does not recommend any late-season N application for soybean production in normal conditions, if interested, producers may apply 25 to 45 pounds N per acre (50 to 100 pounds urea: 46-0-0) during R3 to R4 stages. The following conditions should be considered when deciding if supplemental N may be beneficial.

  • High yielding fields (average yield >70 bushels) with irrigation and no other nutrients shortage.
  • High yielding soybean cultivar. The LSU Agcenter annually publishes results from the LSU AgCenter Official Variety Trial and Core-block demonstrations.
  • The crop was planted at the optimum planting window (mid-April to mid-May) to maximize yield potential.
  • Coarse-textured soils (sandy to silt loam) with low residual soil N concentration (usually fine soils such as clay have high organic matter and release high amounts of N during the growing season where plants are less likely to response to supplemental N).
  • Poor or inactive nodulation. At the V3 to V5 growth stages, there should be at least seven nodules that measure 2 mm or greater. The inside of an active nodule should have a pink or red color. Please read the Nitrogen fixation in soybeans article from the Louisiana Crops Newsletter Volume 10, Issue 4 – May 2020 for more information.
  • Crop experienced drought or water-logged conditions during earlier stages.

Louisiana Soybean Crop Progress and Condition Update – July 2021

David Moseley, LSU AgCenter Soybean Specialist

Soybean Crop Progress

The USDA-NASS survey for the week ending on June 27 indicated 100% of the Louisiana soybean crop was planted (Figure 1). This equaled the planting pace of the 5-year average. However, the planting progress was approximately one to two weeks behind the 5-year average from the beginning of the planting season. Persistent rain events often prevented producers from planting or caused producers to replant. Normally, 2% of the crop would have been planted by March 28; however, only 1% was planted by April 4. On April 11, only 50% of the expected acres were planted. After April 11, the planting progress remained at approximately 60-70% of the 5-year average until May 30 after soybean producers were able to plant approximately 20% of the crop during the week.On June 30, the USDA estimated the Louisiana soybean acres to be 1.1 million. This estimate is up 5% from 2020 and is unchanged from the USDA’s estimate from March.

Producers did not completely catch up to the average 5-year planting progress until June 27, the same week the state-wide soybean crop’s progression to begin the reproductive stage (R1 - onset of flowering) caught up to the five-year average (Figure 2). Warmer temperatures and shorter daylengths will shorten the duration between planting and the R1 reproductive growth stage. It is interesting to see how the percent of plants at R1 is equal to the five-year average soon after the summer solstice (June 20), when the day-length begins to shorten. Planting date research has indicated planting soybean later in the growing season will generally decrease the yield potential. A shorter duration of the vegetative growth stages can lead to shorter plants with less vegetative growth which is one reason late planting can negatively affect soybean yield potential.

The USDA-NASS survey also reports approximately 60% of the soybean crop is in the pod or seed development reproductive stages, but there were no indication of any soybean plants senescing as of July 11. However, according to the progress of a maturity group 4.0 soybean variety planted on March 22 at the Dean Lee Research Station, there may be plants senescing if planted in late-March (Figure 3). Read Identifying Soybean Growth Stages from the Louisiana Crops Newsletter Volume 11, Issue 2 – March 2021 for more information on the soybean growth stages.

Soybean Crop Condition

As of July 11, 78% of the crop was rated at good to excellent. This is the highest rating since June 13. A total of 6% of the crop is reported as poor with 0% as very poor. The very poor to poor rating has dropped considerably since June 23 when a total of 22% was rated as poor to very poor. Persistent rain events continue to occur across the state causing saturated conditions. There have been some reports of soybean leaves turning to a light-green color. Nitrogen deficiency is one reason plants can lose their dark-green color. This can occur If the nitrogen-fixation process has failed. An article discussing applying nitrogen to soybean has been included in this issue of the Louisiana Crop Newsletter.

There have been a few good things during this growing season to consider. The slightly cooler average temperatures over the previous three weeks may have decreased the amount of heat stress on the plants going into summer months. In addition, generally the pest pressure has been reported as low. In some areas, producers have not needed to irrigate due to the rain events. However, it is important to keep in mind research has indicated adequate soil moisture should be maintained through the R6.5 growth stage (Figure 4). Generally, all the pods on all the plants throughout the field should be at the R6.5 growth stage before deficient soil moisture levels will no longer affect yield. When all pods are at the R6.5 growth stage, some plants or most plants will already be at the R7 growth stage where at least one pod on the main stem has turned the mature color (Figure 5). For more information read Wrapping up soybean production with irrigation from the Louisiana Crops Newsletter Volume 10, Issue 6 – July 2020

planting progpng

Figure 1. The 2021 Louisiana soybean planting progress.

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Figure 2. The 2021 Louisiana soybean flowering progress.

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Figure 3. The same maturity group 4.0 soybean variety planted on different dates in 2021. The planting dates and current growth stages (as of July 13, 2021) were: 1: March 22 (approaching R7); 2: April 6 (late-R5); 3: April 29 (early-R5); 4: May 31 (R3); 5: June 17 (R2); 6: July 1 (V1).

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Figure 4. The progression of soybean seed development from beginning pod to the mature seed growth stage.

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Figure 5. The progression of soybean pod and seed development from beginning pod to mature pod.

When to Terminate Irrigation in Corn

Matt Foster, LSU AgCenter Corn Specialist

With much of our early-planted corn denting (Figure 1), kernels are filling weight and size. Since heat unit accumulation has been lower this year, crop development may be a few days behind schedule. As the corn crop approaches maturity, one of the most important management decisions you will make is when to terminate irrigation. Factors such as estimated time to maturity and soil moisture should be considered when making this decision. Corn kernels continue to gain weight and size until physiological maturity or black layer (R6). Previous research has shown that terminating irrigation too soon during the dent stage (R5) can reduce grain yield up to 20%.

Staging corn at the R5 growth stage is done by monitoring the milk line (Figure 1). To see the milk line, break a corn ear in half and look at the cross-section of the top half of the ear (the side of kernels opposite the embryo). The starchy solid interior portion moves from the top of the kernel toward the cob as the kernel matures. Kernels within the R5 growth stage are specifically designated by the progression of the milk line: one-quarter, one-half or three-quarters. Progression of the milk line and time required between each quarter are temperature, moisture, and hybrid dependent. It generally takes around 24 days for the milk line to progress through the entire kernel profile.

Following the progression of the milk line during R5 is a good way to estimate when a field will reach R6. This stage can be identified by a black layer at the tip of the kernel (Figure 1). Once a field reaches black layer, irrigation can be terminated since any stress has little effect on grain yield.

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Figure 1. FROM LEFT, R5/dent; R5.5/half milk line; R6/physiological maturity or blacklayer. LSU AgCenter Photos.

7/15/2021 2:01:32 AM
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