Wheat Grain Fill and Ripening

May 2, 2012 in Uncategorized

Most wheat fields in the county have entered the flowering and pollination growth phase.  Once kernels are pollinated, the grain fill period begins.  Final yield is composed of (number of heads/acre x number of seeds/head x weight/seed x grain yield/acre)  Grain fill is important as kernel size and weight are being determined.  Stress during this period, which lasts roughly one month, can cause yield loss.  Our most common stress is drought.  Wheat will continue to use around .25-.30 of water during grain fill.  Once flowering is complete, it may be beneficial to irrigate if conditions turn dry again.  Below is more information about the grain fill period in wheat:

Grain filling follows anthesis and refers to the period during which the kernel matures or ripens. Within a few hours of pollination, the embryo (rudimentary, undeveloped plant in a seed) and endosperm (area of starch and protein storage in the seed) begin to form and photosynthates (products of photosynthesis) are transported to the developing grain from leaves (primarily the flag leaf). In addition, starches, proteins, and other compounds previously produced and stored in leaves, stems, and roots are also transferred to the developing grain. The grain filling period is critical for producing high yields because kernel size and weight are determined during this stage. Yields will be reduced by any stress (high temperatures, low soil moisture, nutrient deficiencies, and diseases) occurring during grain fill.

Environmental factors affect the rate and duration of the grain filling period. The longer this filling period lasts, the greater is the probability for higher yields. If this period is shortened, yields will usually be lower. In Kentucky, the average length of the grain filling period is one month. The grain fill period can be as few as 25 days or less in high stress environments (hot and dry weather, heavy disease, and nutrient deficiencies) and may exceed 35 days in high yield, low stress environments (disease-free, high soil moisture, and moderate/cooler temperatures). The grain development stages are listed in Table 2-1 (Feekes 10.54 to 11.4; Zadoks 70 to 92). A brief description and comments of the grain filling and ripening stages follows below.

Watery ripe stage: Kernel length and width are established during this stage. The kernel rapidly increases in size but does not accumulate much dry matter. A clear fluid can be squeezed from the developing kernel.

Milk stage: During this stage there is a noticeable increase in solids of the liquid endosperm as nutrients in the plant are redistributed to the developing kernels. During the milk stage a white, milk-like fluid can be squeezed from the kernel when crushed between fingers. By the end of the milk stage, the embryo is fully formed.

Soft dough stage: The kernels are soft but dry. The water concentration of the kernel has decreased so that the material squeezed out of the kernel is no longer a liquid but has the consistency of meal or dough. The kernel rapidly accumulates starch and nutrients and by the end of this stage the green color begins to fade. Most of the kernel dry weight is accumulated in this stage.

Hard dough stage: The kernel has become firm and hard and is difficult to crush between fingers. It can be dented with a thumbnail. Kernel moisture content decreases from a level of 40 percent to 30 percent. At the end of the hard dough stage (Feekes 11.3; Zadoks 87-91), the kernel reaches its maximum dry weight and the wheat is said to be physiologically mature (no more weight is added to the grain). Physiological maturity often corresponds to kernel moisture content between 30 and 40 percent. Previous wheat swathing research at the University of Kentucky at various kernel moisture contents indicated physiological maturity occurred at a kernel moisture content of 38 to 42 percent (with no reduction in yield or test weight if cut at this stage). Harvesting can occur anytime after physiological maturity but often does not occur because of high kernel moisture.

Ripening stage: Kernel moisture content is still high, usually ranging from 25 to 35 percent, when wheat begins to ripen but decreases rapidly with good weather. The plant turns to a straw color and the kernel becomes very hard. The kernel becomes difficult to divide with a thumbnail, cannot be crushed between fingernails, and can no longer be dented by a thumbnail. Harvest can begin when the grain has reached a suitable moisture level (usually less than 20%).

Often harvest does not occur until grain moisture content is close to 15 percent, unless drying facilities are available. It is important for grain quality that the harvest begins as soon as possible. Test weight (and hence grain yield) may be reduced during the ripening process. Decreased test weight results from the alternate wetting (rains or heavy dews) and drying of the grain after the wheat has physiologically matured.

Source:
Herbek, James and Chad Lee.  2009. A Comprehensive Guide to Wheat Management in Kentucky.  Section 2.  Growth and Development.  University of Kentucky Cooperative Extension.  Online.  http://www.uky.edu/Ag/GrainCrops/ID125Section2.html#StemElongation

Irrigating Winter Wheat

April 10, 2012 in Uncategorized

Unlike the wet spring of 2011, this has been a dry spring so far. We have not had a significant rainfall in a month. Topsoil moisture is very dry in most parts of the county and the subsoil moisture has not been recharged in a while. As you can see in the chart below, Delaware is currently “abnormally dry” and I suspect that this will be upgraded by the end of the week.

 



Many growers with irrigation have pumped water on their wheat ground by now. Low humidity, sunshine, and windy conditions over the past few days have increased evopotransporation. With the limited soil moisture reserves and dry forecast, irrigation may play a key role in making this year’s wheat (and barley crop. While irrigated wheat research is somewhat limited, here are some management factors to consider:
  • Irrigated wheat growers report a 3-7 bushel yield increase. This number may be higher in sandier ground and lower in clay ground depending on moisture holding capacity. Estimate existing soil moisture before beginning irrigation to help schedule irrigation. Estimated soil water holding capacity can be found with a soil map.
  • As the wheat plant matures, daily water use continues to climb. Wheat at the jointing stage (F6-F8) is using around .20-.25 inches of water per day. This increases to .25 inches/day and close to .30 inches/day during grain fill.
  • An ideal goal is to recharge soil moisture and provide enough water to get through flowering. Therefore, irrigate as much as possible before the wheat plant reaches the flowering stage. Once wheat goes to flower, it becomes susceptible to Fusarium Head Blight (Scab) and irrigation can make things worse. After flowering, it may be necessary to provide water to help get the plant through grain fill.
  • Consider modifying your fungicide program. Scout frequently for diseases (and insects) and apply a fungicide if necessary. It is very important that the flag leaf (and the leaf below) be kept clean (free of disease and insects). If the weather turns favorable for scab, then consider a fungicide application. It must go on at the right time, which is flowering. Watch for extruded anthers towards the middle of the head first, which should signal the optimal time to spray. This is a narrow application window and must be watched carefully.

Phillip Sylvester, Extension Agriculture Agent, UD, Kent County

Describing Wheat Growth Stages

February 6, 2012 in Uncategorized

Below are video’s from Wisconsin Cooperative Extension describing wheat growth stages.  While our winter’s are not as severe as in Wisconsin where winter kill is a common problem, it’s important to understand growth stages as described in the video’s.  With the mild weather we are experiencing, it is now a good time to begin scouting your wheat fields.  Determine the growth stage it is in, what weed species (broadleaf,  grass, or both) in your fields, and any possible nutrient deficiencies.

 
 

  
Source:  University of Wisconsin Cooperative Extension.  Online.  http://www.youtube.com/user/uwcoopextension#p/c/44D622149CDDD748

General Principles of Nitrogen Management for Winter Wheat

February 1, 2012 in Uncategorized

With the warmer than normal weather, there are questions about nitrogen management in small grains.  Below are some general principles of nitrogen management from Virginia Cooperative Extension:

 
Autumn

The winter wheat plant has a generalized N uptake pattern that is depicted by the curve shown in Figure 1. A crop that is planted on time for a particular location germinates, emerges, and tillers prior to the dormancy period that generally begins in December in Virginia. Dry matter production and thus N requirement is rather low during the autumn, but N is required to establish the crop and promote the production of fall tillers. Fall tillers are those that will begin growth first in the spring, and generally produce heads with more kernels. Root systems are also developed in the autumn, and are generally larger than the top growth. Well-developed roots reduce winter-kill and prepare the plant to efficiently utilize nutrients and moisture from the soil. Nitrogen fertilization in excess of the amount which the plant can utilize prior to dormancy creates the potential for leaching losses of the N. Plants with excessive fall growth are also more susceptible to disease infection and winter-kill. Hence, a moderate amount (15-30 lbs. of N/acre) is all that is needed for establishing a timely-planted winter wheat crop.

Figure 1. Figure 1. Nitrogen uptake pattern for winter wheat grown in the Coastal Plain region of Virginia.

Winter

The wheat crop utilizes very little N during winter dormancy. Nitrogen applied early in the dormancy period is subject to leaching and/or run-off losses. Applying large amounts of N during January on frozen ground, and expecting this N to be available for producing grain in April and May, is not reasonable because of our climatic conditions and the growth pattern of wheat. However, there are situations, particularly on very sandy soils in the Coastal Plain region, in which a small N application in January may be beneficial. If all of the following conditions are met, some N fertilization in January may be useful. First, significant leaching rains between October and December, for example, > 3.5 inches of precipitation during one rainfall event. Second, a thin stand of wheat with pale green color due to lack of available N. Third, an expectation for the specific site that several growing days (temperatures of 50 degrees F or greater) will occur in January and early February. Temperatures in January will likely exceed 50 degrees F several days in the Coastal Plain and Southern Piedmont areas, but not in Northern Virginia or the Valley region. Such conditions might warrant an application of 30 lbs. of N per acre to encourage tillering and root growth. However, potential losses to the environment are great with such applications, and they should be made only after careful consideration of the specific field conditions, and the N application should not exceed 30 lbs. N/acre.

Late Winter/Early Spring

The wheat crop breaks dormancy in late February/early March in most areas of Virginia. As growth begins so does the crop’s requirement for N. Late winter/early spring growth is characterized by further tillering of the crop prior to stem elongation (Zadoks growth stage 30, Figure 2). Since the initial growth is usually rather slow because of cool temperatures, the initial N fertilizer application should be as near to the initiation of growth as it is possible to estimate for the specific site. It is important, however, to realize that fields with low tiller numbers should receive the first N applications so that spring tiller production is not delayed due to a lack of plant-available N. Reference to Figure 1 shows that N uptake is usually not great during the period of mid-February to mid-March. Again, this closely matches the growth or dry-matter production pattern for the crop. Excessive N applications during the early-spring tillering phase can result in spindly plants that are more likely to lodge and be susceptible to diseases such as powdery mildew. Nitrogen applications during this period should not exceed 60 lbs. N/acre if split-spring N applications are planned. Applications greater than 60 lbs. N/acre during late winter have not increased yields when followed with appropriate N fertilization at GS 30.

Figure 2. Figure 2. Growth stages of wheat according to the Zadoks and Feekes scales.

Return to Table of Contents

Stem Elongation

The leaf sheath erection growth phase, GS 30, signals the beginning of stem elongation and the most rapid phase of wheat growth. Two important factors are occurring during this time. First, the potential number of kernels per head is being established during the embryonic formation of the head. Second, rapid N uptake begins (Figure 1). Management must now be directed to maintaining developing heads. Inadequate available N causes tiller abortion with resulting lowered harvest population. Some tillers will always be lost. However, stands with marginal populations at the end of tillering are likely to have lower yields due to low numbers of heads/sq. ft. at harvest. The initial phase of head development is occurring at GS 30. The late winter/early spring N application should be adequate to develop the embryonic head. Visually, the crop should have a medium to dark green color and be vigorously growing by GS 30. If the crop is beginning to show signs of chlorosis (yellowing), then the application of N at this stage is critical for the development of adequate head size. Priority should be given to N treatments for crops showing a lack of adequate N at this stage of growth. The question of N fertilizer amounts at this growth stage will be discussed in a later section of this report. Finally, GS 30 indicates that the wheat plant is about to embark on its most rapid period of vegetative growth in order to build a structure for producing carbohydrate to fill the grain. Figure 1 clearly illustrates the large N uptake from the beginning of April (approximately GS 30) through the first two weeks of May (flowering) for a well-fertilized crop grown under Virginia climatic conditions. Nitrogen fertilizer management must provide for the crop requirement during this phase in order to have adequate leaf area for producing profitable yields. Also, there is very little chance for leaching loss of N fertilizer applied near the beginning of this growth phase due to the extensive nature of the wheat root system by GS 30, relatively high rates of evapotranspiration, and the large amount of N uptake during this time period. Figure 2. Growth stages of wheat according to the Zadoks and Feekes scales.

Grain Fill

Nitrogen uptake during the grain-fill period (Figure 1, early May through June) is relatively low compared to uptake during the stem elongation phase of growth. Plant tissue N is mobilized and translocated to the grain during this period with only small additions coming from available soil N. Our research has shown no yield increases from N fertilizer applications at or after flowering. Foliar applications (10 to 20 lbs. N/acre) of urea at this growth stage have been shown to increase grain protein but not yield. If such applications are made, they should be made in sufficient volumes of water (20 to 30 gallons/acre) to reduce the potential for foliar burn.

Source:
Alley, M. M., Peter Scharf, D. E. Brann, W. E. Baethgen; and J. L. Hammons.  2009.  Nitrogen Management for Winter Wheat: Principles and Recommendations.  Publication # 424-026.  Virginia Cooperative Extension.  Online.  http://pubs.ext.vt.edu/424/424-026/424-026.html

  

Wheat Growth Stages

December 16, 2011 in Uncategorized

The chart below is a good resource when growth staging wheat.  It compares the two scales used to growth stage wheat, Feekes and Zadoks.  Having a understanding of the two scales is helpful as some publications may refer to the Zadok’s scale, see Nitrogen Management for Winter Wheat, while some pesticide labels use the Feekes scale as a method to describe application timings, see Prosaro Label (one of the few fungicides used against Fusarium Head Blight). Winter wheat has a vernalization requirement, which is an exposure to cooler weather for extended period of time.  It is also this time period which signifies the change from vegetative growth to reproductive growth.  Click on the chart to make larger.

Vernalization

Source:
Herbek, James and Chad Lee.  A Comprehensive Guide to Wheat Management in Kentucky.  Section 2. Growth and Development.  University of Kentucky Cooperative Extension.  Online. http://www.uky.edu/Ag/GrainCrops/ID125Section2.html

Understanding Wheat Tillers

December 14, 2011 in Uncategorized

It’s important to understand the tillering stage in wheat.  Many cultural practices such as planting date can influence the number of fall tillers in wheat.  Many wheat fields in the county were delayed due to poor weather and did not get planted until November.  Below is information on what happens during the tillering stage and pictures I took of wheat with tillers.

The tillering stage begins with the emergence of lateral shoots (tillers) from the axils of the true leaves at the base of the main stem of the plant. The tillers are formed from the auxiliary buds located at each crown node. Primary tillers form in the axils of the first four or more true leaves of the main stem. Secondary tillers may develop from the base of primary tillers if conditions favor tiller development. A tiller may also develop from the coleoptile node (coleoptilar tiller), but this occurs sporadically and its appearance is dependent on genotype, planting practices, and environmental conditions. At the base of each tiller is a sheath (small leaf like structure) called the prophyll, from which the tiller leaves emerge. The prophyll acts like the coleoptile and protects the auxiliary bud before it elongates its first leaf to become a tiller. Identifying the prophyll, which encloses the base of the tiller, will help differentiate tiller leaves from the leaves on the main stem and from other tillers. Tillering usually begins when the seedling plant has three or more fully developed leaves. Tillers depend on the main stem for nutrition during their development. Once a tiller has developed three or more leaves, it becomes nutritionally independent of the main stem and forms its own root system.

Tillers are an important component of wheat yield because they have the potential to develop grain-bearing heads. In Kentucky, each plant normally develops two or more tillers in the fall when planted at optimum dates. The total number of tillers eventually developed will not all produce grain-bearing heads. Under recommended plant populations, usually two or three tillers, in addition to the main shoot, will produce grain. Tiller development occurs in the fall until low temperatures stop plant growth. In Kentucky, during the tillering stage, winter wheat goes through the winter months in a dormant condition in which plant growth (including tiller production) essentially ceases due to cold temperature. Tiller production and development resumes in late winter/early spring with an increase in temperature as the plants break dormancy and resume growth. Due to cooler temperatures, late planted winter wheat may have little or no fall tillering because of limited seedling growth or because no wheat has emerged; late planted wheat will rely heavily on spring tiller development. Spring tillers generally contribute less to yield potential than do fall tillers. Consequently, fall tillering is important for winter wheat to achieve maximum yield potential.
Tillers develop sequentially on a plant, resulting in a prioritization for development. The main stem and older (first-formed) tillers have priority to complete development and form a grain-bearing head. This same priority also exists regarding the size of the grain-bearing head on the main stem and subsequent tillers. 
Picture 1.  Wheat plant with main shoot and two fully emerged tillers.  Photo by P. Sylvester

Picture 2. Wheat plant with fully emerged tillers separated from main shoot for visual demonstration.   Photo by P. Sylvester
 Sources:
Lee, Chad & James Herbek.  2009.  A Comprehensive Guide to Wheat Management in Kentucky.  Kentucky Cooperative Extension Pub ID-125. Section 2. Growth and Development. Online. http://www.uky.edu/Ag/GrainCrops/ID125Wheat_Management_Kentucky.html
Pictures by Phillip Sylvester, Extension Agriculture Agent, Kent County, UD.

Split Applications of Nitrogen on Wheat

March 28, 2011 in Uncategorized

Cool and wet weather have slowed down springtime wheat growth in the county.  Many fields in the county overwintered well, especially those seeded during the optimal time (mid-October).  Some fields have yet to receive the first springtime application of nitrogen while others have had both applications.  For those fields that have not had an application of nitrogen, it should occur very soon if possible.  For those fields that have had the first application of nitrogen, I would recommend using the growth stage to determine the timing of the second application.  The cooler weather has slowed growth down, but once warm temperatures return, wheat will resume growth quickly.  Below is an article written by Richard Taylor, UD Extension Agronomist regarding split applications of nitrogen on wheat:

For a number of years, the spring decision of whether to split the nitrogen (N) applied to wheat was often controlled by the price of wheat. When wheat prices were four to five dollars or less per bushel, the return on investment for split N applications was either barely at the breakeven point or below it. Wheat prices this year could encourage growers to again consider if the yield gain, generally about 5 to 7 bu/A, and the environmental and economic impact of less N applied at a single application and subject to leaching, volatilization, and denitrification losses will be enough to incur the risk associated with trying to time and succeed in applying a second N application.

Another factor to consider is whether fall N was applied or if there was adequate residual N available following the previous year’s dryland crop. Even on irrigated ground, residual N could have been present to give the fall planted wheat an excellent start on tiller development. Where an irrigated corn crop was fertigated with N up until tasseling or in fields where a legume crop (soybean or lima bean) was grown, adequate residual N was likely present to give wheat a good start on growth and development.

For fields that didn’t receive fall N and there was unlikely enough residual N present for good fall growth and development, an early application of N at first green-up is critical to obtain maximum tiller production and good yield potential in a small grain crop. In such a case, a split application not only can improve yield potential but can also protect the grower from the loss of a large portion of a large single early application of N due to weather events.

In a four year study in New Castle County that Bob Uniatowski, Research Scientist at the University of Delaware, and I conducted, we found that for high yield wheat a 40 to 60 lb N/A first application followed by a second 60 lb N/A application (total of 100 to 120 lb N/A) was sufficient for maximum economic yield (MEY). The first application occurred between February 15th and March 15th depending on the weather and when wheat green-up occurred. The second application occurred when the tillers assumed an erect position just prior to the first node being visible above the soil surface. For the more typical 60 to 90 bu/A yield potential crop, a split of 40 to 60 lbs N/A at green-up followed by 20 to 40 lb N/A at Feekes 4 to 5 (total of 80 lb N/A) produced MEY.

With the excellent price for wheat this year, the typical yield increase seen with the split of N into two applications, and the potential environmental benefit associated with a lower N application rate at a single point in time, I would encourage all growers to consider this option for maximizing your profitability in 2011.

Article from the Weekly Crop Update, Volume 19, issue 1, written by Richard Taylor, UD Extension Agronomist.

Video Guide to Wheat Growth Stages 10-32.

February 16, 2011 in Uncategorized

Nitrogen Topdressing Rates on Wheat

February 12, 2011 in Uncategorized

The first nitrogen for the late winter/spring applications on wheat will be going on at the end of February. The following is information on determining topdressing nitrogen rates on wheat. The following was originally posted on January 1, 2009 by Gordon Johnson.

The high price of nitrogen (N) fertilizer at the time of wheat planting resulted in many farmers choosing to fore go preplant N. However, insufficient N availability to wheat plants results in low yields and significantly reduced profits compared to a properly fertilized crop.

A harvest objective with current wheat varieties grown in the mid-Atlantic should be 60-70 heads/sq. ft. with at least 30 kernels/head. This means that the wheat plant must develop near 100 tillers by the end of vegetative growth to reach optimum yields (see Figure 1). Nitrogen fertilizer rate and timing are the major tools available after planting to manipulate wheat to produce higher yields per acre. Nitrogen affects heads/sq. ft., seeds/head, and kernel size.

Typically, the first in-season N application occurs at Zadoks growth stage (GS) 25 and is based on wheat tiller density (Figure 1). The purpose of the first N application in a split is to stimulate formation of additional tillers when such stimulation is necessary to achieve optimum tiller density. The main nutritional needs of the crop will be supplied by the second application in the split.


To measure tiller density,

1. cut a dowel rod to a 3-foot length
2. lay the dowel down next to an average-looking row and count all tillers with three or more leaves that are found in the 3-foot length; record this number
3. repeat this count in at least five other locations that are well-spaced around the field
4. average all tiller counts from the field
5. calculate tiller density (in tillers per square foot) with the following equation: tiller density=average tiller count x 4 / row width (in inches)

Figure 2 shows the recommended N rate in response to tiller density at GS 25. If tiller numbers are low, 50/sq. ft. or less, N fertilization at this time is critical for the crop to develop any reasonable yield potential. Fields with low tiller counts should be fertilized before fields with more tillers, if possible. If tiller numbers are high, 100/sq. ft. or more, no N application is needed at this time. When winter rainfall/precipitation is above average and may have lowered the level of residual soil N, you should consider adjusting the recommendation upward.


The appropriate rate for the second application (GS 30) is best determined by tissue N content. See http://www.ext.vt.edu/pubs/grains/424-026/424-026.html for more information.

Total spring N applications (growth stage 25 plus growth stage 30) should not exceed a total of 120 lbs. N/acre in order to avoid problems with lodging and yield loss. For example, if 40 lbs. N/acre was applied at growth stage 25, and tissue test results give a recommendation of 100 lbs. N/acre at growth stage 30, only 80 lbs. N/acre should be applied at growth stage 30.

Reprinted from “Wheat Nitrogen Management in 2009″ by Dr. Wade Thomason Extension Specialist – Grain Crops and Dr. Mark Alley, W. G. Wysor Professor of Agriculture, Virginia Tech

Wheat – Nitrogen and Erect Growth Stage

April 6, 2009 in Uncategorized

The following is more information on nitrogen application in wheat when it becomes erect.

Most wheat is in Feekes growth stage 5.0 now. This is when leaf sheaths are strongly erect. At this stage, the wheat plant seems to stand up. All meaningful tiller development has ceased. Many varieties of winter wheat which are creeping or low-growing during tillering, grow vertically at this stage. The vertical growth habit is caused by a pseudo or false stem formed from sheaths of leaves. At this stage of growth, the size of heads, or number of spikelets per spike, is determined. No effect on yield is expected from tillers developed after Feekes 5.0. Nitrogen applied at Feekes 5.0 can affect number of seed per head and seed size, but will not likely affect number of heads harvested. This is an ideal stage of growth for the spring topdress N application as later applications will not affect the potential number of seed per head. Delaware growers should apply second applications of nitrogen if they have not already and if no nitrogen has been applied, it should go on in the next week.

Some information extracted from “Growth Stages of Wheat: Identification and Understanding to Improve Crop Management” by Travis D. Miller, Professor and Extension Agronomist-Small Grains and Soybeans, Texas A&M University.

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