ISSUE 4 May 25, 2006
SUNFLOWER SEEDING IN DRY SOILS
Reports are that it is getting dry in western areas of North Dakota and depth of seeding of sunflower questions have been raised in recent days. When seedbed conditions are dry then its best to seed deeper into moist soil. The seed should be placed at least into Ĺ to ĺ inch into moist soil. Recommended maximum seeding depths for oilseed sunflower are dependant on seed size and are as follows: 3 inches for # 2 size seed, 2 Ĺ inches for # 3 and 4 size seed and 2 inches for # 5 size seed. Note: The larger the seed number the smaller the seed!! Time to maximum emergence will increase as planting depth increases. Deeper planting depths will increase days to flowering but generally will not effect seed weight, plant height, yield, or seed oil concentration.
Higher seeding rates than normal are recommended when seeding deep. If rain is received and a crust is formed, deep seeded plants will have a particularly difficult time breaking through the crust. Harrowing the crust before the emerging seedlings reach to within one half inch of the soil surface will improve emergence. Percent emergence will decrease as planting depth increases especially for smaller seed sizes. Generally, one can expect at least a twenty percent stand loss when planting large seed ( #2 ) 3-4 inches deep.
ROLLING SOYBEANS AND PEAS
The objective of rolling soybean and field pea fields is to push rocks and large soil clods down to the soil surface and level the soil to allow a low combine cutter bar height during harvest. This will reduce harvest loss by cutting soybean and pea stems below pods instead of cutting above or through low pods and leaving seeds in the field. Soybean fields are rolled after planting, either preemergence (PRE) or postemergence. Advantages with rolling before the crop has emerged are low potential for plant injury and improved seed-to-soil contact. Disadvantages are increased potential for soil-surface crusting and soil erosion.
Rolling soybeans after the crop has emerged will potentially cause plant injury including crushed leaves and cracked or broken stems. Plants will die if the stem is broken below the cotyledon leaves, due to loss of all growing points. Injured plants may be more susceptible to lodging and disease. NDSU research and farmer testimony indicates that rolling between the cotyledon and first trifoliate stages of soybean should limit injury potential. Also, rolling during the warmest part of the day on less turgid plants may reduce injury potential. Afternoons are better than mornings. Soybean rolling trials were conducted three years (2001, and 2003-2004) at the NDSU Carrington Research Extension Center. There was a trend of plant population decline as rolling was delayed from PRE to the first or second trifoliate stage. Untreated soybean and pre-merged soybeans rolled showed no visible injury. Rolling soybeans that were <50% cotyledons emerged, cotyledon stage and 1st trifoliate stages showed injury of 5% or less. Early morning rolling at the 3-4 trifoliate stages caused the most visible injury after 4 weeks compared to all other treatments. Seed yield was similar among the unrolled check and the rolled treatments.
Rolling field peas can be done later than soybeans. The reason for rolling peas is that the stones or soil lumps on the soil surface interfere with pea harvesting. Rolling allows for higher speeds when swathing or direct combining, and reduces guard and sickle section breakage. Peas can be rolled after harrowing or harrow packing if conventional tillage is used or after seeding if direct seeded. Heavy or excessive rolling with wet, heavy soils causes crusting which will interfere with emergence. In such cases, post emergent rolling prior to the 5 leaf stage should be used. All rolling should be carried out on dry days to lessen the spread of disease.
HARROWING FOR WEED CONTROL
Populations of shallow emerging weed seedlings such as green and yellow foxtail, kochia, Russian thistle, pigweed and certain nightshades can be severely reduced by timely harrowing. Harrowing wonít reduce wild oat, volunteer grains or sunflowers and perennial weeds very much due to their deeper emergence. However, control will be higher if they have not yet emerged and are near the soil surface. Extremely wet soil conditions will not allow good weed kill by harrowing.
Harrows should be set shallow and angled back to reduce the potential of crop injury. Light spring tooth type harrow should be used and not the heavy harrows designed for vigorous tillage operations.
Itís best to harrow wheat and barley at the two leaf stage and no later than the three leaf stage to minimize injury potential. Wheat can be harrowed twice while barley should be harrowed only once. Corn can be harrowed between the one and four leaf stage, and sunflower, 2 to 6 leaf stage. Soybeans and dry beans can be harrowed between the 1 to 2 trifoliolate stage. Itís advised not to harrow canola, mustard, crambe or flax seedlings before or after emergence.
Duane R. Berglund
EARLY GROWTH STAGING SMALL GRAINS
Winter wheat and early planted spring small grains are developing rapidly with the arrival of warmer weather. Winter wheat is in the jointing to boot stage and early spring planted crops are in the 4 to 5 leaf stage and will soon begin jointing. The optimum and/or the legal timing of a number of management practices (i.e. herbicide and fungicide applications) is frequently determined by the growth stage of the crop. Therefore, correctly "growth staging" a crop is important in the crop management process. There are a number of different scales (i.e. Feekes, Haun and Zadok) that have been developed to classify the growth stages of small grains. The Haun scale, for example, is an output of NDAWN, which will be describe in more detail later. These growth stage scales are commonly used by researchers when describing experimental methods and results in scientific publications but less so in communicating recommendations to farmers. The timing of management recommendations are most commonly based on leaf numbers or other visible characteristics of the plants. Therefore, in this article I will focus on how to assess these various characteristics and will not delve into the details of growth scales.
When growth staging your crop you should begin by obtaining a representative sample of plants from the field or part of the field of interest. To give you a good feel for an "average" plant, use ten plants selected at random away from the edges of the field. Remove any soil attached to the plant so that you are able to observe the roots and crown. Leaf stage is the most common physical feature used to describe early development of small grain crops. Leaf stage is defined by the number of leaves that have visible collars on the main stem. Care must be taken to ensure that the earliest leaves are included when counting. The first leaf is small and is frequently lost from the plant during normal growth. It has a characteristically blunt tip. Look for the sheath remnants at the crown of the plant if you suspect that the first leaf (or second for that matter) is missing. Count only the leaves on the main stem, which is the tallest and most leafy of the stems. Include only those leaves that have a collar. The plant in Figure 1, for example is in the four leaf stage. Note that a fifth leaf is visible but it is excluded as it has not yet developed to the point of having a leaf collar. When staging plants include all leaves, even those that have been damaged by hail or frost. The total number of leaves that a plant will developed is more or less fixed for a given variety; leaves that are striped from the plant will not be replaced by additional new leaves.
Figure 1. Wheat plant in the 4 leaf stage
with two tillers
Each tiller produced in addition to the main stem is numbered when it becomes visible. There are two types of tillers: those arising from a crown leaf axis and those arising from the coleoptiler node. Only tillers arising from a crown leaf axis are counted when staging. When present there will only be one coleoptiler tiller. The plant in Figure 1 has two tillers and a coleoptiler tiller.
The North Dakota Agricultural Weather Network (NDAWN) can also be used to give you a rough estimate of the growth stage of your crop. Go to the application section of the NDAWN home page http://ndawn.ndsu.nodak.edu/ and select wheat degree days/growth stage, then enter your planting date and select the NDAWN station nearest your farm. Data on the number of wheat degree days and the approximate growth stage of your crop will be provided as output. This tool can be particularly useful if leaves have been lost to frost or hail damage.
Predicting Leaf Stages in Small Grains
Sometimes it is useful to be able to estimate or predict when a certain growth stage will be reached. Plant development is closely correlated to the accumulation of heat units or growing degree days (GDD), much more so than calendar days. Based on plant emergence and historic temperature trends, you can fairly accurately predict when a crop will reach a certain developmental stage. Historic growing degree days are readily available for a number of locations in North Dakota using the NDAWN website at: http://ndawn.ndsu.nodak.edu/application/wheat-app.html
Wheat requires about 140 GDDs and barley about 100 GDDs to produce a leaf. The actual number of GGDs required can vary between varieties, but these values will give estimates that will be accurate enough for most applications. Be sure to use GDDs that were calculated for small grains which use a base temperature of 32 degrees. Other base temperatures are used for corn and sunflower and certain pests.
As an example, if you wanted to know what stage your wheat crop would be in at the end of the week, you could estimate it by using either historical weather data or predicted weather data. Fargo typically accumulates about 29 small grain GDDS daily during the last week in May and 31 GDDs per day during the first week of June. Using these data, you could expect wheat to produce 1.5 leaves during the last week of May and 1.6 leaves during the first week of June. Barley could be expected to produce 2 and 2.2 leaves per week during these same periods.
Extension Agronomist - Cereal Crops