NDSU Crop and Pest Report

Plant Science


ISSUE 5  May 29, 2003

 

INOCULATE SOYBEANS AND OTHER LEGUMES WITH CORRECT BACTERIA

Legume crops such as alfalfa, sweet clover, soybean and dry edible bean fix nitrogen from the soil air to a form usable by the plant. To do this they form a symbiotic partnership with specific strains of compatible bacteria. These rhizobia bacteria enter the root hairs of young legume seedlings and induce the formation of nodules. The nodule is the site of nitrogen transform. by these bacteria.

Soil is the natural home for nodule-forming bacteria. They may or may not be present in adequate numbers, or they may or may not be of the correct strain of rhizobia bacteria to produce effective nitrogen fixing nodules.

Active working and efficient nodules are light pink to reddish in color and are found in clusters along the main root of most legume plants. The nodules will vary in size depending on the species on which they are found. If nodules are white or green they are probably inactive and are not efficient in fixing nitrogen.

The life of nodule-forming bacteria in the soil is influenced by crop history, soil aeration, soil fertility, high temperatures, low soil moisture and soil alkalinity. Bacteria may live for a number of years, but in dry soil they gradually lose their potential to produce nodules. In sandy soils, bacteria may live only two or three years.

The following table lists the specific bacteria name and type that is needed by legumes grown in North Dakota.

 

Inoculant

Legume

Bacteria name

Code or type

Alfalfa/sweetclover

Rhizobioum meliloti

A

Dry beans (pinto, navy, blacks, kidneys, pinks and cranberry)

Rhizobium leguminosarum- (Biovar phaseoli)

D

Field pea/lentil

Rhizobium leguminosarum-(Biover viceae)

C

Chickpea (Garbanzo)

Rhizobium strain

CG

Lupin

Bradyrhizobium sp.

H

Soybean

Bradyyrhizobium japonicum

S

Shelf life of commonly used peat base or liquid inoculants are often very short if not refrigerated. Studies have shown that inoculum stored at 75 degrees F for two to three months has a sharp reduction in living bacteria. If refrigerated at 40 degrees F or lower, the bacteria live for more than a year. Preinoculated seed, if in warm storage or carried over the summer months under warm storage conditions, should be re-inoculated before planting to encourage effective nodulation of the plant.

 

DETERMINATION OF CANOLA AND DRILLED SOYBEAN STANDS BY THE HOOP METHOD

Established stands of are important to growers for both yield potential and weed competition. Minimum stands (plant populations) of 3-4 plants per sq. ft. for canola and 2.3 plants per sq. ft. in soybeans are the low end seedling establishment goals. An easy counting method to determine canola or soybean plant stands is the "hoop or circle" method. Use of a "hula hoop" or making one with a stiff wire or rod would also work. The area of a circle can be calculated:

3.14 x (radius in inches)2

  = sq. feet/circule

144

Below are some calculated examples:

Hoop or circle diameter

Sq. feet/hoop

30 inches

4.9

32 inches

5.6

34 inches

6.3

36 inches

7.1

38 inches

7.9

When checking fields, toss the hoop at 10-12 sampling sites while scouting a field. Sample representative areas and stands throughout the field. Count the number of plants within the hoop at each throw and record. Average the number of plants found over the samples counted. To determine canola or soybean plant stands:

Avg. Number plants/hoop count

  = number of plants per sq. foot

sq. ft./hoop

example: 34 inch hoop with 44 plants ave./hoop count

44

   = 7 plants/ft. sq.

6.3

Number of plants per Acre:

7 plants x 43,560 sq. ft./A=304,920 plants/A

If planting populations are 2 or less per sq. ft. then one should carefully scrutinize the stand. Is the sparse stand fairly uniform throughout the field? If this is true it perhaps can be left to grow, branch and compensate for the low populations. Both canola and soybean will branch and compensate for low stands. Field peas or lentils will usually not respond with branching due to low populations. Other factors to consider would be weed control and competition with weeds, reseeding risks of planting late and hitting hot weather during bloom stage, seed costs, replanting costs, chemicals and possible herbicides residues for other crop choices.

Duane R. Berglund
NDSU Extension Agronomist
dberglun@ndsuext.nodak.edu

 

GROWTH STAGING CEREAL CROPS

The next few weeks are extremely important in determining the yield potential of cereal crops. Yield can be described as a function of the genetics of the crop, the environment and management practices. You canít do a great deal about the environment, and now that decisions on which varieties/hybrids to plant have been made and the crop is in the ground you canít do anything about the genetics. What remains is to ensure good and timely management in order to optimize the varieties planted with the prevailing environment. Timely application of management practices is critical to achieving high yields. Since crop growth and development is affected by the environment and by the variety or hybrid grown, the recommendations for most management practices for which timing is important (e.g. fertilizer topdressing and herbicide application timing, etc.) are based on crop growth stage, rather than calendar date. Therefore, being able to properly identify the growth stage of your cereal crop will be important to ensuring that management practices are applied at the appropriate time. In this article I will briefly review how to determine the growth stage of your cereal crops.

Early Growth Staging in Small Grains

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. 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 1st leaf (or 2nd 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.

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. These tillers are also surrounded by a small membranous structure, called a prophyll, that is useful to distinguish axillary tillers from main stem tillers. When present there will only be one coleoptiler tiller. The plant in Figure 1 has two tillers and a coleoptiler tiller.

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. 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 GDD 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 accumulates about 29 small grain GDDs daily during the last week in May and 31 GDD 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.

Early Growth Staging Corn

Early staging of corn is very similar to that of small grains. The above information regarding the selection of plants used in assessing growth stages applies to corn, though if you have uniform emergence you can probably get by with looking at fewer than 10 plants. Corn rarely produces tillers, so the vegetative staging focuses only on leaf numbers. Leaf stage of the corn plant is determined by counting the number of leaves with visible collars. The first leaf, which is often hard to find intact on the plant, is short and has a rounded tip. So the process is fairly straight forward, find the first leaf and count the leaves with collars.

In corn, management recommendations are frequently made based on the height of the plant (rather than growth stage). For example, certain herbicides can only be applied to corn less than 12 inches tall. The plant height in this case is measured from the base of the plant to the highest point that the leaves reach without stretching them out. Leaves tend to droop as they get larger and plant height during early growth is a measure of where the natural canopy of the crop reaches (not how high the upper most leaf extends if pulled straight).

Predicting Leaf Stages in Corn

The same principles described above for predicting the appearance of leaves in small grains also apply to predicting the appearance of leaves of corn. Corn growing degree days, however, are calculated using a different base temperature (50 degrees) than small grains. Corn requires about 100-125 corn GDD to emerge after planting. During early development (up to 10 leaves) leaves appear after about every 85 GDDs. Based on long term data, in Fargo we typically accumulate 12 GDD daily during the last week in May and 13 GDD daily during the first week in June. Using these data, you could expect corn to produce roughly 1 leaf per week during this two week period. You can find more on predicating growth stages using GDDs at

http://www.agry.purdue.edu/ext/corn/news/articles.03/LeafStagePredict_0520.html

Joel Ransom
NDSU Extension Agronomist - Cereal Crops
joel.ransom@ndsu.nodak.edu

 


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