Tải bản đầy đủ - 0trang
IV. Planting Methods and Equipment
THE MANAGEMENT OF SOYBEANS
seed (Cook et al., 1958). Illinois studies showed little difference in seed
yields when “conventional,” “plow-plant,” “plow-harow-plant,” and “tractor-track” systems were compared (Bowers et al., 1959).
On a Sharkey clay in Mississippi, fall plowing with a moldboard plow
increased soybean seed yields 5 per cent over yields in areas having no
fall treatment but disked in early spring to destroy winter weeds. After
the spring disking of plowed and not-plowed areas, both treatments were
worked with a spring-tooth harrow at 14- to 18-day intervals prior to
planting ( E. E. Hartwig, unpublished).
3. Deep Tillage
Soils having a silty-textured subsoil have a tendency to form compacted layers which restrict movement of water and also restrict root
development. Shattering this layer results in improved yields, especially
in dry years. In the fall of 1953, a Dundee silt loam in Mississippi was
chiseled 16 inches deep. Soybeans planted on May 10, 1954, showed
severe drought symptoms by late June on untreated areas, while soybeans on the treated areas were growing vigorously. In this very dry
year, seed yields on the deep tilled area were 35 bushels per acre as
contrasted to 8 bushels on the untreated area (E. E. Hartwig, unpublished). On soils with hardpans, deep tillage has increased the water
intake, increased root development, reduced drought damage, and improved the stand of cotton. Deep tillage gave no benefits on Sharkey
clay (Grissom et al., 1955).
Hobbs et al. (196l), in Kansas, found that deep tillage at 6 to 24
inches, with chisel-type implements on soils with definite restricting
layers, rarely increased yields sufficiently to pay the cost of the operation.
B. Row WIDTHAND PLANTING
1. Row Width
The row width which will result in maximum yield is dependent
upon length of growing season, growth type of varieties, and fertility
level of the soil. In general, with shorter growing seasons, row widths
narrower than the conventional 36- to 40-inch will result in highest yields.
However, when seed yields of 35 to 40 bushels are produced in 36- to
40-inch rows, increased yields from narrower rows are less frequent. If
post-emergence cultivation is necessary for weed control, then it appears
that row widths cannot be reduced below 28 to 30 inches. If preemergence chemicals satisfactorily control weed growth, the increased
yield from narrow rows must cover the cost of extra planting seed and
also increased quantities of chemicals. Rows too narrow to permit
JACKSON L. CARlTER Ahm EDGAR E. HARTWIG
cultivation would require a broadcast application of chemicals whereas
only a 12-inch band is treated in 36- to 40-inch rows. Consequently, the
cost of chemicals would be at least tripled.
Yields in Minnesota and Illinois in 18- to %-inch rows have been 15per
cent greater than in 36- to 40-inch rows (Lehman and Lambert, 1960;
Pendleton et al., 1960). In Manitoba, increases with narrow row spacing
were so small that it seemed important to adopt the row width in which
best weed control could be achieved with the equipment available (B. R.
Stefansson, personal communication).
In southeastern Kansas, 21-inch rows have produced higher yields
than 42-inch rows. A 75-pound seeding rate has been superior in
21-inch rows while 45 pounds per acre has been the optimum rate in
42-inch rows ( V. H. Peterson, personal communication).
In Virginia, North Carolina, Mississippi, and west Florida, narrow
row widths did not increase seed yield (Hartwig, 1957; R. L. Smith,
1959). Plantings in Arkansas at lower yield levels have, under some
conditions, shown a yield response from rows narrower than 36 to 40
inches (P. E. Smith, 1959). Results from the eastern shore area of
Delaware and Maryland have been variable.
2. Planting Rate
Results for planting rates within the row are, in general, similar for all
production areas. Planting rates of 6 to 12 viable seeds per foot usually
give most satisfactory results. Recommendations in most States will be
nearer the 12 seeds per foot rate. This heavier rate is recommended
largely from the standpoint of early season weed competition and also
for its influence on height of lower seed pod development. Since varieties
differ in seed size, growers should base planting rates on seeds per foot
rather than pounds per acre.
Results from planting OGDEN at rates of 30 to 150 pounds per acre
in west Florida for the years 1950 to 1955 showed little difference in
yields at rates of 30 to 120 pounds, but yields were reduced at rates of 135
and 150 pounds ( R . L. Smith, 1959). Plant spacings of 2 to 3 inches in
the row produced slightly higher yields in Indiana than l-inch or 4-inch
spacings. Plants spaced 1 inch in the row showed a greater amount of
lodging and matured slightly later than did thinner plantings (Probst,
1945). Spacings of 6 and 12 plants per foot produced higher yields in
North Carolina than did the thinner rates. There was greater lodging
at the 12-plant spacing than with 6 plants per foot. Yield differences
were small and not significant in Mississippi from plantings at 6, 9, 12,
18, and 21 seeds per foot. The 6-seed-per-foot rate required a longer
time to give complete ground shading in the row. The 9 and 12 seeds-per-
THE MANAGEMENT OF SOYBEANS
foot rate gave excellent early growth with a not too severe amount of
lodging (Hartwig, 1957).
Along with rates within the row, moderate skips in one row of an
otherwise complete stand have little influence upon the total yield.
Caviness (1961) found that a 2-foot gap in a 16-foot row resulted in a
very small and statistically nonsigngcant yield reduction. A 4-foot gap
resulted in a barely significant reduction, and with a 6-foot gap 95 per
cent of the check yield was produced. Similar results have been secured in
Ohio (L. C. Saboe, personal communication) and in Illinois (R. L.
Bernard and J. L. Cartter, unpublished).
1. After Fall-Sown Grain Crops
The growing seasons for fall-sown grain crops and soybeans are such
that in many areas both can be grown during the same year with nearly
full production of each. One of the requirements is that each be
harvested as soon as it is mature and the other planted immediately.
Weather conditions may upset this schedule. Studies at Stoneville,
Mississippi, indicate that, for mid-June plantings, yields after oats are
approximately 10 per cent lower than for similar plantings where no spring
crop was grown. At Stoneville, October 15 is the best planting date for
oats, and they mature between May 25 and June 15.
One of the problems in double cropping is timely planting of soybeans
after small grain harvest without excessive loss of soil moisture. Plantings
on clay in the delta area of Mississippi have been most successful when
grain straw is burned and soybeans planted immediately without any
seedbed preparation, using planters equipped with a double disk opener.
Equally satisfactory stands have been obtained by planting in shredded
straw but the residue gives problems in cultivation. Burning straw also
kills seedling weeds.
Several workers (Brim et al., 1955; McAlister, 1958; Fullilove and
Reid, 1959) in the coastal plain area have obtained good results in
planting soybeans after small grain by using a lister type planter with
no previous seedbed preparation. In cultivation, the soil thrown out from
the lister furrow is worked back into the row. This method works best
in relatively sandy soils with moderately high rainfall.
In some areas use of oats for silage has proved desirable. This practice
would permit earlier planting of soybeans and would reduce the straw
2. After Peas
In northern areas where peas are grown for canning or freezing,
the crop is harvested in late June or early July, and soybeans have been
JACKSON L. CARTER Ah’D EDGAR E. HARTWIG
planted after peas. Many of the problems are similar to those for planting
after small grain, except that all top growth of the peas is removed in
harvesting. Results obtained in Minnesota and Wisconsin indicate that
soybean yields of 10 to 15 bushels can be produced after a crop of peas
is harvested (J. W. Lambert, J. H. Torrie, personal communication).
D. SPECIALMETHODSOF PLANTING
Many soybean growers have been of the opinion that larger yields
could be produced from a given land area if two crops differing in requirements were planted in alternate rows. A survey of farm practices
with soybeans (Smith and Hope, 1920) showed that farmers believed
that by planting soybeans and corn in alternate rows, each would produce
75 per cent of a full crop, thus giving a 50 per cent greater yield than if
the two crops were grown separately. This theory has been tested in
North Carolina, Ohio, Illinois, and Iowa with alternate rows, paired rows,
and other interplanting patterns. At times interplanting has given small
increases in total production, but it appears that increased management
problems overbalance the production gains.
In many of the older production areas, soybeans have been interplanted in the row with corn. In some cases the corn has been harvested
and the residue plus soybeans grazed with livestock. In other cases the
soybeans were grown only to add nitrogen for the following crop. As
fertilization rates for corn in the southeast have increased and plant
populations have also been increased, soybeans have failed to survive
in the interplantings. Data from North Carolina show no difference in
corn yield between corn planted alone and with soybeans interplanted.
There was no seed production on the soybeans.
The possibilities for planting two soybean varieties of different maturities or growth types in alternate or paired alternate rows has been explored. In Mississippi, interplanting the varieties JACKSON and LEE,
which differ by 12 to 15 inches in height and 12 days in maturity, produced yields equal to the mean for the two varieties grown alone (E. E.
Hartwig, unpublished ) . J. W. Pendleton (personal communication )
found no yield increases in Illinois from interplanting an early variety
in the middle of the rows of a late maturing variety at the time of the
Limited studies have been initiated to determine whether northsouth row direction might permit more light to be received by the soybean plant, resulting in higher yields. Results at Winnipeg, Manitoba, and
at Urbana, Illinois, have shown no effect of row direction on yield (B.
R. Stefansson, J. W. Pendleton, personal communication).
THE MANAGEMENT OF SOYBEANS
Soybeans may be planted with planters designed for row crops or
with a grain drill with all feed cups covered except those needed for
row planting. A row planter with good press wheels provides more
uniform depth and better covering of the seed. In some heavy clays,
the surface layer dries rapidly in the process of seedbed preparation.
In such soils, a double disk opener has been found very beneficial in
getting the seed placed below the loose dry surface into moist soil under
conditions favorable for prompt germination (Fig. 7). If narrow rows
are used, provision must be made for cultivating equipment to accommodate the narrower row spacing.
Double disc opener
FIG.7. Cross section of seed furrows. Effect of djfferent types of furrow openers
on seed placement. The double disk permits placement of seed in moist soil with a
minimum of soil disturbance. (From Mississippi State College Agricultural Experiment Station Information Sheet 576, March, 1958.)
The rotary hoe is very effective in early season weed control in soybeans (Lovely et al.,1958). For later cultivation, conventional row crop
equipment is used.
V. Rotation Practices and Erosion Control
A. EFFECTON SOYBEANYIELDS
The soybean can be used advantageously in many crop rotations, and
no standard rotation can be given that will apply to every farm. Depending upon the use of the crop, soybeans have been classed as soil
improving or soil depleting. Sears (1939) found that where the crop was
plowed under, it returned about 90 pounds of nitrogen per acre, and
where it was harvested for beans and the straw returned to the soil,
there was a gain of about 16 pounds of nitrogen per acre. When the
JACKSON L. C A R T E R AND EDGAR E. HARTWIG
soybeans were combined and the straw burned, there was a loss of
about 3 pounds of nitrogen per acre. Also, under comparable conditions,
Sears estimated that corn, oats, and wheat would remove 40, 26, and
36 pounds of nitrogen, respectively, but his estimates were made for a
rather low (40 bushel) yield of corn. Typical rotations for the midwest
farming areas usually suggest soybeans following corn in the cropping
sequence, as corn can utilize to advantage the nitrogen furnished by
turning under a deep rooted, small-seeded legume sod, whereas, wellnodulated soybeans do not benefit from the high level of nitrogen.
At Stoneville, Mississippi, with good weed control, soybean yields in
a continuous cropping system have been similar to yields produced in
a 2- or 3-year rotation with cotton.
The advantage of soybeans in the rotation cannot be explained altogether on the basis of the returns from the crop, according to Pond
(1950). Some of the other advantages given were ( 1 ) the labor requirements are low; ( 2 ) soybeans do not compete too seriously for labor at
peak periods; (3) soybeans can be planted later than other crops with
reasonable assurance that they will m a t u r e t h i s is especially important
in a wet spring; ( 4 ) as a cultivated crop they aid in weed control; ( 5 )
they stand drought better than some other crops; ( 6 ) soybeans do better
than many other crops on spring plowing; and ( 7 ) soybeans improve
the physical condition of the soil.
A crop rotation in which soybeans do not appear oftener than once
in three or four years aids in controlling certain diseases such as brown
stem rot. Where the soybean cyst nematode is a serious problem, nearnormal soybean yields may be obtained in a 2-year rotation if a nonsusceptible crop is grown during the year out of soybeans (J. M. Epps,
Soybeans improve soil tilth by shading and protecting the soil from
rain. The roots and the bacterial action they foster tend to loosen the
soil mass and make it more easily penetrated by nioisture and by roots
of the succeeding crop. Soybeans leave heavy compact soils in much
better physical condition than do corn and small grains (Calland, 1949).
Soybeans as a crop seem to be less depressing on soil productivity than
corn when judged by crop yield (Strickling, 1950).
Results from studies conducted in Minnesota show that corn yields
following soybeans are greater than those following oats. This yield
increase was attributed largely to greater residual nitrogen in the soil
after a crop of soybeans (Schmid et al., 1959).