Fertility and Row Spacing
S.W. Neill and Carl Hovermale
Kenaf is a very vigorous plant under optimum conditions. Kenaf
can reach canopy in as few as 5 weeks, so fertility applications
need to be made with this factor in mind. Literature review
indicates little yield is gained by split applications of
nitrogen and that a recommended rate would be 150 to 200 pounds
per acre of actual nitrogen.
Trials conducted at Leverette and Stoneville, Mississippi in 1990
and 1991 indicate that 150 pounds of nitrogen should be
sufficient to ensure maximum yields. Increasing nitrogen has
caused the plant to be greener and bushier, but has not increased
yield correspondingly. Depending on the row spacing and
management, a recommendation would be to apply 100 lb/acre N
preplant, and another 50 lb/acre as a postemergence sidedress application.
Trials utilizing multiple rates of phosphorus and potassium with
nitrogen have been conducted with unclear results as to the role
of the phosphorus and potassium. The addition of these
alternative fertilizers does not seem to have an effect on yield
as does nitrogen; however, the effect on the individual plant
(bast ratio) is being studied and will continue in future trials.
Soil test results would be the best vehicle on which to plan
phosphorus and potassium applications.
Row spacing has been investigated at numerous locations across
the country and in other regions of the world. The effort in
Mississippi has been towards a spacing compatible with equipment
readily available at the production location. Spacings
investigated ranged from 10 inches to 40 inches and included
bedded rows (Table 1). The 2year row spacing trial was done at
Leverette, Mississippi on a silt loam soil.
The combined dry stem yield for the 2 years indicated that a
20inch to 30inch row spacing tended to produce higher yields
than either the 10inch or the 40inch spacings. This trial also
indicated that on soils with good external drainage there was not
a need for bedding. The area of manipulation of plant stand by
row spacing is apparent in the final stand counts and attrition
rates. This trial was handthinned to approximately 110,000
plants per acre a month after emergence both years. The plants
continued to thin in the wider spacings, possibly due to nutrient
and sunlight competition and intraspecific crowding.
In the previous article on plant population, the point was made that as the number of plants per acre increased, so did yield. That was also the case in this trial except for the narrowest spacing, where the yield decreased. Plants in the 10inch spacing were shorter and thinner than the other spacings, probably due to competition for nutrients.
Results of these trials indicate spacings for optimum yield would
be between 20inches to 30 inches. Further research is being done
with different varieties and row spacings from 10 to 30 inches.
Indications are that the varieties used show no effect of
spacing, and that yields are higher at the 20inch spacing. The
authors believe higher number of plants per acre at harvest is a
factor to be considered in the selection of row spacing.
Trials conducted at the MAFES South Mississippi Branch on Ruston
fine sandy loam soil provided different results for row spacing
than the Leverette trials. Planting dates were May 15, 1990, May
17, 1991, and May 1, 1992. Row width (8, 20, and 40 inches) was
the main plot and nitrogen rate (0, 50, 100, 150, and 200 pounds
per acre) was the sub plot. A seeding rate of 10 lb/acre remained
constant over row widths. One pint of Treflan per acre was
preplant incorporated before planting. One quart of MSMA was
postdirected using a backpack sprayer for post emergence weed
control. Harvest was accomplished after frost defoliated the
plants and converted to dry matter per acre.
1990 Results
Nitrogen fertilization rate had no effect on plant height or
population. One hundredfifty and two hundred pounds of nitrogen
per acre at planting resulted in kenaf yields of 11,328 and
19,888 lb dm/acre, respectively. This was higher than 0 nitrogen,
which yielded 7,612 lb dm/acre. Applications of 50 and 100
lb/acre of nitrogen per acre resulted in yields of 9,657 and
9,724 pounds of kenaf per acre, respectively, which was not
different from other nitrogen rates.
Row width had no effect on plant height. In 8inch rows, kenaf
yielded 12,170 lb dm/acre compared to 9,593 and 7,764 lb dm/acre
for 20 and 40inch rows, respectively. Kenaf in 8inch and
20inch rows had populations of 157,905 and 136,453 plants per
acre, respectively. This was more than 40inch rows with 84,398
plants per acre. The same amount of seed was planted in each
plot, which leads to the assumption that attrition in thicker
kenaf is higher.
1991 Results
Average kenaf yields ranged from 12,866 lb/acre with 0 nitrogen
to 18,173 lb/acre with 150 lb/acre of nitrogen, but because of
the wide variability within plots, differences in average yields
between nitrogen fertilization rates (Table 2) were not
statistically significant. Kenaf fertilized with 150 or 200
lb/acre of nitrogen was taller and had greater stem diameters
than that fertilized with 50 lb/acre or less. Kenaf plots
fertilized with more 150 lb/acre of nitrogen had lower plant
populations than those with 0 nitrogen.
Kenaf planted in 8inch rows was taller, had a higher plant
population, and produced higher yields than kenaf planted in 20
or 40inch rows (Table 2). The higher plant population may be
responsible for the higher yield in the 8inch rows. There was no
interaction between row width and nitrogen rate.
1992 Results
Kenaf yields ranged from 21,711 lb/acre with 50 lb/acre N to
30,147 lb/acre with 100 lb/acre N, but yield differences
attributable to nitrogen were not statistically significant.
There was no difference in final plant height attributable to N
rate. Kenaf plots fertilized with 150 lb/acre of nitrogen had
lower plant populations.
Kenaf planted in 8inch rows had a higher plant population and
produced higher yields than kenaf planted in 20 or 40inch rows.
The higher plant population may be responsible or higher yield in
the 8inch rows. There was no interaction between row width and
nitrogen rate.
1993 Results
Kenaf yields ranged from 13,993 lb/A with 0 lb N/A to 26,368 lb/A
with 200 lb N/A. Kenaf with 0 nitrogen was significantly shorter
than all other treatments but over 50 lb/acre N, there was no
difference in height. There was no difference in plant population
attributable to nitrogen rates. Stem diameter of kenaf fertilized
with 100 lb/acre or more of nitrogen was greater than when no
nitrogen was applied.
Kenaf planted in 8inch rows had greater stem diameters and
produced higher yields than kenaf planted in 20 or 40inch rows
(Table 3. There was no difference in plant population or final
plant height attributable to row width. There was no interaction
between row width and nitrogen rate.
Table 1. Row spacing effect on combined dry stem yield, Leverette, Mississippi, 19901991.
Leverette Combined
Treatment 1990 1991 Average
--(ton/acre)-
40-in double flat 7.6 6.6 7.10
30-in bedded 7.8 5.8 6.80
30-in flat 7.8 5.8 6.80
20-in flat 7.4 5.5 6.46
40-in flat 7.0 5.4 6.23
40-in double bedded 6.7 5.6 6.14
40-in bedded 6.4 5.6 6.00
10-in flat 7.3 4.7 5.99
Table 2. Effect of nitrogen rate and row width on yield of kenaf,
MAFES South Mississippi Branch Station, 1991.
Row Width (inches)
Nitrogen 8 20 40 Average
0 21,360 8,795 8,503 12,866
50 19,475 16,083 12,438 15,999
100 28,899 12,062 11,042 17,334
150 28,899 14,234 11,296 18,173
200 24,501 14,073 12,311 16,962
Average 24,627A1 13,067B 11,118B
1 Means within a column followed by the same letter are not
different at the (p<.05) level of significance according to DMRT.
Table 3. Effect of nitrogen rate and row width on yield of kenaf, MAFES South Mississippi Branch Station, 1993.
Row Width (inches)
Nitrogen 8 20 40 Average
-------------lb/acre-----------
0 24,049 10,786 7,143 13,9931
50 26,964 10,349 12,319 16,544 BC
100 25,507 22,301 11,444 19,751 AB
150 25,507 14,430 13,776 17,905 BC
200 33,888 21,426 15,598 26,368 A
Average 27,183A 15,859 B 12,056 B
1 Means within a column followed by the same letter are not
different at the (p<.05) level of significance according to DMRT.
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S.W. Neill, former Research Technician at the Delta Branch Experiment Station, Stoneville, is an Environmental Scientist I, YMD Joint Water Management District, Marigold, MS. Carl Hovermale is an Agronomist, South Mississippi Branch Experiment Station, Poplarville, MS.