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Copyright 2005, Board of Trustees, University
Ft. Pierce AREC Research Report FTP-88-3 Ju'y 1988
Evaluation of a Wheat Sorghum Legume Crop Rotation ;
System in South Florida, ... .- J
J. B. Brolmann and P. J. Stoffellal
A wheat (Triticum aestivum L.), sorghum [Sorghum bicolor (L.)
Moench], and legumes crop rotation in south Florida with minimum
tillage was investigated. Legumes included black bean (Phaseolus
vulgaris L.), cowpea [Vigna unguiculata (L.) Walp.], and two species
of pencil flower [Stvlosanthes hamata (L.) Taub.] and [Stylosanthes
guianensis (Aubl.) Sw.]. Establishment and growth of all crops was
satisfactory except for black beans. Highest grain yield of wheat
which was planted in December, was 2730 kg per ha. No increase in
wheat yield was obtained from an additional 35 kg/ha nitrogen side
dressing. Sorghum planted after the wheat harvest, in late April,
responded well to a side dressing of 80 kg/ha nitrogen. Average
sorghum yield at the end of August was 4846 kg per ha. A second
sorghum grain crop of 3620 kg/ha was obtained in December from the
regrowth (ratoon). Cowpea, planted in mid September, was harvested in
Additional Index Words: Triticum, Stylosanthes, Vigna, Phaseolus,
Sorghum, Nitrogen, Minimum tillage.
Crop rotation and minimum tillage are becoming of increasing
interest as components of low energy crop production systems (1, 2).
Climatic conditions in south Florida may allow for year round cropping
provided that moisture and temperature conditions are met for each
Today very little wheat (Triticum aestivum L.) and grain sorghum
[Sorghum bicolor (L.) Moench] are grown in the southern part of
Florida. Preliminary results, however, suggest that wheat can be
grown successfully if planted in December (unpublished data). The
wheat requirement for cold-temperature is largely met during the month
of January. When closely spaced, rapidly developing wheat seedlings
suppress weed growth during the spring. Climatic conditions (low
moisture and cool temperatures) during the winter months are usually
1 Associate Professors, University of Florida, Institute of Food
and Agricultural Sciences, Agricultural Research Center, Fort Pierce,
unfavorable for development of serious pests or diseases. When wheat
is nearing maturity (end of April), dry weather conditions and
relatively high temperatures usually prevail, enhancing the ripening
and harvesting of the seed. Grain sorghum planted in May will mature
in about three and a half months. Warm temperatures and adequate
rainfall during the summer months are favorable for growth.
A third crop, cowpea [Vigna unguiculata (L.) Walp.], black bean
(Phaseolus vulgaris L.), or a forage legume such as Stylosanthes spp.,
can follow the sorghum grain harvest at the end of August. Cowpeas
and black beans mature in about 90 days and mature seeds can be
harvested in early December.
A minimum tillage system can be incorporated into this sequence
by planting sorghum directly into wheat stubble, after a light
application of paraquat to kill oncoming weeds. Another alternative
is to permit the grain sorghum to ratoon, using the second crop for
grain or forage. This second grain crop will then mature in December.
The purpose of this investigation was to evaluate such a wheat-
sorghum legume crop rotation system under south Florida
MATERIALS AND METHODS
A soft winter wheat (FP 77702), a local cultivar from Mas d'
Auge, France, was seeded on 7 December 1979 at the ARC Fort Pierce at
a rate of 100 kg/ha. Rows were spaced 25 cm apart. Plot size was 7.6
x 1.25 m with a total of five rows per plot. Prior to planting, 750
kg per ha of 8-12-20 (N, P205, K20) fertilizer was broadcast. On 22
January, 1980, ammonium nitrate was applied as a top dressing of 35 or
70 kg per ha nitrogen, referred to as W-1 and W-2 treatments,
respectively. Muriate of potash was top-dressed at a rate of 39 kg/ha
to all plots on 31 January. A randomized complete block design with
four replications was used. Wheat was harvested in late April, 20
weeks after planting. The three center rows, each 6 m in length, were
used for yield determination. After harvesting, the plots were
sprayed with paraquat to eliminate weeds remaining in the wheat
A sorghum hybrid, 'Savanna 5-9190', was seeded by hand in rows
between the wheat stubble on 15 March, 1980 at a rate of 100 kg/ha.
The sorghum received a fertilizer application of 500 kg/ha 0-10-20 (N,
P205, K20) and 80 kg per ha of nitrogen (ammonium nitrate) five weeks
after planting. Seven weeks after planting, an additional amount of
80 kg/ha of nitrogen in the form of ammonium nitrate was applied to
those plots which had received low N-treatments (W-l) in the preceding
wheat corp. This treatment is designated as S-2. The treatment not
receiving additional nitrogen will be referred to as S-1. Sorghum was
harvested 15 weeks after planting. After harvesting, paraquat was
sprayed on all plots. This treatment effectively controlled the weeds
with no subsequent injury to the sorghum. All the S-1 plots were
allowed to grow a second grain sorghum (ratoon) crop. Two of the S-1
plots were fertilized in September with approximately 80 kg N per ha
(ammonium nitrate) and 50 kg P205 and 100 kg K20 per ha from a 0-10-20
fertilizer. The remaining two S-1 plots received no fertilizer. One
half of each of these S-1 plots, not receiving any fertilizer, was
planted to Stvlosanthes hamata and Stylosanthes guianensis (Aubl.)
SW., respectively. The Stylosanthes planting and the sorghum ratoon
test were not replicated and data were only used for yield estimation
and establishment evaluation. The ratoon sorghum crop was harvested
at the end of December. All S-2 plots were sprayed again with
paraquat to kill all new sorghum growth. S-2 plots were then divided
into equal quarters. In mid September 1980, a cowpea 'Purple Hull
Crowder' and a blackbean 'Strain 39' cultivar were planted one to each
respective quarter of the S-2 plots. Both legumes were planted in a
two row arrangement. Rows were spaced 25 cm apart and were 3 m in
On 3 October, 1980, a second planting of both legumes was seeded
in the remaining two quarters of the S-2 plots, respectively. Both
plantings received a fertilizer application of 8-12-20 (N, P205, K20)
at a rate of 300 kg/ha.
RESULTS AND DISCUSSION
Total rainfall from the time of planting till flowering was 180
mm. Heading date of wheat was March 14 and first flowering occurred a
week later. Average plant height at maturity was 90 cm. Wheat was
harvested at the end of April 1980. Grain yields are presented in
Table 1. Highest yield obtained from one plot was 2730 kg/ha
(approximately 40 bu per acre). No significant differences occurred
among the N treatments. The low rainfall in spring probably reduced
the effect of the additional 80 kg per ha N application in January.
Sorghum, planted immediately following the wheat harvest,
developed normally during the first five weeks without any
fertilization, probably due to a residual effect of former fertilizer
applications. After five weeks a large plant growth response was
obtained with a 80 kg per ha of nitrogen. A second application of 80
kg per of N resulted in a significantly higher grain yield than that
treatment receiving the single side dress application. (Table 2).
Highest sorghum grain yield from one plot was 5508 kg per ha (81
bushels per acre) and resulted from two applications of 80 kg of N per
ha. Highest combined yields for first and second harvest (ratoon)
were determined for four plots ofly. One plot which had received 80
kg per ha of N after regrowth of sorghum had a total yield of 8790 kg
per ha (131 bu per acre). The fertilized regrowth yielded five times
more than the regrowth which was not fertilized. Precipitation for
the first and second growth period of the sorghum amounted to 460 and
378 mm, respectively.
Cowpeas planted on 16 September 1980 developed strong plants and
began flowering on 28 October, with no indication of .root rot.
However, root rot was present in the blackbeans and severely damaged
the entire plant population. Mature cowpea pods were ready for
harvesting in mid-December, but yield data were not obtained due to
extensive damage to plants and pods caused by, rodents. The second
planting of cowpea and black beans failed to develop into a good
mature stand. From' this is can be inferred that cowpea and black
beans should be planted before 15 September to obtained a successful
crop. Furthermore, when planting blackbeans it is imperative to
control root rot diseases by soil fumigation, soil drench or chemical
The Stylosanthes became well established in the plot. This
legume flowered profusively and produced an abundance of seed.
Further studies are needed to determine the forage potential of
Stylosanthes in a crop rotation system.
The results show that crop rotation and minimum tillage can be
successfully carried out in south-Florida. Full advantage should be
taken of year-round growing seasons and other crop sequences should be
studied in order to utilize the land to its fullest potential.
Table 1. Mean wheat yield in a wheat-sorghum rotation as influenced
by nitrogen levels.
Treatment N level+ Wheat Yield+
W-l 35 2250
W-2 70 2310
+ all plots received 60 kg/ha of nitrogen prior planting.
NS-Non significant F test 5% level.
Table.2. Mean sorghum yield in a wheat-sorghum-rotation as influenced
by nitrogen levels.
N -. levels Sorghum Yield harvest +
-------- kg/ha --------
0 3400 680
80 4840 3620
+ All plots received 80 kg/ha of nitrogen five weeks after planting.
* Mean yield of two plots only.
* Significant F test, 5Z level.
Prine, G. M., K. T. Boote, W. R. Ocumpaugh, and A. M. Rezende. 1978.
Forage and grain crops planted as a second crop during the warm
season in north and west Florida. Soil and Crop Sci. Soc. of
Fla. Proc. 37:109-114.
Barnett, R. D. and W. H. Chapman. 1975. Influence of planting date,
seeding rate and nitrogen fertilization on the grain yield of
soft red winter wheat. Soil and Crop Sci. Soc. of Fla. Proc.