I. D. Teare, D. L. Wright, and D. J. Zimet, North Florida Research and
Education Center, Quincy, FL 32351 (Dept. of Agronomy and Dept. of
Food and Resource Economics, Institute of Food and Agricultural
Sciences, University of Florida, Gainesville, Florida 32611). Research
Four years experience with Tropical Corn LIUrary
in a Doublecrop System *APR 20 1
I. D. Teare, D. L. Wright, and D. J. Zimet University of Fl
Doublecropping winter wheat [Triticum aestivum (L.)] and soybean
[Glycine max (L.) Merr.] is a popular production system in the southern
USA. Need exists for alternative crops to soybean for use in
doublecropping. For instance, a silage or feed-grain crop would be
beneficial to a livestock or dairy operation. Other benefits such as
improved weed, disease, and insect control could also accrue. While
soybean predominates, other crops such as grain sorghum [Sorghum bicolor
(L.) Moench.], sunflower [Helianthus annuus (L.)], and temperate corn
[Zea mays (L.)] have shown varying potentials in doublecropping (Sanford
et al., 1986).
Much of the temperate corn is planted around 15 March in the S.E.
Coastal Plain and is grown as dryland corn. The spring planted
temperate corn is often subject to low yield due to periods of drought
of 6 to 8 weeks during April, May, and early June. This dry period
corresponds to the developmental stages of rapid vegetative growth,
pollination, and ear fill of temperate corn with resultant low yields
unless irrigated, which results in a high energy input crop.
Winter wheat is normally harvested between 1 and 15 June in the S.E.
USA, but may be delayed by excessive rainfall. Doublecropped soybean is
usually planted about 12 June for optimum yields. Temperate corn
following winter wheat is not a suitable double crop in the S.E. Coastal
plain because of the occurance of damaging insects and disease (Sanford
et al., 1988), specifically fall armyworm [Spodoptera frugiperda (J. E.
Smith)] and southern corn rust [Puccinia polysora (Undrew)].
Tropical corn hybrids with satisfactory grain yields at moderate
fertility (120 lb N/A) have become available (DoCanto et. al., 1979;
Goldworthy et. al., 1974; and Taylor and Bailey, 1979). Yet, tropical
corn hybrids generally yield less grain than temperate adapted hybrids
(Yamaguchi, 1974; Muleba, et al., 1983) under high fertility, temperate
climate, and low insect and disease intensities, but they may be useful
as a late summer crop (June to October) in the S.E. United States.
The study was conducted to 1. determine yield potential of tropical
corn hybrids with moderate energy input doubledcropped after wheat, 2.
compare moderate energy input summer tropical corn with moderate energy
input summer temperate corn. 3. compare moderate energy input summer
tropical corn with high energy input spring temperate corn, 4. document
the rainfall and air temperature patterns of the June to October growing
seasons of moderate energy input tropical hybrids over years, and 5.
determine the economic yield comparisons of the above described crops.
MATERIALS AND METHODS
Following the harvest of Florida 302 wheat, tropical corn was
planted no-till into winter wheat stubble with a Brown-Hardin Ro-til
planter-' in 30-inch rows at a population density of 18,000 plants/A.
Tropical corn was grown in a moderate energy input system of 120 lb N/A
and no irrigation drylandd). Tropical corn planting dates were 13 June
1985, 16 June 1986, 24 June 1987, and 8 June 1988. The two tropical
hybrids used were DeKalb XL 560 and Pioneer X-304C in 1985; and Pioneer
X-304C in 1986, 1987, and 1988. In 1987, Asgrow 5509, a temperate
hybrid, was planted as a singlecrop on 26 March in a high energy input
system of high fertility (250 lb N/A), irrigation, and population
density of 30,000 plants/A. In 1988, Asgrow 5509 was planted at a popu-
lation density of 18,000 plants/A on 15 June in a moderate energy input
The research was conducted at the North Florida Research and
Education Center at Quincy, FL on a Norfolk sandy loam soil (fine-loamy,
siliceous, thermic, Typic Paleudult) under natural rainfall conditions
for tropical corn and irrigation for high energy input spring temperate
corn. Herbicides used in the experimental plots were a pre-emerge tank
mix of Aatrex (2-chloro-4-ethylamino-6-isopropylamino-s-tri-azine) @ 1
1/2 qt/A, Lasso [2-Chloro-2'-6'-diethylN-(methoxymethyl)-acetanilide] @
2 qt/A, Paraquat (1,1-Dimethyl-4,4'-bipyridinium ion as dimethyl
sulfate salt) @ 1 pt/A, and a non-ionic surfactant (X-77) at 1 pt/100
gal for weed control [primarily morning glory (Ipomoea spp.)]. Each
year, ammonium polyphosphate (10-34-0) was banded @ 20 lb N/A as a
starter fertilizer on one side of the row, and Furadan [2-(methoxy
carbamolamino)-benzimidazole] was banded at 8 lb/A behind the planter
wheel for lesser cornstalk borer [Elasmopalpus lignosellus (Zeller)]
--/Brown Co., Ozark, AL 32630.
In 1985, fall armyworm were sprayed with Lannate [S-Methyl-N-
((methylcarbamoyl)oxy)-thioacetimidate] on 8 July and 16 July @ 1 1/2
pt/A. In 1986, Lorsban 4E [O,0-Diethyl 0-(3,5,6-trichloro-2-pyridinyl)-
phosphorothioate] @t 3 pt/A was applied for fall armyworm control on 1
July. Nitrogen was sidedressed at 100 lb N/A on 1 July 1985 (when
tropical corn was 24 to 30 inches high), 100 lb N/A on 8 July 1986 (12
inches high), 105 lb N/A on 22 July 1987 (12 inches high), and 100 lb
N/A on 12 July 1988 (12 inches high). A post-directed spray of 2,4-D
(2,4-Dichlorophenoxyacetic acid) @ 1/2 pt/A + Paraquat @ 1 pt/A with a
surfactant (X-77) was applied near mid-July of each of the four years
for weed control. The temperate hybrid in 1987 had the same rate of 100
Ib N/A sidedressed on 20 April, and 2,4-D + Paraquat as a directed spray
1 week later.
Tropical corn was harvested on 3 October, 21 October, 27 October,
and 24 October in the respective four years 1985 through 1988. The
temperate, high-fertility, irrigated, spring-planted plots (Asgrow 5509)
were harvested on 27 August in 1987 and the moderate-fertility, no
irrigation, spring-planted plots were harvested 24 August 1987; while
the summer planted, moderate-fertility, no irrigation plots (Asgrow
5509) were harvested 24 October 1987 from 2 rows, 20 feet long. Grain
moisture was determined with an electronic meter and grain yields were
corrected to 15.5% moisture.
The temperate, high energy input corn (Asgrow 5509) was grown in
adjacent plots at Quincy in the State Performance Trials. The hybrid
was planted in a conventional seedbed with a Brown-Hardin Ro-til planter
on 26 March 1987 after a preplant incorporation of Sutan (S-Ethyl
diisobutylthiocarbamate) @ 4.75 pt/A and Aatrex @ 2 qt/A. The corn was
'fertilized with 250-100-200 Ib N-P-K/A and irrigated with 1 inch of
water eight times during the growing season.
Experimental design was a randomized complete block each year.
There were 3 replications in 1985, 4 replications in 1986, 6 replica-
tions in 1987, and 5 replications in 1988. The State Yield Performance
Trial was also a randomized complete block with 4 replications, and its
inclusion was for the purpose of economic analysis of an intensive
management system compared to a dryland single- and doublecrop system.
RESULTS AND DISCUSSION
In 1985, Pioneer X-304C outyielded DeKalb XL-560 by 37 bu/A or 237%
(64 bu/A vs 27 bu/A, respectively) (Figure 1). Because of its low grain
yield, Dekalb XL-560 was not grown in following years. Comparisons of
grain yields of Pioneer X-304C for all four years are shown in Figure 2
and days of planting, tasseling and harvest can be related to air
temperature and rainfall data in Figure 3. Note that the rainfall
period correlates with planting and tasseling followed by a dry period
at harvest. Rainfall during the summer growing season (planting date to
harvest date) of 1985, 1986, 1987, and 1988 years was 16 inches during
113 days, 25 inches during 127 days, 15 inches during 125 days, and 23
inches during 159 days, respectively. The warm temperatures of June and
July caused the tropical corn to grow much faster than expected so that
the sidedress application of 100 lb N/A at in 1985 at 24-30 inches high
(as recommended with spring-grown temperate corn) was late, reducing the
yield, and hence the change in N sidedress signal to 12 inch high
tropical corn for 1986, 1987, and 1988. The 1985 tropical corn yields
were further reduced by the lodging problem caused by two hurricanes.
In 1985, ninety-five percent of the corn lodged 20 to 300 from the
vertical but did not fall down. The leaning caused the roots to be
exposed during the grain fill period and presumably resulted in less
water and nutrient uptake during ear fill. The reduced yield (88 bu/A)
of Pioneer X-304C in 1988 (Figure 2) is probably related to the dry
period around tasseling (Figure 3).
PIONEER X-304C DEKALB XL-560
Figure 1. Comparison of yields from Pioneer X-304C and DeKalb XL-560 for
1985 (CV = 8.7%). Columns with the same letter are not significantly
different at the 5% level of probability using the Waller-Duncan K ratio
1986 1986 1987 1988
Figure 2. Corn grain yields for Pioneer X-304C in 1985, 1986, 1987, and
1988 (CV = 8.7 for 1985, 10.3 for 1986, 11.5 for 1987, and 10.6 for
1988). Columns with the same letter are not significantly different at
the 1% level of probability using the Waller-Duncan K ratio t test.
2 1 i
,J L 1 LI
-_LL i l_ ^
174 1U 192 201 210 2li 22 237 248 21S
DAY OF YEAR
DAY OF YEAR
Figure 3. Minimum ( 0 ) and maximum (+) air temperatures, and rainfall
during tropical corn growing seasons of 1985, 1986, 1987, and 1988.
Days of year reported in days Julian.
Figure 4 shows the comparative grain yields of Pioneer X-304C grown
in the summer under moderate energy inputs with temperate corn (Asgrow
5509) when grown during the summer (1988) or spring (1987) with moderate
inputs or grown in the spring (1987) with high energy inputs. Moderate
fertility and a dry period during April and May of 1987 with no
irrigation reduced temperate corn yields from 174 bu/A to 47 bu/A. The
summer-grown 1988 temperate corn resulted in 29 bu/A grain yield that
had a high incidence of corn earworm [Heliothis zea (Boddie)] and rice
weevil [Sitophilus oryzae (Linnaeus) damage. The summer-grown,
moderate energy input tropical corn averaged 87 bu/A over the four
years and had very little corn earworm or rice weevil damage.
0 so --
W 6Q 1987- ------ --
40 988 ---
PIONEER X-3040 ASGROW 5509 ASGROW 5509 ASGROW 5609
Figure 4. Comparison (left to right) of tropical corn (Pioneer X-304C)
grown with no irrigation and 120 lb N/A with temperate corn (Asgrow
5509) (a) grown in the summer of 1988 with no irrigation and 120 lb N/A,
(b) grown in the spring of 1987 with no irrigation and 120 lb N/A, (c)
grown in the spring of 1987 with irrigation and 250 lb N/A. CV's were
11.5, 39.2, 45.9, and 10.7, respectively, from left to right.
Yield, cost, price and net return for winter wheat, doublecropped
soybean, singlecropped and doublecropped dryland tropical corn, and
singlecropped temperate corn (irrigated and dryland) are displayed in
Table 1. Yields are from the experiments, cost estimates are based upon
the cultural practices used in the experiments and prices are pro-
jections of 1989 market prices. Dryland temperate corn is the only
singlecrop with a projected negative net return. All other crops have a
projected positive net return. The anticipated net return from an acre
of high energy input (irrigated) temperate corn (spring planted) are
about $35 greater than that of an acre of singlecropped, moderate energy
input tropical corn (summer planted).
Table 1. Yields, costs/A, costs/bu, projected 1989 prices, and net
returns for wheat, doublecropped soybean, single-and double-
cropped dryland tropical corn, and singlecropped temperate
corn irrigated and dryland.
Wheat Soybean Tropical Corn Temperate Corn/'
Double Doule Single- Irrg. Dryland
Variable cost/acre 82 90 120 140 240 125
Fixed cost/acre 30 30 30 40 110 30
Total cost/acre 112 120 150 180 350 155
Yield (bu/acre) 47 25 87 87 174 49
Total cost/bu 2.38 4.80 1.72 2.07 2.01 3.16
Price ($/bu) 4.20 7.50 2.70 2.70 2.70 2.70
Net return/bu 1.82 2.70 0.98 0.63 0.69 -0.46
Net return/acre 85.54 67.50 85.26 54.81 120.06 -22.54
t/Temperate corn singlecropped only.
Doublecropping reduces production costs of both soybean and tropical
corn. The cost savings in tropical corn is $0.35/bu or about $30/A.
Doublecropped tropical corn returns almost $18/A more than double-
cropped soybean. At assumed yields and costs the price of corn would
have to fall by $0.20 for the returns from the crops to be equal.
Conversly, at anticipated prices, doublecropped tropical corn yields
would have to decline by over 6.5 bu for net returns to be equal.
The advantage of tropical corn grown during the summer lies in the
fact that good yields can be obtained with moderate economic inputs by
taking advantage of the summer rains that are fairly dependable for much
of the S.E. Coastal Plain during the period from late June through early
September, which corresponds to the period of highest tropical corn
need, and a predictable early fall drought for maturity and harvest.
The dry fall permits few weeds to germinate and grow as they do when
temperate hybrids mature in late July and early August. Early in the
growing season, IPM practices must be adhered to for control of lesser
cornstalk borer and fall armyworm, but we have observed that tropical
corn husks are tighter than temperate hybrids making it less susceptible
to corn earworm (a particularly bad fall pest), immune to corn smut
[Ustilago maydis (CD) Cda.], and with little incidence of aflotoxin
(Aspergillus spp.). The exterior of the kernel is so hard the rice
weevils find it difficult to enter the kernel and therefore damage to
tropical corn was less than temperate corn when allowed to stand in the
field after maturity. Fertility inputs for corn production are also
lower in a doublecropping program because the tropical corn can utilize
residual fertility from the previous crop.
Our thanks to B. T. Kidd, Biological Scientist II and E. Brown,
Agricultural Technician IV; North Florida Research and Education Center,
University of Florida, Quincy, FL; for plot preparation and management,
data collection, computer processing, and data illustration.
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