Date of Corn Planting in Relation to Biological L:
D. L. Wright, I. D. Teare, R. L. Stanley, Jr.,.
B. T. Kidd, and N. R. Usherwood, ...
No-tillage planting of corn into legume cover crops has many of the ad-
vantages of grass cover crops such as protection of soil from wind and water
erosion but also provides biologically fixed N to nonlegumes in the cropping
system. The purpose of this study was to determine optimum corn (Zea mays L.)
planting date in relation to biologically fixed N from crimson clover (Trifol-
ium incarnatum L.). Field experiments were conducted in 1981 and 1982 on a
Norfolk sandy loam soil (Typic Paleudult). Corn was planted with a ripper
minimum till planter (Brown-Ro-Til) into crimson clover mulch at planting
dates from late February to mid-April.
Planting date affects resultant grain yields of corn. The highest grain
yields were obtained at the earliest planting date (mean of 10.4 Mg ha ) and
the lowest at the last planting date (mean of 3.9 Mg ha1 ) over both years.
However, legume dry matter yields varied from the highest (3.2 Mg ha ) in
1980 when corn plantings were started in April to the lowest (0.5 Mg ha-1) in
1981 when plantings were made earliest. In 1982, total tissue N uptake at
1/Research Report No. NF 88-2 from North Florida Research and Education
Center, Quincy, FL 32351, University of Florida. Agricultural Experiment
Station, Institute of Food and Agricultural Sciences.
/ Professor, Research Scholar/Scientist, Associate Professor of Agronomy,
University of Florida, Vice President, Potash and Phosphate Institute,
Atlanta, GA., and Biological Scientist II, University of Florida.
maturity in corn was 125, 150, and 175 kg ha1 for planting date 1, 2, and 3,
respectively, however, tissue concentration was similar (1.0%) and low in all
planting dates at harvest. Nitrogen produced by the legumes at the earliest
planting date was sufficient to produce highest grain yields each year though
plants were visibly N deficient soon after plants reached a height of 0.5 m.
Corn grain yields were highest at the earliest planting dates when legume dry
matter was lowest. This suggests that grain yield reduction was not due to a
shortage of N and that factors that result in higher corn yields from early
planting are more critical than the N supplied by the legumes.
Additional index words: Crimson clover (Trifolium incarnatum L.), Biological
N, No-tillage, Planting date.
Research from the Southeast USA has shown that corn can be produced suc-
cessfully without preparing a conventional seedbed (Touchton and Stevenson,
1984). Production practices proven under conventional seeding should also
result in best yields when planted under no-till conditions. Corn planted as
soon as soil temperatures allow germination in the spring, usually results in
highest yields and grain quality (Teare et al., 1987; Touchton et al., 1982).
As no-till becomes more accepted as a normal planting routine by growers,
questions arise about N production from legume cover crop. Several years ago,
legumes were used as green manure crops to improve soil tilthand to produce N
for subsequent crops. There is a renewed interest in legumes as a mulch cover
for no-till plantings of corn and grain sorghum to provide some N along with
benefits of the mulch cover. Touchton et al. (1982) found that crimson clover
(Trifolium incarnatum L.) produced enough N to produce as much grain sorghum
(Sorghum bicolor L. Moench) as 135 kg ha1 of commercial N. Grain sorghum
requires a soil temperature of 18-200C for germination, as compared to about
12-130C for corn, and successful plantings are often made near maturity of
crimson clover (mid-April). However, when legumes are used to supply N for
early planted corn, legumes are often in a young, vegetative stage of growth
and have not had sufficient time to produce maximum dry matter yields. Doll
and Link (1957) found that legumes produce more total N if allowed to grow to
maturity (maximum dry matter accumulation). When crimson clover is used for
mulch in no-till corn, maximum dry matter accumulation occurs about 40 to 55
days after the recommended period (April 10 April 20) for planting corn in
the Southeast USA (Wesley, 1979). Mitchell and Teel (1977) measured the
influence of various grass and legume cover crops on corn yields and found
that corn planted into a legume cover crop without commercial N yielded as
well as corn planted into a grass cover crop with 112 kg ha" of applied N.
There is little difference in establishment cost of grass or legume cover
crops and their value for holding soil against wind and water erosion is
similar. However, legumes do have the advantage of N fixation when properly
inoculated. Touchton (1980) noted that the value of N from legumes was ap-
proximately equal to the establishment cost ($20), but other benefits such as;
1) less soil and nutrient loss and 2) better soil tilth are accrued and are
difficult to assess in value. When grain sorghum is planted into a mature
stand of crimson clover, the clover may naturally reseed under favorable
environmental conditions to the extent that no replanting of the clover is
necessary for several years making it an excellent choice as a cover crop
(Duncan, 1980). However, when corn is planted into a mulch crop the legume is
in the vegetative stage and this does not permit seed production for natural
reseeding. Since recommended corn planting dates do not allow legumes to
accumulate maximum dry matter yields, these experiments were conducted to
relate the optimum planting date of corn to amount of nitrogen produced by the
symbiotic relationship between crimson clover and rhizobia fixation of nitro-
gen and dry matter accumulation.
Materials and Methods
Legumes were established in the fall of each year from 1979 through 1981
on a Norfolk sandy loam soil (Typic Paleudult) located at Quincy Agricultural
Research and Education Center in the Southeast Coastal Plain. The cropping
history of the experimental area was a wheat-soybeans double crop system for
each of the previous two years. Initial pH was 5.8 and fertility levels were:
P,20 = 190 kg ha-1, K 0 = 200 kg ha-1, CaO = 720 kg ha- and MgO = 310 kg ha-1
as measured by soil test (double acid extraction). In each of the 3 years
prior to planting crimson clover, the area was harrowed and fertilized. Fer-
tilizer was incorporated to 150 mm soil depth at the rate of 448 kg ha- of
3-9-18 in the fall prior to planting. Inoculated crimson clover seeds were
hand seeded at 22.4 kg ha~ after 15 October. Seed were cultipacked immedi-
ately after planting to obtain better soil-seed contact. An application of
12.4 mm of water was applied to the experimental area after planting to aid
germination and to promote early legume growth. Crimson clover was allowed to
grow until just prior to corn planting time when clippings were made for dry
Approximately 5 days before each corn planting date, 0.9 L ha- of para-
quat (1, 12 dimethyl 4, 4' bipyridinium ion) was sprayed on crimson clover
in 350 L of H20 containing 0.5% non-ionic surfactant (X-77) to eliminate com-
petition to the corn crop. Corn was overplanted by 15% in 760 mm wide rows to
attain a final population of 74 000 plants ha-. Atrazine (2 chloro-4-ethyl-
amino-6-isopropyl amino-l, 3, 5-triazine) and either metolachlor (2-methozy-l-
methylethyl acetamide) or alachlor(2-chloro-2-6-diethyl-N-(methoxy-methyl)
acetanilide) were used as the grass herbicide as an "over-the-top" broadcast
spray when the corn was 0.13 m tall. Corn hybrids used were Ring Around 1502
in 1980 and DeKalb XL71 in 1981 and 1982 which had shown high yield potential
in state yield trials. Both hybrids mature in 100 to 110 days. Corn seed was
planted with a no-till, subsoil unit planter and subsoiling was accomplished
to a depth of 300 mm. Carbofuran (2, 3-Dihydro-2, 2-dimethyl-7- benzofuramyl
methylcarbamate) was applied in a 150 mm band over the row for insect and
nematode control at the rate of 2.2 kg of a.i. ha-1. Corn planting dates were
11 April, 1 May, and 15 May in 1980; 25 February, 27 March, and 17 April in
1981; 5 March, 30 March, and 14 April in 1982.
Following planting, 112 kg ha- of P20,, 224 kg ha~ of K20, 7 kg ha~ of
Zn and 7 kg ha- of Mn were applied over the row. Tensiometers were installed
in rows between plants and maintained throughout the experimental area.
Irrigation water was applied when soil tensiometer readings reached .02 MPa.
Experimental design was a split plot with planting date as main plots and
years the sub plots. Each plot was 9.1 m long replicated 4 times consisting
of 8 rows 760 mm apart. Harvests were made from 4.6 m of the middle two rows
to minimize the border effects. The standard error of the treatment means
were calculated and illustrated in Fig. 2.
Harvested corn yields were corrected to 15.5% moisture. Whole plant
samples were taken to determine N uptake and concentration at four plant
growth stages (0.5 m ht., 1.2 m ht., tasselling and maturity) by kjeldahl
Results and Discussion
The effects of corn planting dates on corn grain yields are shown in Fig.
1. Highest corn grain yields were consistently made at the earliest planting
date. Highest grain yield for Ring Around 1502 (1980) was 9.6 Mg ha1 at the
earliest planting date. This planting date corresponded to the last planting
date in the two succeeding years with DeKalb XL71. This is attributed to the
excellent growing conditions encountered for the legumes in March of 1980 when
258 mm of rainfall fell as compared to 170 mm and 111 mm in 1981 and 1982,
respectively and resulted in more legume dry matter production (Fig. 2).
Crimson clover accumulated about 2.5 Mg ha~ dry matter by mid-April of (1981,
1982, 1983) which corresponds with its maturity date. In 1980, crimson clover
accumulated 3.5 Mg ha1 DM by mid April. Crimson clover did not accumulate
any additional dry matter after mid-April and was in a state of decomposition
at the late April and mid-May planting dates. However, corn grain yields
decreased at each successive date, therefore, it was decided to "dare the
frost" for studies in 1981 and 1982, with the third planting at maturity of
crimson clover. Grain yields from corn planted early into crimson clover in
1981 and 1982 were about 10.5 Mg ha-. Each of the following planting dates
resulted in a sharp drop in grain yield to less than 6 Mg ha- for the April
plantings. We interpretated this data for the three years to be an indica-
tion that early planting of corn is highly desirable regardless of the legume
dry matter accumulation.
Nitrogen Uptake in Corn Tissue
Nitrogen uptake in corn at four growth stages is a quantitative measure of
nitrogen availability in relation to crimson clover dry matter accumulation
and N fixation. Total N uptake by corn at 0.5 m height in 1982 was about 25
kg ha"1. By maturity, the earliest planted corn had a total N uptake of about
125 kg ha1 which compared to 150 and 175 kg ha1 of N for the second and
third planting dates at maturity, respectively. The difference in total N
uptake was attributed to the amounts of dry matter produced in early March as
compared to mid April. Using 20% crude protein as an average value for the
March through May period for crimson clover (L. S. Dunavin, personal communi-
cation) and 0.6 Mg ha-1 dry matter for early March and 2.5 Mg ha1 dry matter
for mid-April, 19.2 and 80.0 kg ha1 of N were produced in the legume biomass
by the 5 March and 14 April planting of corn, respectively. Since higher
amounts of N were available for corn growth at the later planting dates, more
N was taken up as noted in Figure 3. Residual soil N and N fixed in rhizobia
were not measured in the total N uptake of corn since uptake was much higher
than the total amount extracted in the top growth of the legumes. According
to Jones (1967), tissue N concentration was below the critical level (2.25%
indicating nitrogen deficiency) for corn planted at any date for most of the
season. Visual observations of N deficiency (yellow leaf tips and light green
plants) were noted throughout the growing season and substantiated tissue
tests that corn N deficiency started at 0.45 m plant height and became
progressively more severe as corn matured. Olson and Kurtz (1982) found that
N concentration for whole plant samples was less than for the ear leaf sample
and that the critical N concentration for whole plants was 1.9%. Using this N
concentration as a guide to determine when corn became deficient, data shown
in Figure 3 suggests that the period between 0.5 and 1.2 m would be important
for additional sidedress N applications. Nitrogen concentration in corn
tissue decreased rapidly from 0.5 m plant height to maturity in each planting
date even though more N was available from increased legume dry matter yields
at the April planting date. Tissue N concentration was similar and low (about
1%) for all planting dates as corn matured. In spite of the low N concentra-
tion found in corn tissue at maturity, no visual ear malformation was noted
for any planting into the legumes.
Where legumes are allowed to grow to maturity, significant amounts of N
can be fixed to meet the N requirements for a grass crop in the cropping
system (Dunavin, 1982). When legumes are used as a cover crop for N fixation
in corn production, earliness of corn planting is more critical to optimum
grain yields than the value of added N fixed when legumes were allowed to
Other significant benefits derived from using legumes as cover crops in-
clude erosion control, less leaching of nutrients, and decreased water evapor-
ation after stands are chemically killed (Ebelher et al. 1984). The N pro-
duced by the legume during the vegetative stage of growth is rapidly released
upon chemically killing (Hargrove and Wilson, 1984) and is available for corn
growth within a couple of weeks after planting. Nitrogen requirements for
corn are generally higher after corn reaches heights of 0.5 m or more.
Therefore, where legumes are used to supply part of the N requirement, supple-
mental N applications should begin when corn reaches a height of 0.5 m or soon
thereafter. In using legume cover crops, the highest priority should be
placed on planting corn at its optimum planting date, rather than striving for
optimum dry matter production of the legumes.
Doll, E. C., and L. A. Link. 1957. Influence of various legumes on the
yields of succeeding corn and wheat and nitrogen content of the soil.
Agron. J. 49:307-309.
Dunavin, L. S. 1982. Vetch and clover overseeded on a bahiagrass sod.
Agron. J. 74:793-796.
Duncan, R. R. 1980. General sorghum production practices. p. 1-3. In R. R.
Duncan (ed.). Proc. Sorghum Short Course. Univ. of Georgia Spec. Pub.
Ebelhar, S. A., W. W. Frye, and R. L. Blevins. 1984. Nitrogen from legume
cover crops for no-tillage corn. Agron. J. 76:51-55.
Hargrove, W. R., and D. O. Wilson. 1984. Winter legumes as a nitrogen source
for no-till grain sorghum. Agron. Abst. p. 74.
Jones, J. B., Jr. 1967. Interpretation of plant analysis for several
agronomic crops. p. 49-58. In soil testing and plant analysis. Special
Pub. Ser. No. 2. Soil Science Soc. Am., Madison, Wis.
Mitchell, W. H., and M. R. Teel. 1977. Winter-annual cover crop for no-till
corn production. Agron. J. 69:569-573.
NRC. 1984. Nutrient requirements of beef cattle (6th Ed.). National Academy
Press. Washington, D.C. p. 50.
Olson, R. A., and L. T. Kurtz. 1982. Crop nitrogen requirements, utiliza-
tion, and fertilization, p. 567-604. In F. J. Sevenson (ed.). Nitrogen
in agricultural soils. Agronomy Monograph Pub. No. 22. Madison, Wis.
Touchton, J. T. 1980. Soil fertility management for grain sorghum pro-
duction. p. 4-12. In R. R. Duncan (ed.). Proc. Sorghum Short Course.
Univ. of Georgia Spec. Pub. No. 6.
Touchton, J. T., W. A. Gardner, W. L. Hargrove, and R. R. Duncan. 1982.
Reseeding crimson clover as a N source for no-tillage grain sorghum
production. Agron. J. 74:283-287.
Touchton, J. T. and R. E. Stevenson. 1984. Proceedings of 7th Ann.
No-tillage Sys. Conf., Auburn, Ala.
Wesley, W. K. 1979. Irrigated corn production and moisture management.
Univ. of Georgia. College of Agric. Bull. No. 820.
Wright, D. L., I. D. Teare, and B. T. Kidd. 1987. Phenological events of
corn in relation to time of planting. IFAS, Agric. Exp. Stn. Research
Report No. NF 87-3:1-12.
.- "^'^- 1982
0 ;-:- --:
E Pd 1 Pd 2 Pd 3
Figure 1. Corn grain yield in relation to planting date using
crimson clover as a biological source of N in 1980, 1981, and
'-"------1981 20 ="
Pd Pd2 Pd 3
Figure 2. Crimson clover phytomass and total clover N in relation
to planting date prior to planting no-till corn for 1981 and
1982. Total N in crimson clover was ob-
tained by multiplying phytomass by20
Pd 1 Pd 2 Pd 3
Figure 2. Crimson clover phytomass and total clover N in relation
to planting date prior to planting no-till corn for 1981 and
1982. Total N in crimson clover prior to planting was ob-
tained by multiplying phytomass by 3 18.-4% CP)
--_- 1.2 m
Pd 1 Pd 2 Pd 3
Figure 3. Nitrogen content of whole corn plant at four growth stages
(5 March, 30 March, and 14 April) in 1982. Tissue N concentration
considered critical when below 2.25%.