Chapter 3
Nitrogen and Sulfur
G. Kidder
Nitrogen and sulfur are usually absent from peanut fertilization
recommendations in the United States. A brief discussion of the
reasons is included here for the sake of completeness.
Nitrogen
Inoculation with Rhizobium Bacteria
Peanut is a legume which benefits from symbiotic nitrogen
fixation in association with Rhizobium bacteria. The success
of rhizobial inoculation in improving N-fixation of other legume
crops has led to experiments with inoculation of peanuts. Increasing
the amount of effective inoculum, especially in soil where peanuts
have not been planted for some time, is a potential means of
improving the N-fixing capacity of the peanut crop and thus enhancing
crop yield.
Cobb and Whitty (1973) reported increased average yield from
2,700 to 3,400 pounds of nuts per acre where five lb acre-1
of granular inoculant were applied in the planter furrow. The
presence of areas of darker green plants in the un-inoculated
portion of the field indicated that inoculation by native Rhizobium
can easily influence average yields. When they repeated the experiment
on fields that had produced peanuts in the preceding three years,
they found no response to inoculation. Hickey et al. (1974) increased
yield of pods from 1,700 to 3,300 lb acre-1 by inoculation
of Florunner peanuts grown on Lakeland fine sand. The field,
planted to peanuts in 1972, had been cleared of scrub oak in
1970 and planted to watermelons in 1971. In a study conducted
on 13 different fields that had not grown peanuts for at least
15 years, Hiltbold et al. (1983) found no yield response to inoculation
or to fertilizer N. They concluded that even on land where peanuts
had not been grown for many years, modulation and nitrogen fixation
by indigenous rhizobia were sufficient for maximum yield under
field conditions of southeastern Alabama.
While recent reports of increased yields from inoculation are
found in world literature (Raverkar and Konde 1988), inconsistent
results continue to cloud the issue in the United States (Scholar
and Turpin 1988). The random occurrence and widespread distribution
of native legumes of the cowpea cross inoculation group undoubtedly
contribute to the inconsistencies experienced in field trials.
Since seed inoculation is relatively inexpensive and presents
no environmental risk, the Georgia and Florida Cooperative Extension
Services recommend inoculation on land which has not grown peanuts
for over five years (Plank 1985, Whitty 1991). Where indicated,
granular inoculants placed in the seed furrow by a granule applicator
are recommended (Whitty 1991). Other states view inoculation
as an unwarranted operation and expense and do not recommend
the practice.
Application of Nitrogen Fertilizers
Nitrogen fertilization of peanuts in the southeastern United
States has been studied over the years. Older experiments (Killinger
et al. 1947, Scarsbrook and Cope 1956), where peanut yields were
relatively low by current standards (maximum yields <2,600
lb acre-1), serve mostly to show how other production-limiting
fictors have been steadily identified and corrected.
After reviewing the literature on nitrogen fertilization of peanuts,
Reid and Cox (1973) concluded that most American research found
no increase in peanut yields from N fertilization. The less consistent
responses reported from Africa, Asia, and Europe (13 references
cited as positive and eight cited as no response to N fertilization)
could not be readily explained. Lack of sufficient effective
Rhizobium bacteria, differences in soils used for peanut
production, and climatic differences were offered as possible
factors. Furthermore, the common use of ammonium sulfate as the
N source in those parts of the world suggested the possibility
of responses to S rather than N. In an updated review, Cox et
al. (1982) acknowledged that “there seem to be a number
of conditions conducive to obtaining a response from fertilizer
N,” but no strong conclusions were drawn.
Research done in the Coastal Plain in the past two decades has
generally supported the conclusion of Reid and Cox (1973). Walker
et al. (1974) found no response of runner peanuts to N applications
(up to 120 lb N acre-1). Spanish-type peanut yield
increased when fertilized with 20 lb N acre-1, but
did not increase further at higher N rates. They concluded that
N should be left out of Georgia peanut fertilization recommendations.
Ball et al. (1983) found no economic response to application
of 30 lb N acre-1 as ammonium nitrate on Spanish or
Virginia market-type peanuts in North Carolina. Hartzog et al.
(1983) reported no yield response to 100 lb N acre-1
in a three-year study of 13 fields in southern Alabama. Pataky
and Hollowell (1984) reported a reduction in peanut yields when
very high rates of N (up to 416 lb acre-1) were soil
applied in an attempt to control Cylindrocladium black
rot in North Carolina fields.
Pancholoy et al. (1982) reported no yield response from up to
7.5 lb N acre-1 applied as a foliar spray of urea
or to the soil. Walker et al. (1984) found that foliar application
of urea did increase yield of Florunner, Tifrun, and all nonnodulating
varieties on a Lakeland sand. Response of Florunner was curvilinear,
with maximum yield (ca 4,100 lb acre-1) calculated
at 28 lb N acre-1. Response of Tifrun was linear,
with maximum yield (3,800 lb acre-1) at the 45 lb
N acre-1 application rate. Foliar N had no effect
on Early Bunch yield.
Recently, Davis-Carter et al. (1992) reported a 21% yield increase
in Southern runner peanuts from a granular urea application (25
to 100 lb N acre-1). However, no yield differences
were found from the same treatments the following year (Davis-Carter
and Shannon 1993).
Recommendation Summary
The land-grant universities of the southeastern United States
do not recommend application of fertilizer N on peanuts, (Clemson
University 1982, Cope et al. 1981, Donohue and Hawkins 1979,
Hanlon et al. 1990, Plank 1989, Tucker and Rhodes 1987)
with one exception. Auburn recommends 20 lb N acre-1
for Spanish peanuts (Cope et al. 1981). Inoculation is recommended
in Florida (Whitty 1991) and Georgia (Plank 1989) if peanuts
have not been grown on the land for the preceding five years.
Sulfur
Stanford and Jordan (1966) noted that the application of gypsum
and dusting peanuts with S would mean that few responses to fertilizer
S would be expected. Anderson and Futral (1966) added elemental
S to soil in an attempt to separate the effect of S from the
response to gypsum. The yield decreases experienced in the S
treatments were attributed to pH decreases from 5.9 to 5.7 and
5.1 for 60 and 300 lb S acre-1, respectively.
In their treatment of S as a nutrient in peanut production, Reid
and Cox (1973) noted that S is deficient in most soils of the
world where peanut is produced. They state that S per se has
received less attention than most nutrient elements and that
it is probable that many responses attributed to other factors
were in fact responses to incidental S fertilization.
Use of ordinary superphosphate as a phosphorus source (10 to
12% S), gypsum (CaSO4) as a calcium source (18 to
23% S), and dusting with elemental S for leafspot control (as
much as 120 lb S acre-1 yr-1) are all practices
which were often studied without evaluation of the possible effect
of S as a nutrient. Use of sulfate forms of micronutrients or
potassium magnesium sulfate as a K source adds to the difficulty
of determining when the peanut crop is responding to S fertilization.
The value of 20 lb S acre-1 removed in a two-ton crop
(Potash Institute 1972) is an estimate still in use (Kamprath
and U.C. Jones 1986).
Cox et al. (1982) note that there were few reports regarding
S fertilization in the Americas. Studies of S fertilization of
peanut seem to be reported mostly from Asia and Africa (c.f.,
Bahl et al. 1986, Hago and Salama 1987), usually on soils very
different (e.g., high pH clays) from those used for peanut production
in the United States. In the United States, the nutritional effects
of S addition have been mostly implied from studies where S nutrition
was incidental to the main objectives of the research. For example,
Walker et al. (1975) reported that multiple applications of S
to foliage increased yield of Florunner that was not related
to leafspot control; yield of Tifspan did not increase.
The most compelling evidence that S nutrition is not limiting
peanut yields in the U.S. Coastal Plain is found in the Alabama
research of Hartzog and Adams. In their extensive comparisons
of lime and gypsum as Ca sources over many years and soils, gypsum
generally showed no yield advantage over lime (Hartzog and Adams
1973, 1975; Adams and Hartzog 1980). If S deficiency were a major
problem, the gypsum should have produced higher yields since
it supplies both Ca and S.
Recommendation Summary
None of the land-grant universities of the southeastern United
States recommend application of fertilizer S for peanuts (Clemson
University 1982, Cope et al. 1981, Donohue and Hawkins 1979,
Hanlon et al. 1990, Plank 1989, Tucker and Rhodes 1987). However,
several trends in peanut production practices could reduce the
amount of sulfur which is applied to the peanut crop for reasons
other than fertilization. Decreased use of foliar-applied S for
leafspot control, the substitution of lime for gypsum as a Ca
source, and the elimination of unnecessary fertilization will
reduce the S applied to peanuts. These changes could lead to
S deficiencies in the future, and the situation bears watching.
Conclusions
Nitrogen and S fertilization of peanuts has generally not
resulted in increased yields in the U.S. Coastal Plain. Under
current cultural practices, neither nutrient is recommended for
application as fertilizer in the southeastern U.S. peanut-producing
region. Changes in cultural practices which have coincidentally
supplied S to peanuts could result in deficiencies of S in the
future.
Document Prepared by:
Leigh H. Stribling, lstribli@acesag.auburn.edu
Alabama Agricultural Experiment Station
Auburn University |
