Nitrogen Management Experiments
For Upland and Pima Cotton, 1997
J. C. Silvertooth, Plant Sciences Department
E.R. Norton, Plant Sciences Department
Two field experiments were conducted in Arizona in 1997 at two locations
(Maricopa and Marana). The Maricopa experiment has been conducted for eight
consecutive seasons, the Marana site was initiated in 1994. The purposes of
the experiments were to validate and refine nitrogen (N) fertilization
recommendations for both Upland and Pima cotton. The experiments each
utilized N management tools such as pre-season soil tests for NO3--N, in-season
plant tissue testing (petioles) for N fertility status, and crop monitoring to
ascertain crop fruiting patterns and crop N needs. At each location, treatments
varied from a conservative to a more aggressive approach of N management.
Results at each location revealed a strong relationship between the crop fruit retention
levels and N needs for the crop. This pattern was further reflected in final
yield analysis as a response to the N fertilization regimes used. The higher,
more aggressive, N application regimes did not benefit yields at any location.
The management of fertilizer nitrogen (N) is a very important component of any
cotton (Gossypium spp.) production program in Arizona. Water, and N are normally
the most limiting inputs to successful cotton production in most desert soils.
It is important for farmers to use fertilizer N efficiently to maintain optimum
return in yield for the amount of fertilizer N provided. Also, from an
environmental standpoint, it is important to manage fertilizer N so that downward
movement of NO 3--N in the soil profile, can be minimized.
For cotton production systems in the desert Southwest, there are several N
management tools available to manage fertilizer N inputs efficiently in terms of
economic, agronomic, and environmental concerns. Nitrogen management tools
include: residual soil NO3--N levels from preseason soil samples, inputs of
NO3--N through irrigation water, petiole samples taken in-season for NO3--N
analysis, fruit load and growth pattern measurements of the crop in terms of N
needs, and the use of split applications of fertilizer N through the course of
the season (Silvertooth and Doerge, 1990).
Recommendations from University of Arizona Cooperative Extension personnel
concerning N management in cotton usually include these aforementioned tools.
Fertilizer N applications based purely on conjecture or guesswork are
discouraged. The two field experiments conducted in 1997 serve as an extension
of consecutive experiments from 1989 through 1996 (Silvertooth et al., 1990;
Silvertooth et al., 1991b, Silvertooth et al., 1992, Silvertooth et al., 1993,
Silvertooth et al., 1994, Silvertooth et al., 1995, Silvertooth and Norton,
1996 and Silvertooth and Norton, 1997) to develop and refine guidelines for
recommendations concerning the integration of N management tools to improve
overall efficiency for the grower. Objectives for these experiments are: 1) to
compare several fertilizer N management strategies for cotton in terms of N
fertility status of the crop, and yield; and 2) develop refinements in the
fertilizer N recommendations associated with in-season N fertility assessments
using cotton petiole analysis and fruit load development.
Materials and Methods
Field experiments were conducted in 1997 at the University of Arizona Maricopa
Agricultural Center (MAC) and the Marana Agricultural Center (MAR).
Both Upland (G. hirsutum L., var. DP 33b) and American Pima (G. barbadense L.,
var. Pima S-7) were planted on a Casa Grande sandy loam on 13 March at Maricopa.
The experimental structure was a split plot within a randomized complete block design with
three replications. Whole plots were cotton varieties (DP 33b and Pima S-7),
with subplots being N treatments (Table 1).
Subplots were eight, 40 inch rows wide and extended the full length of the
irrigation run (600 ft.). At Marana, only Upland cotton, STV 474, was planted
on 15 April in plots which were eight, 40 inch rows wide and 600 ft. in length,
with N treatments (Table 1) arranged in a
randomized complete block design with four replications. All pest control and
irrigation management practices were carried out on optimum, an as-needed basis
at each location.
Surface soil samples were collected preseason at each location, to which
routine soil analyses were performed.
Basic plant measurements were carried out within each plot on a regular 14
day interval for the entire season. These measurements included plant heights,
number of mainstem nodes per plant, flower numbers per 167 ft.2 area, and the
number of nodes above the top white flower to the terminal (NAWF). Petioles
were also sampled on a routine basis throughout the season and analyzed for
NO3--N. Plant mapping was performed on each distinct treatment (variety and N
treatment) at 14 day intervals during the course of the season. Results from the
plant mapping provide information concerning the percent total fruit retention
(sum of positions one and two on each fruiting branch) for each treatment, a
record of the general vegetative/reproductive balance maintained by the various
treatments over time, and maturity progress.
The N fertilization regimes utilized at each location are outlined in
Tables 2 and 3
for Maricopa and Marana. Final irrigations and harvest dates were 18 August
and 23 October, at Maricopa and 19 August and 9 October at Marana.
Lint yields were obtained for each treatment by harvesting the entire center
four rows of each plot with a two row mechanical picker. Seedcotton subsamples
were collected for ginning, from which lint turnout estimates were made.
Results were analyzed statistically in accordance to procedures outlined by Steel
and Torrie (1980) and the SAS Institute (SAS, 1988).
Fruit retention (FR) and height to node ratio (HNR), and petiole analysis
results are presented for all locations, varieties, and treatments in
Figures 1, 2,
and 3. Lint yield results are presented in Table
Fruit retention levels, plant vigor estimates (height to node ratios, HNR)
developed from the plant mapping data, and petiole NO3-N concentrations are
shown in Fig. 1 and 2 for the DP (NuCOTN) 33b and Pima S-7. Low plant vigor
resulted in low HNRs for most of the season for both the Upland (DP 33b) and
Pima (S-7) varieties. Fruit retention patterns were generally strong for both
varieties all season. With the development of a substantial boll load, which
is indicative of a strong N sink and a high N demand, N fertilizer applications
were carried out for treatments 3 and 4 on 14 May, 9 June, and 20 June.
Very slight visual symptoms of N deficiency became apparent in check plots
for both DP 33b and Pima S-7 in late June (early bloom 1200 to 1500 HUAP).
The DP 33b plots for treatment 3 progressed towards cut-out near 5 August
(approx. 2700 HUAP), which is consistent with a medium season Upland variety
supporting a strong boll load, as this crop was. The final irrigation was
applied on 18 August in an effort to provide adequate soil moisture to
accomplish full development of bolls set by cut-out. Defoliants were applied
on 2 October to all plots.
Plots were mechanically harvested on 23 October. Yield data for both the DP
33b, and Pima S-7 are shown in Table 4.
Significant differences were not detected among the N treatments for either
variety, even with the check (treatment 1). The results from previous seasons
(Silvertooth et al., 1991; Silvertooth et al., 1992; Silvertooth et al., 1993
and Silvertooth et al., 1994), have generally shown a N response, but no yield
benefit in terms of 2X feedback treatment (4), which received a total of
270 lbs. N/acre applied over three applications, or from treatment no. 2, which
received a total of 225 lbs. N/acre, split over four applications. Yields were
optimized (arithmetically) with treatment no. 3 for the Pima S-7 and treatment
no. 4 with 33b. Therefore, one might speculate that some benefit was possibly
gained with the DP 33b by providing slightly higher fertilizer N rates, probably
with the later applications when the plant was carrying a high FR level and was
experiencing low vigor.
The STV 474 at Marana developed a moderate fruit load early
(Figure 3), experienced a small drop in FR near first bloom (~1200 HUAP),
but experienced marked improvement in early to peak bloom (approx. 1,500 to 2,000
HUAP). Plant vigor (HNR) patterns were low early in the season but increased
to moderate levels near the optimum baseline mid-season. In general, based upon
FR and HNR measurements, the crop vegetative/reproductive balance was favorable
for most of the fruiting cycle.
Rates of N fertilization ranged from 0 to 200 lbs. N/acre
(Table 3). In earlier studies, rates up to
350 lbs. N/acre were used. Based upon results from earlier studies at Marana
(Silvertooth and Norton, 1997) a more conservative approach to N fertilization
was employed in 1997. With the strong fruit load, all plots progressed into
cut-out by about 10 August. The final irrigation was applied on 19 August, which
was supplemented by rainfall in late August to accommodate complete development
of bolls set through cut-out. Plots were harvested on 9 October. Lint yield
results (Table 4) revealed no significant
differences among the N fertilization treatments. However, it is interesting to
note that the highest rates of N fertilization with treatments no. 4 and 2 (200
and 150 lbs. N/acre, respectively) provided the highest yields (arithmetically).
The support provided by the staff at the University of Arizona Maricopa and
Marana Agricultural Centers is greatly appreciated. Also support provided by the
research assistants of the University of Arizona cotton agronomy research program
is greatly appreciated.
(do references using order list tagging>
SAS Institute. 1988. SAS/STAT:Procedures. Release 6.03 ed. SAS Inst., Cary, NC.
- Silvertooth, J. C., P. W. Brown, and J.E. Malcuit. 1991a. Basic crop development patterns. Cotton, A College of Agriculture Report. University of Arizona. Series P-87:43-49.
- Silvertooth, J. C., L. J. Clark, E. W. Carpenter, J. E. Malcuit, P. T. Else, and T. A. Doerge. 1990. Nitrogen management in irrigated cotton. Cotton, A College of Agriculture Report. University of Arizona. Series P-81:169-174.
- Silvertooth, J. C., L. J. Clark, J. E. Malcuit, and E. W. Carpenter. 1993. Nitrogen management experiments for Upland and Pima cotton, 1992. Cotton, A College of Agriculture Report. University of Arizona. Series P-94:297-311.
- Silvertooth, J. C., L. J. Clark, J. E. Malcuit, E. W. Carpenter, T. A. Doerge, and J. E. Watson. 1991b. Nitrogen management experiments for Upland and Pima cotton, 1990. Cotton, A College of Agriculture Report. University of Arizona. Series P-87:209-221.
- Silvertooth, J. C., L. J. Clark, J. E. Malcuit, E. W. Carpenter, T. A. Doerge, and J. E. Watson. 1992. Nitrogen management experiments for Upland and Pima cotton, 1991. Cotton, A College of Agriculture Report. University of Arizona. Series P-91:183-198.
- Silvertooth, J. C. and T. A. Doerge. 1990 Nitrogen management in Arizona cotton production. Report 9024. The University of Arizona, College of Agriculture. Tucson, AZ.
- Silvertooth, J. C., E.R. Norton, B.L. Unruh, L. J. Clark, and E. W. Carpenter. 1994. Nitrogen management experiments for Upland and Pima cotton, 1993. Cotton, A College of Agriculture Report. University of Arizona. Series P-96:378-397.
- Silvertooth, J. C., E.R. Norton, B.L. Unruh, J.A. Navarro, L. J. Clark, and E. W. Carpenter. 1995. Nitrogen management experiments for Upland and Pima cotton, 1994. Cotton, A College of Agriculture Report. University of Arizona. Series P-99:311-326.
- Silvertooth, J.C. and E.R. Norton. 1996. Nitrogen management experiments for Upland and Pima cotton, 1995. Cotton, A College of Agriculture Report. University of Arizona. Series P-103:317-332.
- Silvertooth, J.C. and E.R. Norton. 1997. Nitrogen management experiments for Upland and Pima cotton, 1996. Cotton, A College of Agriculture Report. University of Arizona. Series P-108:389-401.
Steel, R.G.D., and J.H. Torrie. 1980. Principles and procedures of statistics. McGraw-Hill, New York.
This is a part of publication AZ1006:
"Cotton: A College of Agriculture Report," 1998, College of Agriculture,
The University of Arizona, Tucson, Arizona,
85721. Any products, services, or organizations that are mentioned, shown, or indirectly
implied in this publication do not imply endorsement by The University of Arizona.
The University is an Equal Opportunity/Affirmative Action Employer.
This document located at http://ag.arizona.edu/pubs/crops/az1006/az10068a.html
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