Using Chlorophyll Meters to Monitor Crop N Status

A Southeast Missouri 319 Demonstration Project

Introduction

During the past decade, scientists have been testing and calibrating the meter for specific crops and regions. However, the meter has largely remained a research tool and has not been widely used on Southeast Missouri row crop farms, possibly from a lack of exposure, the lack of recommendations, and the expense of the meter. Our objective was to establish demonstration sites and evaluate the meter on large-scale fields.

Methods

Site 1: Sam Babb Farm in Mississippi County near Bertrand, MO. This site was planted with Pioneer 3335 and Bt33B13 field corn on March 26, 1999. A set of reference areas, where known quantities of N, was established by applying ammoium nitrate fertilizer at preplant, 5 leaf, and 12 leaf growth stages (Table 1). Beginning at 5 leaf growth stage, chlorophyll meter readings were collected in both the reference areas and the whole field every 7-10 days until early dent growth stage. The newest most expanded leaf with a collar was sampled approximately half the distance from the stalk. This site was irrigated by a center pivot. The reference areas were harvested on August 26, 1999 with a small combine.

Table 1. Reference area factors for the corn demonstration areas.

Preplant N             Sidedress N           Sidedress N
                        at 5 leaf             at 12 leaf
 lbs N/a                 lbs N/a               lbs N/a
 -------                 -------               -------
     0                      0                     0
    50                     50                    25
   100
   150
   200
   250

Site 2: Wheeler Brothers Farms in Stoddard County, near Morehouse, MO. This site was planted with Drew rice seeds on April 28, 1999. The reference areas in this demonstration included varying the both the preflood N and midseason N quantities with urea fertilizer (Table 2). Both chlorophyll meter and plant area board readings were collected about every 10 days from early tillering to 1/2 inch internode elongation at midseason. The newest fully expanded leaf was sampled. Preflood N applications occurred just prior to the establishment of permanent flood and midseason applications were broadcast into floodwater. Reference areas were harvested on September 16, 1999 with a small combine.

Table 2. Reference area factors for the rice demonstration site.

   Preflood N          Midseason N
   ----------          -----------
        0 (lbs N/a)        0 (lbs N/a)
       48                 60
       95                 30x2
      143

Site 3: Zack Tanner Farm in Stoddard County, near Glennonville, MO. This site was planted in popcorn. The reference areas, where known quantities of N, were established by applying ammonium nitrate fertilizer at preplant, 5 leaf, and 12 leaf growth stages. Chlorophyll meter readings were collected every 7-10 days until early dent growth. The newest most expanded leaf with a collar was sampled approximately half the distance from the stalk. This site was furrow irrigated and the reference areas were harvested on August 24, 1999 with a small combine.

Results and Discussion

Table 3. Effect of sidedress N application on field corn yield at specific chlorophyll meter readings.

Chlorophyll reading (SPAD)	Yield w/o 50 lbs N/a Sidedress	Yield with 50 lbs N/a Sidedress	Difference (bu/a)
35.4	137	163	+26
39.9	165	193	+28
41.8	174	188	+14
42.6	158	172	+14
44.2	192	197	+5

Table 4. Chlorophyll Meter Readings at the 11 Leaf growth stage as influenced by preplant N application.

Preplant N         Chlorophyll Reading
  (lbs/a)                (SPAD)
----------         -------------------
     0                    41.8
    50                    43.8
   100                    44.7
   150                    46.0
   200                    46.4
   250                    48.3

Site 2: Rice yields collected from the reference areas were compromised by the occurrence of lodging (Table 5). The severity of lodging was linked with midseason N applications. Where lodging was present, it was difficult to ascertain how much of the yield was unable to be collected by the harvesting equipment. Chlorophyll readings were influenced by the amount of N applied preflood. However, chlorophyll readings remained high when plants received less than recommended quantities of N. Plants remained green, yet were stunted from in adequate N fertilization. In Arkansas, Ntamatungiro et al. (1999) has beeen studying combining chlorophyll readings (to estimate N concentration) with plant area board readings (to estimate biomass) for N uptake calculations. This may be our best option in Missouri.

Table 5. Effect of midseason (MS) N application on yield at specific chlorophyll readings (CR) at midtillering (6/25) and 1/2 inch internode elongation (7/13).

CR 6/25	CR 7/13	with MS	w/o MS	lodge with MS	yield change
35.7	38.9	143	128	+18	+15
38.1	38.1	140	145	+66	- 5
42.2	39.7	126	150	+56	- 24
43.4	41.0	129	148	+51	-19
		bu/a	bu/a	%	bu/a

Site 3: Yields at the popcorn site were very variable. Chlorophyll meter readings did not perform as well as the Mississippi County field corn site. In this demonstration, the meter was less effective at predicting positive yield change from additional sidedress N at the 5- leaf stage (Table 6).

Table 6. Effect of sidedress N application on popcorn yield at specific chlorophyll meter readings.

CR SPAD	Yield with 50 lbsN SD at V5	Yield w/o 50 lbsN SD at V5	Yield Change lbs/a
34.1	2992	3193	- 201
34.4	2868	2709	+159
35.0	3250	2960	+290
35.0	3417	3217	+200
35.6	3023	3090	- 67
36.0	3139	3063	+ 76

Conclusions

Literature:

Ntamatungiro, S., R.J. Norman, R.W. McNew, and B.R. Wells. 1999. Comparison of Plant Measurements for Estimating Nitrogen Accumulation and Grain Yield by Flooded Rice. Agron. J. 91:676-685.

End Notes:

¹ The United States Department of Agriculture (USDA) prohibits discrimination in its programs on the basis of race, color, national origin, gender, religion, age, disability, political beliefs, sexual orientation, and marital or family status. (Not all prohibited bases apply to all programs.)Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, ect.) should contact USDA's TARGET Center at 202-720-2600 (voice and TDD).
To file a complaint of discrimination, write USDA, Director, Office of Civil Rights, Room 326W, Whitten Building, 14th and Independence Avenue, SW, Washington, DC 20250-9410 or call (202)720-5964 (voice or TDD). USDA is an equal opportunity provider and employer.

² USDA-NRCS, University of Missouri Delta Center, and USDA-NRCS respectively.

³ The side inlet demonstration was funded by Region VII, US EPA, through the Missouri Department of Natural Resources, under Section 319 of the Clean Water Act. This grant is administered by the Bootheel Resource and Conservation and Development Council, Inc.

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