October 7, 2005
Version 1.1
Procedure for Measuring Dry matter, Nutrient uptake, Yield and
Components of Yield in Maize
Achim Dobermann
Dept. of Agronomy and Horticulture
University of Nebraska-Lincoln
adobermann2@unl.edu
OBJECTIVE
To quantify aboveground dry matter, yield, components of yield, and nutrient uptake
MATERIALS
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Tape measure to mark the harvest area
Paint (orange or pink), flags or bamboo sticks for marking sampling areas
Paper or nylon mesh bags for drying of grain, cobs, and stover samples
Large cloth or nylon mesh bags (sacks) for final harvest
Tags with plot labels, twine for bundling plants
Marker pens (water-proof)
Portable scale with 10 g accuracy for gross fresh weight determination (0-10 kg range)
Digital scale (0-2000 g, 1 g accuracy) for fresh and dry weight determination of subsamples
Heavy duty knives or machetes for cutting plants and chopping stover samples
Large drying oven
Plant sample grinder
Grain moisture meter
25 ml glass or plastic bottles or containers for storing ground plant samples
Sticky labels
A safe and dry storage area for samples, protected from rodents and insects.
Fig. 1. Materials needed for sampling
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October 7, 2005
Fig. 2. Portable scale of of 0-15 kg (left) and 0-2000 g (right)
If a portable scale is not available, take the entire sample to the lab.
SAMPLING PRINCIPLES
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A 6-plant sample at R6 stage (physiological maturity) is collected to determine nutrient
concentrations in grain and stover and obtain the harvest index.
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Plot grain yield and final plant population density are measured from a larger harvest area
(4 rows x 3 m length; in some cases, it could be 3 rows x 3m, see individual workplans).
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Final plot dry matter yield is estimated from the grain yield measured at harvest and the
harvest index obtained from the 6-plant sample collected at R6 stage.
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Plant nutrient accumulation in grain, cobs, and vegetative parts is calculated from nutrient
concentrations measured in the R6 sample and the estimated final dry matter fractions.
6.00 m
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1.5 m
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30 plants with 20cm plant spacing
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Rows
Irrigation canals and path
Fig. 3. Example for a sampling strategy at R6 stage in the central harvest area of an experimental plot (6
m x 6 m, 8 rows @ 75 cm row spacing).
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October 7, 2005
Fig. 4. Example for a sampling strategy at R6 stage in the central harvest area of an
experimental plot (6 m x 6 m, 8 rows @ 75 cm row spacing).
NOTE: Sampling is done by row-meters rather than by harvest area. Thus, if some plants are
severely damaged in a row, choose a different 3-m stretch in that row (see example in Fig. 4)
so that you sample four 3-m rows or a total row length of 4 x 3 = 12 m.
SAMPLING
This procedure describes a standard harvest approach in which aboveground biomass is
divided into three components: (1) stover, (2) cobs, and (3) grain. Stover includes stems,
leaves, and husks. Two samples are collected, a 6-plant sample at physiological maturity
(black layer) and a grain yield sample from a larger area at final harvest. Both samples are
used to calculate final dry matter yields and plant nutrient accumulation.
Essential steps are:
(a) Collect a 6-plant sample at physiological maturity (blacklayer) from within the
harvest area to obtain the harvest index and nutrient concentrations in stover and
grain.
(b) Harvest all remaining ears from the harvest area about 1-2 weeks after blacklayer and
determine the whole fresh weight of all ears. Get a subsample of 6 ears, shell it and
determine grain moisture content.
(c) Final grain yield and total aboveground dry matter are then calculated from (b) and
(c), including adding back the grain of the six plants sampled at blacklayer stage.
6-plant sample at physiological maturity (R6)
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Identify the appropriate sampling date (growth stage) by checking plants on a daily basis
during the later stages of grain filling. It is important to sample as soon as the black layer
stage has been reached and before significant leaf loss has occurred.
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October 7, 2005
R6
Physiological maturity or black layer stage, 45-55 days after silking. At least 90%
of all kernels on the ear have reached their maximum dry matter accumulation,
which is indicated by the presence of a clearly visible black layer. Husks and
lower leaves on the plant are no longer green, but top leaves of the plant and the
stalks are still green. Average kernel moisture content is about 30-35%.
Black layer formation occurs progressively from the tip ear kernels to the basal
kernels of the ear. When R6 stage is approached, frequently check the maturity
stage by collecting an ear from a plot (not from border rows and not from within
the harvest area). Along a row of kernels in an ear, cut kernels to identify how far
black layer formation has reached down the ear.
black layer
Diagnostic criterion: >95% of all kernels on the ear have a blacklayer in
>50% of all plants examined. Ignore aborted kernels on the ear tip.
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Identify the designated harvest area of four rows with each 3m length centered within a
larger 8-row x 6 m treatment plot using bamboo sticks and a ribbon:
 Select four 3-m rows as needed to avoid large skips with severe plant damage (see
Fig. 4), but leave at least 1 m border at each row end. For measuring the 3-m row
length, place the first bamboo stick in between two neighboring plants (Fig. 5,
left), then place the second bamboo stick after exactly 3 m.
 Use a plastic ribbon to mark the plants in the four 3-m rows that should be sampled
(Fig. 5, right).
Fig. 5. Place the first bamboo stick in between plants and the second after 3m row lengths
(left). Then mark the harvest area with a ribbon (right).
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October 7, 2005
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NEW In the harvest area of each plot, measure and record the row width (RW) between
the four rows at the beginning, the middle, and end of each row to get an average of row
spacing for the treatment plot.
Count and record the number of plants (nPlantH), ears (nEarH) and prolific plants
(nProlH) in the harvest area. Only count ears if they have a significant no. of kernels
filled, i.e., if necessary, slightly remove husks to check on this. Prolific plants are those
that have two or more ears per plant, but empty ears do not count!
Collect 6 plants within the harvest area. Select plants that are representative for the
harvest area (Fig. 6): compare the stem diameter of plants in the harvesting area and look
for evenly spaced plants with no or little damage. Then select plants that are
representative in stem diameter.
Fig. 6. The six plants sampled individually for the 6-plant sample should have a
representative stem diameter.
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Cut the whole plant near the soil surface using a machete. Carefully peel the husks from
the ears (husks are designated as part of stover yield and must remain on the stalks).
Remove the ears from the plant and place them in a pre marked paper bag (6-plant ear
sample, Fig. 7, left). Tie the remaining 6 stalks together with twine and attach the
appropriate label (6-plant stover sample, Fig. 7, right).
Fig. 7. The 6-plant sample is separated into the 6-plant ear sample and the 6-plant stover
sample (right).
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October 7, 2005
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6-plant stover sample: Process the stover samples quickly after sampling. Avoid long
exposure of samples to sun or contamination by soil. Weigh the total fresh weight of the
whole 6-plant stover bundle (FWV6pl, g).
Out of the 6 plants, select a subsample of 2 to 3 representative plants for further
processing. Strip off all leaves, cut them into pieces, and place them into a pre-labeled
paper bag (brown bag). Cut the stalks of the selected plants into small pieces (about 5 cm
long, Fig. 8) and add them to the same paper bag. Make sure that no biomass is lost
during this process. Weigh the chopped stover subsample (chopped leaves + stalks) to
determine the fresh weight of the stover subsample, FWVsub, g).
Dry the stover subsamples at 70 ºC to a constant weight (for about 2 weeks). Avoid
overpacking the drying oven so that good air circulation is maintained. After 10 days
check the weight of 3 samples daily to identify when a constant weight is achieved.
Remove samples from drying oven and weigh immediately to determine the final ovendry weight of the subsample (DWVsub, g).
Fig. 8. Chop stalks into smaller pieces.
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6-plant ear sample: Transport the 6-plant ear sample to the research station for further
processing. Pre-dry the ear sample (sun-dry) to facilitate better shelling. Count and record
the number of ears in the 6-plant sample (nEar6pl). After sun-drying, determine the total
fresh weight of the ear sample (FWE6pl). Separate sample into cobs [C] and grain [G]
using a corn sheller or by hand. Make sure that all ears are completely shelled and no
grain is lost. Weigh the grain immediately after shelling (fresh weight of the whole grain
sample, FWG6pl, g). Take a subsample of approximately 200 grams grain and transfer it
to a pre-labeled paper bag. Weigh the subsample making sure to tare the balance on the
appropriate paper bag (fresh weight of the grain subsample, FWGsub, g). Dry it at 70 ºC
to constant weight (for about 1 week) and record the dry weight (DWGsub, g). Place all
cobs in a pre labeled paper bag and determine the fresh weight of the cob sample
(FWC6pl). Dry the grain and cob subsamples at 70 ºC to constant weight. Remove
samples from drying oven and weigh immediately to determine the oven-dry weight of
cobs (DWC6pl, g).
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October 7, 2005
Final harvest
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Final harvest for determining grain yield can be done on the same day the R6 sample is
collected, or, preferably, about 1-2 weeks later, when grain moisture has dropped to about
20-25%.
Carefully hand-pick all remaining ears in the 4 rows x 3 m harvest area. Peel the husks
from the ears and pick the ears without husks. Place all ears in a cloth or nylon mesh bag.
Add a label.
Weigh the entire ear sample, taring the balance with the cloth bags used, to obtain the
total fresh weight of ears (FWEH, kg).
Take a subsample of 6 to 10 representative ears and place those into a labeled plastic bag
(NOTE: if yield is high and ears are large, 6 ears are sufficient for this subsample. If yield
is low and ears are small, take 10 ears instead). It is important to avoid any moisture loss
from those 6 ears, i.e., do not expose those samples to sunlight and process them very
quickly, on the same day, either in the field or in the laboratory. First, determine the fresh
weight of the 6 ears (FWEH6). Immediately following this, shell the 6 ears and determine
the fresh weight of grain (FWGH6). Immediately measure grain moisture content (MCH)
using a grain moisture meter.
100-seed weight measurement: Count 100 seeds of the grain sample. Dry this sample @
105 C for 2 days, cool in dessicator & weigh to determine the 100-seed dry weight
(DHSW).
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October 7, 2005
GRINDING OF PLANT SAMPLES AND CHEMICAL ANALYSIS
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Store all dried grain, cob, and stover samples collected at R6 stage under dry conditions,
protected from rats and insects. Try to process them further as soon as possible.
Grind samples to coarse plant material and transfer small sub-samples of ground plant
material (about 20 grams) into glass or plastic containers.
Grind all dried grain, cob, and stover samples collected at R6 stage to 20 mesh size in a
plant mill. Note: if samples have been stored for several weeks before grinding, pre-dry
them for 10-20 hours at 70 C to facilitate easier grinding.
Conduct chemical analysis of N, P, and K concentrations in plant tissue.
CALCULATIONS
All calculations are done in a spreadsheet template containing all equations needed. All
nutrients are reported on elemental basis.
Default values:
Row width
RW = 0.75 m
Sample size at R6:
B = 6 plants
Harvest area:
H = 9 m (3 rows x 3 m)
Dry matter and yield:
Oven-dry weights of the 6-plant sample at R6 (DWV6pl):
Stover
DWV6pl (g) = (DWVsub/FWVsub) x FWV6pl
Cobs
DWC6pl (g) = (DWC6pl/FWC6pl) x (FWE6pl – FWG6pl)
Grain
DWG6pl (g) = (DWGsub/FWGsub) x FWG6pl
Cob harvest index (cobHI):
cobHI = DWG6pl/(DWG6pl+ DWC6pl)
Harvest index (HI):
HI = DWG6pl/(DWV6pl + DWG6pl+ DWC6pl)
Shelling percentage (SHELL):
R6 (PM):
SHELL6pl = FWG6pl/FWE6pl
H:
SHELLH = FWGH6/FWEH6
Plot grain yield (plotGY, grams per harvest area, adjusted to 15.5% moisture content):
plotGY (g) = (FWEH) x SHELLH x [(100 – MCH)/84.5] + (FWE6pl) x
SHELL6pl x [(100 – MC6plt)/84.5]
Grain yield adjusted to 15.5% moisture content (GY):
GY (t/ha) = (plotGY/1000) x (10000/RW/H)/1000
Grain dry matter yield estimated from 6-plant sample at R6 (GDMB, oven-dry):
GDM6pl (kg/ha) = (DWG6pl/1000/B) x POP
Grain dry matter yield estimated from whole harvest area (GDM, oven-dry,):
GDM (kg/ha) = GYMg x 1000 x 84.5/97
Cob dry matter yield (CDM):
CDM (kg/ha) = GDM/cobHI – GDM
Stover dry matter yield (VDM, stems, leaves, husks):
VDM (kg/ha) = GDM/HI – GDM – CDM
Total dry matter yield (TDM = grain + cobs + stover):
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October 7, 2005
TDM (kg/ha) = GDM + CDM + VDM
Components of yield:
No. of plants & ears:
Plants
Ears
Prolific plants
Barren stalks
POP (no/ha) = nPlantH x 10000/RW/H)
EARS (no/ha) = nEarH x 10000/RW/H)
PROL (%) = nProlH/nPlantH x 100
BARR (%) = 1-((nEarH - nProlH)/nPlantH) x 100
100-seed weight (HSW, oven-dry):
HSW (g) = (HSW/nSeeds) x 100
No. of kernels per ear:
KERNE (no.) = 1000 x GDM/Ears x 100/(HSW x 1.03)
No. of kernels per square meter (sink size):
KERNm (no) = EARS x KERNE/10000
Plant nutrient accumulation
N shown as example:
gUN (kg/ha) = GDM x gN/100
cUN (kg/ha) = CDM x cN/100
vUN (kg/ha) = VDM x vN/100
UN (kg/ha) = gUN + cUN + vUN
grain
cobs
stover
total
Comments
. All calculations are done in a spreadsheet template containing all equations
needed. Use metric units (g) for weighing and basic calculations. All nutrients are
reported on elemental basis.
a. Grain yield is adjusted to a standard moisture content of 15.5%. Dry matter yields
of grain, cobs, and stover refer to oven-dried dry matter, which typically contains
about 3% residual moisture after drying at 70 ºC. Oven-dry matter is used for
calculation of total nutrient uptake because plant nutrient concentrations obtained
from tissue analysis are always expressed on oven-dry matter basis as well. If
laboratory analysis suggests residual moisture greater than 3%, further corrections
of the results can be made.
b. If sampling areas or row widths differ from the default values, change variables
RW, B and H in the spreadsheet.
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Exclude at least 1 m from sampling at each end of the experimental plot.
c. Collecting the 6-plant sample must be done as soon as physiological maturity has
been reached to avoid nutrient losses from senescing plant tissues. In addition to
leaf drop, in humid climates, minerals such as K may be leached from leaves.
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October 7, 2005
LIST OF ABBREVIATIONS
Raw data entry
RW
row width
B
biomass sample size
H
harvest area
DW
dry weight
FW
fresh weight
Sample identifiers:
G
grain
C
cob
V
stover (stems, leaves, husks)
sub
sub-sample
Calculated variables:
POP
no. of plants per area
EARS
no. of ears per area
PROL
% prolific plants (with two grain-bearing ears)
BARR
% barren plants (with no grain-bearing ears)
HSW
100-seed weight
KERNe
no.of kernels per ear
KERNm no.of kernels per square meter
plotGY
plot grain yield
GY
grain yield (adjusted to 15.5% moisture)
TDM
total aboveground dry matter
SDM
stem dry matter (stalks)
LDM
leaf dry matter (stalks)
RDM
reproductive organs dry matter (whole ears)
GDM
grain dry matter at harvest
CDM
cob dry matter at harvest
VDM
vegetative dry matter at harvest (stalks, leaves, husks)
cobHI
cob harvest index
HI
harvest index
UN
Total N uptake
UP
Total P uptake
UK
Total K uptake
m
no. of plants
row meters
g/sample
g/sample
plants/ha
ears/ha
%
%
g
g/harvest area
bu/acre or Mg/ha
kg/ha
kg/ha
kg/ha
kg/ha
kg/ha
kg/ha
kg/ha
kg/ha
kg/ha
kg/ha
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October 7, 2005
STEP-BY-STEP CORN HARVEST PROTOCOL
ACTIVITY
1. Mark the 4 rows x 3 m harvest area with paint or sticks.
Avoid areas with very uneven crop stand. Leave at least a 1m border on each end.
2. Measure the row width in the harvest area
Count the number of plants in the harvest area
3. Count number of ears in the harvest area.
4. Count number of plants with two or more ears per plant in
the harvest area.
5. Collect 6-plant sample at physiological maturity. Select 6
plants randomly within the harvest area. Separate into ears
and stover (stalks, leaves, husks).
6. Process 6-plant stover sample
Determine total fresh weight of all 6 plants
Select 2-3 plants as subsample for further processing. Strip
off leaves. Chop leaves and stalks into small pieces (5 cm
long) and place into the same paper bag. Determine fresh
weight.
Dry to constant weight at 70º C, determine dry weight.
Safely store stover samples for nutrient analysis
7. Process 6-plant ear sample
Record the number of ears in the 6-plant ear sample
Sun-dry ears for better shelling
Determine total fresh weight of all ears (just before shelling)
Shell all ears, avoid any grain losses
Take subsample of about 200 g grain, determine fresh
weight
Dry grain subsamples at 70º C to constant weight, determine
dry weight
Weigh all cobs and determine fresh weight
Dry cob samples at 70º C, determine dry weight
Safely store dried grain and cob samples for nutrient analysis
8. Pick ears from harvest area (without the husks and silks)
Determine fresh weight of the entire ear sample (kg)
Take a subsample of 6 to 10 ears and place in a plastic bag.
Determine fresh weight of the ear subsample.
Shell ear subsample and weigh grain
Immediately measure grain moisture
Take subsample of 100 kernels
Dry sample @ 70º C for 2 days, weigh immediately
9. Grind all stover, grain, and cob sub-samples (6 plant
samples) for chemical analysis. Store samples in glass or
plastic containers.
Date
Variable in
spreadsheet
at R6
stage
R6
R6
R6
RW
nPlantH
nEarH
nProlH
Blacklayer
(R6)
FWV6pl
FWVsub
DWVsub
nEar6pl
FWE6pl
FWG6pl
FWGsub
DWGsub
FWC6pl
DWC6pl
Harvest
FWEH
FWEH6
FWGH6
MCH
HSW
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