Procedures for Measuring Dry matter, Nutrient uptake, Yield and Components of Yield in Maize

Achim Dobermann and Daniel T. Walters

Dept. of Agronomy and Horticulture

University of Nebraska-Lincoln

Objective

· To quantify aboveground dry matter, yield, components of yield and plant nutrient accumulation at key growth stages of maize.

Definition of Growth stages¹

Determine the actual growth stage by examining about 10 randomly selected plant per plot. The staging system employed divides plant development into vegetative (V) and reproductive (R) stages. Each specific V or R stage is defined only when 50 percent or more of the plants in the field are in or beyond that stage. Subdivisions of the V stages are designated numerically as V1, V2, V3, etc. through V(n), where (n) represents the last leaf stage before VT for the specific hybrid under consideration. The first and last V stages are designated as VE (emergence) and VT (tasseling). The (n) will fluctuate with hybrid and environmental differences. Each leaf stage is defined according to the uppermost leaf whose leaf collar is visible. The first part of the collar that is visible is the back, which appears as a discolored line between the leaf blade and leaf sheath. The characteristically oval-shaped first leaf is a reference point for counting upward to the top visible leaf collar. Beginning at about V6, increasing stalk and nodal root growth combine to tear the small lowest leaves from the plant. Degeneration and eventual loss of the leaves results. To determine the leaf stage after lower leaf loss, split the lower stalk lengthwise and inspect for internode elongation. The first node above the first elongated stalk internode generally is the fifth leaf node. This internode usually is about one centimeter (0.4 inch) in length. This fifth leaf node may be used as a replacement reference point for counting to the top leaf collar.

The six reproductive stages mostly concern development of the kernel and its parts. All of the stage descriptions are the beginning or initiation of the stage unless otherwise stated. Kernel descriptions of the R2, R3, and R4 stages generally apply to all kernels on the ear, but kernels from the middle of the ear should be used to judge the stage. Kernel descriptions of the R5 and R6 stages pertain to all kernels on the ear. The top ear of a prolific plant should be used to judge the stage unless the stage of the lower ears is specifically desired.

VE	Emergence
V1	First leaf (rounded leaf)
V2	Second leaf
V3	Third leaf
V6	Sixth leaf. Growing point and tassel are above the soil surface and the stalk is beginning a period of increased elongation. The nodal root system is now the major functioning root system. Sets of roots elongating from the three to four lowest nodes.
V(n)	nth leaf
VT	Tassel. Last branch of the tassel is completely visible and silks have not yet emerged. Begins 2-3 days before silk emergence. Plants have almost attained full height.
R1	Silking, begins when any silks are visible outside the husks.
R2	Blister, 10-14 days after silking. R2 kernels are white on the outside and resemble a blister in shape. The endosperm and its now abundant inner fluid are clear in color and the tiny embryo can be seen upon careful dissection.
R3	Milk, 18-22 days after silking. R3 kernels are yellow on the outside, and the inner fluid is now milky white due to accumulating starch. Silks are brown and dry or becoming dry
R4	Dough, 24-28 days after silking. Milky inner fluid has thickened to a pasty consistency.
R5	Dent, 35-42 days after silking. All or nearly all kernels are dented or denting and the shelled cob is dark red in color.
R6	Physiological maturity, 55-65 days after silking. All kernels on the ear have attained their maximum dry matter accumulation. A black or brown abscission layer has formed. Black layer formation occurs progressively from the tip ear kernels to the basal kernels of the ear. Husks and many leaves are no longer green. Average kernel moisture content at R6 (black layer formation) is 30-35%.
H	Final harvest. Kernel moisture content is below 20%.

¹ Ritchie S. W. and J. J. Hanway. 1993. How a corn plant develops. Special Report 48 Iowa State University. http://maize.agron.iastate.edu/corngrows.html

Common Sampling stages for biomass and nutrient uptake studies

V6 6 leaves, end of early vegetative growth (about 5% of total final dry matter yield and NPK uptake)

VT Tassel, end of vegetative growth (maximum vegetative biomass, about 50% of total final dry matter yield, 60-70% of N uptake, 50% of P uptake, 80-90% of K uptake)

R6 Physiological maturity (100% of total final dry matter yield and NPK uptake)

H Final harvest (usually few days to several weeks after R6 to reduce grain moisture)

Materials

Paint (orange), flags for marking sampling areas

Paper bags, plastic, cloth or nylon mesh bags for harvest

Wire tags with plot labels, t

Twine for bundling plants, stapler

Balance with 1 g accuracy for gross fresh weight determination (0-20 kg range)

Balance with 0.1 g accuracy for fresh and dry weight determination (0-1500 g range)

Chipper or heavy duty paper cutter

Drying oven, plant grinder

Seed counter

Grain moisture meter (Dickey-John)

25 ml plastic (HDPE) bottles or containers for sample storage

Labels

Sampling principles

A 12-plant sample is used to estimate dry matter (DM) and plant nutrient accumulation at V3 to R5 stages (Fig. 1). This sample is either processed as whole aboveground biomass or separated into stalks, leaves, and reproductive organs (ears, tassel). A 6-plant sample at R6 stage (physiological maturity) is used to determine nutrient concentrations in grain and stover, obtain the harvest index, and determine components of yield. Plot grain yield and final plant population density are measured from a larger harvest area (default: two 20 ft row segments). 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. 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. Default values in the spreadsheet refer to experimental plots with a 30” (0.762 m) row spacing, but different row spacing and sample sizes can be entered.

Fig. 1. Sampling areas within a typical experimental plot (50’ x 20’, 8 rows @ 30’’ row spacing).

I. Sampling for measuring dry matter and nutrient accumulation at different growth stages (V3 to R5)

The 12-plant sample procedure described is most suitable for studies in which few key growth stages are sampled, typically V6 (end of early vegetative growth) and VT (end of vegetative growth) or an additional reproductive stage such as R3. Two options for sample processing are described, namely:

(1) Determination of dry matter and nutrient uptake in whole aboveground biomass.

(2) Determination of dry matter and nutrient uptake in stems, leaves, and reproductive organs.

Sampling using a 12-plant sample

Identify the appropriate sampling date (growth stage) by regularly checking plants. Select and mark a 30-ft (9.144 m) row segment to be used for sampling (e.g., rows 2 or 3 in Fig. 1). Avoid areas close to the plot border, but include areas with normal planter skips. Count and record the number of plants in the 30-ft row segment (nPlant). Beginning at one end, cut every 5^th plant regardless of size or stature, until a total of 12 plants have been collected (12-plant biomass sample, B). Cut plants close to the soil surface. Place all plants head down in large cloth bags or bundle them. Avoid leaf losses, long exposure of samples to sun, or contamination by soil by processing the samples immediately.

Sample processing at V3 to R5 stages: whole plants [worksheet V3-R5]

· For samples collected from V3 to V6 stages, weigh the whole sample to obtain the total fresh weight of the 12-plant biomass sample (FW_B, g). Tare the bag before weighing. Dry the whole sample at 70 ºC to constant weight. Avoid overpacking the drying oven so that good air circulation is maintained. After 7 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 record the final oven-dry weight of the sample (DW_B, g). Grind samples and transfer ground material to pre-labeled 25-ml HDPE bottles.

· For samples collected from V7 to R5 stages, weigh the whole sample to obtain the total fresh weight of the 12-plant biomass sample (FW_B, g). Tare the bag before weighing. Chop the whole 12-plant sample into smaller pieces using a heavy duty paper cutter or a "Vermeer" chipper. A chipper is preferred because it does a rapid job and provides a uniform chip size for subsampling. Take a representative subsample of 400 to 500 g immediately after weighing the total fresh weight to avoid moisture loss and record the fresh weight of the subsample (FW_Sub, g). Dry subsamples at 70 ºC to constant weight. Avoid overpacking the drying oven so that good air circulation is maintained. After 7 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 record the final oven-dry weight of the subsample (DW_Sub, g). Grind samples to 20 mesh and transfer to pre-labeled 25-ml HDPE bottles.

Sample processing at V3 to R5 stages: plant parts[worksheet V3-R5 parts]

· For samples collected from V7 to R5 stages, weigh the whole sample to obtain the total fresh weight of the 12-plant biomass sample (FW_B, g). Tare the bag before weighing. Immediately after weighing the total fresh weight select five representative plants for further processing. Carefully separate each plant into stems, leaves and reproductive organs (ears, husks, tassel). Immediately after separating the plant parts record the fresh weight of the stems (stalks) subsample (FW_S-sub, g), leaves subsample (FW_L-sub, g), and reproductive organs subsample (FW_E-sub, g).

· Dry subsamples at 70 ºC to constant weight. Avoid overpacking the drying oven so that good air circulation is maintained. After 7 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 record the final oven-dry weight of the stems subsample (DW_S-sub, g), leaves subsample (DW_L-sub, g), and reproductive organs subsample (DW_E-sub, g). Grind samples and transfer ground material to pre-labeled 25-ml HDPE bottles.

Chemical analysis

Submit all samples for chemical analysis at the end of the season when all plant samples have been processed. Include three anonymous duplicate samples to assess repeatability and two anonymous standard plant samples to assess accuracy of the chemical analysis.

Calculations

All calculations are done in a spreadsheet template containing all equations needed. Use metric units (g) for weighing and basic calculations. English units are only used for final yield reporting. All nutrients are reported on elemental basis.

Default values: Row width RW = 0.762 m (30”)

Biomass sample size: B = 12 plants

Row length stand count rPOP = 9.144 m (30 ft)

Plant population density (POP):

POP (plants/ha) = nPlant x (10000/RW/rPOP)

Whole-plant samples:

Oven-dry weight of the whole biomass sample (DW_B):

DW_B (g) = (DW_sub/FW_sub) x FW_B

Total Dry matter (TDM):

TDM (kg/ha) = (DW_B/1000/B) x POP

Plant parts samples:

Fresh weight of the whole 5-plant subsample (FW_B-sub):

FW_B-sub (g) = FW_S-sub + FW_L-sub + FW_E-sub

Stem dry matter (SDM):

SDM (kg/ha) = ((DW_S-sub*FW_B/FW_B-sub)/1000/B) x POP

Leaf dry matter (LDM):

LDM (kg/ha) = ((DW_L-sub*FW_B/FW_B-sub)/1000/B) x POP

Reproductive organs dry matter (RDM):

RDM (kg/ha) = ((DW_E-sub*FW_B/FW_B-sub)/1000/B) x POP

Total dry matter (TDM):

TDM (kg/ha) = SDM + LDM + RDM

Total nutrient accumulation (UNu):

UNu (kg/ha) = xDM x Nu/100 Nu = nutrient concentration in biomass (%)

Comments

· All calculations are done in a spreadsheet template containing all equations needed. Use metric units (g) for weighing and basic calculations. English units are only used for final yield reporting. All nutrients are reported on elemental basis.

· 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 sampling areas or row widths differ from the default values, change variables RW, rPOP, B and H in the spreadsheet.

· If plant population counts are only done in the harvest area at maturity, use these values also for nPlant in the worksheets describing sampling at V3 to R5 stages. Change rPOP to the appropriate value.

· Exclude at least 1 m from sampling at each end of the experimental plot.

· In experiments with large plot sizes (>200 m²), collect samples from two separate sampling areas within each plot and process them separately.

· The procedure described assumes that the available plot area is large enough to avoid repeated sampling within the same row. If that is not feasible, use a larger row length and sample every nx3rd plant, where n is the number of sampling stages within a season.

· Another approach for sampling at different growth stages is collecting a “random" plant sample within one or more rows. However, “random” sampling is often associated with a strong bias toward selecting "nice" plants. Mid-season dry matter estimates obtained with this method tend to be consistently higher than final dry matter taken with large samples. Moreover, CV's are often higher than those in the "every 5^th plant" method.

· Sampling about 1 m row (5 contiguous plants) is recommended for studies that require frequent sampling for measuring more subtle changes in dry matter accumulation and partitioning over time, particularly where plot sizes are small. It requires uniform plant stand and great care. Pre-mark (flag) the 5-plant sampling locations to be used at different growth stages. Each sampling location represents about 1 m of row, which corresponds to about 5 plants at typical densities. Stagger the rows sampled and make sure that at least one meter separates sampling locations in adjacent rows, e.g.:

___ ___ ___

II. Sampling for measuring yield, components of yield and plant nutrient accumulation at maturity

This procedure describes two standard approaches in which aboveground biomass is divided into three components: (1) stover, (2) cobs, and (3) grain. Stover includes stems, leaves, and husks. The sum of stover and cob yield represents the amount of crop residues remaining in the field (excluding roots). Two samples are collected, a 6-plant sample at physiological maturity and a grain yield harvest area sample from a larger area at final harvest. Both samples are used to calculate final dry matter yields and plant nutrient accumulation.

Procedure II-1

This procedure allows staggering of sampling activities, i.e., sampling of the 6-plant sample strictly at R6 stage, whereas final harvest can be conducted within 2-3 weeks later after grain moisture has decreased to facilitate better shelling. It requires shelling of the whole harvest area sample. Shelling can be done directly in the field or outside, in which case labor and transportation become limiting factors. Essential steps are:

(a) A 6-plant sample at physiological maturity is sampled from outside the final two harvest rows to obtain the harvest index and nutrient concentrations in stover, cobs, and grain.

(b) All ears from a 40- or 60 ft harvest area sample are shelled and the grain fresh weight of this whole sample is recorded.

(d) Final grain yield adjusted to 15.5% moisture is then calculated from (b) and (c).

(e) Final stover dry matter is calculated from (d) and the HI obtained in (a). Plant nutrient accumulation is calculated from (a), (d), and (e).

(f) 100-seed weight is measured on a subsample.

6-plant sample at physiological maturity (R6)

A 6-plant sample is used to measure the harvest index and nutrient concentrations in grain and other plant parts at R6 stage. Identify the appropriate sampling date (growth stage) by checking plants on a daily basis. Sample as soon as the black layer stage has been reached and before significant leaf loss has occurred.

· Collect 6 plants around the grain yield harvest area. These plants must be representative for the harvest area. Choose two adjacent plants from each of the three sides of the grain yield harvest area that do not include a border row (Fig. 1). Cut the plants off at the ground, just above the brace roots. 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 (Ear sample). Tie the remaining 6 stalks together with twine and attach the appropriate label (Stover sample). Sample processing does not have to occur on the same day. Consider accumulating a large enough number of samples and the rent a chipper for processing them in one day (see below). In any case, the wet weight must be taken on the day of processing, not before. Avoid long exposure of samples to sun and store samples in a cool, dust-free place.

· Ear sample: Determine the total fresh weight of the ear sample (FWE_B). Separate into cobs [C] and grain [G] using a corn sheller. Make sure that all ears are completely shelled and to catch all of the grain. It is important to use the appropriate bucket under the sheller to minimize grain loss. Some ears may retain several kernels of corn after going through the sheller. These ears can be caught and the remaining kernels removed by hand. Weigh the grain immediately after shelling (fresh weight of the whole grain sample, FWG_B, g) and take a subsample that is approximately 200 grams. Weigh the subsample making sure to tare the balance on the appropriate paper bag (fresh weight of the grain subsample, FWG_sub, g). If the cob is required, select a few cobs after half of the ears have been shelled. This is required because the first cobs coming out of the sheller are from the previous sample. Place the cobs in a pre labeled paper bag and determine the fresh weight of the cob sub-sample (FWC_sub). 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 cob subsamples (DWC_sub, g) and grain subsamples (DWG_sub, g). Grind the dried subsamples to 20 mesh, transfer samples to pre-labeled 25 ml HDPE bottles and submit for analysis with other plant samples.

· Stover sample: Weigh the total fresh weight of the 6-plant stover sample (FWV_B, g). Chop the plants up with a tractor-driven chopper or a chipper/shredder. Carefully homogenize the chopped sample. Take a representative subsample of about 500 g immediately after weighing the total fresh weight of the vegetative sample. Place the subsample in a paper bag with the tag from the bundle. Weigh the subsample after taring the balance with the appropriate paper bag (fresh weight of the stover subsample, FWV_sub, g) and dry it at 70 ºC to a constant weight. 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 oven-dry weight of the subsample (DWV_sub, g). Grind samples to 20 mesh in a plant mill and transfer ground material to pre-labeled 25-ml HDPE bottles.

Final harvest

A larger harvest area is used to measure grain yields and components of yield. Harvest should be done shortly after collecting the R6 sample, but longer waiting periods may be appropriate to reduce grain moisture or spread out workload.

· Mark the designated harvest area. The default value is to sample two 20-ft row segments (H = 12.192 m) centered within a large 4-row area (Fig. 1). Mark the first and last plant in each segment sampled with bright orange paint or flags. Count and record the number of plants (nPlant_H), ears (nEar_H) and prolific plants (nProl_H) in the whole harvest area.

· Carefully pick all ears. Peel the husks from the ears and pick the ears without husks. Husks are designated as part of stover yield and must remain on the stalks. Place all ears from a sampling plot in a pre-labeled cloth or nylon mesh bag. Shell the grain from the cob with either a corn sheller or combine. Avoid loss during shelling. Collect the entire seed sample from the sheller in a bushel basket. Weigh the entire seed sample, taring the balance with the bushel basket. Determine the fresh weight of the seed sample (FWG_H, g) and field grain moisture content (MC_Harv) using a grain moisture meter (dickey-john). Take a subsample of about 100 g seed and record the fresh weight of the subsample (FWG_sub,g), dry it at 70 ºC to constant weight and record dry weight (DWG_sub,g).

· 100-seed weight measurement: Count 300 seeds of the subsample using a seed counter (nSeeds). Dry this sample @ 103 C for 17 hrs, cool in dessicator & weigh to determine DHSW.

Procedure II-2

This procedure is a more labor-efficient alternative to procedure II-1 because only the 6-plant sample and part of the harvest sample are shelled. However, the 6-plant sample must be fully representative of the final harvest area and processing of ears from the 6-plant sample must be done very accurately to obtain a correct shelling percentage. Essential steps are:

(a) A 6-plant sample at physiological maturity is sampled from within the final two harvest rows to obtain the HI and nutrient concentrations in stover, cobs, grain, moisture content of grain, shelling percentage on fresh basis, and 100-seed weight.

(b) Completely shell the ears of the 6-plant sample, determine the shelling percentage on fresh weight basis, and moisture content of grain.

(c) Harvest all remaining ears from the 40- or 60 ft harvest area sample on the same day (or shortly thereafter) and determine the whole fresh weight of ears. Shell a subsample and determine moisture content.

(d) final grain yield is then calculated from (b) and (c), including adding back the grain of the six plants processed separately

6-plant sample at physiological maturity (R6)

· Mark the designated harvest area. The default value is to sample two 20-m row segments (H = 12.192 m) centered within a large 4-row area (Fig. 1). Mark the first and last plant in each segment sampled with bright orange paint.

· Count and record the number of plants (nPlant_H), ears (nEar_H) and prolific plants (nProl_H) in the harvest area.

· Collect 6 plants within the grain yield harvest area. These plants must be representative for the harvest area (Fig. 1). Cut the plants off at the ground, just above the brace roots. 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). Tie the remaining 6 stalks together with twine and attach the appropriate label (6-plant stover sample).

· Ear sample: Processing of the 6-plant ear sample must be done quickly to avoid changes in grain moisture content. Count and record the number of ears in the 6-plant sample (nEar_B). Determine the total fresh weight of the ear sample (FWE_B). Separate sample into cobs [C] and grain [G] using a corn sheller. Make sure that all ears are completely shelled and to catch all of the grain. It is important to use the appropriate bucket under the sheller to minimize grain loss. Some ears may retain several kernels of corn after going through the sheller. These ears can be caught and the remaining kernels removed by hand. Weigh the grain immediately after shelling (fresh weight of the whole grain sample, FWG_B, g) and measure the grain moisture content (MC_6plt) using a grain moisture meter (dickey-john). Take a subsample of approximately 200 grams grain. Weigh the subsample making sure to tare the balance on the appropriate paper bag (fresh weight of the grain subsample, FWG_sub, g). Dry it at 70 ºC to constant weight and record dry weight (DWG_sub,g). If the cob is required, select a few cobs after half of the ears have been shelled. This is required because the first cobs coming out of the sheller are from the previous sample. Place the cobs in a pre labeled paper bag and determine the fresh weight of the cob sub-sample (FWC_sub). 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 cob subsamples (DWC_sub, g). Grind the dried subsamples to 20 mesh in a grain mill, transfer samples to pre-labeled 25 ml HDPE bottles and submit for analysis with other plant samples.

· Stover sample: Consider accumulating a large enough number of samples and then rent a chipper for processing them in one day (see below). In any case, the wet weight must be taken on the day of processing, not before. Avoid long exposure of samples to sun and store samples in a cool, dust-free place. Weigh the total fresh weight of the 6-plant stover sample (FWV_B, g). Chop the plants up with a tractor-driven chopper or a chipper/shredder. Carefully homogenize the chopped sample. Take a representative subsample of about 500 g immediately after weighing the total fresh weight of the vegetative sample. Place the subsample in a paper bag with the tag from the bundle. Weigh the subsample after taring the balance with the appropriate paper bag (fresh weight of the stover subsample, FWV_sub, g) and dry it at 70 ºC to a constant weight. 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 oven-dry weight of the subsample (DWV_sub, g). Grind samples to 20 mesh in a plant mill and transfer ground material to pre-labeled 25-ml HDPE bottles.

Final harvest

Harvest should be done on the same day or shortly after collecting the R6 sample.

· Carefully pick all remaining ears in the 40- or 60- ft harvest area. Peel the husks from the ears and pick the ears without husks. Husks are designated as part of stover yield and must remain on the stalks. Place all ears from a sampling plot in a pre-labeled cloth or nylon mesh bag.

· Weigh the entire seed sample, taring the balance with the bushel basket, to obtain the total fresh weight of ears (FWE_H, g).

· Take a subsample of 6 ears, shell it, and immediately measure grain moisture content (MCharv) using a moisture meter (Dickey-John). Its is important that shelling and moisture measurement are done quickly after harvest, on the same day.

· 100-seed weight measurement: Count 300 seeds of the subsample using a seed counter (nSeeds). Dry this sample @ 103 C for 17 hrs, cool in dessicator & weigh to determine DHSW.

Chemical analysis

Submit all samples for chemical analysis at the end of the season when all plant samples have been processed. Submit all vegetative samples collected at V3 to VT stages and V, PW, and S samples collected at R6 for chemical analysis of plant nutrient concentrations. Include three anonymous duplicate samples to assess repeatability and two anonymous standard plant samples to assess accuracy of the chemical analysis. As a minimum, plant nutrient analysis is required for grain and stover sampled at R6. Nutrient concentrations in cobs can be estimated by regression once a large enough database has been established.

Calculations

Default values: Row width RW = 0.762 m (30”)

Sample size at R6: B = 6 plants

Harvest area: H = 12.192 m (two 20 ft row segments)

Dry matter and yield:

Oven-dry weights of the 6-plant sample at R6 (DWV_B):

Stover DWV_B (g) = (DWV_sub/FWV_sub) x FWV_B

Cobs DWC_B (g) = (DWC_sub/FWC_sub) x (FWE_B – FWG_B)

Grain DWG_B (g) = (DWG_sub/FWG_sub) x FWG_B

Cob harvest index (cobHI):

cobHI = DWG_B/(DWG_B+ DWC_B)

Harvest index (HI):

HI = DWG_B/(DWV_B + DWG_B+ DWC_B)

Shelling percentage (SHELL):

Procedure II-2: SHELL = FWG_B/FWE_E

Plot grain yield (plotGY, grams per harvest area, adjusted to 15.5% moisture content):

Procedure II-1: plotGY (g) = FWG_H x [(100 – MC_harv)/84.5]

Procedure II-2: plotGY (g) = (FWE_H) x SHELL x [(100 – MC_harv)/84.5] + (FWE_B) x SHELL x [(100 – MC_6plt)/84.5]

Grain yield adjusted to 15.5% moisture content (GY):

GY_M (Mg/ha) = (plotGY/1000) x (10000/RW/H)/1000

GY_bu (bu/acre) = GY_M x 1000/62.776

Grain dry matter yield estimated from 6-plant sample at R6 (GDM_B, oven-dry):

GDM_B (kg/ha) = (DWG_B/1000/B) x POP

Grain dry matter yield estimated from whole harvest area (GDM, oven-dry,):

GDM (kg/ha) = GY 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):

TDM (kg/ha) = GDM + CDM + VDM

Components of yield:

No. of plants & ears:

Plants POP (no/ha) = nPlant_H x 10000/RW/H)

Ears EARS (no/ha) = nEar_H x 10000/RW/H)

Prolific plants PROL (%) = nProl_H/nPlant_H x 100

Barren stalks BARR (%) = 1-((nEar_H - nProl_H)/nPlant_H) x 100

100-seed weight (HSW, oven-dry):

HSW (g) = (DHSW/nSeeds) x 100

No. of kernels per ear:

KERN_E (no.) = 1000 x GDM/Ears x 100/(HSW*1.03)

No. of kernels per square meter (sink size):

KERN_m (no) = EARS x KERN_E/10000

Plant nutrient accumulation

N shown as example:

gUN (kg/ha) = GDM x gN/100 grain

cUN (kg/ha) = CDM x cN/100 cobs

vUN (kg/ha) = VDM x vN/100 stover

UN (kg/ha) = gUN + cUN + vUN total

Comments

· 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.

· If sampling areas or row widths differ from the default values, change variables RW, rPOP, B and H in the spreadsheet.

· Exclude at least 1 m from sampling at each end of the experimental plot.

· In experiments with large plot sizes (>200 m²), collect samples from two separate sampling areas within each plot and process them separately.

· 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.

· It is important that the 6-plant sample is representative of harvest index in the final harvest area. Therefore, do not sample heavily damaged plants (e.g., hail damage).

· Plot the two estimates of grain dry matter yield (GDM_B at R6 and GDM at harvest) as a quality control measure (see default graph and regression estimates in worksheet “Maturity”). GDM_B tends to be 10-15% larger than GDM, but both estimates should be highly correlated with a slope close to 1 and a high R² value. Poor correlation (small R²) may be due to individual outliers in the graph. Significant deviation of the slope from 1 indicates a systematic bias in sample processing. Reasons for both must be clarified.

List of abbreviations

Raw data entry
RW	row width	m
rPOP	row length used for stand count	m
B	biomass sample size	no. of plants
H	harvest area	row meters
DW	dry weight	g/sample
FW	fresh weight	g/sample
Sample identifiers:
G	grain
C	cob
L	leaf (including husks at maturity)
S	stalk
V	whole vegetative organs (stems, leaves, husks) if no separation was done
sub	sub-sample

Calculated variables:
POP	no. of plants per area	plants/ha
EARS	no. of ears per area	ears/ha
PROL	% prolific plants (with two grain-bearing ears)	%
BARR	% barren plants (with no grain-bearing ears)	%
HSW	100-seed weight	g
KERNe	no.of kernels per ear
KERNm	no.of kernels per square meter
plotGY	plot grain yield	g/harvest area
GY	grain yield (adjusted to 15.5% moisture)	bu/acre or Mg/ha
TDM	total aboveground dry matter	kg/ha
SDM	stem dry matter (stalks)	kg/ha
LDM	leaf dry matter (stalks)	kg/ha
RDM	reproductive organs dry matter (whole ears)	kg/ha
GDM	grain dry matter at harvest	kg/ha
CDM	cob dry matter at harvest	kg/ha
VDM	vegetative dry matter at harvest (stalks, leaves, husks)	kg/ha
cobHI	cob harvest index
HI	harvest index
UN	Total N uptake	kg/ha
UP	Total P uptake	kg/ha
UK	Total K uptake	kg/ha
UCa	Total Ca uptake	kg/ha
UMg	Total Mg uptake	kg/ha
US	Total S uptake	kg/ha

Objective

Definition of Growth stages1

Common Sampling stages for biomass and nutrient uptake studies

Materials

Sampling principles

I. Sampling for measuring dry matter and nutrient accumulation at different growth stages (V3 to R5)

Sampling using a 12-plant sample

Sample processing at V3 to R5 stages: whole plants [worksheet V3-R5]

Sample processing at V3 to R5 stages: plant parts[worksheet V3-R5 parts]

Chemical analysis

Calculations

Comments

II. Sampling for measuring yield, components of yield and plant nutrient accumulation at maturity

Procedure II-1

6-plant sample at physiological maturity (R6)

Final harvest

Procedure II-2

6-plant sample at physiological maturity (R6)

Final harvest

Chemical analysis

Calculations

Dry matter and yield:

Components of yield:

Plant nutrient accumulation

Comments

List of abbreviations

Definition of Growth stages¹