Protocol for correct cassava harvest in Cassava five-factorial trials. Basic steps to follow so as to properly harvest cassava yield with little damage to the roots.

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Protocol for cassava harvest in
Cassava five-factorial trials
By
Stefan Hauser

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The cassava in the cassava density trial will be harvested row by row, consisting usually of
6 plants. Segmentation by planting density is not required because the position along a
line in the field will define the density which is according to the sequential number of the
cassava rows along the density gradient (being 23 rows from 100 cm to 50 cm distance).
The first row has to be removed as border as well as the lines of cassava to the left
and right of the 6 net plot lines. Please refer to Graph “Cassava harvest plan” below.
The harvest starts with the removal of border plants. This should happen with
care not to break branches from plot plants. All border plant material has to be removed
from the plot and discarded such that it cannot be mixed with plot plant material.
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Once all border plants are removed, the plot plant harvest starts with counting
the number of living plants per row (enter in column “Plants”). A row is the equivalent to
the plants inside the red box in the Cassava harvest plan (see diagram below).
Plant count is followed by counting the number of main stems (stems originating from the
planting stick) (enter in column “Main stems”) and the number of first level branches (only
branches originating from main stems) (enter in column “Primary branches”). Please
ensure these data is written in the appropriate columns of the harvest sheet. Once
counting is finished the form is given to the weighing station staff for later entry of root
counts and masses of plant parts.
The harvest supervisor has to verify that all counts are done before plants are harvested.
1a

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Then the plants of a row are uprooted and taken to the side – check
immediately for any broken off roots, such roots will be dug out, and merged with the roots
of the entire row.
It is strongly recommended not to cut stems or branches before uprooting because the
dissecting of the plants of one row needs to be done such that there is no mix up with
other rows (the latter is mostly impossible if stems or branches are cut before uprooting) –
as they often are tangled with neighboring plants and remain hanging in the plot.
First the green skinned (often leaf – bearing) branches or stems are removed (broken off
at the level where the color changes) and placed in a bucket. The remaining stem (usually
brown or grey skinned) is cut off at the level of the former planting stick and all stems are
placed in a bucket. The roots are cut off from the planting stick and separated into those fit
for consumption or processing and those deemed unsuitable (small, crocked, rotten). The
planting sticks are collected into one bucket. The roots fit for consumption (OK roots) are
collected into one bucket and the roots unsuitable for consumption (bad roots) are
collected into another bucket.
1b

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Thus all plants of one row are dissected into 5 parts:
Green stems (leaved or not),
Grey or brown stems (usually mature and suitable as planting material),
Former planting sticks,
OK roots (fit for consumption or processing) and
Bad roots (unsuitable for consumption or processing)
Once all plants of one row have been dissected and parts filled into the
appropriate buckets the buckets are moved to the weighing station and weighed in the
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order the plant parts are listed (see above). Enter the biomass data into the
harvest sheet.
Do not weigh the plant parts in the buckets in which they are delivered to the weighing
station, you need to use one bowl or bucket that is tared off (mass on balance set at
ZERO) and all material need to be placed in that bowl to ensure differences in bucket
mass do not bias the data. Control the empty bowl mass and clean from time to time.
For the OK roots and the bad roots the number of roots needs to be counted before
weighing and the numbers need to be entered into the sheet (column “no. OK roots” and
“no. bad roots”).
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When all plant parts were weighed subsamples of green branches main stem
and OK roots need to be taken. However, because we do not need a subsample from
every row but only from every density section the sub-sampling will be done as follows:
Row 1, 2, and 3 [distance= 100cm] one subsample (per above described plant part),
Row 4, 5, 6, and 7 [distance 90 cm] one subsample,
Row 8, 9, 10 and 11 [distance 80 cm] one subsample,
Row 12, 13, 14 and 15 [distance 70 cm] one subsample,
Row 16, 17, 18 and 19 [distance 60 cm] one subsample,
Row 20 to 23 [distance 50 cm] one subsample.
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To collect the different plant parts from the rows of same density it is advised to have at
least 6 crates or large basins or baskets lined up into which the material is collected until
all rows of the same density are harvested, Then the cutting up of selected plant parts will
start until all subsamples of the density section are taken and weighed fresh. All remaining
material after sub-sampling should be discarded at a sufficient distance to avoid mixing of
material from different density sections. It is possible that in the mean time the first plant
parts for sub-sampling from the next row arrive at the balance therefore you need a
second set of crates basins or baskets into which these parts are collected.
Thus 3 plant parts times 6 density sections = 18 sub samples per main plot for dry matter
determination. The harvest supervisor is required to ensure the 18 subsamples are
correctly taken and handled until they reach the oven.
Once a cassava row has been harvested, dissected, weighed counted and sub-sampled
the next row is uprooted and the procedure is repeated with all data entered in the next
line on the data sheet.

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Data collection sheets will be provided to enter all parameters.
Equipment:
 Table for staff to write on and to weigh subsamples
 Balance for raw materials weighing (the large one for up to 60 kg)
 Platform to place the balance (best a pallet or a large plank that is wide enough so
that all feet of the balance are securely on the plank – it is advisable to have a spirit
level at hand to set the balance horizontally to avoid biased mass determination.
 Table balance to weigh the fresh subsamples
 Paper bags for the subsamples and spares in case bags rip. (minimum 1200 for 4
replicates or 900 for 3 replicates)
 Markers to write on subsample bags
 Buckets (48 liters for the bulky material, 12 liters for the small materials (bad roots
for instance)
 Spare batteries for the balances or small generator to supply current.
 Cutlasses to dissect the plants
 Wooden blocks on which subsamples are cut up.
 Kitchen knives (large to cut up root samples)

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
Subsample handling:
Subsamples need to be processed and fresh weighed without any delay as water losses in
the process of taking the sample, cutting up and weighing will affect the DM content and
thus consequently may bias estimations of the dry matter yield of the respective plant
parts.
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Subsample fresh mass should be 250 to 500 gram. Do not spend time to
adjust the sample mass if slightly over or under the 250 to 500 gram. Enter the subsample
mass into the harvest data sheet.
Therefore it is recommended to have two teams working in two plots, using the same
balances but having staff for each team that handles the subsamples.
Subsamples are to be oven dried at 60°C to constant mass, then weighed and the mass
being entered into another data sheet (to be supplied).
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Note : it is advisable to have a fair number of extra buckets as it is possible that materials
of one plant part to not fit into one bucket.
By using buckets of different colors you can help avoid errors by always using the same
color for the same plant part. This may reduce the error risk when weighing – i.e. green
bucket always leaves, yellow bucket always stems, brown bucket always roots (use a
small one for unsuitable roots and a big one for OK roots) etc.
Before weighing at the weighing station roots first need to be cleaned of any attached soil
then checked if they are fit for processing. Any discovered rotten roots can be moved to
the bad root bucket.

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