Within the manual Protocols for experimental plot sampling, handling and processing of cereals in field experiments
by G.J. Rebetzke (Greg.Rebetzke@csiro.au), A. van Herwaarden, B. Biddulph, C. Moeller, R. Richards, A. Rattey and K. Chenu.
Harvest index cuts are critical in understanding the timing of water use (pre- vs post-flowering) and in estimating total biomass. They also allow for estimation of spike number and a backup estimate for plot yield.
Method
As each plot reaches full maturity (dry with no green tissue) it is to be cut for harvest index determination. This is readily achieved by:
- Part the edge row and insert a quadrat perpendicular to the direction of the row. We typically use a quadrat size of 3-4 rows, each being 40-50cm long.
- With a sharp, serrated knife or secateurs, cut the stems inside the quadrat at ground level (Fig. 24). Try and retain as much dried leaf as possible. Do not sample from edge rows.
- Tie the cut bundle and attach a tag indicating the plot. Collect all tied bundles and store until ready for processing. Ensure samples are stored dry and away from pests such as rodents.
- During this entire process, it is important to handle the bundle carefully. As they are dry, it is easy for stems to be broken and lost, as well as for grain to fall out of the heads.
- We can usually sample about 15 plots/hour/person using this method.
- A rice-binder (Fig. 25) can be used to cut and bundle large numbers of plots quickly and consistently. We routinely sample 40-50 plots/hour/person with a rice-binder.
For processing of each sample:
- Record the weight of the bundle before opening on a workbench.
- Carefully subsample a representative third to a quarter of the stems (ensure that a minimum of 40 stems are present in this subsample) and then record the weight of this subsample.
- Count the number of fertile culms (stems with heads) and sterile culms (stems which do not produce grain) in the subsample. Record these values.
- Air-dry the sample at 35∘C (often harvest maturity is dry enough). Sometimes you may want to retain a sample of the dried stem and leaf tissue for chemical analysis. After counting the spikes in the subsample, cut off the ears just below the bottom spikelet and place them with the original sample for threshing. The earless stems with leaves can then be placed into a paper bag for later grinding and analysis.
- Place the subsample together with the original sample and then thresh. Collect the seed for weighing. Record this weight and retain this sample for 100 grain weight, screenings and hectolitre weight estimation. Calculate harvest index as: 100x(total grain weight/total bundle weight).
- Correct for number of stems with heads in the subsample to total stem number with heads in the original bundle through the calculation: Total bundle weight/(subsample weight/no. stems with heads). Repeat for stems without heads.
Biomass of the different plant components (optional):
Before point 4 (above), separate the different plant components (stem+sheath, leaves, head, grain) of 20 random spikes and obtain their dry weights. Follow the procedure for 4-6 for the rest of the sample.
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Figure 24. The procedure used in cutting mature samples for harvest index and biomass determination.
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Figure 25. The use of a rice-binder in cutting large numbers of plots for harvest index and biomass determination.
Other resources
Appendix 1. Text description of phenological scale, Zadoks decimal code (DC).
Appendix 2. Picture description of phenological scale, Zadoks decimal code (DC).
Zadoks JC, Chang TT, Konzak CF (1974) A decimal code for the growth stages of cereals. Weed Research 14(6),415-421. doi: 10.1111/j.1365-3180.1974.tb01084.x
Notes and troubleshooting tips
Literature
Download complete manual: Protocols for cereal field experiments_Nov2012.pdf
Health, safety & hazardous waste disposal considerations