Tea, Frost and a Six-Day Harvest Window in Kameyama
The tea cooperative in Kameyama, Mie Prefecture, has 120 member farms working 340 hectares, almost all of it the Yabukita cultivar grown for sencha. Its records show:
| Item | 1980 | 2020 |
|---|---|---|
| Average date of first spring picking | April 28 | April 12 |
| Days per year at 35°C or above | 12 | 27 |
| Members aged 65 or over | 24 | 82 |
| Price index, first-pick sencha (2000 = 100) | - | 88 |
Twelve members have left the cooperative in the past five years, and most of their fields are now abandoned. Harvesting is done by riding machines, so every field must be picked inside a six-day window. In 2021 warm weather brought the buds out early, a late frost followed, and 30% of the first crop was lost. At the annual meeting one member proposes switching to a later-budding cultivar, another proposes building shading frames to sell kabusecha at a higher price, and a third proposes selling the abandoned fields for a solar plant. The cooperative has limited capital and few young members.
1. Using the data, explain why an earlier picking date is a problem even though tea plants grow faster in warmth.
Read the worked answer
The shift itself: picking moved 16 days earlier (April 28 → April 12), while days at 35°C or above rose from 12 to 27. The growing season starts sooner and is hotter.
Three separate problems follow:
- A narrower window. Warmth speeds bud development, so the gap between 'ready to pick' and 'too coarse' shrinks. Because riding machines mean all 340 ha must be picked within six days, the cooperative can no longer stagger plots; quality falls, and the price index at 88 (−12% since 2000) is consistent with that.
- Frost exposure. In 1980 the average picking date fell after the frost season. Now bud break arrives while frost is still possible - in 2021 early warmth plus a late frost destroyed 30% of the first crop. Earlier growth is not extra growth if it is then frozen.
- Labour timing. The same six days now compete with other spring work, and 82 of 120 members are 65 or over, so the cooperative cannot simply work longer hours.
What the data does not show: total annual yield. Warmer conditions may raise second and third crop volumes, which could partly offset the first crop. Before acting, the cooperative should put total yearly yield and revenue beside these figures.
2. Which proposal would you recommend to the cooperative, and how do the age structure and the 12 departures constrain the choice?
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Test each option against the constraints.
Later-budding cultivar - the correct biological fix: it restores the gap between picking and frost and widens the harvest window. But replanting takes about five years before the new bushes yield. With 82 of 120 members aged 65+ and 12 leaving in five years, most members cannot carry five income-free years. Do it only on the 12 abandoned fields as a trial (~30 ha) with public replanting subsidies - those fields have no owner waiting for income, so the wait costs least there.
Shading for kabusecha - uses existing bushes, works within one season, and raises price per kilogram, which answers the 88 price index directly. But it needs labour in the peak weeks and capital per hectare, and heavy shade in a hotter summer raises leaf damage. Feasible on maybe 10 ha of the best plots, not on 340.
Solar sale - instant cash and no labour, but it permanently removes farmland, the fields are scattered, and tariff rates fall over time. It solves the cooperative's cash problem by ending part of the cooperative.
Recommendation: shading on the best 10 ha this season, the later cultivar on the abandoned fields as a five-year trial, and no sale of land yet. Sequence risk rather than betting on one option - with an ageing membership, the cheapest mistake is the one that can be reversed.
3. Propose one indicator the cooperative should record every year to detect this risk early, and explain how it would be used.
Read the worked answer
Indicator: the frost-free gap per plot. For each plot record three dates each spring:
- Bud-break date (萌芽日) - when new shoots first appear;
- Last frost date - the final morning the plot records frost (a cheap minimum thermometer, or the nearest official station);
- Picking date.
Then calculate: gap = picking date − last frost date, and window = days between bud break and the leaves becoming too coarse.
How it is used: if the gap shrinks toward zero, the plot is entering the 2021 situation and frost protection (fans, sprinklers, covers) or a shift to a later cultivar is needed on that plot. If the window shortens below six days, machine capacity is the binding limit and harvesting must be staggered by cultivar rather than by date.
Why this indicator: it costs almost nothing, uses records members already keep, and it is measured per field - so it shows which land is at risk instead of averaging the whole 340 ha. A single cooperative-wide average would hide exactly the plots that need deciding first.