Tomatoes or Sorghum? A Smallholder Weighs a Supermarket Contract
Mpho farms 8 hectares of sandy loam 20 km from a district town of 45,000 people. Rainfall averages 430 mm, but the last five seasons ranged from 180 mm to 610 mm, and the rains now often start in December rather than October. Mpho grows 6 ha of sorghum and 2 ha of maize for home use and local sale; in poor years sorghum yields fall to about 300 kg per hectare. A supermarket chain has offered a contract for 150 crates of tomatoes a week from May to September, when prices peak, and will collect from the farm. Each crate holds about 15 kg. Mpho's borehole yields 1.5 litres per second of water at 900 mg/l dissolved solids. A drip system can be bought on credit at a high interest rate. Labour is Mpho, two adult relatives, and hired pickers at harvest. A tomato crop needs about 5,000 m³ of water per hectare per season, and drip irrigation is roughly 60% efficient.
1. Using a water budget, decide how much land Mpho can realistically put under tomatoes, and what should happen to the rest of the farm.
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Step 1 – Water available
1.5 l/s × 86,400 s = 129,600 litres a day = about 130 m³ a day. Over a 150-day season (May–September): 130 × 150 ≈ 19,400 m³ of water pumped.
Step 2 – Water actually reaching the crop
At 60% efficiency, only 19,400 × 0.6 ≈ 11,600 m³ is available to plants. The rest is lost in conveyance, evaporation and uneven drip delivery.
Step 3 – Area supported
11,600 m³ ÷ 5,000 m³ per hectare ≈ 2.3 hectares. That is a maximum with no allowance for domestic use, livestock, pump downtime or storage losses. A prudent figure is 1.5–2 ha.
Step 4 – Does that meet the contract?
150 crates × 15 kg = 2,250 kg a week. Over 20 weeks: 45 tonnes. At a realistic 25–30 t/ha under drip, 1.5–2 ha yields 37–60 t - so the contract is achievable at the upper end, but vulnerable to a single bad pest or heat event.
Step 5 – The rest of the farm
Keep 5–6 ha under sorghum and maize with improved seed and row planting. This protects household food and spreads risk: if the borehole fails or prices collapse, the family still eats.
Decision: 1.5–2 ha of tomatoes under drip, 5–6 ha of rain-fed staples, and a written clause agreeing a reduced volume in poor seasons rather than defaulting on the whole contract.
2. Explain the risks of this contract and how Mpho could reduce each one.
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1. Water risk. The borehole is the single source; a pump failure in July would kill the crop within days. Reduce by: a storage tank sized for at least three days, a spare pump or service contract, and mulching to cut evaporation.
2. Market risk. The supermarket can reject loads on quality, and a glut in May can drop prices even though the contract is fixed. Penalties for under-supply can exceed the profit. Reduce by: a written agreement on grades, rejection rules and partial-delivery penalties; a second buyer such as local traders or schools; and staggering planting dates so harvest peaks do not all fall in one week.
3. Production risk. Tomatoes are perishable, pest-prone and heat-sensitive; 32 °C-plus days cause flower drop. Reduce by: shade netting or a windbreak, integrated pest management, and using a variety suited to hot, dry conditions.
4. Financial risk. Credit at a high interest rate must be repaid even in a failed season. Reduce by: borrowing only for the drip line and seed, not for a vehicle; and repaying from the first two months of sales.
5. Labour risk. Harvesting 2,250 kg a week needs pickers at short notice. Reduce by: agreeing a regular picking day and a share of the work with a neighbour.
The general principle: the contract converts a weather risk into a contractual risk, so the clauses and the back-up supply matter as much as the agronomy.
3. Suppose rainfall falls by 15% and the rains start a month later. Explain how Mpho's plan should change.
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What changes physically
- A 15% cut takes the average from 430 mm to about 365 mm, and the poor years move from 180 mm toward 150 mm. Sorghum yields of 300 kg/ha in bad years would become more frequent.
- A later onset shortens the growing season and pushes maize, the thirstier crop, into a hotter, drier period, raising the risk of failure at flowering.
What changes in the plan
- Shift the crop mix toward early-maturing sorghum and cowpea rather than maize. Sorghum tolerates heat and short seasons; cowpea adds nitrogen and a cash pulse.
- Reduce tomato area, not increase it. Less rain means more reliance on the borehole, and recharge will also fall, so the 1.5 l/s cannot be assumed to last. Cutting to about 1 ha and negotiating a smaller contract is safer than chasing volume.
- Invest in water storage and soil moisture - tanks, mulching, tied ridges, and contour furrows to capture what rain does fall.
- Re-negotiate timing. If rains start in December, planting dates and the contract delivery window must shift or Mpho will be supplying into a falling market.
Reasoning to state clearly: the rainfall change affects Mpho through two channels at once - less rain for rain-fed staples and less recharge for the borehole that feeds the tomatoes. That double exposure is why the answer is to reduce the irrigated area rather than to expand it to compensate for lost staple yields.