Tomato Fruit Cracking Under Drip Scheduling
A farmer irrigates 0.5 ha of staked tomato under drip. The system delivers 4 L/h per emitter with emitters spaced 30 cm and laterals 1 m apart. The farmer has been running the system for 3 hours every second day. Recently the crop has shown: (a) radial cracking and concentric cracking on ripening fruit, (b) blossom-end rot on about 8% of fruit, and (c) some wilting of plants near the ends of laterals. Soil tests show adequate calcium in the soil but the farmer has been fertigating with a high-potassium mix. The farmer wants to increase irrigation to fix the wilting and also apply a calcium foliar spray to fix the rot.
1. Assess whether more irrigation and a calcium foliar spray are the right responses to blossom-end rot in this situation.
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Blossom-end rot (BER) is a calcium transport disorder, not usually a soil calcium shortage. Calcium moves in the xylem with the transpiration stream and is poorly redistributed, so it reaches poorly transpiring tissues like the fruit tip only when water flow is steady. The soil test already shows adequate calcium, so a foliar spray is unlikely to help: foliar Ca moves little into fruit, and the problem is delivery, not supply.
The more likely driver here is irregular water supply. The farmer irrigates every second day in 3-hour blocks, which gives large wet-dry swings. Combined with the high-K fertigation mix, which competes with Ca and Mg uptake, and the wilting at lateral ends (suggesting pressure/flow problems at the far end), the crop is experiencing fluctuating moisture and possibly uneven salinity. The correct response is to stabilise and even out moisture - smaller, more frequent irrigations, checking emitter uniformity and pressure at the far ends - and to review the K:Ca:Mg balance of the fertigation programme, not to add more water in bigger pulses or spray calcium.
2. Using the system specifications, estimate the application depth per irrigation event and comment on whether the current schedule is likely to be causing the cracking.
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Emitter spacing 0.30 m, lateral spacing 1.0 m, so emitters per square metre = 1 / (0.30 × 1.0) = 3.33 emitters/m². Each delivers 4 L/h, so application rate = 3.33 × 4 = 13.3 mm/h.
A 3-hour run therefore applies about 13.3 × 3 ≈ 40 mm per event. Applied every second day, that is an average of about 20 mm/day - a very heavy pulse for tomato, well above typical crop demand. That large, infrequent pulse wets the root zone deeply and then dries it, producing exactly the wide moisture swings that cause radial cracking (fruit splits when a dry period is followed by a big water influx and rapid fruit expansion) and contribute to BER.
Judgement: The schedule is a plausible cause of the cracking. The farmer should shorten and split the runs (e.g. smaller depths more frequently) to keep moisture even, verify actual delivery with a catch-can test, and check pressure/emitter clogging at the lateral ends causing the wilting.