Posts Tagged ‘ DFT ’

Issue 98: Greenhouse Production In Japan

January/February 2008
Authors: Mike Nichols & Bruce Christie

Although Japan has a large protected cropping industry, only a small proportion of growers use hydroponic systems, with an emerging trend towards plant factories. Report by Mike Nichols & Bruce Christie

In January 2007, we accepted an invitation to speak on organic hydroponics at the 24th SHITA conference in Tokyo, Japan. It was a very rushed visit, but we took the opportunity of looking at the progress being made in Japan in both plant factories and greenhouse crop production. This article will only look at greenhouse crop production, and plant factories will be the subject of a future article.

There are some 52,000 hectares of greenhouses in Japan, and a further 14,000 hectares of rain shelters. The bulk of the greenhouses are covered in plastic film, and less than 5% of the greenhouses are glass clad. Sixty-nine percent of the total greenhouse area is used for vegetable production, only 17% for flowers, and 14% for fruit tree production.

In such a high-tech country as Japan, it is somewhat surprising to find the area of greenhouses devoted to soilless culture is only 1,500 ha (which is comparable to only 3% of the total protected cultivation area). Although there are a range of hydroponic systems used, rockwool predominates followed by the deep flow technique (DFT), and three quarters of the crops grown hydroponically are vegetables. In Japan, melons, strawberries, and watermelon are all classified as vegetables and make up 30% of total greenhouse vegetable areas.

Our visit was in late January, the middle of the northern hemisphere winter, and our observations must clearly be tempered with this – coming from the middle of a New Zealand summer it is all too easy to be critical of production being undertaken in the most difficult part of the year.

In fact, it would be fair to say that with one exception we were very favourably impressed with what we were shown. We only had time to view a few properties in Chiba Province (just north of Tokyo), but learnt a great deal in just two days.

Chiba Province is at latitude 36°N, but has a far better winter climate than one might anticipate, as winter is the dry season, with very little cloud, and better levels of insulation than one might initially anticipate.

Presentation and freshness was paramount at this Farmers Market.

Our first visit was to a farmers’ market, housed in a specially planned building, and selling a very wide range of locally produced fruit and vegetables. Presentation and freshness was paramount, and the local farmers were clearly providing the local consumers with what they required with minimal ‘food miles’ and possibly a small carbon footprint! Of course, it is still possible that for out-of-season production the carbon footprint would still favour imported produce from a southern hemisphere country producing in the summer with lower production costs!

Our first visit was to a greenhouse strawberry producer. Producing ripe strawberries in the middle of the winter demands real attention to detail, and we were most impressed with the appearance of the crop. It was being grown in rockwool slabs on raised troughs, which were watered and fed using a recirculating hydroponic system. Surprisingly, both honeybees and bumblebees were being used for pollination with excellent results, and the price in the shop was even more impressive. We estimate that the price was between NZ$20-25 per tray, or around NZ$200/kg!

Honeybees and bumblebees are used for strawberry pollination.

In Japan, strawberries are classified as a vegetable crop.

This strawberry crop is grown in rockwool slabs on raised troughs.

The crop did not compare well with the greenhouse strawberry crops seen in Belgium (Nichols, 2006), but of course that was in the middle of the summer.

Perhaps the most interesting aspect of production was the area set aside for runner production – a key component of any out-of-season strawberry growing.

We use tip runners at Massey University (Nichols, 2002), but at this property runners were rooted into individual pots placed just below the rockwool slabs. It looked to be a more labour intensive and tedious system than tip runners.

Our next visit was to a greenhouse tomato producer. This was a little disappointing because the technology of greenhouse tomato production has developed tremendously over the past 20 years, and this was rather like visiting a time warp. High wires and layering are the keys to efficient production these days and yet this house still had low wires and layered so the fruit essentially sat on the floor.

Seedlings are grafted onto resistant rootstocks.

This house has low wires with the fruit sitting on the floor.

This operation is a small family business.

This was very much a family operation, which suggests inevitably that agribusiness will eventually take over greenhouse crop production, if only because it enables the manager to have sufficient time to keep up-to-date with new developments, and to re-invest in new technology.

Of course, it was not all bad; the next crop of seedlings had been grafted onto resistant rootstocks, the fruit quality looked excellent, and the small pack-house was simple but effective.

Deep flow hydroponic systems using floating rafts are something that we have little experience with in New Zealand. One of the main reasons for visiting Japan at this time was to get a feel for the potential of the system for leafy vegetables, particularly with reference to aquaponics. Not that Japan has developed any aquaponic systems to date, but they are well advanced with deep flow systems.

Soilless culture represents only 3% of the total protected cultivation area.

Our third visit was to a grower who produces about 250t per year of mitzudamo (also known as mizuna) from a 0.8ha greenhouse operation using a very sophisticated floating raft system. This is a continuous year-round operation, which starts with five or six seeds per cell being automatically sown on a block of polyethylene foam cells. Following germination in a controlled temperature room, the plants are grown on for a short time, before the individual cells are automatically transplanted by machine into holes in the expanded polystyrene floating rafts, then transferred to the deep flow system.

The initial rafts have their holes close together. When the plants have grown sufficiently they are again transplanted automatically by machine into floating rafts with holes at a wider spacing. The only difference between rafts is the number of holes per raft.

Seedlings are grown in small plant factories.

Mizuna seedlings with their roots suspended in solution.

Seedlings are automatically transplanted by machine into holes in the polystyrene floating rafts.

Typical DFT growing system.

Seedlings are automatically transplanted into rafts with wider hole spacings.

Harvesting rafts of leafy vegetables is still a manual process.

This small pack-house is simple but effective.

The final product ready for distribution.

A key component of successful transplanting is to ensure that the roots all hang down through the hole, and this is achieved by means of a water stream at transplanting.

The next visit was interesting because it involved the growing of spinach in a hybrid floating raft/NFT system. A similar propagation technology was used to the mitzudamo grower, but because spinach is very susceptible to root-borne diseases (e.g. Phytophthora), each planting was modularised with independent reservoirs.

High root temperatures can also increase disease risks so each reservoir incorporated a heat interchange coil, which could be used to cool the nutrient solution in the summer – between crops it could be used to pasteurize the nutrient solution by circulating hot (80°C) water through the heating coil, a novel way of reducing disease problems.

This spinach crop grown in a hybrid raft/NFT system.

Open view of the hybrid raft/NFT system.

A healthy crop of spinach.

Spinach can be susceptible to root disease problems.

Independent nutrient reservoirs prevent any disease spreading.

This grower had also started to use plant factories for some of his crop production, but in this case only for the propagation stage. We saw both tomato seedlings and lettuce seedlings grown in small plant factories, and there is little doubt in our minds that although the development of plant factories for many crops may be some years away, the use of plant factories for seedling production is here and now, if only to ensure the provision of good quality seedlings exactly when required, without reference to time of year or weather conditions. The speed with which quality seedlings can be produced on demand is outstanding.

The same cannot be said about the crop of lettuce being grown in the greenhouse from these seedlings, however. Botrytis was starting to appear, and could easily have been controlled with a single application of fungicide while the plants were small. This would have the effect of preventing Botrytis spores germinating on older leaves as they died due to old age. Initially, Botrytis normally only infects dead plant material – if the older leaves are protected by a suitable fungicide before they die, then Botrytis infection can be minimised.

An alternative strategy is to ensure that the humidity in the greenhouse is kept below 90%, but in practise this is difficult to achieve at the base of a lettuce crop. Botrytis spores require the presence of liquid water if they are to germinate and infect plants, and keeping the humidity down reduces this risk, as well as reducing the risk of tipburn on the leaves.

About the author

Drs Mike Nichols and Bruce Christie are horticultural research scientists at the College of Sciences, Massey University, Palmerston North, New Zealand. Email: or

• Nichols, M.A. (2002), Strawberry tip runners, Practical Hydroponics & Greenhouses, 64, 34-5.
• Nichols, M.A. (2006), Berry Fruit in Belgium, Practical Hydroponics & Greenhouses, 90, 41-46.