Stressed-out tomatoes need natural help.
From an article by Steve Mc Veigh in Farmer's Weekly, November 24, 2000

When Jacques Marais replaced vines with
another money-spinner - tomatoes - he found
an excellent remedy for osmotic stress

TOMATOES give the annual turnover of Roodehoogte, Jacques Marais' fruit and table grape farm in the Robertson district, a welcome shot in the arm.

Mr Marais gows 10 hectares of vines and three hectares of apricots. One hectare of vineyard is replaced every year as part of an ongoing cyclical planting programme.

When the old vines are removed, crops of field tomatoes are planted for two years instead to "rest" the soil. Poles and trellising wires, left in place when the vines are removed, provide support for the tomato plants.

You'll always find about a hectare of field tomatoes at Roodehoogte on land being rested between vine plantings, farm manager Werner Saunders explains. This means that the tomatoes are always grown on virgin land, and they have no negative effects on either the soil or the vines which will follow them.

This versatile enterprise also produces 1.5ha of onions and sweetcorn annually and about a hectare of green peppers and "undercover" tomatoes grown in tunnels.

When Farmer's Weekly paid Roodehoogte a visit, 1.2ha of P355 were just coming into full production. This longlife, restricted growth table tomato is ideally suited to their field production system. The RS4053 (Cromex) variety is grown in the tunnels and shadehouses.

There are two plantings of field tomatoes a year at Roodehoogte - one early and one late in the season. Cool conditions usually decrease tonnages during the early season. With improved stress management, Werner has increased the early crop by 41.4%.

Strategies for optimising yields

Tomato seed is germinated in seedling trays in Roodehoogte's tunnels. Seedlings destined for field cultivation are transplanted into standard tunnel production bags containing a pine shaving medium in July and August.

The young tomatoes are kept in one of the tunnels until they are well established in their bags, then hardened off and moved outdoors in September. The first crop is usually harvested in early November and the last at the end of January.

The tomatoes aren't planted in the soil. They are left in their planting bags, carefully positioned directly beneath the button drippers used to irrigate that vineyard block.

Fertiliser is fed directly into the planting bags with irrigation water, concentrating nutrient in the root zone. Young plants are irrigated four times a day until they are properly established.

Once roots protrude from the drainage holes in the bags and penetrate into the soil below, the plants are irrigated twice a day.

The 1,2 hectare block of land currently being used for field tomatoes is on a slope, so tomatoes growing on the lower levels tended initially to get more water than those higher up.

When they tried to balance their water scheduling, the plants at the top of the slope came under considerable osmotic stress.

After consulting the experts, they decided to keep on scheduling irrigation in favour of the lower part of the block. The top half was treated experimentally with Yield-Plus, a natural product which helps plants cope with stress and produce a good crop under less than optimal conditions.

Quinton Kruth (left) and Stephen McLean of Yield-Plus
confer with Werner Saunders (centre).

Yield-Plus is an organic plant solution based on a derivative of L-cysteine, a naturally occurring organic amino acid which has an antioxidant effect on another amino acid - proline - found in the plant, Trevor Nelson of Yield-Plus explains.

Proline enables plants to tolerate certain kinds of stress for longer periods than they would ordinarily be able to. Adrenalin has a similar effect on human beings in stressful situations.

Research done over a period of 30 years substantiates claims that increased cysteine levels enable plants to produce higher levels of proline, Trevor says. Proline synthesis raises sugar levels, as excess proline is converted to glutamates. This give the plants greater vigour and enhances osmotic functions, protein synthesis and carbon cell development.

The net result is healthier, stronger plants with greater resistance to disease, stress and drought, which utilise available nutrients and produce a crop more efficiently under stressful conditions caused by excessive heat, lack of moisture, cold and other environmental factors.

Treated plants can cope with stress and do not immediately invoke primitive defence mechanisms like shedding flowers and fruit, or slowing down metabolic processes. These reactions would normally retard growth and reduce fruit load and yield quality and uniformity.

Roodehoogte's tomato vines were sprayed with 600ml/ha of Yield-Plus, buffered with pH Green-Plus to a pH of 5.0, two weeks before flowering. Follow-up sprays of 300ml/ha were administered every two weeks.

Sprayed plants grew more evenly and produced more consistent yields than untreated plants lower down the slope. Medium-sized tomatoes are easiest to market, Quinton Kruth, manager: Western Cape for Yield-Plus Agricultural Products, points out.

Treated plants yielded a more uniform crop of medium-sized tomatoes than untreated plants. Quality and colour were noticeably better, treated tomatoes were definitely sweeter and yields were substantially higher.

Untreated rows produce less uniform tomatoes

The treated section produced its crop between seven and 10 days before the rest of the field and continued bearing later in the season, Werner Saunders confirms.

Roodehoogte's average field tomato harvest is 45 tons/ha at this stage of the season, Werner says. The better-irrigated but untreated portion of the field yielded 43,231 tons/ha. The osmotically stressed but treated portion produced 61,128 tons/ha - an increase of 41.4%. Without the treatment, Werner estimates that the osmotically stressed portion of the block would only have produced about 40 tons/ha - 52,8% less.

This would represent a loss of between R25 353,60 and R59 158,40 per hectare, at a market price of between R1,20 and R2,80 per kilogram for first grade tomatoes.

Treatment with Yield-Plus cost about R540/ha. According to Quinton Kruth, yield increases more than covered this expenditure. Jacques Marais has decided he will no longer have "control" areas in his tomato fields. "Everything on my farm will be treated with Yield-Plus in future"