Chile's Institute of Agricultural Research (INIA) has found the productivity of Aconcagua Valley table grape growers is impacted by suboptimal levels of air capacity in their soil.

Around 300 people attended a recent international seminar on the use of rootstocks in grape production - a key element of the INIA study, testing how rootstocks affected Thompson Seedless variety productivity over three years.

The researchers found an air capacity above 12% increased productivity substantially, but 80% of vineyards in the valley were below this range.

The Aconcagua Valley accounts for around 20% of Chile's table grape exports.

The study concluded low air capacity and high compaction were the biggest problems in the soil, mostly caused by an excess of water.

In the face of these problems, growers can at least take comfort in the fact the study found significantly higher productivity rates for vineyards where rootstocks were used, with an average of 2,271 boxes per hectare compared to 1,770 boxes without rootstocks.

The rootstocks Freedom and Richter showed the highest performance, with the latter leading to an average 2,900 boxes per hectare.

Speaking at the seminar, Subsole technical director Gabriel Marfán said the effectiveness of rootstocks depended on whether there were existing deficiencies in the soil; if the soil was good and didn't have compaction or excess irrigation, the differences were not as marked, however the use of rootstocks was still beneficial for the vigor of plants.

International experiences

Jennifer Hashim, consultant and researcher with the Andy Walker program in California, said while Chile's soil and weather were similar to her state, the challenge was finding the right combination of varieties and rootstocks that could resist nematodes.

In her studies, the Ramsey rootstock has proven to be the most appropriate for California's high salinity soil and resisting nematodes. She said resistance was not the only goal however, as attaining vigorous plants with good fruit flavor and color was a priority too.

Pieter Raath from South Africa's Stellenbosch University, said growers in his country had been using rootstocks for years with 80% of new plantings using the Ramsey or Richter types.

"We have simplified things by sticking to two rootstock patterns that have been successful for us. This has been a long effort and I think Chile has the advantage of knowing these experiences and has the precaution to have fewer mistakes," he said.

"When I speak with friends in Chile they tell me they tell me their biggest problem is that a lot of fruit falls, and we don't have these problems thanks to rootstocks, which make plants more vigorous."

The profitability challenge

Gabriel Selles, who heads up INIA's La Platina project, said the industry's biggest challenge was to get back in black, and to do this growers needed to achieve better productivity.

"Table grapes require determined management, and this management requires people, who are becoming more scarce and expensive every day, so the challenge is raising productivity, because you will always require labor and this has to be funded," he said.

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