California soil toxins worsened by drought

California soil toxins worsened by drought

Lack of water will take away one of the weapons California growers can use to combat soil toxins.

Salinity and scarcity of water were very much in the spotlight at the 2014 California Plant and Soil Conference in Fresno.

Multiple speakers showed pictures of what they labeled “California snow,” salt that had precipitated out atop soil where trees and other crops fight to grow.

They painted a grim picture of a year in which sparse winter rains have done little to drive toxic minerals deeper, away from plant roots. They said an expected lack of available water will take away one of the weapons growers can use to combat the toxins.

 

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But they also talked of water management and steps growers are taking to find salt-tolerant crops or varieties and research on just how “tough” some crops can be.

Among those looking for crops that can survive the less than friendly soils on the Central Valley’s west side is Gary Banuelos, a researcher with the Agricultural Research Service in Parlier.

Banuelos said the villain is not simply limited to salts. Also included as potentially toxic are selenium and boron. He talked of alternate crops for high salt and boron conditions.

Leaching in tiled fields has been one way of coping with the toxins, he said. But leaching boron out of the root ball requires three times the amount of water than that required to leach salt.

“It can be done with water, but it’s almost non-existent (this year),” Banuelos said. “That’s why a lot of land is fallow.”

Banuelos has been looking for plants that can grow in toxic soils, including some varieties of poplars for biomass to generate electricity, cacti with fruit that can be used in juice and other products, grasses that may be blended into cattle feed, mustard, broccoli, safflower and other plants.

“We’re always looking to at least being able to earn between $1,000 and $1,500 an acre or otherwise the crop will not even be considered,” he said.

Others who addressed the conference included:

• Rick Snyder, with UC Davis Cooperative Extension, who had some advice on evapotranspiration-based scheduling during a drought.

He said producers need to take into account fog, morning dew, solar radiation or light interception by the foliage and other factors.

Applying less water will reduce deep percolation, he said, but it could result in higher salinity with the rooting zone so that eventually, deficit irrigation will become more problematic, especially if practiced over a long term drought.

 

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He said producers may want to sort out a percentage of irrigation availability that will still bring profit, idling some land if necessary to assure they have a percentage they can apply to achieve that goal.

In some cases, he said, it might be better to reduce the area planted and apply more water to smaller cropped area to maintain higher production.

If water supplies are inadequate, Snyder said, it is best to irrigate orchards and vines at about the same frequency as in non-drought years, but apply less water per irrigation.

Salt tolerance

• David Doll, University of California farm advisor for Merced County, who talked of salinity tolerance in almonds.

He said almonds are sensitive to soluble salts and high levels of sodium, chloride and boron. Like Banuelos, he said salinity can be managed by leaching, but that practice is not always possible with low water availability, poor water quality, a high water table and some soil types.

 

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He said almond rootstocks vary in their ability to tolerate saline conditions. A 20-year study showed that peach rootstocks showed increasing signs of sodium toxicity with the leaves. But trees grafted to peach almond hybrid rootstocks were larger and produced higher yields.

Some almond varieties show sodium leaf toxicity before others. Greater sodium toxicity was found in the Fritz variety in comparison to Nonpareil, for example.

• Dan Putnam, UC Davis authority on alfalfa, who said that crop is a major consumer of water but may be capable of tolerating higher salt levels than previously thought.

Putnam said there is evidence of significant variation among alfalfa lines in salinity tolerance.

Some degraded water that could not be used on food crops can be used on alfalfa, he said, adding that alfalfa is in higher demand than many other salt-tolerant plants.

While salinity may trigger a decline in percentage of germinated seeds, Putnam said, “that doesn’t scare us; we can live with a 40 per cent level.”

• Blake Sanden, UC irrigation and agronomy adviser in Kern County, who conceded there are “long term management issues and research gaps” when it comes to salinity tolerance in pistachios.

Despite many small-scale field trials over the past 30 years, he said, almost no marginally saline water in the San Joaquin has been used for long term production.

Sanden characterized a buildup of boron in the soil as “a potential boron time bomb.” His research showed a doubling of total boron in the soil after nine years.

Without 6 to 10 inches of rainfall or fresh water winter irrigation for leaching every one to two years, he said, high levels of boron could render growing of the crop to be not sustainable.

His research showed greater salinity coming from well water than surface water. But, he added, the economics of using cheaper pumped saline water may outweigh the return when using considerably more expensive canal water.

• Dennis Corwin, with the Agricultural Research Service in Riverside, who talk of using site-specific irrigation management to address soil salinity.

The approach involves precision agriculture used to maximize yields despite variability within a given field. Equipment is used to measure electrical conductivity within a field, which can be influenced by properties that include salinity, water content, sol texture, density, organic matter and temperature.

In addition, soil samples are taken based on gathered with mobile electromagnetic induction equipment.

Inputs are then applied only “where, when and in the amounts needed,” Corwin said. That also can minimize environmental impacts, he said.

 

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