Research shows treatment equals or surpasses other methods
When a crop input reduces costs without hurting yields, word gets around quickly. Take zinc-treated rice seed for example. In Arkansas, rice acreage planted with zinc-treated seed grew over 15-fold in one year, from around 10,000 acres in 1999 to perhaps as many as 250,000 acres in 2000.
"We've gone from a few producers buying zinc-treated seed and not really knowing what they had, to this," said Nathan Slaton, Arkansas Extension rice specialist.
In fact, it's been so successful that after just two years of research, Slaton was comfortable with recommending - where needed - a 0.25 to 0.5 pound of zinc per hundredweight of seed for the 2000 growing season. "A third year of research conducted in 2000 continues to support previous work showing that zinc seed treatments perform equal to soil- or foliar-applied zinc."
What's the reason for such sweeping acceptance? "All our research on zinc-treated seed has shown very positive results, very good yields and low cost compared to the standard foliar- or soil-applied methods," Slaton said. "It's a quarter to a fifth of the cost. There's no special trip. The zinc is on the seed. The distribution is perfect. The only way you can mess it up is by not applying it on the seed at the correct rate."
Slaton noted that zinc deficiency is most prevalent on silt and sandy loam soils with high pH. "Generally, as pH increases, zinc availability to the plant decreases."
Slaton estimates that 25 percent of Arkansas rice acreage falls into this category. It's been on these acres that the increase in zinc-treated seed has taken place. "We (Arkansas) generally don't have a problem with zinc deficiency on clay soils."
The importance of zinc has long been known to Arkansas producers, according to Slaton. "In one test this year, we saw a 100-bushel yield difference between plots without zinc and those treated with zinc. If you leave a deficiency untreated the entire year, a lot of times, the plants will struggle but recover. The range in plant yield response is typically between 10 bushels and 100 bushels per acre."
A University of Arkansas rice research verification trial also un derscored the need for zinc on high-pH, silt loam soils, according to Slaton.
"We looked at the soil tests on the field and thought that it was a prime candidate for zinc, although the farmer indicated the field did not have a history of zinc deficiency. We put out some foliar treatments to monitor it, and sure enough, when he flushed the rice the first time, it got sick everywhere except where the zinc was applied."
Currently, there are three recommended ways to apply zinc on rice, foliar at preflood; a granular at preplant; or a seed treatment. Research indicates that all three provide the same level of benefit. But low cost is what makes zinc-treated seed so popular.
"Depending on your seeding rate, a high estimate for the seed treatment of zinc would be $4 to $5," Slaton said. "A foliar zinc application will cost $5 to $12 an acre for product - depending on whether you go with a zinc sulfate or an EDTA chelated solution - plus the cost of the application."
A granular application may cost $8 to $12 an acre for 10 pounds of actual zinc per acre. "If that's the only thing you're putting out, there'll be another $3 to $4 charge for application."
Slaton adds that the soil-applied method of zinc treatment is not only costly, but it's not very efficient either. In fact, the recommended rate of soil-applied zinc is 40 times the amount of crop removal.
"If you yield 150 bushels of dry rice, you're only removing a quarter pound of zinc," Slaton said. "Yet we're recommending that you apply 10 pounds an acre. That's because you can't get adequate fertilizer distribution going with anything less than that."
An advantage of soil-applied zinc is that there is a residual benefit to future crops. Over time, this has resulted in high soil-test levels of zinc in some fields. This winter, UA added soil-test zinc to pH and soil texture as factors to consider for recommending a zinc treatment. Slaton noted that soils generally contain 3 to 5 pounds of native zinc.
While soil-test zinc levels and other factors may not warrant a recommendation for zinc, Slaton notes that rice producers may nonetheless be nervous about leaving off a zinc treatment.
"If you're planting early, and your soil-test level is borderline or you just don't want to eliminate your zinc application, this is an ideal situation to use the zinc seed treatment at a lower rate just as an insurance policy on high-pH, silt loam soils."