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Are you guessing on rice fertility?

Increasing the yield potential on your precision-graded rice fields may be as simple as pulling soil samples and following your state-recommended fertility guidelines, according to Tim Walker.

Walker, a research assistant at Mississippi State University in Starkville, Miss., says the deep cuts made to precision grade a field with a 0.1 to 0.2 slope often result in decreased fertility and a shortage of nutrients available to the rice plant.

When the top of the soil is shaved off, about a foot of which is usually organic matter, that “deep cut” area is often left with sulfur and zinc deficiencies.

However, farmers can often obtain significant economic responses simply by applying fertilizer in these deep cut areas, Walker says.

After landforming a field, Walker recommends taking at least one set of soil samples from the deep cut areas, one set in the filled areas and one set in the areas where very little dirt has been moved.

“You are almost guaranteed to have a nutrient deficit in the cut areas,” he says. “Often, the soil from the deep cut areas is put on top of the fill areas, so your nutrient deficiency in those areas could be the same as it is in the cut areas. That is why soil samples should be taken from the fill areas as well as the deep cut areas of a field.”

Often the nutrient information obtained from soil samples can take the guesswork out of fertility management, providing you with the information needed to correct deficiencies and increase yield potential.

In his Mississippi on-farm field studies, Walker is studying rice yield responses on landformed fields to varying rates of nitrogen, chicken litter, phosphorus, potassium and zinc.

“In our research with cut fields, we haven't seen a statistically significant yield response by increasing nitrogen applications above what is recommended by Mississippi State University,” he says. “It is a management issue with nitrogen. If you can get that flood applied rapidly after the fertilizer application, you should be able to stay with the recommended rates.”

While only Lemont and Priscilla varieties were included in Walker's research before this year, he has added Wells and Cocodrie to his 2001 field studies. “In our 2000 work, Lemont did not show an increase in yields on cut fields by going over the 180 pounds of nitrogen per acre recommended by Mississippi State University. Priscilla, also, statistically showed no yield increase to additional nitrogen.”

Whatever nitrogen application rate a grower chooses, Walker cautions growers on applying all of their nitrogen in one pre-flood application. Instead, he suggests growers apply two-thirds of the total nitrogen pre-flood and one-third mid-season.

Current Mississippi guidelines recommend a rate of 180 pounds per acre of nitrogen for Priscilla, Cocodrie and Wells. For each of these three varieties, the recommendations call for 67 percent of the total nitrogen to be applied pre-flood when the rice plant is approximately 6 to 8 inches tall. The remaining 33 percent should be applied at mid-season.

Nitrogen application recommendations for Lemont differ slightly although the 180-pound rate remains the same. “The nitrogen application on Lemont should be applied 50 percent pre-flood, 25 percent mid-season at 0.5-inch internode elongation, and 25 percent seven to 10 days after 0.5-inch internode elongation,” Walker says.

Walker is seeing some increase in yield in response to very high rates of chicken litter on lighter soils. However, he says, he hasn't seen the same effect on clay soils even with applications of 1,000 pounds or more of chicken litter per acre.

“An application of 1,000 pounds of pelletized chicken litter per acre increased the rice yields on sandy loam soil by 42 bushels (dry weight) over the untreated check in our study. The general trend we are seeing is that as litter rates are increased, yields are increased. To see any increase, though, it will take a rate above what is generally recommended,” Walker says.

Growers may also not see a significant yield increase to fertilizer amendments such as phosphorus, especially on silty clay soils.

“If you are going to be leveling fields, pull a few soil samples from the cut areas and see what you've got out there. If phosphorus is up in the 70 to 80 range, though, you probably won't see a yield response to a phosphorous application,” he says. “Each of the silty clay fields in our study tested high in phosphorus in the cuts and in the fill areas, and additional phosphorous applications did not increase our yields.”

Walker is also studying the yield effects, if any, landformed fields have to potassium and zinc treatments. “This year is the first year for us to look at these fertilizer amendments, and our data, including studies on both silt loam and clay soils, will be ready in late fall 2001,” he says.

For those growers with high-pH soils, Walker says the first thing to do is flood their rice fields as quickly as possible. “If it takes longer than 10 days to achieve a flood on the entire field, you may want to consider using ammonium sulfate as your pre-flood source of nitrogen,” he says. “If urea is used, and the fields are straight-leveed, you can consider fertilizing only the paddies that can be flooded within five days, and delay fertilize applications for the lower paddies until a time which would allow them to be flooded within five days.”

“I have seen cuts in Sharkey clay soil that are 6 or 7 feet deep and have no nutrient deficiencies and no significant resulting yield reduction. However, I have also seen cuts in silt loam soil that are only 8 to 10 inches deep with phosphorus and zinc deficiencies. In every case, the soil test would have called for the application of the deficient nutrient,” Walker says.

“The general trend is that as clay content decreases, the possibility of nutrient deficiency in the cut areas increases.”


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