Watch for the ‘Eddie Haskell’ of nitrogen loss

Vicky wanted me to talk a little about early season nutrient management. Since this is not my area of expertise, I turned to Toni Spencer with M&J Fertilizer in Winnie, Texas.

Virtually all her rice farmers apply products that contain the NBPT urease inhibitor reduce urea.

NBPT inhibits a common soilborne enzyme called urease. This enzyme catalyzes a reaction that combines water with urea (hydrolysis) to produce ammonia gas, which escapes into the atmosphere. Thus, NBPT reduces the amount of volatile nitrogen lost to the rice crop.

NBPT-treated urea can reduce ammonia loss by 50 to 90 percent. So if you cannot flush or flood your fields immediately after urea application, you should consider using an NBPT product. High temperatures, wind and lots of crop residue can exacerbate ammonia production and subsequent nitrogen loss.

Another source of nitrogen loss caused by specific soil microbes was cleverly and expertly described by Dr. Winston Earnheart, Mississippi crop consultant, at the recent National Conservation Systems Cotton and Rice Conference in Baton Rouge, La. One of these microbes is Nitrosomonas spp. which Winston dubbed the “Eddie Haskell” of nitrogen loss.

Many of you youngsters do not remember Eddie, but he was the bully and suck-up on the “Leave It To Beaver” TV show back in the 1950s and ‘60s.

Everyone watched this family comedy and grew to detest Eddie, who bullied Beaver Cleaver while making nice with Beaver and Wally’s parents, Ward and June Cleaver. Anyway, this bacterium converts ammonium (which can be taken up by rice plants) to nitrite in an oxidation reaction in the soil.

Nitrites and soil particles are negatively charged and since negatives repel, nitrites leach out of the rice plant root zone. Another soil microbe, Nitrobacter spp., then converts nitrites to nitrates in another oxidation reaction. Nitrates are also negatively charged, so they, too, can be lost to the rice plant.

Thus, you can say Nitrobacter spp. is Eddie’s evil cousin. However, there are products that can reduce these nitrogen losses. One of these products is DCD which has bacteriostatic activity — it slows the rate of conversion of ammonium to nitrites, increasing the amount of nitrogen fertilizer available to your crop.

Consult with your university agronomists, crop consultants and industry folks to see if it pays for you to use these products to increase your nitrogen-use efficiency.

Way furrow-irrigated rice pros and cons before embarking

Sam Atwell
MISSOURI
Agronomy Specialist
atwells@missouri.edu

How do I make a profit in 2017? Is there any way to decrease input cost? Can I change my operation to make it more economical, like switching to furrow-irrigated or row rice?

It’s a big deal if we can remove all or most levees from rice fields and maintain yields. New technology offers changes and the never ending need for continued research. These are questions producers are asking themselves and us.

Let’s take a look at furrow-irrigate rice or rice grown on beds with irrigation down the middles like other row crops. When growers ask whether they should switch to furrow-irrigated rice, my answer is a typical university one—“it depends.”

I’m accused of being on both sides, which is true, because it depends on your situation and management skills. It depends on “why and if” you want or need to make adjustments on your farm.

If the problem is water, soil, topography, crop rotation or economics, all are valid reasons for making changes, but they don’t carry the same weight. Saving money by pumping less water is the probably the hardest to justify.

If lack of water from a weak well means you can’t hold a flood, then you probably will not solve it with furrow-irrigated rice. However, if it’s because of sandy soils, then furrow irrigation may be exactly the solution.

If you have a sloping field with lots of levees, furrow irrigation often works well. Crop rotation is another good reason to consider furrow-irrigated rice, especially if you have heavy clay soils that wick well.

If you have what I call good rice soil—clay base with silt on top—and a good well, you will be hard pressed to equal it with furrow-irrigated rice. I have not seen any research where furrow irrigation increases yields over flooded under good conditions.

The goal for most Missouri growers using furrow-irrigated rice is to grow the crop on problem fields and not lose money. If you can stand slightly lower yields and offset it with lower input costs, then furrow irrigation should be considered and tried. But buyer beware.

University of Missouri researchers have studied furrow irrigated rice since 1988. The pros and cons are discussed in MU G4361 publication, published in 1993. It is available online at http://extension.missouri.edu/p/G4361.

Sulfur and zinc fertilizer sources are important

Dr. Dustin Harrell
LOUISIANA
Extension Rice Specialist
dharrell@agcenter.lsu.edu

Nitrogen, phosphorus and potassium are the first nutrients we generally think of for plant nutrition. It is important to remember that sulfur and zinc are also important plant essential nutrients needed for rice development. A soil test is good at determining if sulfur or zinc is limiting in your soil and if you need to apply additional sulfur or zinc to maximize rice yields. However, the fertilizer source is important to both these fertilizer nutrients to be adequately used by rice.

Sulfur must be in the sulfate form (SO₄) to be used by plants. Ammonium sulfate, zinc sulfate and other sulfate fertilizers are excellent sources of sulfur. Elemental sulfur (S₂) fertilizer (commonly 0-0-0-90 S) is not a good fertilizer source to use in-season for rice because the sulfur is not in an immediately available form. The elemental sulfur must be converted to the sulfate form before it can be made available for rice.

This conversion is called sulfur oxidation and it is done by sulfur oxidizing bacteria. Most of the sulfur oxidizing bacteria require…drum roll please…oxygen.

Once the rice is flooded, generally very little elemental sulfur will be converted into sulfate sulfur. In upland conditions, elemental sulfur oxidation to sulfate sulfur is a slow process that can be influenced by several factors including the size of the fertilizer (powdered will be oxidized faster), temperature, soil pH, soil water content, oxygen availability and the amount of sulfur oxidizing bacteria in the soil.

In upland conditions, conversion of large granules of elemental sulfur, like those in the picture, will be very slow. For example, one study illustrated that for a granular size similar to the one in the picture, only 2 percent of the elemental sulfur would be converted in a one-month period.

Therefore, applications of elemental sulfur for rice in-season for a soil that is deficient in sulfur is not recommended. However, applications of elemental sulfur are recommended in the fall and winter to bring soil test sulfur levels up and also to help lower soil pH.

Similarly, zinc must be in a soluble form to be used by rice immediately. Generally, we would like to see producers use zinc fertilizer sources that are at least 50 percent water soluble. Less soluble forms, like zinc oxide, are not immediately available and are not recommended for rice grown in a soil that is limiting in zinc during the growing season. The water solubility of zinc fertilizers is stated on fertilizer labels.

Nitrogen best management strategies

Dr. Jarrod T. Hardke
ARKANSAS
Associate Professor/Rice Extension Agronomist
University of Arkansas Cooperative Extension Service
jhardke@uaex.edu

Early cool and wet conditions during the preflood nitrogen (N) application window have caused continued problems in recent years. Whether growing a variety or a hybrid, overall yield potential is set by the efficiency of our preflood N application.

When preflood N is applied onto dry soil at the four- to five-leaf stage and a flood is applied timely, plants take up 60 to 70 percent of the total N applied over the course of three weeks. Uptake increases throughout the three week period with about 10 percent uptake in week one, 20 percent in week two and 30 percent in week three.

The preferred preflood N management option is always to apply NBPT-treated urea onto dry soil and establish the permanent flood in a timely manner (~ 7 days) to incorporate N below the soil surface. If faced with soil conditions that are not dry and before resorting to any other N application option, wait until the final recommended time to apply N based on the DD50 Rice Management Program.

Upon reaching the end of the recommended window with muddy soil conditions, apply NBPT-treated urea to muddy soil and attempt to let the soil dry before establishing the flood. If applying N to mud, some amount of N will be lost. If you’re attempting to increase the N rate, only do so slightly (~20 pounds N higher). Watch the crop closely and apply extra N if N deficiency occurs.

As a last resort when reaching the end of the recommended window with standing water on the field, begin “spoon-feeding” N into the water in small quantities every seven days. Small quantities mean 46 pounds N per acre (100 piybds urea per acre). Do not, for any reason, apply the entire recommended preflood N rate in one application into standing water.

Research has shown that on varieties, five applications each of 100 pounds of urea are needed to reach yields competitive to those achieved when the preflood is applied to dry soil. Waiting until the end of the recommended window to begin spoon-feed applications is preferred to beginning earlier as the smaller rice plants take up less N from the earliest applications.

While increased N rates result in increased production costs, delays in N application past the final recommended time based on DD50 result in yield declines. Beginning N in a timely manner ensures greater yield potential and reduces the potential for further costs incurred from loss of weed control.

Manage every field on a case-by-case basis. Use of the DD50 Rice Management Program can help to time management decisions in these situations (http://www.DD50.uaex.edu).

Draft a plan for early season control of late watergrass

Dr. Whitney Brim-DeForest
CALIFORNIA
Extension Agronomist
University of California, Davis
wbrimdeforest@ucanr.edu

In rice cropping systems, weeds are one of the greatest contributors to yield loss. In California, the potential yield losses in drill-seeded fields are 100 percent when weeds are uncontrolled. In continuously flooded fields where water suppresses some weed species, potential yield losses from uncontrolled weeds are around 35-60 percent. To reduce yield loss, weeds are best managed early—by about 30 days after seeding.

In California, late watergrass is the first weed to emerge at the beginning of the season. It can come up equally well under flooded and flushed irrigation systems, and it easily outcompetes rice to cause high yield losses of up to about 50 percent. In warm weather, it may even emerge before rice, so it is essential to have good control as soon as possible.

Many late watergrass populations are herbicide resistant, so if you suspect resistance, it is a good idea to get your population tested before planning your herbicide program for the season. The University of California offers a free testing service to rice growers and pest control advisers. If you collect and submit seeds in the fall, you will get your results by the following spring.

Several herbicides are available to control late watergrass early in the season. In both flooded and drill-seeded (flushed) systems, a pre-plant application of Abolish is a good option. Adding Halomax or Sandea as a tank-mix with Abolish can significantly increase late watergrass control. In a drill-seeded system, Prowl H2O can also be used pre-plant.

In a continuously flooded system, the granular herbicides for late watergrass control are Bolero, League MVP, Granite GR or Cerano. Bolero, League MVP and Granite GR have the added benefit of sedge and broadleaf control as well.

There are many foliar herbicide options and tankmixes available for growers that drain early in the season, too many to list here. But for the best late watergrass control, all herbicide applications should be made as close to the one- to three-leaf stage of rice as possible.

In fields with heavy populations of susceptible late watergrass, or herbicide-resistant late watergrass (mimic), using a stale seedbed with an application of a non-selective herbicide, such as glyphosate, before planting can reduce late watergrass populations by as much as 80-90 percent.

To effectively use a stale seedbed, flush or flood fields as soon as possible after seedbed preparation. For late watergrass, it takes about two weeks for most of the population to emerge. If flooded, block the drains after flooding and allow water to recede into the soil.

Then go in and spray with a non-selective herbicide. Allow about 48 hours after application to ensure complete uptake of the herbicides, then flood and seed rice into the water.

As always, for best results and to reduce the chances of selecting for herbicide resistance, all herbicides should be applied at the maximum labeled rate and appropriate timing. Happy planning!

Nutrient management cannot be overlooked

Dr. Bobby R. Golden
MISSISSIPPI STATE UNIVERSITY
Extension Rice Specialist
bgolden@drec.msstate.edu

Many of you have heard me speak over the past several years about soil sampling and/or maintaining adequate soil fertility as a foundation for yield. Every fall I get the same call from numerous producers, I really don’t like the cost associated with fertilization, so I think I’m going to cut back.

My response is generally, “Let’s look at your soil test values and see if we can reduce anything.” In most of the scenarios, if we cut our fertility rates we would end up harming our yield potential. Therefore let’s use the capital we spent on having soil samples collected, processed and analyzed to work for us.

That means building a solid base of P, K and S (potassium, potash and sulfur) fertility to start the season off solid. Starting off with a sound fertility base will allow producers to get full benefit from every other input throughout the remainder of the growing season.

Perhaps the nutrient we encounter the most deficiencies with in Mississippi rice production is phosphorus. This is not surprising if you look at recent data from the International Plant Nutrition Institute (IPNI). During 2015 about 75 percent of soil samples taken in the state were below established critical levels for P.

Furthermore, IPNI data suggest that nutrient removal in grain-to-fertilizer-use ratios for phosphorus is > 5.0 for most of the rice-growing region. This means that annually we are removing a great deal more P than we are providing with fertilizer.

Over the past decade, Mississippi State University researchers have been evaluating when and how much phosphorus is needed to produce optimal rice yields. Most everyone has heard of the 4 R’s of fertilization and this research aims to address two of the four, which is the right time and rate.

Our research suggests that applying P (50 pounds P₂O₅/ac) to soils that test at levels generating a recommendation yield 11 bushels per acre greater compared to an untreated control. This data set also showed that we may need to reconsider application timing on our high pH soils.

When we only evaluate soils with a pH > 7.5, it appears that maximal benefit received from P fertilization occurs when P is applied in the springtime, with the greatest rice grain yields observed when P was applied at the two-leaf growth stage (Fig 1).

On soils with pH < 7.5, application time was not as critical, and yield benefits from P application were similar among application times ranging from fall to the two-leaf stage.