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P,K essential nutrients

The topic for this month is fertility, which is crucial to producing high rice yields and quality. I can’t emphasize enough the value of sampling your soil now for analysis, so you can apply the proper amount of P and K before the season begins.

However, I have heard from producers who relate that results of their soil analyses are highly variable. This either means your soil differs in these nutrients, or the analysis itself is variable. Another possibility is that you are not following soil sampling instructions carefully. So, if you are concerned about this, you can take at least two samples from the same location and see if the samples come back with similar results.

Also, as far as P and K are concerned, many of our farmers are producing very high yields on both main and ratoon crops. In 2009, many of our Texas rice farmers produced over 10,000 lb/A from two crops. These high yields logically result in more P and K extracted from the soil compared to lower yields.

Also, some of our rice farmers bale straw from main crop harvest. This straw can release nutrients back into the soil, but if straw is removed from the field, these nutrients are lost, which means soil P and K levels may need to be supplemented. At any rate, P and K are essential nutrients for your rice crop. Current prices in the eastern Texas rice belt are approximately $500 per ton for 18-46-0 and $520 per ton for 0-0-60.

At the time of writing this article, Texas rice fields are sopping wet due to a wet winter – so far. This is good news for our farmers suffering from the effects of Hurricane Ike. I have spoken with numerous farmers who grow rice in the southern parts of Jefferson and Chambers Counties where salt water covered their fields for days following Ike. These farmers did not plant rice in 2009, but many will plant this year because soil/water salt concentrations have been reduced significantly due to the heavy winter rains. Although this does not fall strictly under fertility issues, it definitely is related to soil issues. In addition, our wet winter will help the supply of irrigation water to our rice farmers this year. As you well know, water and fertilizer go hand-in-hand.

If you have recently precision-leveled your fields, you may want to consider applying poultry litter, which can improve productivity on poor ground. Dr. Dustin Harrell – LSU rice agronomist – recently gave a presentation to our Texas rice farmers on poultry litter. Basically, poultry litter contains about 60 pounds each of N, P and K per ton on a dry basis. However, this varies tremendously, so you should analyze each batch for these nutrients. The best time to apply poultry litter is just prior to drill-seeding. Incorporating the litter is recommended.

The current cost of urea for the eastern Texas rice belt is about $430 per ton, but this price may increase as the planting season approaches. Given a price of $430 per ton of urea, if you apply a total of 150 lb N/A, your urea cost will be about $70/A; if you apply 200 lb N/A, your cost will shoot to over $90/A, and this does not include application costs. So, correct rates and timings of applications of N fertilizer, such as urea, can maximize your revenue, decrease the chance of lodging and reduce disease problems.

I will not go into the specifics of fertilizer management because recommendations vary by soil type, variety, planting date, stage of growth, etc. Refer to current university and private industry recommendations, as well as your own knowledge and experience specific to your fields. However, from speaking with other scientists, farmers and consultants – as well as my own personal experiences – when your crop runs out of N and your fields turn yellow and appear non-uniform in height, N deficiency is present and the stressed plants have difficulty “catching up.” This is why I normally apply PD N a little before actual PD in my research plots. If I wait to actual PD, my crop does not catch up. Of course, I am basing these observations on small plots, which sometimes do not translate effectively to commercial field conditions.

As always, I have to put a bug spin on this article. We have found that increasing N at PD to compensate for rice water weevil damage is not effective. We also have found that increasing N prior to flood does not help rice tolerate subsequent rice water weevil damage.

I think the most important aspect of rice production management is TIMING. All your decisions – cultural, agronomic and pest management – are based on timing. This is why you must regularly scout your fields to make decisions to most effectively utilize your crop inputs. Planting season is rapidly approaching, so check out your rubber boots to make sure they are leak-free. Walk your fields and don’t spend all of your time in your pick-up. Your job is not virtual; it’s real!

I thank Toni Spencer, Randy Waligura and Dr. Dustin Harrell for providing information for this article.

Optimize N efficiency

Water and nitrogen fertilizer efficiency has come a long way in recent years. This increase in efficiency has been mainly led by the increase in fuel and fertilizer prices. Even though our efficiency has improved, there is always room for more improvement.

Water means everything in being the most efficient with preflood nitrogen applications.

We have products like Agrotain, which help prevent volatilization. Also, we are seeing other nitrogen loss mechanisms on heavier clay soils like nitrification and denitrification.

To help prevent nitrogen loss, it is still essential to flood rice fields soon after the preflood nitrogen application. If flooding should take longer than seven days, other management practices may be necessary to help optimize nitrogen efficiency. These other management practices may include using multiple inlet irrigation or making split preflood nitrogen applications where only the top half of the field gets a nitrogen application until a third to half of the field is flooded. Then the remaining portion of the nitrogen is applied to the bottom half. A lot of yield can still be left on the table if flooding takes longer than a week. Therefore, it is extremely important to flood rice fields effectively and efficiently.

Mississippi’s nitrogen recommendations have not changed much from previous years. We still recommend a total of 180 lb N/A for clay soils and 150 lb N/A for silt loam soils. For semidwarf varieties (excluding CL 151) grown on clay soils, we recommend 120 to 150 lb N/A applied preflood and then followed with 30 to 60 lb N/A at midseason. On silt loam soils, we recommend 90 to 120 lb N/A at preflood and 30 to 60 lb N/A at midseason for semidwarf varieties (excluding CL 151).

Since excessive lodging occurred with CL 151 in 2009, our nitrogen fertilizer recommendations have changed for that variety. Our nitrogen recommendations for CL 151 are as follows: For clay soils, apply 90 to 120 lb N/A at preflood, 30 to 60 lb N/A at midseason, and 30 lb N/A at boot split; and for silt loam soils, apply 90 lb N/A at preflood, 30 lb N/A at midseason and 30 lb N/A at boot split. Boot split nitrogen applications have been a good tool to help prevent lodging problems in hybrids and other inbred lines. As a result, we believe that a boot split nitrogen application will help prevent an extensive lodging problem with CL 151.

We have also seen issues with phosphorus in the Mississippi Delta. The price of diammonium phosphate (DAP) has subsided from the highs in 2008 and is currently being sold for about $450/ton. While that is still high, phosphorus will be needed on some soils that are deficient.

Soil sampling will be the best asset in determining whether or not phosphorus or any other nutrient is needed in a fertility program. If the soil test results for phosphorus fall into the medium category, I would suggest starting to add phosphorus into the program.

A blend of 50 lb/A of ammonium sulfate and 50 lb/A of DAP applied at the one- to two-leaf stage is a good option to start adding some phosphorus back into the soil as well as supply early season nitrogen for improved vegetative growth. Where phosphorus deficiency is a serious problem, DAP at 100 lb/A will be needed to correct the deficiency.

I would recommend soil sampling this spring before planting season begins. This practice, too, is very valuable in making sound agronomic and economical fertilizer recommendations.

Poultry litter guide

When I think about discussing fertility of rice or any major crop for that matter, I think about the government official who suggested the U.S. Patent office could be closed because everything that could be invented had been. I think this was noted in the 1800s. You would think everything we need to know about rice fertility has already been done. I would agree that the simple stuff has been done; now, we are getting into the tough problem areas.

Dr. Dustin Harrell continues to review our phosphorus and potassium recommendations for rice. This year he will take one study off-station because he needs an area deficient in one or more nutrients, a condition hard to find on the research station.

Last year, and in 2008, he set up test plots in a farmer’s field where the grower had encountered serious production problems for several years. The problem had been diagnosed as localized decline, a problem we have worked on for a long time. Dr. Gary Breitenbeck studied the problem for a couple of years, during which he discovered that rice plants suffering from this malady accumulated very high levels of aluminum and iron in their tissues. At the last Rice Technical Working Group meeting, he presented data on this research. Scientists in the audience suggested zinc could be the key.

Dr. Harrell decided to test that hypothesis. He applied 0, 5, 10, 15 and 20 pounds of actual zinc per acre to small plots. He got positive responses both years and determined an optimum rate was five pounds at the 2008 location and 15 pounds at the 2009 location. He intends to continue this research in 2010.

This is an example of a nutrient that has been well researched, for which recommendations have been published and for which additional research is still pertinent. I deliberately left a few things out of the above paragraph. For example, the soil pH of the 2009 field was around 7.9. However, high pH alone will not account for the problem because we have other soils (notably in the Red River alluvium) that have an equally high pH that do not exhibit this set of problems. As you can see, the more we know, the more we need to know.

In the past few years, there has been an increased interest in the use of poultry litter in rice production. In most of the rice-growing area of Louisiana, poultry litter has been too expensive (mainly because of transportation costs) to use. In other states, where the poultry industry and rice-growing areas enjoy relative proximity, the cost has not been prohibitive. Questions posed by growers, especially in the southwest Louisiana growing area, prompted Dr. Harrell to put together a publication summarizing current information on poultry litter and its use on the silt loam soils in southwest Louisiana.

A Guide to Poultry Litter Use in Louisiana Rice Production, is available through your local county agent or can be downloaded from the rice Web page at:

There are several points Dr. Harrell makes regarding poultry litter. First, every batch of poultry litter is different; therefore, it should be tested for nutrient and water content. The nutrient value can be affected by diet, bedding material, age and other factors. The form can vary from pellets, fresh to composted. Last year, a grower applied some to one of our verification fields. The stuff had everything from large chunks of concrete to dead birds in it – pretty nasty stuff.

Poultry litter contains nitrogen, phosphorus and potassium as well as several micronutrients and organic acids. About 25 percent of the nitrogen contained in the poultry litter will count towards the normal recommended preflood nitrogen. All of the phosphorus and potassium found in the litter can be applied towards the needs of the rice crop during the first year.

In south Louisiana, the nitrogen and potassium needs often exceed the phosphorus needs based on soil testing. If poultry litter is applied at rates high enough to satisfy these needs on a repetitive basis, phosphorus may accumulate and eventually become a problem. To avoid potential environmental problems and save money, poultry litter should be applied at a rate to satisfy the phosphorus needs of the plant. If more nitrogen or potassium is required, it can be added through traditional fertilizer products.

Dr. Harrell recommends applying poultry litter and supplemental potassium (if necessary) as close to planting as possible.

He also made several observations about poultry litter. The responses of litter applied on precision-leveled clay soils are generally not as great compared to precision-leveled silt loam soils. Even distribution of litter at rates below one ton per acre is difficult. Continued use of litter can increase organic matter, soil structure and cation exchange capacity (CEC), but not from a single application. The publication contains formulas and an example of how to calculate the amount of litter needed based on a soil test.

Effect on yields

In California, preplant nitrogen (N) is commonly applied as incorporated aqua-NH3 followed by a small amount (20-30 lb/A) of surface applied “starter” N in liquid or granular form. The idea is that the starter supplies the seedling with N until the roots reach the aqua-NH3. But does the addition of starter N produce higher yields? Not so, according to Bruce Linquist, UCD. Using large scale on-farm studies, Dr. Linquist demonstrated that applying all N as aqua-NH3 produced higher yields than the split aqua-NH3 starter practice when equal amounts of total N were applied. Seedlings treated with starter were slightly greener, but this did not translate to higher yields. In terms of yield, an all aqua-NH3 program is a more efficient use of your fertilizer dollar.

Additionally, when the starter is applied as an unincorporated liquid, a large portion of the N can be lost to the atmosphere before the field is flooded. Such losses may become increasingly important should air quality concerns ramp up in the future.

If you are considering not applying preplant surface N on a portion of your field to test this practice, be sure to increase your aqua-NH3 proportionally. You can read the results of this study and other UC rice projects on the California Rice Research Board Web site (

Managing herbicide-resistant weeds has led to changes in irrigation management to accommodate new herbicide chemistry. Farmers increasingly use foliar-active rather than herbicides applied into the water. Consequently, water levels must be lowered or fields completely drained before application of some herbicides.

What happens to the fertilizer N and plant growth when a field is drained for an extended period? Under flooded conditions, the fertilizer N is a reduced form (NH3). Once the field is drained, it oxidizes to nitrate (NO3). Upon reflooding, the nitrate is converted to N gas (N2), which is lost from the soil. Nitrogen loss is about 2 lb/A per day in a drained field.

If the field is drained for 10 days awaiting herbicide application with a ground-rig, which is not unusual, then the N loss compares to the amount of “starter” typically applied.

Moreover, such drain periods can reduce biomass and penalize yields of popular California varieties. In a 2009 study, an extended drain reduced biomass and yield of M206 by eight percent and 13 percent, respectively.

Also, keep in mind that drained fields allow other weeds to germinate, such as sprangletop, which can then become a problem later in the season. If you must drop the water, get the flood back on as soon as possible.

Here is a final note on phosphorus and potassium to keep in mind. The liquid “starter” is an N-P-K blend. Phosphorus left on the surface is ideal for algae growth. Add warm water temperatures, and you’ve the makings of a big problem. Fields are increasingly infested with blue-green algae (Nostoc), sometimes called “black” algae.

Blue-green algae, because of a gelatinous coating on its filaments, is very difficult to control with copper sulfate. Incorporate the phosphorus into the soil. Research has shown that in fields where P fertilizer was not incorporated into soil, the P levels in the outgoing water were five times greater than the levels in the incoming water soon after planting.

An adequate level of soil P, based on the Olson extraction method, is between 10 to 15 ppm for most rice soils in the Sacramento Valley. The rice soils in California contain high levels of native potassium. Some rice farmers have never applied K fertilizers. In recent years, K deficiencies are increasingly common, especially late-season deficiencies. A potassium-deficient field in the late season has a slight rusty red appearance.

There is about 40 lb/A of K in the rice grain and about 85 lb/A in the straw. If you incorporate your straw, replace the K removed in the grain when you fertilize. If you bale the straw, add an extra 45 lb/A to your annual K application rate. An adequate level of soil K, based on sodium acetate extraction, is between 70 to 80 ppm.

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