Rice fertility research


Fertility research is one of the oldest areas of agricultural research, which might insinuate there is little left to investigate. If that were true, we would not get so many questions from growers each year about rice fertility; these questions drive research

Dr. Dustin Harrell has primary responsibility for rice fertility research in Louisiana. Several parts of his research program involve nitrogen timing, rates and modification of nitrogen fertilizers. In our Rice Research Verification program we apply two-thirds of the nitrogen day of or one day prior to establishing permanent flood and the remainder at or before internode elongation (green ring). Sometimes we include a small amount of nitrogen with an application of phosphorus and potassium at planting, which will provide a “boost” to seedlings, but will contribute little, if any, toward yield. It does help by allowing earlier flood establishment when seedlings respond well to it.

did not specify one-third of the total nitrogen at mid-season because it may not be one-third of the intended total. That is one advantage of splitting the nitrogen application into two events. In a rainy, cloudy summer, we might reduce our intended total. Conversely, if we observe the crop showing nitrogen deficiency well before mid-season, we might increase the amount to compensate for an apparent nitrogen deficiency or loss. If everything goes according to schedule, it obviously is two-thirds up front and one-third later.

Dr. Harrell has also tested several products containing the active ingredient N-(n-butyl) thiophosphoric triamide (NBPT). Agrotain, Arborite AG and N-Fixx are the three he has evaluated so far and another is planned for 2013. All of the products containing NBPT work, according to Dr. Harrell. There are other products purported to improve fertilizer use efficiency introduced and sold without unbiased research to support the claims. If Dr. Harrell has not tested them or if in his testing they did not work, we do not use them in the verification program. Next summer, Dr. Harrell will evaluate innovative phosphorus and zinc fertilizer sources. There are a few promising products worth taking a good look at, but research is expensive so I recommend leaving it to the researchers. Much like the television commercial showing a doctor trying to pitch major league baseball, the advice is the same. Stick to what you know best and rely on others for their expertise; I know I do.

A good example of an area of research that needs more investigating is the N-STaR test for soil nitrogen. In 2011, Dr. Harrell’s research showed outstanding promise. The 2012 season’s results were different. According to Dr. Harrell, 80 percent of the fields tested required more than 100 pounds of nitrogen per acre. Of the remaining 20 percent, half that were fertilized with less than 100 pounds of nitrogen per acre produced yields less than comparable fields fertilized with higher rates of nitrogen. In our Cameron Parish verification field, we only applied 65 pounds of nitrogen per acre. Yield was disappointing, but the field had very little disease. The grain produced the highest test weights I have seen in the verification program. We agreed the proper rate would probably have been around 90 pounds of nitrogen.

When I made this statement at grower meetings, I was asked the question, “When you say pounds of nitrogen do you mean units of nitrogen?” The correct answer is no, I mean pounds of nitrogen. Urea is 46 percent nitrogen. One hundred pounds of urea contains 46 pounds of nitrogen. Ammonium sulfate is 21 percent nitrogen. One hundred pounds of ammonium sulfate contains 21 pounds of nitrogen.

When we recommended 65 pounds of nitrogen, the farmer applied 141 pounds of urea. To determine this, simply divide 65 pounds by .46. If we had used ammonium sulfate, it would have required about 310 pounds of fertilizer – 65 pounds divided by .21 = 309.5.

Dr. Harrell will continue to fine-tune N-STaR recommendations for Louisiana soils. They are also working on calibrating the test for clay soils. At present, the system is designed for silt loam soils and is one of the more interesting areas of fertility research to come along in a while.

Timely flood is key


Urea cost for 2013 are projected to be above $500/ton. Nitrogen is a vital component to producing excellent rice yields. Therefore, nitrogen is not an input that can be reduced to offset the high cost without sacrificing rice yield, unless you are above our current recommendations. As a rule of thumb for current varieties grown in Mississippi, we recommend a total of 165-180 lb N/A for clay soils and 150 lb N/A for silt loam soils. For semi-dwarf varieties (Rex and Cocodrie) 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. For varieties that are susceptible to lodging (CL151 and CL111) on clay soils, decrease the N rate to 90 to 120 lb N/A at preflood followed by the remaining 45 lb N/A at mid-season to help reduce the potential for lodging. On silt loam soils, we recommend 90 to 120 lb N/A at preflood and 45 lb N/A at mid-season for all varieties.

The key to getting the most out of your nitrogen is a timely flood. Ideally, we would like to have a flood established within five days after the nitrogen has been applied. Getting a flood established outside that five-day window can lead to nitrogen loss due to volatilization. If you find yourself outside that window, there are a couple of things you can do to help prevent losing your valuable nitrogen. I would first consider multiple-inlet irrigation. This will help get the flood established quicker and allow for more flexibility in your irrigation program. Also consider using Agrotain-treated urea. Agrotain will protect the urea from volatilization up to 10 days after application and will be the most beneficial on the areas of the fields that are not flooded within five days.

Phosphorus is another essential element to consider in a fertility program. We are beginning to see a few more phosphorus deficiency problems every year. I would encourage you to pull some soil samples to see what your phosphorus levels are running, especially on heavy cut soils. If your phosphorus soil test levels are running less than 70 lb P2O5/A (Lancaster extractable levels), I would consider including phosphorus into your fertility program. You might not see a yield response across every acre by applying phosphorus. However, you have to begin thinking about establishing and maintaining good soil phosphorus levels to produce rice in the future.

Where phosphorus deficiency is a problem, the best time to make an application is from the 1- to 5-leaf stage. DAP (18-46-0) at 100 lb/A could supply enough phosphorus as well as supply early season nitrogen for improved vegetative growth.

N to win

Rice Extension Agronomist
University of Arkansas,
Division of Agriculture

Improved nitrogen (N) fertilization is the primary focus for University of Arkansas Division of Agriculture fertility specialists in 2013. Over the past several years, Drs. Trent Roberts, Rick Norman and Nathan Slaton have been developing the N-STaR program. NSTaR (Nitrogen Soil Test for Rice) is a field-specific soil N test that is intended to provide a prescription N rate.

The purpose of N-STaR is to determine the yield-maximizing N rate based on the soil’s native N fertility. It is important to note that the goal of the N-STaR program is to get the correct N rate for your field. This means that in some cases it may recommend less N, and in some cases it may recommend more N. But the rate that N-STaR recommends should maximize your rice yield when the field is properly managed. In 2012, N-STaR was commercially available for rice grown on silt loam soils. In 2013, N-STaR-based N rate recommendations for fields with clay soils will also be available to growers.

When collecting soil samples for evaluation by the N-STaR lab, soil samples from silt loam soils need to be collected from the zero to 18- inch depth, while samples from clay soils need to be from the zero to 12-inch depth. This year, Dr. Roberts will be continuing his work providing validation of N-STaR recommendations. For more information, or if you are interested in cooperating with researchers on a testing location, contact the N-STaR lab at nstarlab@uark.edu.

Research by Dr. Norman has indicated that in fields where a flood can be applied timely and maintained throughout the season, it is possible to see the full benefit of your N fertilization program with a single pre-flood, optimum application and avoid the costs associated with an additional application at mid-season. Conditions critical for use of the single, optimum pre-flood N application method are that the field can be flooded timely and treat urea with the urease inhibitor NBPT or ammonium sulfate. The pre-flood N rate for the single, optimum pre-flood method can be calculated for each rice variety by simply adding 15 to 25 pounds of N per acre to the pre-flood rate recommended for the two-way split application method. If maintaining a flood is a concern, there are university recommendations available for how to most effectively distribute the rates for pre-flood and mid-season fertilizer applications. If it is preferred to use both a pre-flood and a mid-season application, the recommendation is now to use a single mid-season application made between beginning internode elongation and one-half-inch internode elongation. For hybrids, rather than a mid-season application, growers should fertilize at the boot stage to see the greatest benefit from this application.

Being able to flood fields in a timely manner is another important concern for rice growers. When timely flooding may be difficult and conditions for ammonia volatilization exist, the University of Arkansas Division of Agriculture recommends treating urea with one of the four NBPT urease inhibitor containing products: Agrotain, Arborite, Factor or N-FIXX. These products provide a benefit when a field cannot be flooded in two days or less for silt loam soils and seven days or less for clay soils.

There are no changes to current recommendations for phosphorous (P), potassium (K), or zinc (Zn), according to Dr. Slaton. However, it is important to be aware of the increased nutrient removal that occurs when rice or soybean crop residues are baled and removed from fields after grain harvest. Removal of K is of the greatest concern in these situations, and silt loam soils have the greatest risk for experiencing increased incidence and severity of K deficiency in the absence of a proper fertilization program.

I would encourage you to try the N-STaR program on your farm this season if you have not already done so. If given an opportunity, this program has the ability to improve rice production on your farm by perfecting your N fertilization rate. Proper N fertilization has the added benefit of reducing lodging and lowering disease incidence, problems commonly associated with N over-fertilization.

Thank you to Drs. Rick Norman, Nathan Slaton and Trent Roberts for their hard work improving fertility management in Arkansas and for their input on this article.

Phosphorous management

UCCE Rice Farm Advisor

In the California rice production area, less than 10 percent of soils are phosphorous(P)- limited. This means that in most soils, you will not see yield increases when applying P fertilizer. However, over time, P levels can be depleted and cause a yield reduction. To avoid this situation, you need to determine the P status of your fields and adjust your P rates if needed.

There are two common methods to determine the P status of the soil, a soil test and plant tissue analysis. When doing a soil test, the P level in the soil is adequate when the Olsen P test shows a P concentration above 6-9 ppm. When doing plant tissue analysis, the Yleaf should be sampled about 35 days after seeding (the Y-leaf is the most recently fully expanded leaf). When P concentrations in the Y-leaf are above 0.2 percent, P levels are adequate.

The problem with tissue analysis is that by the time the results are received, the window for P application has passed. Nevertheless, the result from the tissue analysis can be used to make P application decisions next year.

Another way to determine the P status of your soil is to develop an input-output P budget. You can combine the results of your soil test and P budget to determine if a P application is needed and in what amount. Phosphorus fertilizer is relatively immobile in soils. Unlike N, P is not lost through gasification and little is lost with irrigation water or through leaching. Think of the soil as a P bank. You “deposit” P when you apply a P fertilizer, and you “withdraw” P when you harvest the grain and straw. To be efficient, you want to deposit enough P to maximize yields.

To develop a P budget for a specific field, you need to estimate your yearly average P application (in lbs P2O5/ac added) and yield (in cwt/ac) for the past 5 years. Then, use the P budget tables developed by Dr. Bruce Linquist (available on the Fact Sheets section of the UC Rice Project Web site, http://ucanr.edu/sites/UCRiceProject), to determine if you have a positive or negative budget. If the P budget is negative, you are extracting more P than you are adding; if it is positive, you are building up P in the soil.

You can combine results from the soil test and P budget to determine how much P you need to apply. When the soil test indicates that P levels are above 20 ppm and the P budget is positive, you don’t need to apply any P fertilizer, there is enough P in the soil and increasing the level of P will not have any benefit. When the soil test shows P levels above 6 ppm, all that is needed is a maintenance P application. This means that you need to add as much P as you are extracting with the grain/straw.

Use the P budget tables to determine how much P fertilizer is needed for the expected yield in your field so that the P budget is close to zero. When the soil test indicates that the P level is below 6 ppm and the P budget is negative, you need to add P fertilizer to the soil to bring up your P soil account. You can start adding as much P as needed so that your P budget becomes positive. In subsequent years, monitor your yield and P levels to make any further adjustments.

Benefits of using urease inhibitors

Rice Research Entomologist

I recently returned from the 16th Annual Conservation Systems Cotton & Rice Conference held in Baton Rouge, La. This Conference teams up rice farmers with scientists who present their latest production practices and research results. Topics include all aspects of rice production such as land preparation (conservation tillage), planting, varietal selection, pest management, rice nutrition, water management, harvesting operations and economics.

The atmosphere is cordial and informal, which encourages useful exchanges and knowledge transfer. I highly recommend this meeting to all rice producers, crop consultants and rice scientists. Please contact John LaRose or Robin Moll at rmoll@mafg.net for information regarding this annual meeting. If you want a copy of this year’s program and/or the Conference Proceedings, contact John, Robin or me (409-658-2186; moway@aesrg.tamu.edu).

We are approaching the planting season, so we must be familiar with the latest fertility recommendations for our 2013 rice crop. I can’t emphasize enough the value of soil sampling at this time to serve as a guide for your fertility program.

Also, check with your state rice research/Extension team to find out about the N-STaR nitrogen testing program. Basically, this soil sampling technique quantifies native nitrogen in your soil. Dr. Trent Roberts, University of Arkansas, at the above conference, recommended taking your N-STaR soil samples as early as harvest of your previous crop, but you can still get good results by taking them now before planting. The more native nitrogen in your soil, the less nitrogen you need to apply, which can be a huge money savings for you as well as possibly reducing your disease pressure and lodging potential. For more information on the N-STaR program contact the NSTaR lab at nstarlab@uark.edu.

Speaking of money, today I talked with Toni Spencer, who works for M&J Fertilizer Company in Winnie, Texas. Toni says the current cost of urea is about $500/ton, DAP (18-46-0) is about $580/ton, and potash (60 percent potassium) is about $560/ton. Toni says there is a definite trend for our rice farmers east of Houston to increase P and K and decrease N applied to their rice crops.

She also reported that many of these same farmers are applying a urease inhibitor impregnated on urea. The use of the urease inhibitor NBPT, tradename Agrotain, has increased dramatically over the past four or five years in southeast Texas. When you apply urea to the soil, urease (an enzyme produced by bacteria in the soil) reacts with water to eventually transform the applied urea to ammonia, which is a gas (containing nitrogen). This gas then escapes into the atmosphere. Urease inhibitors block this enzyme to slow the volatilization process; thus, increasing the efficiency of urea application. Some research indicates as much as 20 percent of applied nitrogen can be lost through volatilization.

Toni says the cost of Agrotain is about $60/gallon, and most of her farmers use between 72 oz and 1 gallon/ton of urea. Logically, the longer you leave urea on the soil surface before a flush or flood, the more nitrogen will be lost to the atmosphere. So, if you have large cuts requiring a long period of time to flush or flood, the use of a urease inhibitor may be cost-effective.

Also, this technology has beneficial environmental advantages because less gas escapes into our atmosphere. Toni also mentioned that USDA-Natural Resources Conservation Service may provide incentives to farmers who use urease inhibitors, which helps reduce greenhouse gas emissions. You may want to contact your local USDA folks or County Extension Agent to obtain more information since you may qualify for this program.

In short, use your state university rice fertility research results as a guide to developing your own fertility program. The 2013 Texas Rice Production Guidelines Bulletin 6131 will be available soon. This publication will have the latest fertility management information specific to Texas. You can access these Bulletins at https://beaumont.tamu.edu/eLibrary/ExtensionBulletins_ default.htm.

Finally, do not purchase and apply nutrient products that are lacking scientific, replicated efficacy data!

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