Fertility Management

Fertilizer — not too much, not too little

ss-wayDR. M.O. “MO” WAY
Rice Research Entomologist

This month’s topic is fertility management. As you know, I’m a bug fella, so I’m no expert on fertility management, although I do know N, P and K are increasingly expensive. Since the majority of Texas rice farmers produce both a main and ratoon crop, fertility management is complicated and crucial to producing good yields and milling quality for both crops The trick is to apply just the right amount of N, P and K for your situation.

According to the 2014 Texas Rice Production Guidelines, the cost of fertilizer plus application for the main crop is about $220 per acre. This represents about 25 percent of total direct expenses to produce a main crop in Texas! For the ratoon crop, the cost is about $53 per acre, which represents about 30 percent of total direct expenses. Also, we are all familiar with the environmental concerns relative to contamination of our precious water resources with agriculturally applied fertilizers. It’s to our benefit and to the benefit of the environment to apply just what our crop needs – not too much and not too little. Obviously, this also applies to pesticides.

The first step is to sample your soil for N, P and K needs. Rice soil scientists are finding that our soils have surprisingly high concentrations of “native” nutrients, which means reduced requirements for applied fertilizers. In addition, even I know the importance of flushing or flooding a field as soon as possible after application of N fertilizer. The longer you wait to flush or flood, the more N you lose to volatilization and denitrification, especially during hot, dry, windy conditions. Consider adding a urease inhibitor to your urea if you don’t expect a timely flush or flood.

ss-way-rice-cropUniform distribution of N fertilizers also is important. My project hand-applies urea into small plots – like feeding chickens, but we are feeding our rice plants. Unlike chickens, rice plants don’t move (really?), so non-uniform distribution of urea can have severe consequences, all the way to yield. I have personally observed poor spread of urea in some of my plots, which leads to clumped patterns of stunted or overly stimulated vegetative growth. This eventually has detrimental effects on yield.

Another problem I sometimes observe is once the plant turns yellow and is in obvious need of N, it is difficult for the plant to “catch up” following a subsequent N application. This means you must check your crop daily, particularly when it approaches PD, to make sure it is not running out of N.

For instance, Drs. Dou, Tarpley and McCauley in the Nitrogen Management section of the 2014 Texas Rice Production Guidelines state, “If rice plants appear nitrogen-deficient, apply nitrogen before the PD stage.” In other words, don’t wait for the crop to reach PD before applying N if the crop begins to appear yellow and/or non-uniform in height. It has been my experience that any stress on the crop, including N deficiency, can result in reduced yields.

For more information specific to N requirements vs varieties, please go to https://beaumont.tamu.edu/eLibrary/ExtensionBulletins_default.htm and click on the 2014 Texas Rice Production Guidelines. Then scroll down to pages 21-26. If you want hard copies of Bulletin-6131, contact me at (409) 658-2186 or moway@aesrg.tamu.edu

ss-linquistConsider the 4 R’s

UCCE Rice Specialist

The rise of fertilizer costs makes us all mindful of efficiency. Application of the 4 R’s (right rate, right source, right timing and right placement) to N fertilizer will help ensure that it is being used efficiently. In water-seeded California rice systems, this means aqua-ammonia (aqua-N) injected three to four inches below the soil surface just before flooding the field for planting. Injection of aqua-N, combined with keeping fields flooded, makes this an efficient practice with fertilizer N being less subject to loss.

As much of the targeted N rate as possible should be as aqua-N; however, most growers also need to apply phosphorus (P), which is usually applied as a starter blend. Since most available P sources contain some N (usually as ammonium phosphate), we recommend using P sources with the lowest amount of N possible (i.e. 11-52-0). The N contained in this P fertilizer should be considered as part of the targeted N rate. The right time and placement of this starter is just before flooding with a light incorporation. However, this fertilizer can also be applied three to four weeks after planting without a yield penalty.

We recommend a late application of the starter blend when algae is a problem. Algae growth is suppressed during crop establishment by delaying the P application until the rice leaves have emerged through the water surface. A number of growers have also been applying N fertilizer following the application of some herbicides due to possible root damage. Applying the starter fertilizer at this time is a feasible option as long as it is not applied too late. Most growers use an N rate based on past experience. In studies conducted with growers, we have found that many are over or under applying N fertilizer. Using GPS and yield monitors, it is possible to accurately determine the correct N rate. We suggest applying the typical N rate to most of the field, but in a representative portion of one of the checks, apply one strip across the field at 25 lb aqua-N/ac above and another at 25 lb aqua-N/ac below the targeted N rate.

The strips need to be at least as wide as the combine header and marked with stakes as soon as they are applied. Monitor these strips throughout the season. Harvest each strip separately using a combine equipped with a yield monitor and compare the N rates with an adjacent strip of the standard rate. Compare yields to tell if N was over or under applied. By doing this over years in multiple fields and keeping good records, it is possible to fine-tune N rates to optimize yields with the lowest amount of N possible.

Fertility and Optimal Profitabilityss-walker

Rice Agronomist
Extension Rice Specialist

In the January 2014 column, I spoke of the possibility of Mississippi growers moving back towards “normal” rice acreage. This column will address key points to consider in managing those acres for optimal profitability.

For years in our state when you spoke of fertility, most assumed you were speaking of nitrogen, and there were two major questions. How much should we apply and how should we split it? The Mississippi Rice Promotion Board got serious about investigating soil fertility issues related to rice in the late 1990s, which has resulted in a very strong On-Farm Fertility research program. The premise of this program was to expand beyond the experiment station and address soil fertility issues where they occur. In any given year, our program may reach out to 10-15 “On-Farm” sites to conduct N, P, K, S and Zn research. The results of this program have been very beneficial.

Other than the need for N on practically every acre, the second most problematic nutrient in Mississippi rice is phosphorus (P). Two major cultural practices have influenced the need to increase P applications in our state. Land leveling became wide spread in the 1980s and continued through the 1990s. Still today, many growers will level ground where corn, cotton and soybean will be the major crops. However, before returning to the upland crop rotation, growers may plant rice for two or three years to help “get the soil in shape” after leveling.

There are two major soil orders in the “Delta,” which are Alfisols and Vertisols. Vertisols are very deep soils and, other than compaction and reduced microbial activity, nutrient concentrations are high to very high several feet deep into the profile. Alfisols tend to not be as fertile deep into the profile. Phosphorus tends to decrease greatly six to 10 inches deep into the profile. For this reason, the MSU Extension Service recommendation is to apply 40 to 60 pounds of P2O5 after leveling fields regardless of the soil test recommendation.

Another factor that impacts P availability is soil pH. Soils in the Delta are slightly acidic to acidic in nature. However, groundwater used for irrigation is alkaline and can have very high concentrations of bicarbonates. We essentially lime our rice soils each year when we irrigate. As I view numerous soil reports each year to provide an opinion on fertility needs, I seldom see pHs below 6.5. This is especially true if the fields have had rice in the rotation for several years. To be honest, on older rice soils, the pH is typically in the 7s and can go as high as 8.3. Fortunately, I’ve never viewed a soil sample in Mississippi that was above 8.3. This would point to a much greater problem caused by sodium.

As pH increases from 6.5, P availability decreases. On soils where P is marginal and pH is above 6.5, the chances of seeing a response from P fertilizer increases. The University of Arkansas Soil Testing Laboratory has done an excellent job of using both soil pH and Mehlich 3-extractable P in making P fertilizer recommendations. Data generated in our program suggests the same is true for the Lancaster extractant used by Mississippi State University (MSU).

Many growers like to apply a small amount of N when rice is fully emerged and beginning to put on leaves. If pH is high and soil test P is marginal, diammonium phosphate (DAP) is a good source of N and P. It also can be blended with ammonium sulfate if less P is needed. The key is to not apply more than 30 pounds of N per acre during early vegetative growth. The more N that is applied more than a week before the flood, the greater the chance is to lose the N via nitrification/denitrification.

When all other nutrients are at appropriate levels, N provides the greatest return on investment and requires the greatest attention to detail in managing it. Rice grain yield does not typically respond in a linear manner to N. More is not always better. The rice states’ land grants do an excellent job of providing N rate guidelines for each publicly released variety including Clearfield pure lines. The Nitrogen Soil Test for Rice (NSTaR) developed by the University of Arkansas promises to improve on rate recommendations because it can be applied on a field-by-field basis. Our experience in Mississippi with N-STaR has been favorable on coarse-textured soils but has not performed well on clay soils. Currently, my suggestion in Mississippi is to start with coarse-textured soils that have a history of lodging and/or disease. Dr. Trent Roberts with the University of Arkansas has published an information sheet that can be found at www.aragriculture.org/crops/rice/NSTR_protocol_siltloam_ 2012_2013.pdf. This guide can be used to sample and submit samples to the University of Arkansas lab.

Protection of urea that is applied preflood to minimize loss is critical to achieve optimum returns on the N investment. Ammonia volatilization can be greater than 20 percent on coarse-textured soils accompanied by weather conditions conducive to volatilization. The best way to ensure against volatilization losses is to apply urea onto dry soil then flood within three to five days. This is not possible on every acre; therefore, nitrogen stabilizers can provide value in these situations. In research conducted in Mississippi, stabilizer products that contain NBPT at 20-27 percent and applied at three to four quarts per ton of urea have stabilized urea from ammonia volatilization losses for up to 10 days after application. Products that claim to stabilize N from volatilization that do not have NBPT at the rates specified above have not proven effective in our experiment.

Maintaining adequate soil test levels of P and K are important for overall productivity. To know what to do is to know where you are. If it has been a while since you’ve soil tested, it is a good investment. The MSU Extension Service personnel can assist with the process of sample delivery as well as interpretation of the results. Please consider your nutrient needs to give your farm the best opportunity to capitalize on the genetic gains that have been achieved through breeding. If we can assist, please don’t hesitate to call.

ss-atwellBuilding a Plan

Agronomy Specialist

It’s another year, and I hope that you have already finished planning for your 2014 rice crop. Like any professional event, now is the time to visualize making your 2014 rice crop. After deciding on acreage and selecting fields and varieties, building a fertilizer plan is next on the list.

Most rice is in a rotation with soybeans, so below is a chart for nutrient removal from last season’s soybean and rice crops. From soil sample reports and this chart, you can judge how to put your fertility program into your seasonal rice crop. The desired soil phosphorus should be (45 lbs/ac) and potassium (220 lbs + 5X CEC).

Rice varieties differ in the amount of nitrogen (N) fertilizer required to produce optimum grain yields. Amounts can range from 0 to 180 lbs N/acre with 150 pounds being most common. Two N application options are as follows: 100 percent applied pre-flood on dry soil (only when able to maintain timely and seasonal flood) and about 70 percent applied pre-flood on dry soil with remainder (45 lbs N/acre) applied as a single mid-season application. Treat urea with an NBPTcontaining urease inhibitor if timely flood application is a concern (less than two days for silt loam soils, less than seven days for clay soils) or use ammonium sulfate. N sources include urea (46-0-0), DAP (18-46-0) and ammonium sulfate (21-0-0-24).


Every Field is Different

Rice Extension Agronomist
University of Arkansas,
Cooperative Extension Service

Sometimes we forget just how unique every field is, even just across the turnrow. There was a great example of this in 2013. On a verification field (Field #1), growers followed university recommendations and yielded well over 200 bu/A. They planted another field (Field #2) across the turnrow on the same day, so they decided to follow the exact same recommendations throughout the season. In the end, Field #2 yielded 20-30 bu/A lower than Field #1. How can that be? It was just across a turnrow. Well, N-STaR recommended a reduced nitrogen (N) rate (30 lbs N/A less) for Field #1, and this same reduced rate was used on Field #2. Unfortunately, Field #2 was second-year rice while Field #1 had been planted to soybean the previous year. So Field #2 needed more N because of consecutive years of rice production.

This example indicates the uniqueness of every field and the need to sample each field individually when using the N-STaR program. You may be tempted to use the N-STaR recommendation from one field on adjacent fields, but, remember, those fields have not been treated exactly the same, and the soils may not be the same. University of Arkansas recommendations indicated the need to add 20 lbs N/A when you have rice following rice in rotation, which also supports the differences in yield between those two fields. It seems simple enough, but it’s an easy mistake to make.

N-STaR is now a standard recommendation by the University of Arkansas for silt loam and clay soils. Sample depth differs by soil type – 18-inch deep samples for silt loam soils and 12-inch deep samples for clay soils. These differences are based on active rooting depth of rice plants on the different soil types and the amount of available native soil nitrogen within that soil depth range. Some soil types you may think of as a clay, while they are actually more like a silt loam The reverse is also true.

For this reason, if you have any doubts about your soil type – consult the N-STaR lab (nstarlab@uark.edu) prior to taking samples. Samples can be taken immediately following harvest of the previous crop all the way up to planting your rice. The purpose of the N-STaR program is to provide a prescription N rate for a particular field – it is not necessarily intended to lower (or raise) the N rate. The correct N rate can help reduce input costs, lodging and disease incidence. Recent research has indicated that in fields where N-STaR recommends a N rate of 100 pounds or less, it can be put out as a single preflood application if you can maintain an adequate season-long flood.

Speaking of soil sampling – don’t forget your standard soil sample. (Sorry, you can’t use your N-STaR samples for your standard sample or vice versa). The most yield-limiting nutrient in your field is the one you have the least of. Cutting corners on standard soil sample practices and not applying sustainable rates of phosphorus, potassium and zinc is a mistake. Over time, these nutrients can become yield limiting even if the deficiency isn’t severe enough that visual symptoms are evident. Every field is unique. Avoiding blanket recommendations will help to eliminate many problems and ultimately improve your economic bottom line. When it comes to fertility management, we have the tools and the talent to produce a high-yielding, profitable rice crop. Let’s make sure we give the crop what it needs.

Thank you to our rice fertility management team – Drs. Rick Norman, Nathan Slaton and Trent Roberts – for their hard work and support of Arkansas rice production.

Same Questions Applyss-saichuk


At the producer meetings held throughout the state earlier this year, I listened to Dr. Harrell’s presentation based on his fertility research with interest. In the last 25 years, the LSU AgCenter’s recommendations for nitrogen (N) fertilization timing have changed very little. We still get some of the same questions we got 25 years ago. What happens when you apply urea on dry, moist or flooded soils? Will using a NBPT product reduce nitrogen volatilization losses? How much overall N loss from volatilization and nitrification/denitrification can I expect? NBPT is an abbreviation for N-(n-butyl) thiophosphoric triamide, the active ingredient in Agrotain, N-Fixx, Arborite AG and Factor. All of these products are added to urea fertilizer and temporarily delay the breakdown of urea. This, in turn, inhibits ammonia volatilization losses from urea.

Let us take a look at each question. Research has repeatedly confirmed that urea should be applied to dry soil and the field flooded as soon as possible to maximize nitrogen use and minimize nitrogen losses. In Dr. Harrell’s studies, urea was applied to dry soil and then flooded 10 days later, producing an average yield of 9,319 lbs/A. Where it was applied to a moist soil, the average yield was 7,369 lbs/A. When it was applied into a flooded field, the yield was 4,167 lbs/A. The data is blatantly convincing.

Several years ago, we had applied herbicide to our verification field, but before we could follow it with our N application, we got 12 inches of rain. Because the field was flooded and weed control was good, I made the decision to go against the research data and lost. Next to us, our cooperator’s father drained his field and then applied nitrogen. The difference was dramatic, and I had to look at it all year long. When we harvested, it only added insult to injury. Last year, when much the same situation presented itself in one our verification fields and the farmer called to ask if he could just increase the nitrogen and drop it into the water, he got an emphatic “NO!” from me.

With the introduction of the NBPT products, the second question presented above came up. In the same study by Dr. Harrell, he also included urea treated with an NBPT product. The results were the same when applied into the flood as if the urea had not been treated. NBPT-treated urea applied to dry soil, moist soil and flooded plots produced 9,059 lbs/A, 8,394 lbs/A and 4,780 lbs/A, respectively. Treating urea with an NBPT product can help reduce volatilization losses on moist soil but cannot improve nitrogen use efficiency when urea is dropped into a flooded field on young rice. The volatilization losses measured by Dr. Harrell were lower in the flooded plots than the dry, but nitrogen utilization efficiency was drastically lower when the fertilizer was applied in flooded situations. When this measurement is combined with the consistently lower yields, it tells us there is more going on than just volatilization losses. The bottom line is, “Do not apply nitrogen into a flood on young rice.”

Invariably, when this data is presented, the issue of topdressing with nitrogen at mid-season arises because it appears contradictory when we recommend N be applied to dry soil in one instance then say it is okay to apply it to flooded rice in another. The recommendations are not contradictory. Young rice has a very small root system, needs very little N and cannot utilize much N at that time. Rice at midseason has a much more extensive root system, a high demand for nitrogen and can utilize it. At that stage of crop development, water uptake by the crop creates a downward movement of water, and nitrogen is carried along with the water. These factors add up to a totally different situation making N application into a flood practical.

See more about rice fertility in Rice Varieties and Management Tips 2014, which is available through your local county agent or online at lsuagcenter.com/en/crops_livestock/crops/rice/Publications/.

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