Friday, May 17, 2024

P and K Management

Dr. Bruce LinquistDr. Bruce Linquist
UCCE Rice Specialist

Application of the four Rs (right rate, right source, right timing and right placement) helps ensure high fertilizer use efficiency. Last year we discussed the four Rs of fertilizer N; this year I will touch on how they apply to phosphorus (P) and potassium (K) management in conventional water-seeded rice systems.

The first question is whether or not to apply fertilizer P. We recommend a maintenance application of P if soil P test (Olsen-P test) values are between six and 15 ppm. Since P primarily only comes into a field through fertilizer applications and the major loss is what is removed in grain at harvest, it is easy to calculate a maintenance rate. A maintenance P application, which replaces the P removed by harvested grain, can be determined by multiplying your expected grain yield by the P (or P2O5) concentration in the grain. The P concentration in grain averages 0.23 percent (or 0.52 percent P2O5). Therefore, if historical field yields are 8,500 lb/ac, then your maintenance P rate would be 44 lb P2O5/ac (8,500 x 0.0052 = 44).

If straw is removed following harvest, then the P rate should be increased by about five lb P2O5/ac. If soil P values are less than six ppm, a higher rate should be considered, which will help build up soil P. Most P sources available are as ammonium phosphates and are mixed with other fertilizers to make a starter blend. When fertilizer P is applied before planting, it should be lightly incorporated into soil to avoid algae problems. If you have severe algae problems, the P can be applied up to 30 days after planting, which helps reduce problems associated with algae as the rice plants have come through the water surface by this time. Applications of P within this 30-day window do not negatively affect rice yields.

Potassium is different than P in that irrigation water contains a significant amount of K (irrigation water can supply eight to 13 lb K2O/ac). Potassium also moves around the field with the water; therefore significant amounts of K can leave in the tail water during both the growing and winter fallow seasons. Given this, we recommend only applying K based on the needs of the immediate growing season. Do not attempt to build up soil K.

We suggest considering K applications if soil K levels are below 120 ppm and definitely if levels are below 60 ppm. Recent studies showed that soils east of the Sacramento River typically have lower soil levels, and these soil K levels get lower the further east one goes into the red soils on the far eastern side of the valley. The rate required to correct K deficiencies has not been thoroughly studied in California but will differ based on soil type as soils differ in their ability to replace available K. In some studies on the eastern side of the valley where soil K values were below 60 ppm, between 50 to 120 lb K2O/ac were required to achieve maximum yields. We recommend using KCl (muriate of potash) as the K source unless sulfate is deficient in which case sulfate of potash can be used.

Potassium is usually applied with P in the starter blend and can be applied in the same scenarios as mentioned above for P. At harvest, most of the K is in straw. The straw contains up to 1.4 percent K (grain contains about 0.27 percent); therefore, complete straw removal in a crop that yielded 8,500 lb/ac would result in the removal of about 120 lb K/ac (140 lb K2O/ac). Therefore, straw removal mines the field of K reserves and will require higher K inputs.


ss-hardkeDr. Jarrod T. Hardke
Rice Extension Agronomist
University of Arkansas, Cooperative Extension Service

Fertility Foundation

Entering a highly volatile season, it’s easy to want to cut corners. The first corner many growers reach, and therefore the one most often cut, is basic fertility management. It’s not difficult to understand the thought process when making a decent profit looks tough this year. Where can I save a little cash up front? – I’ll cut back on my fertilizer! Well, maybe you had the thought without the exclamation point, but you had the thought nonetheless.

In truth, basic soil fertility is the last place we should be cutting corners. You wouldn’t start a marathon in old running shoes, so why would you start a rice season with inadequate fertility? With profit margins already narrow for 2015, cutting corners with fertilization can put us at risk of giving up bushels we can’t afford to lose. Every bushel counts in a year like this. Apply fertilizer carefully to limit waste rather than making blanket cuts. To save money on fertility – soil sample and follow a nutrient management plan. Apply only the amounts of fertilizer recommended by the soil test results to improve your bottom line. Soil test recommendations are based on the premise that you will get a positive yield response to fertilization. In the past few years, early season nutrient deficiencies have shown up regularly. In many situations, proper early season fertilization could have prevented efforts to play “catch-up” and nurse sick rice back to health.

For optimum efficiency, preflood nitrogen should be applied onto dry ground just prior to flooding.
For optimum efficiency, preflood nitrogen should be applied onto dry ground just prior to flooding.

No one is out there planning to cut their nitrogen fertilizer rate this year. Nitrogen is the “money” nutrient, right? Keep in mind that your yield can be limited by whatever nutrient it starts to run out of first. Nitrogen is only worth the money to produce big yields when all other nutrients are in the proper balance. Reach a point where you’re running out of another nutrient, and nitrogen can’t make up the difference. However, if you’re interested in a prescription nitrogen rate for your field, consider the N-STaR program – soil samples taken especially to provide field-specific nitrogen fertilizer recommendations. Keep in mind that N-STaR soil sample depths are 18 inches for silt loam soils and 12 inches for clay soils (standard soil sampling for other nutrients requires a 4-inch soil sample).

Speaking of nitrogen fertilization, it’s extremely important to get it right. Using urea treated with a product containing NBPT improves nitrogen efficiency by limiting nitrogen loss due to ammonia volatilization. These products, when properly applied to urea, can protect against ammonia volatilization for up to 10 days as fields are flooded. Oftentimes, we apply very large amounts of urea to rice just prior to flooding. This can result in “streaking” throughout the field and prevent us from reaching our maximum yield potential. To help prevent streaking when applying fertilizer in large amounts, consider having the fertilizer split-applied in alternate directions (i.e. half applied east-to-west and the other half north-to-south).

Be efficient with fertility management in 2015. Lay a solid foundation relying on research-based fertility recommendations. Plan to get smart with your fertility management this year to improve your bottom line.

DustinHarrellDr. Justin Harrell
Extension Rice Specialist

The ‘right time’ to apply phosphorus

The International Plant Nutrition Institute (IPNI) put together the 4R Nutrient Stewardship System to help producers make sound nutrient management decisions regardless of individual situations. The most efficient nutrient management decision can generally be made when you consider the “right source, right rate, right time and right place” for your particular cropping system.

So what is the “right time” to apply phosphorus (P) in a rice cropping system? How much yield do you lose when you delay P fertilization? These are the types of questions that we have been trying to answer in our research program. The answer to the first is very easy and is the same for all crops, not just rice. Fertilizer P should be applied to the crop just before the crop needs it. This allows the crop to take it up before the nutrient gets “tied up” in the soil. The answer to the second question is not so straight forward.

harrell 1A trial was recently conducted near Mamou, La., on the LaHaye farm in an effort to put numbers to the yield loss that would be associated with delayed fertilizer applications. The soil at the location was a silt loam soil with a pH of 6.2 and had a Mehlich-3 soil test P concentration that ranged from 2.4 to 7.4 throughout the field, which made it fall into the very low soil test P category. In the trial, triplesuper phosphate (TSP) was surface broadcast at a rate of 120 lb P2O5 per acre at one of five different times of application. Times of application included: at planting, preflood (four- to five-leaf rice), midtillering (two weeks after flooding), green ring and 50 percent heading. The yield results of the trial can be seen in Figure 1.

You can see from the figure that maximum yield occurred when P fertilization occurred at planting (8,608 lb/A) and the lowest yield occurred when no P was applied (5,585 lb/A). That accounts for a 54 percent yield reduction when P fertilizer was not applied. A 12 percent yield loss was observed between the at planting and preflood application timings; however, this was not statistically significant. Approximately 32 percent yield was lost when waiting until midtillering or green ring to apply P fertilizer. A yield loss of 52 percent was observed when P fertilization did not occur until 50 percent heading.

harrell 2The bottom line is that P fertilizer in rice needs to be applied before tillering and flooding – the earlier the better. If P fertilizer cannot be applied just before or at planting, an alternative is to apply P around the 2-leaf stage of development coinciding with the first Newpath application in Clearfield rice. If you are in a water-seeded system and scumming of the water is a problem, then a preplant incorporation of the fertilizer is probably the best route to choose.


ss-wayDr. M.O. “MO” Way
Rice Research Entomologist

 N Trials Are Key

Proper fertilizer management is essential. Too much nitrogen (N) can lead to excessive vegetative growth; delay in maturity; increased sheath blight severity; greater chance for blast, false smut and kernel smut problems; and increased likelihood of lodging. Symptoms of N deficiency include darker green rice on the levees, dark and light green areas scattered throughout the field; yellowish older leaves and green younger leaves on rice; and fewer tillers.

Heavy infestations of rice water weevil produce the above N-deficiency symptoms because severe root pruning results in failure of rice plants to take up N from the soil. Scout your fields frequently and adjust timings and rates to make sure the crop does not “run out of N.” If you are applying preflood N, try to apply on dry ground as close to flood as possible. You can add a urease inhibitor to your N fertilizer if you cannot flood your field in a short time period. Scientists in each rice-producing state conduct variety x N trials to provide N management guidelines.

For Texas, Dr. Fugen Dou, located at the Beaumont Center, conducts these trials at both Beaumont and Eagle Lake – Beaumont soils are fine (clay) while Eagle Lake soils are coarse (sandy loam). In general, N recommendations for clay soils are greater than for sandy soils, and Texas N recommendations for non-hybrid varieties have increased over the years.

Sanders, left, and Vawter worked at the David R. Wintermann Rice Research Station at Eagle Lake for 30 and 38 years, respectively.
Sanders, left, and Vawter worked at the David R. Wintermann Rice Research Station at Eagle Lake for 30 and 38 years, respectively.

Current recommendations for total N for Catahoula, Cheniere, CL161, Cocodrie, Presidio and Sabine are 220 and 200 lb/acre for clay and sandy soils, respectively. For CL111, Cl151 and CL161, total N is 190 and 170 lb/acre for clay and sandy soils, respectively. For hybrids, recommended total N is 150 and 120 lb/acre for clay and sandy soils, respectively. For more information, go to https://beaumont. pdf. Pages 21-26 discuss N fertility management. In closing, I want to thank Jack Vawter, Farm Research Services Manager, and Billy Sanders, Technician II, for their many years of dependable and excellent service. They both retired in January.

Dr. Fugen Dou co-authored this article.


ss-atwellSam Atwell
Agronomy Specialist

MO Fertility Plan

Now is the time to visualize making your 2015 rice crop, which includes building a fertilizer plan. Most rice is in a rotation with soybeans, so consider nutrient removal in pounds per bushel from last season’s soybean and rice crop. Make sure you put enough fertilizer out for both crops. From your soil sample reports and these considerations, you can make a judgment on how to put your fertility program into your seasonal rice crop. Your 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, ranging from 0 to 180 lbs. N/acre with 150 pounds being most common.

Screen Shot 2015-02-16 at 8.13.04 AMTwo N application options are as follows: 100 percent applied pre-flood on dry soil (only when able to maintain timely and seasonal flood) or 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 NBPT-containing 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. Nitrogen sources are urea (46-0-0), DAP (18-46-0) and ammonium sulfate (21-0-0-24). Tables below are recommendations for pounds of P and K where soil samples range from low, to medium, to high to very high, and the grower is shooting for 200 bu/acre yield.

Zinc (Zn) deficiency normally occurs on silt and sandy loam soils or on precision-graded fields. Apply 10 pounds of Zn as a granular fertilizer before emergence on silt and sandy loam soils when Zn levels are less than 4.1 ppm and pH is greater than 6.0. Apply liquid Zn sources at a rate to deliver at least one pound of actual Zn per acre. Apply Zn to the seed at a rate of 0.25 to 0.5 pounds of Zn per hundredweight of seed. Sulfur is most likely to be needed on sandy soils and may be needed when the SO4-S soil test level is less than 10 ppm or a deficiency has occurred in the past. One hundred pounds of ammonium sulfate equals 24 pounds of actual S, which will supply sufficient amounts of sulfur.


Bobby GoldenDr. Bobby Golden
Extension Rice Specialist

Nutrient Removal

An increase in Mississippi rice acreage has created a situation outside of the standard rotation with soybean that may impact fertility management considerations in 2015. Consider Table 1, which illustrates crop nutrient removals for rice:soybean and corn:soybean rotations. If we are moving into rice from a corn:soybean rotational situation, we have removed roughly around 20 lbs more P2O5 and K2O in a rotational year than we do in our standard rice:soybean rotation. Therefore, traditional application rates and/or fertilizer blends may need to be adjusted.

On clay soils, the predominate deficiency we observed in 2014 was related to phosphorus. Thus, P nutrition for rice grown on clay soils should be of utmost priority. Our producers routinely applied a small amount of DAP (50 lbs product) shortly after rice emergence as starter fertilizer for the last few years. This application has served us well, but may not contain enough P for soils that test low in phosphorus. Therefore, additional P will be needed.

Unlike our clay soils, rice seeded on silt loam textured soils requires direct attention to soil test K levels. In 2014, on fields that had been out of rice and moved back in, we observed instances of K deficiency, which in some cases was severe. Be aware of the K removal from extremely high-yielding soybeans grown in rotation with rice, as subsequent rice yield can be severely limited by lack of K nutrition. Proper identification of low soil K by routine soil analysis is key to growing high-yielding rice on lighter-textured soils.

goldenIf we miss on providing adequate P and K to the rice crop, we are limited on the return we will get from our nitrogen. When considering N fertilization, remember Mississippi State University annually conducts variety by nitrogen rate trials and provides N-specific recommendations for commonly seeded varieties in Mississippi in the rice variety trial publication. Most of the Mid-South universities evaluate nitrogen stabilizers. The general consensus among the group is that products containing the active NBPT applied at rates between 1.6 -1.8 lbs a.i./ton of urea have been effective in reducing volatilization.

Soil sampling on a regular basis, which provides the foundation for a roadmap for high yields, and routine soil analysis are critical to help aid producers with P and K fertilizer decisions on a tight production budget. The best way to save money on fertilization is to know the nutritional status of your soil.



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