Don’t Run on Empty

Don’t Run on Empty

The saying goes, “a ¼ tank is better than an empty tank.” That’s going to be very appropriate for the 2025 growing season. In a year where nothing really pencils out, it’s going to be tempting to strip this machine down to the frame to skin a profit.

Fertility is always a tough area to talk about cuts and adjustments, but this year, everything has to be under the microscope.

In rice, nitrogen is front and center. Most of our N rate recommendations are already aimed at optimization and don’t leave room for reductions. Stay the course there and maximize efficiency by treating urea with an NBPT product.

For varieties, consider going with a single pre-flood N application (rather than a two-way split) where you can flood quickly and maintain an initial flood for three weeks. This can help us save on total N applied. For hybrids, there isn’t really anything to change — our yield goals are met by our pre-flood apps with the additional N at late boot providing a small yield bump while improving milling and standability.

Zinc, while not required in large amounts, is crucial in rice production. Don’t skimp here — where a soil test calls for it, we need to apply Zn sulfate in our pre-plant mix, which prevents deficiencies and builds soil test levels. If forced to use a foliar Zn product in-season, it will cost as much without increasing soil test levels. Granular Zn provides more bang for the buck.

For phosphorus, we can get away with lowering rates in many situations, but we don’t need to completely omit recommended applications. On soils with pH greater than 7 and in the Low or Very Low soil test categories, do not reduce rates.

Potassium gives us the most flexibility. We know that we can reduce rates in the short-term and have a safety net of tissue sampling in-season and applying additional K then if needed. We recommend using the Potash Rate Calculator (https://agribusiness.uark.edu/decision-support-software.php) to fine-tune our K fertilization program.

At the end of the day, an 0-30-60 can take care of a lot of acres from a P and K standpoint. Remember that for most nutrients, we don’t yet have reliable tissue sample recommendations for managing the crop in-season (K is the exception). For nutrients other than K, tissue sampling is still primarily a diagnostic tool — it helps identify an issue or isolate a deficiency but isn’t a good predictor of yield-limiting nutrient levels that would benefit from an additional in-season nutrient application.

Make smart adjustments in 2025. Reducing rates is one thing, but omitting recommended fertility entirely is risky. We can save money if we choose wisely, but there is still a certain degree of “spending money to make money” that has to occur with our fertility program. Let us know if we can help.

Coating Fertilizer has Benefits

The day finally arrived where a former rice weed scientist turned Extension specialist has been asked to write a fertility article. Admittedly, not a whole lot has changed from a nitrogen-management standpoint in Texas in recent years. One thing that’s different down here is we tend to use less mid-season nitrogen than most of the other rice-growing areas of the country to minimize kernel smut issues later in the season.

We had no shortage of rain prior to permanent flooding in 2024, with the majority of that falling in April and May. Unfortunately, our pre-flood urea was going out on a large portion of acres during the same timeframe. I immediately thought back to my days at Louisiana State University when Dr. Dustin Harrell would have demonstration plots each year showcasing nitrogen losses when urea was applied on muddy ground, versus dry ground, versus flooded ground. That is where I first learned of urease inhibitors and have been a believer ever since.

Urease inhibitors like Agrotain are urea coatings that slow down urease enzyme activity and protect your nitrogen investment. Urease is the enzyme responsible for the breakdown of the NH4+ our rice loves to NH3, which is lost as a gas and ultimately unavailable to rice. Research has suggested that up to 24% of the nitrogen you paid for can be lost due to ammonia volitization, compared with a 5%-6% loss when treated with Agrotain. This is especially true when conditions are less than ideal, such as damp or muddy ground like we had in 2024, which can rapidly speed up the volatilization process.

In addition to muddy ground, urease inhibitors are just as beneficial on dry ground in situations where flooding might be delayed after urea is applied or in those larger fields that are just too big to flood up quickly. The more days you wait, the more nitrogen will be lost; however, if the field can be flooded within a day or two, Agrotain is probably not needed. According to LSU, if you can’t get the water to it on dry ground in three to five days after urea is applied, use a urease inhibitor.

If a weed scientist is going to write his thoughts on fertilizer, he better write at least a little bit about herbicide-coated fertilizer. In my final few years at LSU, a fellow grad student was revisiting herbicide-coated urea for a couple of new products. In this day and age, we are looking for any way to cut costs without jeopardizing yield, and impregnating fertilizer for certain applications can help. These applications are typically safer on rice, less prone to off target movement, and can save the grower an additional trip over the field.

Novixid is a relatively new product from Corteva and is a great candidate for fertilizer impregnation. For those who don’t know, Novixid is a pre-packaged mixture of Loyant and Grasp. These applications, like others mentioned, are also situational and aren’t necessarily something I would recommend blanketing the world with. At minimum, you want at least 150 pounds per acre of fertilizer going out. Second, you want your weeds to be four inches or less. Typical weeds controlled by this application are rice flatsedge, yellow nutsedge, alligatorweed, ducksalad, and other aquatic/semi-aquatic species. Additionally, these treatments work best when weeds are 70% submerged or more, so applications will be directly into the floodwater. Please consult the label for additional instructions and weeds controlled or suppressed.

Reducing Fertilizer Input Costs

I have had a couple of calls already this year asking how to reduce fertilizer costs. I believe these questions are largely related to low rice prices and growers wanting to reduce input costs. Here are a few strategies to help reduce fertilizer input costs.

If you routinely apply top-dress nitrogen, consider applying all the N you would normally apply as a top-dress as aqua-N before planting. We have done a lot of research on this, and we have seen no benefit of splitting the total N rate. If fields remain flooded early in the season, all this N is efficiently used. This saves cost as aqua-N is a cheaper N source than ammonium sulfate (typical top-dress N source). Also, you avoid the airplane costs associated with topdressing. I am often asked about the benefits of the sulfur in ammonium sulfate. While we are adding S, I have never seen sulfur-deficient rice in California, and our soil and plant S concentrations have always been above critical levels.

Was your field fallow last year? For the past four years, we have been doing research at the Rice Experiment Station on how to manage N fertilizer in a rice field when the previous year’s rice was in fallow. I have written about our findings more extensively in previous articles. The bottom line is that there is more soil N available from fields that were fallowed the previous year. Thus, if you have a field coming out of fallow (and it had been in rice prior to that), you can reduce your N fertility rates. Our research shows that rates can be reduced by 20-40 pounds of N per acre.

Importantly, for both above strategies, it is important to keep a close eye on the crop around panicle initiation (40-45 days after planting) to see if it is displaying any signs of N deficiency. This can be done with Leaf Color Charts, a Green Seeker, or plant analysis — all of which have been discussed before. If the crop is showing signs of deficiency, apply N.

Finally, test your soil. You may not need to apply phosphorus (P) and potassium (K) fertilizer. I recommend applying a balanced fertility program that balances the P and K removed from the field in harvested grain (and maybe straw) with what is applied as fertilizer. This is especially the case when soil tests are not used as it ensures an adequate supply of these nutrients. However, a decision can be based on a soil test. If your soil P levels are above 12 ppm (Olsen P/soil bicarbonate test), consider not applying P as these soil P levels are adequate. Similarly, if your soil K levels are above 120 ppm, you may not need to apply K fertilizer. In areas on the east side of valley, especially the red soils, higher soil K levels may be necessary.

Rice Phosphorus

Phosphorus is a constituent of nucleic acids and is needed for several plant-essential processes including photosynthesis, respiration, energy storage, and energy transfer among others. Rice removes P from the soil as an orthophosphate ion, primarily H2PO4- or HPO4-2. Fertilizer P is always expressed as a percent P2O5 equivalent and on a fertilizer label is located as the second number (example: 0-46-0).

Soil test P and soil-test-based fertilizer recommendations can be reported as either P2O5 equivalent or P. Convert P to P2O5 equivalent by dividing by 0.44. Convert P2O5 equivalent to P by multiplying by 0.44. Soil P is most available to plants in soils with a pH around 6.5. Typically, plant-available P is decreased as a soil becomes more acidic or alkaline. When a rice soil is flooded and becomes anaerobic (no oxygen), the pH of the soil migrates towards neutrality over time regardless of the initial pH; therefore, in most cases, P becomes more available to rice after permanent flood establishment.

Rice takes up approximately 0.0086 pounds of P2O5 (0.02 pounds of P) per pound of dry rice harvested. Approximately 75% of the P taken up is contained in the harvested grain. Use-soil-test based fertilizer recommendations: LSU AgCenter’s Soil Testing and Plant Analysis Laboratory uses the Mehlich-3 soil test extraction to extract P and determine fertilizer needs. Soil test results are given in ppm of extractable P, while fertilizer recommendations are given in pounds of P2O5 per acre. Phosphorus fertilizer rates should be determined from a recent soil test.

Phosphorus fertilizer is most efficient in rice production when applied just before planting until permanent flood establishment (fifth leaf to first tiller). Research has shown that P fertilizer applications after this time (often referred to as “rescue” applications) are beneficial; however, yields will be reduced as compared to earlier P application timings. Recent research with ratoon rice production in Louisiana has shown that an additional 30 pounds of P2O5 was needed to maximize ratoon yields from a soil testing low in extractable P. The additional 30 pounds can be included with the first crop application or applied immediately after first crop harvest prior to reflooding. Phosphate fertilizers are commonly blended with potassium and nitrogen fertilizers to provide site-specific fertilizer needs of the producer. Commonly used P fertilizer sources in rice include: triple superphosphate (0-46-0), diammonium phosphate (18-46-0), monoammonium phosphate (11-53-0), and MicroEssentials SZ (12-40-0-10S-1Zn).

Nutrient deficiency symptoms of phosphorus appear when a plant becomes deficient in P. Phosphorus is mobile in the plant and will translocate from the older (lower) leaves into the newer (upper) leaves. Symptoms include stunted plants with slender stems while leaves tend to have a very dark green color that stand erect. Phosphorus deficiencies also result in reduced tillering and slower development of the plant with necrosis (death) of leaves beginning with the oldest leaves.