Aim for efficiency
Dr. Jarrod Hardke
Rice Research Entomologist,
University of Arkansas, Cooperative Extension Service
Repeat after me — when I look to cut costs this year, I will not cut my fertility program. Again, I will not … you get the idea. The first nutrient the plant starts to run out of is the one that is most yield-limiting. While we focus on nitrogen (N) fertility, don’t forget everything else.
So what fertility can you potentially reduce? The University of Arkansas System Division of Agriculture has revised its soil test recommendations for phosphorus (P) (Table 1). The take-home message is that a lower soil test P level is now needed before P fertilizer is recommended.
For instance, the previous range for the “Very Low” category was ≤ 15 ppm but is now < 9 ppm. There continues to be a distinction in the recommendations between soils with pH above or below 6.5. Remember, standard soil test samples for nutrients such as P and potassium (K) should be taken at a 4-inch depth.
Timing for midseason N applications also has changed. Previous recommendations called for midseason N applications to be made between beginning internode elongation (BIE or “green ring”) and ½-inch internode elongation. The new recommendation is to apply midseason N in one application a minimum of three weeks after the pre-flood N application AND internode elongation has started. Both conditions must be met before the application is made. Although this change does not result in a direct cost savings, it greatly increases the chance of receiving the maximum yield benefit from the application.
Using N-STaR sampling to obtain field-specific N rate recommendations can potentially reduce N input costs. The soil sample depth for N-STaR is 18 inches for silt loam soils and 12 inches for clay soils.
Another possibility for reducing N inputs would be to use an optimum single pre-flood N rate, which omits the need for a midseason application while reducing the total units of N needed. The single pre-flood method saves N by using 20 units less than a typical season-total N recommendation.
In order to use the optimum single pre-flood method, several conditions must be met: 1) treat urea with an approved NBPT product or use ammonium sulfate, 2) apply urea onto dry soil, 3) be able to flood timely, and 4) be able to maintain the flood for at least three weeks. For more information on Arkansas rice recommendations, visit http://www.uaex.edu/rice.
Two nitrogen issues test California growers
Dr. Bruce Linquist
UCCE Rice Specialist
This year due to the drought, a lot of fields were not flooded as usual and many weren’t even disked after harvest. There may be a lot of standing undecomposed rice straw at the start of the season.
If this is the case, your N rates will likely need to be increased. Having a lot of straw in the field will “bind” the fertilizer N (we call this N immobilization) and make it unavailable during the first few weeks of the season. This immobilized N is typically available later in the season once the straw has decomposed.
The second issue is the top-dress N application. There has been an increasing trend for a top-dress N application — usually ammonium sulfate — around panicle initiation (PI). Although top-dress N applications are not necessarily a bad idea, they’re often unnecessary.
Top-dressing N is expensive as it requires an airplane, and the fertilizer is expensive relative to aqua-ammonia. Top-dress N applications are absolutely needed if the plant is N stressed, which typically shows up as yellowing of lower leaves.
That said, I suggest planning so a top-dress N application is unnecessary. Research conducted on-station and on-farm has shown that if an adequate amount of N is applied at planting, a top-dress is not needed to achieve maximum yields.
If you find yourself constantly needing a top-dress N application at PI, you might want to increase your preplant N rate. I don’t want you to necessarily take my word on this, but I encourage you to do your own testing to see if this is really necessary. A simple test involves three treatments across a field: (1) standard preplant N rate with no top-dress; (2) standard preplant N rate with top-dress and (3) increased preplant N rate with no top-dress.
The total amount of N in treatments 2 and 3 should be the same, and this will tell you if yield improved with a split. Having treatment 1 in the field lets you know if a top-dress or increased N rate was necessary to begin with. At harvest, use a combine with a yield monitor to test for differences within the treatments.
This year we’d like to coordinate with growers who are doing this to determine results across a number of fields and to share findings with others. Please contact me if you would like to participate.
Be on the lookout for new rice pest
Dr. M.O. “MO” Way
Rice Research Entomologist
I wanted to alert readers of Rice Farming about a new Texas pest of rice we discovered attacking the ratoon crop last fall. It is the rice delphacid — Tagosodes orizicolus — a planthopper in the order Homoptera; family Delphacidae.
It is related to leafhoppers, so it has piercing-sucking mouthparts that it inserts into the vascular bundles of rice leaves. These planthoppers suck up plant juices and cause “hopperburn” when populations are high, which they were last fall. Symptoms of hopperburn are dead or discolored foliage (brown/orange); presence of honeydew (planthoppers excrete a sweet, sticky substance); and sooty mold fungus that grows on honeydew resulting in a black film on foliage.
We found the pest widespread in high numbers on ratoon rice in Brazoria, Wharton, Waller, Matagorda, Colorado, Fort Bend and Jackson counties. In fact, some fields averaged more than 300 planthoppers per five sweeps of a sweep net. Infestations were found relatively late during heading and grain maturation. Nevertheless, yield and possible quality losses were obvious. We’ve received no reports of planthoppers and/or damage east of Houston.
The pest is native to Central America, so we don’t know how or when it got here. It may have been here for awhile because populations were so high last fall. This species was found in Louisiana in the 1950s, then simply disappeared. It may not be able to survive our winters, but again, we just don’t know.
We’re trying to find out more about its life history, host range and how to best control it. Check your fields for this pest as soon as rice emerges. If you suspect you it, please contact your local rice scientists or me at 409-658-2186 or email@example.com.
Sensor helps optimize nitrogen management
The optimal amount of nitrogen required for rice crops changes from year to year. In fact, most producers are aware that their yield levels change significantly, but they may not be aware that the yield response to additional N changes as well.
In Southeast Missouri, the common management practice is to apply most of the N (70-120 lbs/ac) pre-flood. Then a permanent flood is immediately established. The remaining N, typically 30-45 lbs/ac, is applied based on the plant N status at midseason. Determining the plant status can be challenging for producers.
However, recent research from the University of Arkansas has indicated that the newer varieties do not always respond to midseason N when an adequate amount of pre-flood N has been applied.
We set up an experiment to compare Nitrogen Use Efficiency (NUE) and yield from three N management strategies. The results are for Southeast Missouri, but they could have a broader application. Dr. A.J. Foster, Extension agronomist specialist, and I established a small plot experiment starting in 2014 at the Missouri Rice Research Farm to evaluate using remote sensing technology to make a midseason N application. The treatments involved two rice varieties (Jupiter, a medium grain, and Roy J, a long grain), three N application strategies and an untreated check.
The 2014 treatments were 120 lbs N/ac pre-flood; a pre-flood application of 120 lbs N/ac with 30 lbs N/ac midseason; and a pre-flood application of 120 lbs N/ac with midseason N based on Greenseeker remote sensor recommendations. The sensor readings were collected at stem elongation.
In 2015, two treatments were added: 150 lbs N/ac pre-flood and 180 lbs N/ac pre-flood, which served as a reference strip for the sensor.
Results from the small plot replicated study found the rice variety did not affect yield and nitrogen use efficiency (NUE). Applying 120 lbs N/ac all pre-flood proved to be the optimal strategy to maximize both yield and efficiency.
The mid-season strategy was the least efficient. The sensor-based strategy provided decision support to maximize the use of a midseason application. These results indicate that applying adequate (120 lbs N/ac) pre-flood N in combination with using a sensor to determine midseason N rate offer potential for increasing Nitrogen Use Efficiency, optimum yield and maximizing profitability in Missouri.
Dr. Bobby Golden
Extension Rice Specialist
Phosphorus deficiency of rice seems to be a continual issue in the Mississippi Delta each year. In 2015, we experienced what I would consider an above-average amount of P deficiency related issues. Phosphorus deficiency in rice can be characterized by stunting, and leaves may appear very dark green to almost bluish in color. The most distinctive characteristic of P deficient rice is erect spindly leaves with minimal tillers on the plant (Picture 1). Younger tissue may appear healthy while older tissue can turn brown and become necrotic in severe cases.
Research to correlate and calibrate soil tests to describe the relationship between rice grain yield and phosphorus first began in 2002, and the program has been maintained with multiple trials placed across the Delta annually.
Currently with 34 site-years of data in the model, we still have difficulties explaining rice grain yield response with soil test P data on low P testing soils. Soil test data suggest that when Lancaster P is below 30 lbs P/ac, we have a great chance of observing a yield response when applying P. But in many instances, even when soil test P is extremely low (< 10 lbs P/ac), we may not observe a statistical yield response.
Coupling pH with soil test P data has helped, but more research valuating P fertilization and its relationship with grain yield at differing initial soil test P levels is needed for more precise recommendations. In general, when a site has a soil test P level that responds positively, we average an 11 bu/ac increase with as little as 50 lbs P2O5/ac.
What we have seen over the past 10 years is when phosphorus is needed, we observe a measureable yield increase, and timing of the P application is as important as the rate applied. In general, optimum P fertilization timing in Mississippi is somewhere between preplant and the one- to two-leaf stage of rice growth and development.
Keep crop fertility
Dr. Dustin Harrell
Extension Rice Specialist
The ratoon rice crop, also known as the second crop, is important economically to South Texas and Louisiana rice farmers because it traditionally yields approximately one-third of what the main (first) crop yields with few additional inputs. In 2015, Louisiana ratoon rice yields were the highest ever recorded, with many fields averaging one-half or more of what the main rice crop yielded. After such an exceptional ratoon season, I thought I’d cover some of the basic fertility recommendations for the second crop.
Nitrogen (N) fertilizer should be applied on dry ground, and the field should be re-flooded as soon as possible after the main crop is harvested. Research has shown that a single application of N at 90 lbs N/ac will maximize ratoon yields in most years for both rice hybrids and rice varieties.
Some farmers like to split N applications for the ratoon crop, with the first coming after harvest, flushing it in, followed by a second application about 10 days later. However, this method has not shown to be superior to the single application in research.
Two things to keep in mind is the ratoon crop needs about 80 to 90 days to mature after the first harvested and that the first frost will kill the plant. That means the main crop should be harvested by Aug. 15 if you want the greatest chance of a successful ratoon crop.
The more N that is applied to the ratoon crop, the longer it takes to mature. Therefore, if you want to attempt a ratoon crop after Aug. 15, reduce the N rate by 6 lbs N per day. I personally believe that by Sept. 1, you do not want to apply any fertilizer N.
Phosphorus (P) and potassium (K) soil test-based recommendations in Louisiana are intended only for the main rice crop. Recent research has shown that an additional 30 pounds of P2O5and K2O fertilizer is needed to maximize ratoon yields when grown on soils testing very low, low or medium in soil test P and K.
The additional P and K fertilizer can be applied with the main crop P and K fertilizer or after harvest of the main crop. I prefer to split the applications to minimize potential nutrient losses and to maximize nutrient availability in the ratoon crop.
Ratoon stubble management practices have been shown to increase ratoon yields, reduce the incidence of disease (mainly Cercospora), even maturity and increase grain quality. Stubble management practices include post-harvest mowing (flail or bush-hogging) to about 8-inches or post-harvest rolling of stubble.
The only disadvantage is that stubble management practices delay maturity of the ratoon crop by two weeks. Therefore, stubble management practices after Sept. 15 are not encouraged.