Rice Mid-Season Nitrogen

A simple method is needed to aid farmers with midseason N decisions in rice in the Mississippi River Delta region. Experiments were conducted from 2004 to 2006 at Glennonville and Portageville, Missouri to evaluate visual and digital image measurements at internode elongation for predicting rice yield response to midseason N applications.

Example images (left to right- low preflood N to high preflood N) collected at internode elongation with a digital camera from 80cm X 115cm areas in rice plots. Values in the lower right corner of photos were the proportion of green pixels in images counted with Sigma Scan software.

Yardstick method


A yardstick was floated on floodwater between two center drill rows and the numbers visible were counted. Inch digits on the yardstick were approximately 2.0 mm tall. Standing between adjacent rows and leaning over the sampling rows, we counted the inch numbers showing on the yardstick (not hidden by rice leaves) out of 36 numbers possible. When a rice leaf obstructed the view of one digit in a two-digit number to the point that it the whole number was not recognized, we did not count that number. The person taking the measurements always kept both eyes open during the readings.

Conclusion. No yield response was produced from midseason N when fewer than 13 numbers were showing on a yardstick floating between drill rows or more than 64 % of the pixels in digital images of plots were green.

Harvesting Rice

After several weather delays, we completed the harvest in our center pivot field in South Africa. Late in the season, we had another flush of weeds that emerged through the rice that had to be killed with herbicide before harvest. Shown below are photos made by Linda S. at the farm. Right before harvest a heavy rain storm knocked a lot of grain from the rice panicles.


Milk stage rice

I returned to the United States on March 1. Jim Heiser, my research associate, is at the research farm managing the final irrigations and will be helping with harvest and grain storage. Most of the Nerica 4 rice panicles are mature now but the Nerica 11 and 14 still have a couple of weeks before the grain is mature. We are already making plans for the next growing season. In November 2011, we will plant one half of the irrigation experiment in Supra Rice from Zambia and the other half in Nerica 4 rice. In small plots, we will also plant about 25 conventional and 50 hybrid lines from Kenya.

Over the winter months, we plan to make three improvements to the center pivot equipment. (1) This year the rice plants were taller and greener close to the pivot point and became yellow and small at the edges of the center. To improve mixing of the N fertigation solution with the irrigation water, we will move the injection port down the supply line before the red filter and use an insert diffuser in the port.
(2) The EZ plan was programmed to leave a 5 degree dry area for the entrance road from the east. This was done to conserve water and keep the road from staying muddy. It worked twice but on the third irrigation, the system watered the road then turned off in the rice. The degrees on the Field Boss were incorrect. Since the system already has a GPS receiver for the precision system, I suggest that the GPS also be used to track the degree settings for Field Boss instead of the current angle setup.
(3) Finally, work is need on communication between Field Boss and the radio transmitter. Sometimes when the system is moving and applying water, I need to stop it because of rain. Pusing the stop button halts the pivot from walking but the pump continues running down the hill at the reservoir. To get the pump to stop, I open the radio box and click an orange lever. This stops the pump, but is not how the system should function.

Rice Heading

Most of the rice plants under our center pivot in South Africa are starting to head with some panicles in the milk stage. People often ask me how’s your rice doing under the pivot. Without meaning to dodge their question, my usual reply is, “well, it depends on which part of the field you are talking about.” Thankfully, there are some places in the field that will make satifactory rice yields. See photo on right for good area. There are definitely good and bad areas and my quest now is to determine why the bad areas are that way. Some of the reasons are obvious. For example, our experiment has designed to include low irrigation water treatments causing the plants to stress in those zones. It does not make the field look “pretty” but it will provide important data that we need to understand rice water use. Also, on the far north side, from the beginning, we had a very poor stand because of trash (leaves and stems) in the Nerica seed which clogged the drill at planting. At first, the planter driver stopped every few meters to clean out the stopped up drills but after several hours of doing this it was decided to keep going and hope for the best. Unfortunately, where there is not a good stand of rice, weeds and grass will always fill in the gaps. Another early season problem that we had was glyphosate resistant volunteer maize. It was the thickest stand of volunteer maize in a field that I have ever seen. But, most of that is gone now thanks to Clincher herbicide and slashing.

We finally have the beetles under control after two insecticide sprays. The last chemical sprayed was AviGard, mercaptotion (250ml per 100 liters water). It took about 18 hrs to work but most of the beetles eventually died except the ones in the photo on the right that were mating.
One of my concerns with this rice crop is plant height variability (“waveness” across the field) and yellow plant color in some areas. Usually, fertigation helps correct this problem. To help diagnosis the problem, we collected tissue samples from “good’ and “bad” areas of the field.

The results of the tissue test are shown above. In case, it’s too small to read- main differences are Good rice: 4.0% N, 0.23%S, and 500.6 mg Mn/kg; Bad rice: 2.98%N, 0.15%S, and 258.8 mg Mn/kg. It is late to try and correct the low N, S, and Mn but we can use this for planning next year’s fertility program. What I do not know is whether the low tissue levels in the “Bad” rice was caused by low soil fertility levels or an indirect effect from herbicide injury. Yesterday, I noticed a interesting part of the field. The rice in this area is over waist high and has large panicles.

In the photo on the right, look at the taller rice in the center background. I plan to take soil samples from this area and compare it to a “bad” area to see if there is an obvious fertility difference that we need to address in next year’s fertilizer program.

The photo to the left shows a closer look at the tall rice.

Tough Beetles

Our first rice crop in South Africa has really had its “ups and downs”. The photo below was taken this morning in one of the healthiest parts of the field. Rice in the north side of the field is in the late boot or early flower growth stage. Two weeks ago, by accident, we “hammered” the rice with 2,4-D to prevent wild watermellon and Wandering Jew weeds from taking over. Normally, 2,4-D injury causes the rice flag leaf to temporarily turn down at a 90 degree angle instead of standing straight up as normal, but oddly this did not happen on the Nerica rice.

Instead, the herbicide made most of the plants turn a yellow color which caused me to question if the problem might, in fact, be nitrogen or sulfur deficiency. We pulled tissue samples for testing from green and yellow areas to determine N and S content. I am still waiting for the results from the South Africa lab. In the meantime, I began to second guess the wisdom of my request to make the 2,4-D application. But, alas with more time to recover, I think it might have been the right choice. There are still rice plants in the field on south side of the that we slashed that are sick (we did not order enough Clincher to control the volunteer corn). But in the non-slashed areas on the north side, the rice is beginning to look almost normal again and most of the broadleaf weeds were controlled. If nothing else, it will help reduce the weed seed bank for next year’s crop. Unfortunately, now we have a new problem. Actually it is a old problem that I did not take serious enough at the time.
In mid-December, Matt Rhine scouted the field and found black and yellow beetles feeding on the tassels of the volunteer maize (corn). When I arrived on January 1, the beetles were eating the corn pollen but did not show any interest in the rice plants. See corn photo on right. I sent copies of my photos to Dr. Kelly Tindall, entomologist at the University of Missouri-Delta Center, for identification. Without having an actual specimen to observe, she could not give an absolute ID but thought it was Diabrotica sp. (same genus as corn rootworm). This may be the adult stage of the worm that lays eggs in the soil and attacks corn roots the following year. No one knows what the impact of the soil larvae of the beetle will have on next year’s rice because their behavior is very species dependent. They may attack the rice seedling roots just like they would young corn roots. Or they may totally ignore the rice. Kelly also said that, in the US, there are species that will only lay eggs in corn fields and they overwinter as eggs and that is why a corn-soybean rotation is successful. Soybeans are not a host for the pest. A good non-grass crop, such as cow peas, to rotate with pivot rice would be a big help for reducing insect and diseases in the rice. In hind-sight, for this rice crop, I should have sprayed the with insecticide in early January. When most of the corn died from Clincher or from slashing with a mower, I forgot about the beetles and focused on other problems.

Now that the rice is starting to flower, the beetles are back in very high numbers feeding on the pollen from the rice heads. On Tuesday, four days ago (2/1) we sprayed lambda-cyhalothrin (150 ml/ha) to control the beetles. For prevention of diseases such as blast, on Thursday (2/3) we sprayed pyraclostrobin (800 ml/ha). My chemical supplier warned me that lambda-cyhalothrin may not do a complete job. He was correct. Although it significantly reduced the numbers, there are “hot spots” in the field where beetles are still alive and feeding on the rice heads. We special ordered carbaryl insecticide, a more potent “beetle killer”, which is scheduled for delivery on Monday (2/7). We will spray carbaryl at rate of 3 liters /ha.
Fortunately most of the rice plants are in the late boot stage, just now getting ready to flower. The photo below shows panicles from two plants. The one on the bottom flowered early and probably was attacked by beetles. The panicle on the top, is just starting to flower. Hopefully, we can still protect it with carbaryl insecticide. If anyone sees this photo below and recognizes the symptoms of the brown panicle as something other than indirect effects of beetle attack, please contact me.




Growing a new crop in an area often brings unexpected problems. That’s why they call it research. I hope my tardy reaction to control the beetles will help a farmer in the future avoid my mistake.

Small plot variety test

The rice that we are using in our irrigation experiment is a Nerica variety from Benin, Africa. But we are also evaluating seven other rice lines planted on two dates in a small variety test. We received the seeds from the USDA-GRIN rice seed bank in the United States. The rice was inspected while is was actively growing to certify that it was free of diseases. Before we could bring the seeds to South Africa we had to apply for and receive import permits and phytosanitary certificates. Matt Rhine brought the seeds with him when he came in October. Each small plot is three drill rows wide x 1 meter long. We are evaluating Best 2000, Cirad 141, Nerica 6, Zhe 733, a Nerica4 x Wells cross, IAC 201, and Cardi 70-3. Dr. Anna McClung did the initial screen of rice lines for drought tolerance and provided us with the seeds for our trial. Judging by the overall growth and plant color the IAC 201 and Cardi-70-3 are looking the best at this time.

An important part of the irrigation study is the weather station. By using equations based on solar radiation, temperature, wind speed, and relative humidity we are able estimate how much water the rice plants are using each data. To get accurate weather results the station can not be near trees or other obstructions and be near the rice field where the experiment is being conducted. Shown below is the weather station that we setup for the study.

January Weather

I am an agronomist, but much of my time has been spent, so far, setting up and configuring an electronic weather station. Actually this was not the hard part. The real challenge was linking station by radio signal to a router in an office. From there it will be transfered via the internet to Columbia, Missouri. We had several frustrating moments, but late this afternoon we had a victory. With help from the staff at agricultural bulletin board at Mizzou, I successful downloaded the weather data remotely in our cottage from the station located at the edge of the rice research field. Click on the link below to view real-time weather updated in 5 minute intervals.

We apparently have a “upstream” block, keeping us from completing the connection to University of Missouri at Columbia. Hopefully, we will be able to resolve the problem soon.