Nitrogen Management

Still a lot to learn about this important nutrient

Published in the April 2009 Issue Published online: Apr 03, 2009 David Elison
Viewed 86 time(s)
It seems at times that we get stuck on one note and just keep playing it until we become insensitive to it.

I hope that this is not the case as we continue to learn more about nitrogen and how much this plant nutrient is required for sugarbeet growth and quality. In fact we have been working with and complaining about the ill effect of too much brei nitrogen in beet roots and how it adversely effects sucrose extraction in the factories for many years now.

Fortunately, we have made progress through the years. Collectively as a sugar producing entity we have seen a decrease in the average brei nitrate reading in the beets being produced.

 

Early Studies

In the mid-1980s when we started working on reducing brei nitrates, over half of our fields were averaging around 500 ppm. Today the averages are: 27 percent of fields below 249 ppm (which is best case), 73 percent above 250 ppm, (which is still too high), but 77 percent of fields are below 450 ppm N which is indeed progress compared with where we started almost 25 years ago.

The concern is still the same though and we have learned to measure this better. Data shows that for every 100 ppm increase in brei nitrate, sugar percent decreases by 1/2 percent.

We know we can increase profitability by continuing to decrease brei nitrate down to where it needs to be but the challenge is the same as it has always been—how do you do it?

In the early 1970s the research conducted showed that 8 lbs. of N per ton of beets produced was the level at which tons with sugar could be produced.

At the time, 10 and even 12 lbs. were considered acceptable. As time has progressed additional work has been done to further verify or more tightly refine the benchmark requirement figure of 8 lbs. of N per ton of beets produced.

The findings from these studies have invariably collaborated two basic ideas.

First, that 8 lbs. per ton is adequate and above for nearly all of our production areas and situations.

Secondly is the fact that for most good production soils and situations it is still too much.

U of I soils extension specialists have taken a stab at this over the years. Steve Petrie in the latter ‘80s showed that 8 lbs. was adequate and above and that below 8 lbs. was where the real sugar production set.

Terry Tindale repeated this same conclusion when he worked with nitrates in sugarbeet. In addition, he tried to account for the mineralized nitrogen which comes into the nutrient system during the production season from breakdown of organically bound N in previous crop residues.

This process is quite variable by nature. One of the difficult, yet delightful truths about our soils in the Snake River Plain production areas is that the amount of mineralization of N in most given years is very good, and above average, when compared to other areas. However, even with this unpredictable variable, the data which he generated demonstrated that the best sugar per acre was produced when N inputs where below the 8 lbs. per ton of beets produced.

 

Effects of Input

Virtually all beet sugar production areas in the world have addressed the effects of too much N on sugar production.

They all have come to the same conclusions that N input has to be properly managed so that as the crop reaches 6–8 weeks before harvest the available nitrogen is at a low enough level so as to not interfere with slowing of vegetative growth. And also low enough levels of uptake so as to not be deposited in root storage cells along with the sugar.

The conclusions about the information necessary to accomplish this are also the same although the approaches at deriving this information may be different.

Some companies require mandatory sampling of beet fields’ soil profile to over four foot of depth. Reporting this information to agriculturalists is important so that additional N inputs to the crop can be determined.

Often a cap of additional N to the crop is used, regardless of rotation or soil type. We have used the pounds N per projected ton of beets to be produced as a tool for many years now, and it is as good a tool as any when we get it right.

The question is do we have it right in all cases? Is 8 lbs. N where we need to be or is it less than 8 lbs. N per ton?

’05 & ’06 Trials

In trials conducted in 2005 and 2006 by Amalgamated,(*1) the response to four different rates of nitrogen input to the beet crop on five different beet varieties was studied.

These took place in grower fields and were plot formatted and replicated eight times. For statistical purposes, four replications are good and six is normal. Eight replications means that the results from this study should be easily repeatable.

In 2005 the trials were conducted in the Jerome area. In 2006, they were repeated in the Jerome area and in the Minidoka area. In 2005 the results for best ERS/acre ranged between N use of 4.3–5.7 lbs. of N per ton of beets produced.

In 2006, at the Jerome site, the best ERS/acre ranged between 2.8–6.2 lbs. N per ton of beets produced, except for one variety which came in at 7.2 lbs.

The use of 4.3 lbs. however was within 106 lbs. of sugar ERS /acre for this same variety.

At the Minidoka site in 2006, the best ERS/acre ranged between 4.4 – 6.4 lbs. N per ton of beets produced, except for one variety which came in at 8 lbs. per ton being best.

This field had some Rhizomania pressure so it was not surprising to see this.

The conclusions from this study stated that the current recommendation of 7–8 lbs. of N per ton of beets to be produced should be further fine tuned, and that “growers should use historical fertilizer, yield, and brei nitrate information from their own fields in developing a nitrogen management program that is specific to their needs.”

 

Acequia & Glenns Ferry Trials

In the past year, 2008, two Nitrogen use trials were conducted by Amalgamated.(*2) One trial was near Acequia, northeast of Rupert and the other was near Glenns Ferry.

The trials involved nitrogen inputs of 5, 6, 7 and 8 lbs. of N per ton of beets and assessing the yield and quality results.

The design involved random plots with six replications which consisted of 6 rows, each 40 ft. in length.

The soil was sampled in each individual plot to 3 ft. of depth at Acequia and 2 ft. of depth at the Glenns Ferry location.

This difference was in relation to the friability of soil profile depth at the two different sites. Carry-over N was established and then each plot was fertilized to the desired N level for the prescribed rates N per ton.

Irrigation and all other cultural practices were conducted the same as they were in the rest of the field.

At the Acequia site the results showed that 6 lbs. used as the projected need resulted in the best ERS/acre produced.

However, because tonnage produced was higher than past production averages for the field which was used as our yield goal, the actual use was at only 5 lbs. of N per ton of beets produced. (SEE CHART 1)

 

Results

The best tonnage and best sugar percent combination was produced with 6 lbs. of N per ton projected yield and was also the best ERS/acre producer as well as the best dollar return per acre producer. (SEE CHART 2)

The brei nitrate readings at harvest were all very low at harvest on all input levels of N.

This was most probably because of the more complete accounting of carryover N as well as the fact that the plots were located in a contiguous area of the field and hence less variability existed compared with the whole field.

At the Glenns Ferry site, the results showed that just less than 5 lbs. of N per actual ton of beets produced resulted in the highest ERS/acre. At this rate the highest ERS/acre also results in the highest dollar return per acre. (SEE CHART 3)

 

Even though the highest tons/acre were produced at 8 lbs. N, the best combination of tonnage and sugar was produced at the 5 lbs. N per ton produced rate. This is quite often the case particularly in actual field production. The highest possible tonnage is not necessarily the best return when the sugar is not there with it. (SEE CHART 4)

 

Roundup Ready Fields

With the use of Roundup Ready beet culture, it has been observed, first in our production trials and then by most everyone this past year in their own fields, that the vegetative growth of the developing plants is not slowed when it comes to weed control.

The natural result of this reprieve from the slowing effects of the phytotoxicity caused when conventional beet herbicides were being applied is that the vegetative plant growth is not slowed for three-plus weeks in May and June. This means that the growth to full canopy is achieved earlier as well as the uptake of nitrogen to accomplish this growth.

Because 80–85 percent of the nitrogen which the crop uses in an entire year is utilized to produce a canopy, it now becomes even more imperative that any nitrogen inputs to the crop be done well ahead of their anticipated need.

In western Idaho this means applying as early as the first part of May. For other areas, the middle to the end of May would not be too soon.

In our study this past year, we also pulled petioles starting as soon as the foliage allowed for it and we sampled about every 10 days.

Just as predicted, the basis of our observations for growth in Roundup Ready beets the two years previous, the growth pattern of earlier uptake of N and hence earlier decline of N in petiole tissue was evidenced.

At the Acequia site the 5 lbs. N per ton application showed petiole N fell below 1,000 ppm the last week in July. The 6 and 7 lbs. rate N per ton, fell below 1,000 ppm the first week in August and the 8 lbs. per ton rate the middle of August.

This compares to the first of September as the time to drop below 1000 ppm, according to the petiole curve which we have been using in non-roundup varieties fertility culture.
(SEE GRAPH 1)

As stated above the application timing of nitrogen inputs to the crop is a critical part of managing. At the Glenns Ferry site, the fertilizer urea which we applied to bring inputs up to requirement went on the same week, (the first week in June), as the Acequia site.

In retrospect, these plots should have been fertilized 2–3 weeks earlier because of their earlier planting and growth.

The petiole curves generated from these plots also shows this. (SEE GRAPH 2)

When the regimen of petioles began, the trend was on the increase, interestingly enough and then finally started down. If the fertilizer had been in place 2–3 weeks earlier the draw-down of the curve would probably have been more in line with dropping below 1,000 ppm around the end of July to the middle of August.

 

Suggestions For Use

Now, with the above information in hand here are some suggestions about how to possibly use this information to more tightly manage the nitrogen input to the beet crop.

The first information which one should look at is the tare-sugar ledger data which is received first during harvest on a daily delivery basis.

This information lists tons and sugar but also brie nitrate and conductivity. If the brei nitrates are above 200–250 ppm then they are too high. It would be best to look at the production stats for the last three times which a field was rotated into sugarbeets.

Look up the soil sample information as well as the fertilizer invoices for what was applied each of these years.

 

Questions To Ask

Was the soil sample adequate? Did I sample deep enough to account for all the carried over N?

Was the NO3 as well as the NH4 nitrogen accounted for and added together when determining the total ppm N for each foot of profile?

What constant was used as a multiplier when converting ppm N to lbs. of N?

How do these questions apply to my particular soil type? How many lbs. of N were actually applied during the course of the season?

And most important, when was the fertilizer applied? Was nitrogen applied later than it should have been?

Then lastly, and probably most important is how many lbs. of N were actually made available to the crop for each ton of beets produced?

This can be determined by adding the carried over N determined from the soil sample to the lbs. N applied as fertilizer and then dividing the amount by the tons per acre produced.

This gives a figure of how many lbs. of N were used to grow each ton of beets. If the figure is 8 or more lbs. per ton and the brei nitrates are over 250 ppm then the figure needs to be reduced.

As has been shown above, our best indications show that closer to 6 lbs. per ton of beets is where we need to be.

Additional information regarding nitrogen management and understanding this important nutrient is available in the updated grower guide book for this year. Please take the time to read through this information and consider it.