EFFECT OF FERTILIZER PLACEMENT ON SUGARBEET STAND

John J. Gallian

Recent data compiled by Amalgamated Sugar Company shows that the average stand count company-wide is 90-100 plants per 100 ft of row, with a range of 60 to 150 plants per 100 ft of row. Within this range, for every 10 plant increase in stand per 100 ft of row, the return to the grower is $55.00 per acre. The potential exists, therefore, to significantly increase profits by managing for improved stands with little additional cost.

A large percentage of growers apply fertilizer in a manner that is toxic to germinating sugarbeet seed and emerging young plants, and each year some growers lose enough stand to warrant replanting. For example, when fertilizer is impregnated with RoNeet herbicide, a minimum of 200 lb of approved fertilizer ingredients must be incorporated to 2-3 inches according to the label. This incorporation provides the most effective herbicide activity but is not the optimum fertilizer placement. Many growers practice shallow fertilizer incorporation without herbicide impregnation. Each year we observe fields with poor stands as a result of either ammonium or salt toxicity because of improper fertilizer placement.

In greenhouse experiments, urea was mixed with field soil at concentrations duplicating those achieved in the field with common application rates incorporated to two inches. Rates of urea were 0, 60, 120, 180, 240 and 254 lb/acre equivalents. The 254 lb rate was that applied to a field in which 70% stand loss was observed in June 1991. Herbicide was not added in these experiments. Only the effect of the fertilizer was measured. Sugarbeet seed was planted in the pots, plant emergence counts were taken on a daily basis and ammonium concentration was monitored throughout the experiment. Emergence and ammonium concentrations are given in the following table.

Effect of Urea at Rates Equivalent to Field

Application and Incorporated to Two Inches

* We are unsure how high the ammonium concentration reached
in the 180, 240 and 254 lb/A treatments because we did not have
the capability to measure above 50 ppm.

With elevated greenhouse temperatures we expect that ammonium is formed at a considerably higher rate than at most temperatures found in the field at planting. However, soil temperatures during the planting season often are high enough to result in ammonium concentrations sufficient to cause injury or death of seedlings as evidenced by frequent stand loss. In addition, we've probably experienced some stand reduction short of complete loss more often than we've realized.

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Presented at the Sugarbeet Schools on February 3 and 5, 1992.

Fertilizers that have a high salt index elevate soil soluble salts to levels toxic to germinating sugarbeet seed. Established sugarbeet plants can tolerate considerably high levels of soluble salts; as much as 8 mmhos/cm EC without a reduction in growth. Germinating seed are much more sensitive and will be delayed about three days germinating and show at least a 5% reduction in total germination with only a 3.7mmhos/cm EC. Therefore, we advise that above an EC of 3.0 mmhos/cm there is a danger of affecting germination. The following table shows how potassium chloride and ammonium sulfate can elevate soluble salts when added to soil at the equivalent field rate of 200 lb/acre incorporated to two inches.

Change in Soil Soluble Salts By Adding Various Fertilizers

Each fertilizer was mixed with field soil at the equivalent
field rate of 200 lb/A incorporated to 2 inches.

With either sprinkler or furrow irrigation, salts can be accumulated in the seed zone greatly exceeding 3.0 mmhos/cm when the average salt concentration for the field is well below 3.0. In addition, we cannot expect to have perfectly uniform fertilizer distribution under field conditions. If we have an average EC test of 3.0 mmhos/cm in a field, we can be certain that parts of the field will have much higher soluble salt.

Managing fertilizer placement to reduce the probability of ammonium or salt toxicity can greatly improve sugarbeet stands with little or no increase in costs. Radical changes in soil pH alone will adversely affect sugarbeet germination. The effect of the material and its placement on pH should also be considered. We observe the most problems in the field where the full fertilizer amount is applied with shallow incorporation shortly before planting. There are several practices that can alleviate the problem, but each grower must evaluate what works best in his operation. We recommend against impregnation of fertilizer with herbicide. The risks may be too great. Deeper incorporation of fertilizer will help as will fall application. Split applications to reduce the amount applied at planting will not only reduce salt and ammonium concentration near the seed, but also improve fertilizer efficiency.

Know your soil. Investigate whether your practices on your soils may result in a problem. When seed is germinating and, if possible, before emergence, take a shallow soil sample from only the seed row and have it analyzed for ammonium and soluble salts. If the ammonium concentration is about 10 ppm or greater and/or the soluble salts about 3.0 or greater, you may have a problem and may wish to change your practices in the future to ensure better stands. We may be safe if the weather remains cool, but it's a risk to count on it.