Research
Report Submitted to the Maine Potato Board
- January 2007 -
Project Title: Initial Evaluation of Different N Sources for Potato Production.
Personnel: Peter Sexton UMCE Crops Specialist, Potato Program
Randy Smith MAFES Superintendent, Aroostook Research Farm
Summary:
Several sources of organic N were compared to conventional N fertilizer for their effect on yield and incidence of Rhizoctonia and common scab on tubers in ‘Kennebec’ potatoes. The following sources of N were evaluated: ammonium sulfate, ammonium nitrate, urea, canola meal, soybean meal, and mustard meal. The respective seed meals were derived from mechanically extracted oilseeds (i.e. no solvent extraction). All the materials were broadcast and harrowed in before planting at a rate to deliver 150 lbs of N per acre. A control treatment (no N fertilizer) and an ammonium nitrate treatment of 75 lb N per acre were also included in the trial. Potassium was broadcast before planting at a rate of 212 lbs K2O per acre. Phosphorous was applied at a rate of 98 lbs P2O5 per acre after planting and before hilling. The trial was conducted at the Aroostook Research Farm on a field with an initial pH of 6.6. Soil tests showed the following nutrient levels: P, 23 lb per acre; K, 163 lbs per acre; Mg, 326 lbs per acre; Ca, 4112 lbs per acre; nitrate-N, 20 lbs per acre; B, 0.5 ppm. Individual plots consisted of four rows 25’ in length. Each treatment was replicated four times in a randomized complete block design.
Leaf and petiole samples were collected during the season and are currently being analyzed for nutrient content.
There were significant treatment effects on total yield and
on yield of tubers greater than 4 ounces in size (Table 1). There was a trend for Rhizoctonia incidence
to be lower where organic sources of N were used; however, data were highly
variable and treatment effects were not significant. All the treatments had
similar levels of scab (data not shown).
Nitrogen equivalence was estimated by regressing total yield against
ammonium nitrate (Fig. 1) and using this as a standard. For example, the soybean meal treatment had
a total yield of 302 cwt per acre. The
regression analysis predicts that applying approximately 90 lbs of N as ammonium
nitrate would provide the same yield.
Therefore, the soybean meal treatment is assigned an “estimated N
equivalence” of 90 lbs per acre. In
other words, 150 lbs of N applied as soybean meal generated a yield similar to
application of 90 lbs of N as ammonium nitrate. The results of this trial suggest that canola and mustard meal
either mineralize N more readily than does soybean meal, or that they may
provide some other factor besides N which benefits growth of the potato
crop. However, this is only one
season’s data – these treatments should be evaluated in further trials before
definite conclusions can be drawn.
Table 1. Total yield, and yield greater
than 4 oz for Kennebec potatoes grown with different N sources. Each N source was applied at a rate of 150
lbs of N per acre, with the exception of a control treatment (no applied N),
and a treatment of ammonium nitrate at 75 lbs of N per acre. Nitrogen equivalence was estimated based on
the response of total yield to application of ammonium nitrate.
|
Treatment |
Total Yield |
> 4 oz. Yield |
Rhizoctonia Incidence |
Estimated N equivalence |
|
|
(cwt/ac) |
(cwt/ac) |
(%) |
(lbs /acre) |
|
Ammonium Sulfate |
360 |
324 |
35 |
---- |
|
Urea |
355 |
315 |
5 |
---- |
|
Mustard meal |
345 |
300 |
14 |
175 |
|
Ammonium Nitrate |
326 |
278 |
25 |
---- |
|
Canola meal |
321 |
287 |
4 |
131 |
|
Soybean meal |
302 |
265 |
3 |
91 |
|
Ammonium Nitrate – 75
lb per acre |
291 |
256 |
36 |
---- |
|
Control |
214 |
161 |
37 |
---- |
|
|
|
|
|
|
|
Mean |
314 |
273 |
19.8 |
------ |
|
CV (%) |
11.8 |
15.8 |
123.2 |
------ |
|
LSD (0.05) |
54.7 |
63.6 |
NS |
------ |
Figure 1. Total tuber yield, and yield greater than 4 oz. in size, versus rate of nitrogen applied as ammonium nitrate for Kennebec potatoes grown at the Aroostook Research Farm in the 2006 season. Each point represents yield from an individual ammonium nitrate plot in the trial.