Onion Production Survey

for Malheur County, Oregon and Idaho - 2008

 

 

Lynn Jensen

Malheur County Extension Service

Oregon State University

Ontario, OR

 

 

Introduction

Growers in Malheur County, Oregon, and Idaho were surveyed regarding onion production.  Resources were not available to survey growers for production practices on all crops, so onion was chosen as most representative of Malheur County agriculture.  Previous studies identified onion production as one of the primary sources of nitrate and Dacthal (DCPA metabolite) movement into groundwater in Malheur County.  Dacthal herbicide has since been replaced with an herbicide less likely to move through the soil profile into ground water.  However, the question to be answered was whether growers have been able to better utilize nitrogen.

 

Results 

All surveyed growers in Malheur County and most growers in Idaho were using soil testing to determine residual levels of nitrogen prior to planting onion (Table 1).  This is up from 62 percent in 1989.  The percent of growers using tissue (root) testing for nitrogen management during the growing season remained constant, but there was a trend for growers who are new to onion production to use the technique more than growers with a long history of onion production (Fig. 1).

 

 

Table 1.  Onion crop survey for Malheur County, Oregon, and Idaho, February 2008, compared to 1989 Malheur County survey.

 Survey area

 Malheur Co. 2008

   Idaho    
2008

Malheur Co. 1989

Onion acreage represented

3,328

3,001

4,167

Average onion yield

789 cwt*/ac

783 cwt/ac

621 cwt/ac

Average number of years growing onions

28.7

26.8

25.8

Average onion acreage/grower

128 ac

150 ac

93 ac

% of growers soil testing

100%

95.5%

62%

% of growers using tissue testing

34.6%

22.7%

33%

Number of insecticide applications for thrips/year

 

5.5

 

5.5

 

3.6

Number of fungicide applications/year

3.3

3.4

3.6

 * 1 cwt = 100 lb

Fall-applied nitrogen was down by 17 percent in 2007 compared with1989 (Table 2). 

The number of side-dress nitrogen applications has increased in Oregon from 1.6 to 2.25 times as growers distribute nitrogen more uniformly throughout the growing season.  The average amount of nitrogen applied at each side-dressing application has been reduced from 116 lbs N/acre in 1989 to 78 lbs N/acre in 2007.  The total amount of applied nitrogen is 9.5 percent lower in 2007 vs. 1989, from 284 lbs N/acre to 257 lbs N/acre.

 

 

Table 2.  Nitrogen use in furrow-irrigated onions for Malheur County, Oregon, and Idaho, February 2008, compared to 1989 Malheur County survey.

 

Malheur Co. 2008

     Idaho     2008

Malheur Co. 1989

Average onion yield (furrow)

769 cwt/ac

782 cwt/ac

621 cwt/ac

Fall applied N (lb/acre)

81

105

98

Number of sidedress applications

2.25

1.6

1.6

Pounds N applied/sidedress application

78

97

116

Total sidedressed N

176

155

186

Total applied N

257

260

284

 

In addition, about 20 percent of the onion acreage in 2007 is irrigated by drip rather than the conventional furrow irrigation used by all growers in 1989 (Table 3).  This system uses less water and other inputs.  Growers using drip irrigation reported using 175 lbs N/acre versus furrow irrigators who were using 257 lbs N/acre.

 

 

Table 3.  Nitrogen use in drip-irrigated onions for Malheur County, Oregon, and Idaho, February 2008.

 

 

Malheur Co.

Idaho

Average onion yield (drip)

814 cwt/ac

788 cwt/ac

Fall applied N (lb/acre)

40

70

Number of N applications through system

9

9

Average pounds N/ac injected/application

15

9.4

Total N applied through drip system

135 lb/ac

85 lb/ac

Total applied N

175 lb/ac

162 lb/ac

 

Onion productivity per applied N was 307 lbs of onions/lb of N for furrow-irrigated onion and 465 lbs of onions/lb of N for drip-irrigated onion (Table 4).  This compares to 219 lbs of onions/lb of N in 1989.  If nitrogen use on the drip-irrigated acreage in Malheur County is factored into overall nitrogen use, then total nitrogen use for onion production is reduced to 240.6 lbs N/acre.  This is a 15 percent reduction in nitrogen use for onion growers in Malheur County.  Growers using drip irrigation applied nitrogen 9 times through their drip system compared to 2.25 times as sidedressed nitrogen under furrow irrigation practices.  The number of insecticide applications increased from 3.6 to 5.5, due to increased resistance to insecticide.

 

 

Table 4.  N use efficiency of furrow- versus drip-irrigated onion production for Malheur County, Oregon, and Idaho, February 2008, compared to 1989 survey.

 

Malheur Co.
2008

Idaho
2008

Malheur Co. 1989

Yield (cwt/ac) – furrow

789

783

621

Total applied N (lb/ac) – furrow

257

260

284

Yield (lbs onions/lb applied N)

307

301

219

 

 

 

 

Yield (cwt/ac) – drip

814

788

-

Total applied N (lb/ac) – drip

175

162

-

Yield (lbs onions/lb applied N)

465

486

-

 

 

 

 

 

 

Conclusions

 

The results of this survey suggest that while nitrogen use has decreased slightly (15%), nitrogen efficiency has increased dramatically from 219 lbs onions/lb of N to 307 lbs onions/lb of N for furrow-irrigated onions.  It is even better for onions grown under drip irrigation.  Some of this increase is probably due to higher yielding onion varieties, but some is due to better irrigation and nitrogen use practices.

 

Figure 1

Figure 1.  Percent of growers using tissue testing on onions, arranged by number of years they have produced onions in Malheur County, Oregon, and Idaho, 2008.