"On Farm" Implementation of Lower Nitrogen Fertilizer Inputs Through Nitrogen Accounting and Validation of Organic Matter Mineralization

Clinton C. Shock, Erik B. G. Feibert, and Dale Westermann
Malheur Experiment Station
Oregon State University
Ontario, Oregon, 1997

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Introduction

The objectives of this study were to examine the amount and importance of N mineralized from soil organic matter in commercial sugar beet fields and to make observations of sugar beet plant N uptake in N fertilizer trials conducted by beet fieldmen in commercial fields to improve our understanding of beet responses to N fertilizer.

Sugar beet nitrogen fertilizer guidelines are based on either fall or spring nitrate-N levels to 3-foot depth in the soil and total plant needs estimated at 8 lb N/ton of beets. These assumptions provide estimates for N fertilization which have been useful for many years. To make beet production and processing as efficient as possible, it is important to use only the N fertilizer needed to grow the crop. In the cases where soil organic matter mineralization is large compared with residual soil nitrate or fertilization, the current guidelines could overestimate crop fertilizer needs.

When sugar beets receive N in excess of their needs, total beet yield and leaf growth are high, but both beet sugar content and total sugar yields can be depressed. Extra nitrate and ammonium in the beet pulp reduce sugar factory efficiency.

Methods

Sugar beet fieldmen have conducting N fertilizer rate trials in growers fields during the last few years. These trials have the basic structure of large plots with several N rates and one to three replicates. In general the recommended N fertilizer rate is based on the soil nitrate present in the soil profile to a depth of 3 feet in each field and a yield goal for that field. Other large field plots are treated with twice the recommended N rate, half the recommended N rate, and no fertilizer as the check. In a some of the fields with high residual nitrate, the fieldman and grower opted to leave all plots unfertilized. Ten fields were studied between Parma, Idaho, and Vale, Oregon, in 1996. Twelve growers' fields were studied through harvest in 1994 and an additional eight fields in 1995 between Brogan, Oregon, and Burley, Idaho (Table 1). Several other fields were set up each year, but their experimental value was lost in cultivation or harvesting errors.

The growers took care of all of the cultural practices, and the fertilizers were applied in cooperation with fertilizer industry representatives. Sugar beet fieldmen kept track of crop progress and coordinated the harvest, collecting data on yield and quality based on the entire field plots. Beets were evaluated for total yield, tare, sucrose content, conductivity, and beet pulp nitrate by the Amalgamated Sugar Co.

Additional work was done by the Malheur Experiment Station. The percent sugar extraction and recoverable sugar were calculated based on empirical formulas. Soil samples were collected in the spring for estimates of N mineralization via three methods: anaerobic incubation, aerobic incubation, and the buried-bag method. Twelve to fourteen representative beets with their leaves and crowns were harvested from each plot just before harvest then taken to the Malheur Experiment Station. Leaves and crowns were dried, weighed, ground, and analyzed for total N content. The beets were weighed fresh after the leaves and crown were removed, ground, and a subsample of the beet pulp was weighed wet, oven-dried to determine dry matter content, then analyzed for total N content. Beet N uptake per acre in the leaves, crowns, and beets was calculated based on the clean beet yield of each plot, the ratio of beet dry weight to fresh weight, the proportion of dry crown and leaf tissue to dry beet in the tissue samples, and the tissue sample N contents.

Total available soil N supply was calculated based on the sum of spring available nitrate and ammonium, any applied fertilizer N, and N mineralization (estimated by anaerobic incubation or seasonal N balance). Nitrogen use efficiency was calculated for each plot by dividing the total plant N uptake by the total available N supply for each plot and multiplying by 100. Nitrogen mineralization was also estimated by aerobic incubation and buried bag methods.

Results and Discussion

Spring soil nitrate N ranged from 61 to 399 lb N/acre, depending on the field (Table 2). Optimistic yield goals ranging from 25 to 40 ton/acre of beets implied N fertilizer needs of 0 to 216 lb N/acre. The lowest applied N rates were 0 lb N/acre at twenty two of the thirty sites.

The 1994 season was favorable for high yields (Table 3), and all cooperating growers kept weeds and diseases under control. The 1995 season was far less favorable, with lower temperatures and cloud cover during the growing season. Repeated rainfall events in 1995 made efficient N use difficult and reduced residual nitrate and ammonium in the fields at harvest. Repeated hail during 1995 in the Treasure Valley was damaging at certain locations. The 1996 season was more favorable.

The highest-yielding N fertilizer rates ranged from 0 to 205 lb N/acre depending on the field studied. Sugar beet response to N fertilizer varied substantially. Reasonable yields were routinely obtained near Vale, Ontario, and Nyssa with low rates of N fertilizer (Tables 2 and 3). Clear increases in beet yield and sugar production occurred on shallow soils with irrigation apparently in excess of evapotranspiration. Beet pulp nitrate at 0 applied N suggested that there was excessive N supplies in many fields, even without any fertilizer nitrogen (Table 3). Beet petiole nitrate levels were consistent with high yields at low N fertilizer inputs in these fields (data not shown).

The optimal N rate was determined independently for each field based on the highest yield of recoverable sugar. Beet plants at the optimal applied N levels contained 126 to 439 lb N/acre at harvest depending on the field (Table 4). Anaerobic incubation estimates of N mineralization ranged from 88 to 285 lb N/acre, depending on the field (Table 5). Mineralized N appears to be a large N source averaging 163 lb N/acre over the 20 fields (Table 4). Fields with high spring residual nitrate are not necessarily going to have high rates of N mineralization; fields with low spring residual nitrate are not necessarily going to have to low rates of N mineralization , r2 = 0.029, based on 1994 and 1995 data.

In 1994, the anaerobic incubation estimates of mineralized N ranged in the same order of magnitude as field method using N balance. The N balance method was based on measuring residual soil nitrate and ammonium at harvest and plant N content at harvest, then subtracting all known available N sources. The N balance was not comparable in 1995, as would be expected after a season with untimely rainfall events. In 1996, fields with suspected heavy irrigation showed low available N balances. The buried bag method of N mineralization was laborious and provided numbers similar and less than the anaerobic method. The aerobic method of soil incubation provided estimates of N mineralization in the same range as the anaerobic method, but the numerical values were more erratic.

At the most productive N level tested at each site, sugar beets were able to recover between 35.4 and 90.4 percent of the estimated total N supply (based on the sum of soil nitrate and ammonium to the 3-foot depth, fertilizer N, and N mineralization in Table 4). The one efficiency of 125.7 percent occurred in a field irrigated with considerable nitrate in the irrigation water. Efficiencies less than 75 percent appear to be related to very high N supply at 0 N applied, irrigations and rainfall in excess of evapotranspiration, or sugar beet cyst nematode.

Conclusions

1. The mineralization of organic matter provided on average 163 lb N/acre per year, but the fertilizer guides assume that only 30 to 50 lb N/acre will be mineralized.

2. Nitrogen fertilizer guides overestimated crop fertilizer needs. Nitrogen fertilization was of marginal benefit for sugar beets when nitrogen mineralization is high on deep soils without excessive irrigation. In these studies, N fertilization was often counter productive.

3. The anaerobic incubation method of estimating N mineralization was useful.

Acknowledgments

These trials depended of the work of many growers and fertilizer fieldmen, without which the effort would have been impossible. We extend special appreciation to Del Traveler, Terry Tindall, Stacy Camp, Bill Walhert, and Bob Huffaker, Don Bowers, Dave Elison, Steve Lund, Clark Millard, Bob Komoto, Monty Saunders, Saud Hafez, Ray Winegar, Rod Faham, Al Scott, Lou Wettstein, and Terry Miller.

The financial support of the beet growers associations, Amalgamated Sugar, and the Oregon Department of Agriculture is gratefully acknowledged.

Table 1. Characteristics of 20 sugar beet fields used for soil N mineralization studies in 1994, 1995 and 1996, Malheur Experiment Station, Oregon State University, Ontario, Oregon. 
Field Location Soil texture Soil pH Soil organic matter  Soil depth Variety Planting 

date

Irrigation system Comments Previous crop
1994     % feet          
Burley sandy loam 8.4 1.25 > 6 MH 9455 April 11 side roll cyst nematode Beets
2 Minidoka silt loam 8 1.5 2.5 PM-9 March 19 side roll rock at 2-3 Wheat
3 Minidoka silt loam 8 2.35 2.5 WS 91 March 20 side roll rock at 2-3 Wheat
4 Jerome loam 7.55 1.05 2.5 WS 91 April 25 side roll rock at 2-3 Potatoes
5 Nyssa silt loam 7.65 1.4 >6 PM-9 last week March furrow   Onions
6 Ontario-Vale fine sandy loam 7.5 1.6 >6 PM-9 March 7 furrow   Onions
7 Ontario-Vale silt loam 7.75 2.2 >6 PM-9 March 12 furrow   Onions
8 Ontario-Nyssa fine sandy loam 7.4 1.75 >6 PM-9 2nd week March furrow   Onions
9 Nyssa silt loam 7.9 2.1 >6 PM-9 March 26 furrow B deficient Potatoes
10 Vale silt loam 7.6 2.05 >6 PM-9 March 18 furrow   Onions
11 Brogan silt loam 7.6 1.6 >6 RSW-81 March 14 furrow   Onions
12 Ontario silt loam 7.6 1.5 >6 PM-9 April 5 furrow   Beans
1995                  
1 Buhl silt loam 8.1 1.2 >6 PM-9 May 10 furrow   beans
2 Burley silt loam 8.1 1.49 2.5 Beta 8422 April 10 side roll   wheat
3 Rupert sandy loam 7.8 1.28 >6 WS 62 April 20 furrow   beans
4 Minidoka silt loam 8.2 1.65 2.5 PM-9 April 4 side roll   potatoes
5 Nyssa silt loam 7.6 1.45 >6 PM-9 March 30 furrow rhizoctonia onions
6 Vale silt loam 7.8 3.29 >6 PM-9   furrow   potatoes
7 Ontario silt loam 7.7 1.43 >6 PM-9 March 29 sideroll   potatoes
8 Nyssa silt loam 7.4 1.47 >6 PM-9 March 27 furrow rhizoctonia, flooding beans
1996                   
1 Ontario silt loam 8.5 1.5 >6'     furrow    
2 Nyssa silt loam 7.8 1.7 >6'     furrow    
3 Parma silt loam 8.0 2.2 >6' PM-9 April 11 solid   radish
4 Nyssa silt loam 7.7 1.4 >6'     furrow    
5 Vale silt loam 8.0 1.4 >6' WS 91 April 8 furrow   onions
6 Vale silt loam 8.0 1.4 >6' WS 91 April 8 furrow   onions
7 Vale silt loam 8.0 1.3 >6' WS 91 April 8 furrow   onions
8 Ontario silt loam 7.8 1.2 >6' WS 62 March 19 furrow   onions
9 Ontario silt loam 7.8 1.5 >6' WS 62 March 25 furrow   onions
10 Ontario silt loam 7.8 1.5 >6' WS 91 March 26 furrow   onions

Table 2. Optimistic yield goals, soil nitrate, recommended N fertilizer rates, grower's preferred N fertilizer rates, and best fertilizer N rates for 1994, 1995 and 1996, Malheur Experiment Station, Oregon State University, Ontario, Oregon. 
Field Location Optimistic

yield goal

Soil

nitrate 0-3 ft

Total N needed for optimistic yield goal Recommended N fertilizer for optimistic yield goal Growers' preferred N rate Lowest N rate used in trial  Highest yielding N rate for the trial 
1994 ton/acre - - - - - - - - - - - - - - - - - - - - - - - lb N/acre - - - - - - - - - - - - - - - - - - - - - - -
1 Burley 28 164 224 60 80 0 40
2 Minidoka 35 171 280 109 110 0 110
3 Minidoka 35 85 280 195 205 80 205
4 Jerome 35 155 280 125 50 0 25
5 Nyssa 40 207 320 113 NA1 0 0
6 Ontario-Vale 40 284 320 36 75 0 0
7 Ontario-Vale 40 238 320 82 0 0 0
8 Ontario-Nyssa 40 148 320 172 NA 60 60
9 Nyssa 40 165 320 154 NA 60* 80
10 Vale 40 356 320 -36 150 0 0
11 Brogan 35 165 280 115 100 0 0
12 Ontario 40 104 320 216 NA 0 0
1995              
1 Buhl 25 199 200 1 100 0 0
2 Burley 25 61 200 139 160 80 160
3 Rupert 35 95 280 185 120 19 171
4 Minidoka 25 105 200 95 163 0 85
5 Nyssa 30 115 240 125 100 35 35
6 Vale 40 122 320 198 150 0 150
7 Ontario 34 108 272 164 170 80 80
8 Nyssa 32 138 256 118 100 0 40
1996              
1 Ontario 40 190 320 130 80 0 40
2 Nyssa 40 188 320 132 125 0 30
3 Parma 40 289 320 31 200 200 NA
4 Nyssa 40 164 320 156 75 0 0
5 Vale 40 399 320 0 100 0 0
6 Vale 40 399 320 0 100 0 0
7 Vale 40 357 320 0 100 0 0
8 Ontario 40 254 320 56 100 0 0
9 Ontario 40 261 320 59 100 0 0
10 Ontario 40 261 320 59 100 0 0
*Boron deficient part of field.

1NA: data not available.

Table 3. Beet yield and quality at the best N rate for each of 20 growers' fields, Malheur Experiment Station, Oregon State University, Ontario, Oregon, 1994, 1995 and 1996. 
Summary of characteristics Highest yielding plant performance
Field Location Optimistic yield goal Soil nitrate 0-3' Most productive N rate for trial Clean beet yield Sucrose Conductivity Extraction Recoverable sugar Pulp nitrate
1994 ton/acre lb N/acre lb N/acre ton/acre %   % lb/acre ppm
1 Burley 28 164 40 24. 0 16.9 0.73 86.4 6,998 187
2 Minidoka 35 171 110 35.5 18.1 0.73 86.5 10,799 148
3 Minidoka 35 85 205 39.2 17.4 0.9 84.2 11,479 na
4 Jerome 35 155 25 32.7 16.8 1. 00 82.8 9,064 411
5 Nyssa 40 207 0 31.3 15. 0 0.84 84.7 7,950 552
6 Ontario-Vale 40 284 0 40.9 15.8 0.87 84.4 10,925 483
7 Ontario-Vale 40 238 0 34.8 13.7 1.09 81 7,708 701
8 Ontario-Nyssa 40 148 60 39. 0 16.7 0.68 87.1 11,342 294
9 Nyssa 40 165 80 33.4 16.2 0.72 86.4 9,372 283
10 Vale 40 356 0 38.3 14.8 0.98 82.7 9,406 581
11 Brogan 35 165 0 29.4 14.9 0.95 83.1 7,280 629
12 Ontario 40 104 0 45.6 16.2 0.75 86.1 12,732 175
1995                  
1 Buhl 25 199 0 21.3 16.9 0.60 88.1 6,352 145
2 Burley 25 61 100 22.9 19.2 0.88 84.6 7,452 178
3 Rupert 35 95 171 31.9 16.6 0.77 85.8 9,110 313
4 Minidoka 25 105 85 21.4 16.6 0.62 87.8 6,787 152
5 Nyssa 30 115 35 25.2 16.3 0.72 86.4 7,078 243
6 Vale 40 122 150 31.4 14.9 1.06 81.6 7,630 691
7 Ontario 34 108 80 28.0 17.6 0.64 87.7 8,649 161
8 Nyssa 32 138 40 31.8 16.9 0.71 86.7 9,283 194
1996                  
1 Ontario 40 190 40 43.5 14.5 1.09 86 10,876 739
2 Nyssa 40 188 30 36.9 16.6 0.74 86.3 10,572 303
3 Parma 40 289 200 34.1 15.1   86 8,856  
4 Nyssa 40 164 0 33.5 15.4 1.02 84 8,667 599
5 Vale 40 399 0 31.0 16.2 1.00 86 8,638 546
6 Vale 40 399 0 31.0 16.1 1.00 86 8,585 546
7 Vale 40 357 0 33.5 15.8 1.02 86 9,104 481
8 Ontario 40 254 0 32.3 15.9 0.73 86 8,833 343
9 Ontario 40 261 0 33.1 15.6 1.03 86 8,881 596
10 Ontario 40 261 0 29.8 15.5 0.99 86 7,945 576

Table 4. Comparison of soil nitrogen supply, beet plant nitrogen content, and N use efficiency at harvest for beets grown at the highest-yielding N level in 20 fields. Malheur Experiment Station, Oregon State University, Ontario, Oregon, 1994, 1995 and 1996. 
    Best plant performance N supply Plant N content    
Field Location Beet yield Recoverable sugar Most productive N rate for 1994 trial  Spring soil nitrate -N 0-3 ft Spring soil ammonium -N 0-3 ft Estimate of N-mineralization (anaerobic) Total available N supply Leaves Crown Beets Total Total plant N content at harvest per ton of beets N use efficiency1
1994 ton/acre lb N/acre lb N/ton %
1 Burley 24. 0 6,998 40 164 23 112 339 70 20 94 184 7.65 54.2
2 Minidoka 35.5 10,799 110 171 17 172 469 63 18 148 229 6.65 48.9
3 Minidoka 39.2 11,479 205 85 14 167 470 98 23 187 308 7.82 65.4
4 Jerome 32.7 9,064 25 155 16 135 331 103 15 145 263 8.07 79.5
5 Nyssa 31.3 7,950 0 207 64 88 359 127 18 150 295 9.42 82.3
6 Ontario-Vale 40.9 10,925 0 284 30 149 459 122 19 225 366 8.93 79.9
7 Ontario-Vale 34.8 7,708 0 238 32 251 520 162 17 197 376 10.87 72.4
8 Ontario-Nyssa 39 11,342 60 148 48 115 371 111 23 180 314 8.06 84.6
9 Nyssa 33.4 9,372 80 165 31 97 373 87 27 129 243 7.26 65.1
10 Vale 38.3 9,406 0 356 39 236 631 165 35 226 426 11.06 67.5
11 Brogan 29.4 7,280 0 165 48 224 2 437 2 100 37 164 301 10.08 68.9 2
12 Ontario 45.6 12,732 0 104 49 292 2 445 2 123 46 226 395 8.65 88.8 2
1995                          
1 Buhl 21.3 6,352 0 199 NA3 95 294 88 8 78 174 8.20 59.2
2 Burley 22.9 7,452 100 61 17 158 336 79 5 65 149 6.50 44.4
3 Rupert 31.9 9,110 171 95 NA 195 461 92 9 116 217 6.79 47.1
4 Minidoka 21.4 6,787 85 105 NA 130 320 52 6 77 135 5.80 42.2
5 Nyssa 25.2 7,078 35 115 34 121 305 52 4 70 126 5.00 41.3
6 Vale 31.4 7,630 150 122 27 210 509 130 13 112 255 8.10 50.1
7 Ontario 28.0 8,649 80 108 24 189 401 55 9 98 162 5.80 40.4
8 Nyssa 31.8 9,283 40 138 30 136 344 72 8 136 216 6.80 62.8
1996                          
1 Ontario 41.8 10,568 40 190 14 141 346 129 53 265 439 10.40 125.7
2 Nyssa 36.9 10,572 30 188 27 130 375 80 33 193 306 8.30 81.4
3 Parma 34.1 8,856 200 289 11 172 672 109 47 185 341 10.10 50.9
4 Nyssa 33.5 8,667 0 164 42 125 331 84 50 170 304 9.10 91.7
5 Vale 31.0 8,638 0 399 46 285 730 80 43 135 258 8.30 35.4
6 Vale 31.0 8,585 0 399 46 253 698 91 31 170 294 9.50 42.1
7 Vale 33.5 9,104 0 357 42 177 576 54 31 138 223 6.70 38.7
8 Ontario 32.3 8,833 0 254 36 111 401 84 100 179 363 11.20 90.4
9 Ontario 33.1 8,881 0 261 43 144 448 120 40 201 361 10.90 80.7
10 Ontario 29.8 7,945 0 261 43 93 397 92 52 192 336 11.30 84.9
1Total plant N content as a percent of the total available N supply.

2N mineralization estimate by season-long N balance.

3NA: data not available.

Table 5. Estimates of N mineralization made in 30 growers' sugar beet fields by two different methods, Malheur Experiment Station, Oregon State University, Ontario, Oregon, 1994, 1995, and 1996. 
        N-mineralization estimate
Grower Location Soil texture Organic matter Anaerobic incubation Available nitrogen balance
1994   % - - lb N/acre - -
1 Burley sandy loam 1.25 112 NA
2 Minidoka silt loam 1.5 172 NA
3 Minidoka silt loam 2.35 167 NA
4 Jerome loam 1.05 135 283
5 Nyssa silt loam 1.4 88 238
6 Ontario-Vale fine sandy loam 1.6 149 238
7 Ontario-Vale silt loam 2.2 251 304
8 Ontario-Nyssa fine sandy loam 1.75 115 125
9 Nyssa silt loam 2.1 97 61
10 Vale silt loam 2.05 236 251
11 Brogan silt loam 1.6 149 224
12 Ontario silt loam 1.5 159 293
1995        
1 Buhl silt loam 1.2 95 NA
2 Burley silt loam 1.49 158 -11
3 Rupert sandy loam 1.28 195 12
4 Minidoka silt loam 1.65 130 3
5 Nyssa silt loam 1.45 121 16
6 Vale silt loam 3.29 210 NA 
7 Ontario silt loam 1.43 189 48
8 Nyssa silt loam 1.47 136 38
1996        
1 Ontario silt loam 1.5 141 339
2 Nyssa silt loam 1.7 130 166
3 Parma silt loam 2.2 172 -28
4 Nyssa silt loam 1.4 125 -43
5 Vale silt loam 1.4 285 -13
6 Vale silt loam 1.4 253 23
7 Vale silt loam 1.3 177 31
8 Ontario silt loam 1.2 111 197
9 Ontario silt loam 1.5 144 219
10 Ontario silt loam 1.5 93 196