Objective:

To evaluate variety-specific nitrogen use response of irrigated spring wheat for agronomic performance.

Summary:

Eight spring wheat cultivars were grown under four different nitrogen levels as a split plot, randomized complete block design, with four replications, where nitrogen levels represent the whole plot factor and the spring wheat varieties were the sub plot factor. The four nitrogen treatments included no added fertilizer and 150, 281, and 412 pounds/A, respectively, based on soil test N levels plus supplemental N fertilization. For the irrigated study, irrigation was applied when necessary to keep soil moisture from falling below 50% of the plant available water. Other agronomic management procedures are detailed in Table 1.

 

Table 1. Agronomic Data   

Seeding Date: 4/22/2015 Herbicide 5/20/2015
Julian Date: 112   13.7 fl oz/A Huskie complete + 0.5 lb/A AMS
Seeding Rate: 20 plnts/sqft Pesticide: 6/19/2015
Previous Crop Canola   12 fl oz/A Quadris + 1.92 fl oz/A Warrior II
Tillage: Conventional Harvest Date: 8/5/2015 (Dryland)
Soil Type: Fine Sandy Loam Julian Date: 217
Soil Test: 19-6-111 Harvest Date: 8/12/2015
Fertilizer: __-48-115 Julian Date: 224

 

Irrigated

Nitrogen treatment had significant effect on physiological maturity, moisture content, yield, protein, and test weight (Table 2). Volt had the highest yield at 106.3 bu/A with 281 lbs N, while Cabernet had the least yield at 57.8 bu/A with 412 lbs N. The 150 lbs/A total N consistently showed yield response across varieties. Except for Volt and McNeal, the 281 lbs N/A reduced yield. The highest N at 412 lbs/A significantly reduced yields (Figure 2).

The known inverse relationship between yield and protein is evident (Figure 1 and 2). Increased N supply consistently increased protein across varieties with irrigation. For irrigated spring wheat, test weights has inverse relation with N supply. The lower the N supply the higher the test weight, as N supply increased, test weight decreased (Figure 3). Increased N beyond 150 lbs/A is not economically justifiable with this year’s protein premium/discount. Plant height, seed size, thousand kernel weight and falling number were not influenced by the N treatment, but appeared strongly related to variety.

 

Table 2. Effect of N levels to agronomic performance of irrigated spring wheat         

Variety  HT PM* SS MC YLD PRO TWT TKW FN
in days seeds/lb % bu/A % lb/bu g sec
19 lbs N (no added fertilizer)
Brennan 22.5 83 12484 4.4 64.8 14.4 63.4 36.4 424.0
Buck Pronto 26.5 82 10483 5.1 75.8 13.0 63.2 43.4 370.0
Cabernet 22.5 83 11525 5.3 79.5 12.2 63.6 39.5 317.0
Expresso 25.8 84 11270 5.1 75.2 13.8 63.2 40.3 303.0
McNeal 27.5 83 10863 5.3 78.5 11.8 62.6 41.9 508.0
Solano 22.5 84 10537 5.5 81.8 13.2 63.7 43.2 360.0
Volt 28.3 85 12015 5.9 87.6 12.0 64.4 37.9 390.0
WB Rockland 23.3 84 10468 4.6 68.3 14.6 62.8 43.4 307.0
150 lb N (soil + fertilizer)
Brennan 22.3 86 12059 5.3 78.5 15.0 63.4 63.4 398.0
Buck Pronto 26.5 85 10352 6.2 91.9 13.8 62.7 62.7 375.0
Cabernet 22.0 84 11521 6.0 88.5 12.6 63.6 63.6 316.0
Expresso 27.5 86 10879 7.0 104.4 13.9 62.5 62.5 306.0
McNeal 29.5 86 10796 6.8 101.8 13.2 62.5 62.5 457.0
Solano 25.3 86 10679 6.7 99.1 13.9 63.0 63.0 350.0
Volt 28.0 86 12150 6.8 101.2 12.7 64.0 64.0 369.0
WB Rockland 24.5 86 10357 6.3 93.4 15.0 62.3 62.3 341.0
281 lb N (soil + fertilizer)
Brennan 23.0 85 12025 4.9 72.2 16.0 62.2 62.2 383.0
Buck Pronto 26.8 85 9828 5.9 87.3 15.1 60.9 60.9 360.0
Cabernet 21.8 85 11415 5.7 85.2 13.9 62.5 62.5 319.0
Expresso 26.3 87 10931 6.9 102.3 15.0 60.7 60.7 301.0
McNeal 32.0 87 10387 6.9 102.8 14.2 60.5 60.5 461.0
Solano 25.5 87 10573 6.6 98.3 14.8 61.1 61.1 358.0
Volt 28.3 87 11780 7.2 106.3 13.8 62.4 62.4 366.0
WB Rockland 24.0 87 10213 6.2 92.2 16.1 60.1 60.1 328.0
412 lb N (soil + fertilizer)
Brennan 23.8 86 12113 4.2 62.4 16.3 61.4 37.5 409.0
Buck Pronto 26.0 84 10113 5.4 80.3 14.9 60.3 44.9 367.0
Cabernet 23.0 86 11384 3.9 57.8 14.2 61.8 40.0 331.0
Expresso 24.8 86 11081 5.7 84.4 15.3 59.9 41.0 295.0
McNeal 27.8 87 10246 6.4 94.2 14.6 60.1 44.3 461.0
Solano 24.8 86 10706 5.8 86.7 15.2 61.1 42.4 342.0
Volt 26.0 86 11926 6.4 95.3 14.1 62.8 38.1 361.0
WB Rockland 24.8 87 10149 5.3 79.1 16.7 59.8 44.7 315.0
CV 12.3 2.2 8.0 16.1 17.0 9.6 2.7 7.8 15.2
LSD ns 1.8 ns 0.8 11.8 0.8 2.0 ns ns
Pr>F(0.05)-N 0.107 0.003 0.088 0.002 0.002 <.0001 0.009 0.105 0.291
Pr>F(0.05)-Var <.0001 <.0001 <.0001 <.0001 <.0001 <.0001 <.0001 <.0001 <.0001
Pr>F(0.05)-NxVar 0.168 0.936 0.801 0.121 0.127 0.134 0.843 0.607 0.002
HT: height, PM: physiological maturity *(duration from emergence), SS: seed size, MC: moisture content, YLD: yield, PRO:protein, TWT: test weight, TKW: thousand kernel weight, FN: falling number, ns: nonsignificant         

 

Bar graph showing the Yield response to N levels of an irrigated spring wheat on fine sandy loam soil

Figure 1. Yield response to N levels of an irrigated spring wheat on fine sandy loam soil

 

Bar graph showing the Protein response to N levels of an irrigated spring wheat, fine sandy loam soil

Figure 2. Protein response to N levels of an irrigated spring wheat, fine sandy loam soil

 

Bar graph showing the test weight response to N levels of an irrigated spring wheat, fine sandy loam soil

Figure 3. Test weight response to N levels of an irrigated spring wheat, fine sandy loam soil

 

Dryland

No yield response for N application was observed due to extreme drought year. Volt had the highest yield and Brennan had the least. Nitrogen treatment had significant effect on increased protein up to 150 lbs N/A (Table 3). Despite protein advantage at 150 lbs N/A, application of N during such dry season on fine sandy loam soil with only 4.7 inches plant available water (PAW) cannot be justified (root zone 50% PAW at planting + rainfall, see Figure 5).

 

Two line graphs showing the pring wheat yield response to total N supply per water regime, and their corresponding protein quality

Figure 4. Spring wheat yield response to total N supply per water regime (left) and their corresponding protein quality (right). Same letter assignment indicates that they are not significantly different.

 

Line graph showing the adjusted gross return of N application for two water regimes

Figure 5. Adjusted gross return of N application for two water regimes

For irrigated spring wheat in 2015, adjusted gross returns diminished with N application resulting to more than 150 lbs total N. For dryland spring, N application did not provide any economic advantage (Figure 5) despite the increased protein with N supply (Figure 4, right). Thus, for extreme drought like this year, reduction of N input should be considered. 

 

Table 3. Effect of N levels to agronomic performance of dryland spring wheat         

Variety  HT PM* SS MC YLD PRO TWT TKW FN
in days seeds/lb % bu/A % lb/bu g sec
19 lbs N (no added fertilizer)
Brennan 19.9 76 14800 9.5 40.7 14.1 62.5 30.9 459
Buck Pronto 22.2 77 13103 9.6 44.6 13.7 61.5 34.8 420
Cabernet 17.6 76 14134 10.0 43.9 13.3 62.2 32.4 343
Expresso 22.0 78 13250 11.0 47.5 14.3 61.6 34.3 307
McNeal 23.8 77 14031 10.3 45.2 13.0 60.8 32.4 537
Solano 21.8 77 12524 10.3 49.4 13.9 62.2 36.3 390
Volt 23.0 78 14717 11.5 49.9 12.7 62.8 30.9 418
WB Rockland 19.6 79 12311 10.6 39.8 15.0 61.5 36.9 315
150 lb N (soil + fertilizer)
Brennan 19.9 76 15644 9.4 41.9 14.5 62.3 29.0 455
Buck Pronto 22.1 76 13458 9.5 46.1 14.2 61.1 33.8 407
Cabernet 17.3 76 14841 9.5 42.6 13.8 61.6 30.6 348
Expresso 22.4 79 13283 10.2 52.8 15.1 62.0 34.2 322
McNeal 23.3 78 13821 9.9 49.4 13.7 60.7 32.8 507
Solano 21.2 77 12375 10.0 51.4 14.7 61.8 36.6 388
Volt 23.5 78 14128 9.9 53.9 13.0 63.6 32.6 433
WB Rockland 20.9 78 12481 9.8 45.7 15.5 61.7 36.4 341
281 lb N (soil + fertilizer)
Brennan 19.9 76 15313 10.1 37.7 15.0 61.9 29.7 424
Buck Pronto 21.9 76 12776 10.0 42.8 14.6 60.9 35.6 411
Cabernet 17.5 77 13493 10.6 40.2 14.1 61.6 33.9 338
Expresso 21.9 78 12864 11.4 48.0 15.1 61.2 35.4 301
McNeal 24.6 77 13728 11.8 46.4 14.1 59.9 33.1 507
Solano 20.8 79 12272 11.4 43.3 14.8 61.5 37.1 360
Volt 23.1 79 14320 12.0 55.9 13.3 62.5 31.7 388
WB Rockland 21.0 79 12042 11.1 43.5 15.8 61.2 37.8 314
412 lb N (soil + fertilizer)
Brennan 20.3 77 15098 9.8 35.8 15.1 62.0 30.1 415
Buck Pronto 23.0 76 12781 9.9 40.7 14.7 61.0 35.5 397
Cabernet 17.8 76 14032 10.1 37.5 14.0 61.8 32.4 326
Expresso 23.0 79 13032 12.1 44.0 15.4 60.5 34.8 276
McNeal 23.9 78 13280 11.7 45.5 14.3 60.5 34.2 523
Solano 21.0 78 12533 11.1 45.3 14.9 61.5 36.2 352
Volt 23.6 79 14635 10.8 47.4 13.3 63.0 31.0 404
WB Rockland 20.8 78 11963 12.4 37.3 15.1 60.7 38.0 301
CV 10.5 1.8 8.9 12.6 15.5 6.4 1.6 8.9 18.3
LSD ns ns ns ns ns 0.6 ns ns ns
Pr>F(0.05)-N 0.699 0.450 0.259 0.275 0.357 0.007 0.247 0.262 0.123
Pr>F(0.05)-Var <.0001 <.0001 <.0001 <.0001 <.0001 <.0001 <.0001 <.0001 <.0001
Pr>F(0.05)-NxVar 0.921 0.469 0.651 0.087 0.288 0.822 0.082 0.670 0.012
HT: height, PM: physiological maturity *(duration from emergence), SS: seed size, MC: moisture content, YLD: yield, PRO:protein, TWT: test weight, TKW: thousand kernel weight, FN: falling number, ns: nonsignificant