2016 Management Yield Potential

Transcription

1 2016 Management Yield Potential Adriano T. Mastrodomenico and Fred E. Below Crop Physiology Laboratory Department of Crop Sciences Univeristy of Illinois at Urbana-Champaign Table of contents Introduction... 2 Materials and Methods... 3 Yield Results - Champaign, IL... 7 Yield Data - Yorkville, IL Yield Data - Harrisburg, IL Characterization of Workhorse and Racehorse Hybrids Summary of Hybrids Agronomic Characteristics References... 48

2 Introduction Maize yield increases since the 1930s have been due to genetic improvement and better crop management practices (Duvick, 2005). Because maize genotypes interact with crop management in producing yield, understanding the dynamics between plant genetics and agronomic management will provide the opportunity to obtain the maximum yield potential of the hybrid using a corresponding recommended agricultural management. In addition, continued increases in corn yield will depend on a hybrid s ability to utilize resources more efficiently when grown under greater planting densities (Tollenaar and Lee, 2002) and under favorable agronomic conditions (Boomsma et al., 2009). Nonetheless, increased plant density needs to be in synergy with other intensified management factors, such as better soil fertility, in order to minimize the current maize yield gap that exists in the U.S. Corn Belt (Ruffo et al., 2015). Current commercial breeding programs select and develop elite hybrids using a high N fertilizer rate (280 lbs N acre -1 ) and a standard plant density (32,000 plants acre -1 ), only evaluating a hybrid s yield responses to different crop management practices at the precommercial stage. Therefore, there are limited reports of genetic variability of elite hybrids for different N-use traits (Bertin and Gallais, 2000). The genetic improvement in yield response to N fertilizer in maize hybrids is well documented (Ding et al., 2005; Coque and Gallais, 2007; Haegele et al., 2013). However, these previous studies used a small representation of elite maize hybrids across limited number of environments, which may have underestimated the genetic diversity of current maize hybrid yields in response to N fertilizer supplementation. In addition to the genetic improvements in nitrogen use efficiency, tolerance to increased plant density is one of the most valuable agronomic advances since the development of the maize hybrid (Duvick, 1977). The most recent maize yield record in the U.S. (532 bu acre -1 ) was achieved with a plant density (50,000 plants acre -1 ) much greater than common agronomic practices (National Corn Growers Association, 2015). The maize world yield record grown under high plant density indicates that the genetic gain of maize is still far from a plateau and that current maize hybrids exhibit greater crowding stress tolerance when compared to their predecessors (Tollenaar and Wu, 1999). Increased plant density reduces the yield from individual plants, but increases light interception, and to a lesser extent, seed number per ground area, therefore increasing the sourcesink ratio (Borras et al., 2003). One of the possible reasons for the success of increasing plant density to increase maize yield is due to the lack of the ear size to have correspondingly increased with yield in hybrids, causing a reproductive-sink limitation (Egli, 2015). The reproductive-sink limitation hypothesis supports the fact that the yield potential of individual plants have not increased over time, rather maize hybrids have increased their stress tolerance, including the ability to tolerate higher plant densities (Tollenaar and Lee, 2002; Duvick, 2005). One of the future challenges of maize breeding will be selecting genotypes with greater yields in response to increased plant density with concurrent yield stability across environments (Tokatlidis and Koutroubas, 2004). Breeding programs targeting for maize hybrids with improved tolerance to high plant density and N fertilizer response need a comprehensive 2

3 evaluation using a representative number of commercial maize hybrids at different N rates and plant densities evaluated in multiple environments. The objective of the Management Yield Potential (MYP) trial is to identify Racehorse hybrids, or hybrids with adaptability to high yield environments (i.e. responsive to crop management), and Workhorse hybrids, or hybrids with acceptable yields in a low fertility environment (i.e. tolerant to N loss). In our approach, Racehorse hybrids are the genotypes that have greater yield increases in the following categories: (i) N fertilizer (RTN, yield change between 0 and 280 lb N acre -1 at 32,000 plants acre -1 ), (ii) an intermediate plant population (IntRTP, yield response between 32,000 and 38,000 plants acre -1 at 280 lb N acre -1 ), (iii) maximum plant population (MaxRTP, yield change between 38,000 and 44,000 plants acre -1 at 280 lb N acre -1 ), and (iv) narrower row spacing (RTR, yield change between 30 and 20 inches row spacing at 44,000 plants acre -1 and 280 lb N acre -1 ). Conversely, hybrids with high Check Plot yield (at 0 lb N acre -1 ) and a high initial yield increase with N (InitN, yield change between 0 and 60 lb N acre -1 at 32,000 plants acre -1 ) were considered Workhorse hybrids. Materials and Methods For 2016, the trial was planted using a precision plot planter with variable seeding rate capability (SeedPro 360, ALMACO, Nevada, IA) at Champaign, IL (24 April), Yorkville, IL (20 May), and Harrisburg, IL (26 April). Plots were 17.5 feet in length with 30 or 20-inch row spacing and two rows in width. Force 3G insecticide was applied at planting and Lumax EZ (3.25 qt/a) was applied prior to planting as a pre-emergence herbicide. Nitrogen treatments were broadcast applied with urea at 0, 60, and 280 lb N acre -1 between the V4-V6 developmental stages at Champaign, IL (24 May), Yorkville, IL (20 June), and Harrisburg, IL (01 June). Forty seven hybrids represented by seven different seed brands, with relative maturities ranging from days were evaluated (Tables 1a and 1b). Treatments included: (i) 32,000 plants acre -1 at 30-inch row space and 0 lb N acre -1, (ii) 32,000 plants acre -1 at 30-inch row space and 60 lb N acre -1, (iii) 32,000 plants acre -1 at 30-inch row space and 280 lb N acre -1, (iv) 38,000 plants acre -1 at 30-inch row space and 280 lb N acre -1, (v) 44,000 plants acre -1 at 30-inch row space and 280 lb N acre -1, and (vi) 44,000 plants acre -1 at 20-inch row space and 280 lb N acre -1. Treatment (vi) at Champaign was planted at 64,000 plants acre -1 in the 20-inch row space and instead of the desired 44,000 plants acre -1 due to a problem in the configuration of the planter s software. At maturity, plots were harvested with a two-row plot combine and grain yield is reported as bushels acre -1 at 15.5% moisture concentration. The treatments were arranged in a split block experimental design with four replications. Data were analyzed using analysis of variance with the PROC MIXED procedure of SAS (SAS V8 Institute, Cary, NC) and means were separated using Fisher s protected LSD test at the 0.10 level of significance. Normality for residuals and outlier observations were evaluated using Proc UNIVARIATE in SAS. Row space, hybrid, N fertilizer rate, and plant population were considered fixed effects, while block and interactions with blocks were considered random effects. Hybrids were ranked from 1 to 10 using the PROC RANK procedure of SAS to generate scores for Check Plot, initial N response (InitN), maximum response to N (RTN), intermediate yield response to population (IntRTP), maximum yield response to plant population (MaxRTP), 3

4 and yield response to row space (RTR). This assessment provides scores for each parameter and hybrid within each location, and combined across all locations using the overall yield for the hybrid. Scores for each parameter (and the indices) ranged from 0 to 10, with 0 being the least yield increase compared to the overall average, and 10 being the greatest yield increase compared to the overall average, with average ranking a 5. Racehorse and Workhorse indices were estimated using a multiple regression approach with the Smith-Hazel index (Smith, 1936; Hazel, 1943). The data for yield response to narrower row spacing at Champaign was not included in the Racehorse index analysis. Moreover, the genotypic and phenotypic variance-covariance matrices among all the parameters were estimated using restricted maximum likelihood in PROC MIXED of SAS (Holland, 2006). Index weights (vector) for each parameter were estimated by multiplying the phenotypic covariance matrix, the genotypic covariance matrix, and a vector of weight 1 (Eq. 1). Racehorse and Workhorse indices were calculated using the relative weights to each parameter multiplied by the scores (Eq. 2 and 3). b n = P 1 Ga [1] Racehorse index = b 1 IntRTP + b 2 MaxRTP + b 3 RTN + b 4 RTR [2] Workhorse index = b 5 Check + b 6 InitN [3] Where b is the vector of the weights of the indices, P 1 is the inverse matrix of the phenotypic variance-covariance, G is the matrix of the genetic variance-covariance, and a is the initial weight. Yield Results - Champaign, IL The following three sections correspond to the yield results for each treatment and hybrid, and the yield responses to different agronomic management factors. The next six tables (e.g. Tables 2 to 7) describe the yield rank of the hybrids under different N conditions across different row space and planting population arrangements. Yield values for all treatment combinations are described in a summary table (e.g. Table 8). Yield response to different agronomic managements (e. g. Figure 1) is described for each location. 4

5 Table 1a. A list of 47 hybrids evaluated in the Management Yield Potential trial in 2016 grown at Champaign, Yorkville and Harrisburg, IL. Hybrids are sorted by relative maturity ranging from 102 to 120 days. Hybrid Brand Company CRM Harrisburg Champaign Yorkville G02W GT Golden Harvest Syngenta 102 x G03H GT Golden Harvest Syngenta 103 x G06N Golden Harvest Syngenta 106 x 4644DGVT2P Croplan Winfield 106 x x x G07B A-EZ0 Golden Harvest Syngenta 107 x x x G07F Golden Harvest Syngenta 107 x x x STXRIB Channel Monsanto 108 x x x 4895SS/RIB Croplan Winfield 108 x x x 5887VT2P Croplan Winfield 108 x x x DKC59-50SS DEKALB Monsanto 109 x x x G09E EZ0 Golden Harvest Syngenta 109 x x x DKC60-87SS DEKALB Monsanto 110 x x x 6068RIB Stone Monsanto 110 x x x G10S EZ0 Golden Harvest Syngenta 110 x x x G10T GT Golden Harvest Syngenta 110 x x x 6110SS/RIB Croplan Winfield 110 x x x P1197AMXT Pioneer Pioneer 111 x x x G11F A Golden Harvest Syngenta 111 x x x 6065SS/RIB Croplan Winfield 111 x x x D52VC91RIB Dyna-Gro CPS 112 x x x G12J A Golden Harvest Syngenta 112 x x x G12W GT Golden Harvest Syngenta 112 x x x 6265SS/RIB Croplan Winfield 112 x x x 5290DGVT2P Croplan Winfield 112 x x x P1257AMXT Pioneer Pioneer 112 x x x P1311AMXT Pioneer Pioneer 113 x x x DKC63-71SS DEKALB Monsanto 113 x x x STXRIB Channel Monsanto 113 x x x 6594SS/RIB Croplan Winfield 113 x x x 6640VT3P Croplan Winfield 113 x x x D54DC94RIB Dyna-Gro CPS 114 x x x DKC64-34SS DEKALB Monsanto 114 x x x 6458RIB Stone Monsanto 114 x x x P1479AM Pioneer Pioneer 114 x x x G14R GT Golden Harvest Syngenta 114 x x x 7087VT2P/RIB Croplan Winfield 114 x x x D55VC77RIB Dyna-Gro CPS 115 x x x DKC63-60SS DEKALB Monsanto 115 x x x G15Z Golden Harvest Syngenta 115 x x D56VC46RIB Dyna-Gro CPS 116 x x x DKC66-74SS DEKALB Monsanto 116 x x x STXRIB Channel Monsanto 116 x x x G16K Golden Harvest Syngenta 116 x x 6718RIB Stone Monsanto 117 x x x 7927VT3P/RIB Croplan Winfield 117 x x x 8621VT2P/RIB Croplan Winfield 117 x x x G18D GT Golden Harvest Syngenta 118 x x 5

6 Table 1b. A list of 47 hybrids evaluated in the Management Yield Potential trial in 2016 grown at Champaign, Yorkville and Harrisburg, IL. Hybrids are sorted by company and brand names. Hybrid Brand Company CRM Harrisburg Champaign Yorkville D52VC91RIB Dyna-Gro CPS 112 x x x D54DC94RIB Dyna-Gro CPS 114 x x x D55VC77RIB Dyna-Gro CPS 115 x x x D56VC46RIB Dyna-Gro CPS 116 x x x STXRIB Channel Monsanto 108 x x x STXRIB Channel Monsanto 113 x x x STXRIB Channel Monsanto 116 x x x DKC59-50SS DEKALB Monsanto 109 x x x DKC60-87SS DEKALB Monsanto 110 x x x DKC63-71SS DEKALB Monsanto 113 x x x DKC64-34SS DEKALB Monsanto 114 x x x DKC63-60SS DEKALB Monsanto 115 x x x DKC66-74SS DEKALB Monsanto 116 x x x 6068RIB Stone Monsanto 110 x x x 6458RIB Stone Monsanto 114 x x x 6718RIB Stone Monsanto 117 x x x P1197AMXT Pioneer Pioneer 111 x x x P1257AMXT Pioneer Pioneer 112 x x x P1311AMXT Pioneer Pioneer 113 x x x P1479AM Pioneer Pioneer 114 x x x G02W GT Golden Harvest Syngenta 102 x G03H GT Golden Harvest Syngenta 103 x G06N Golden Harvest Syngenta 106 x G07B A-EZ0 Golden Harvest Syngenta 107 x x x G07F Golden Harvest Syngenta 107 x x x G09E EZ0 Golden Harvest Syngenta 109 x x x G10S EZ0 Golden Harvest Syngenta 110 x x x G10T GT Golden Harvest Syngenta 110 x x x G11F A Golden Harvest Syngenta 111 x x x G12J A Golden Harvest Syngenta 112 x x x G12W GT Golden Harvest Syngenta 112 x x x G14R GT Golden Harvest Syngenta 114 x x x G15Z Golden Harvest Syngenta 115 x x G16K Golden Harvest Syngenta 116 x x G18D GT Golden Harvest Syngenta 118 x x 4644DGVT2P Croplan Winfield 106 x x x 4895SS/RIB Croplan Winfield 108 x x x 5887VT2P Croplan Winfield 108 x x x 6110SS/RIB Croplan Winfield 110 x x x 6065SS/RIB Croplan Winfield 111 x x x 6265SS/RIB Croplan Winfield 112 x x x 5290DGVT2P Croplan Winfield 112 x x x 6594SS/RIB Croplan Winfield 113 x x x 6640VT3P Croplan Winfield 113 x x x 7087VT2P/RIB Croplan Winfield 114 x x x 7927VT3P/RIB Croplan Winfield 117 x x x 8621VT2P/RIB Croplan Winfield 117 x x x 6

7 Yield Results - Champaign, IL Table 2. Grain yield of the 44 hybrid entries grown under agronomic conditions of 32,000 plants acre -1, 0 lb N acre -1, and 30-inch row spacing at Champaign, IL in Rank Hybrid Grain yield Rank Hybrid Grain yield bu acre -1 bu acre STXRIB VT3P DKC64-34SS SS/RIB G11F A VT2P/RIB D54DC94RIB G12J A RIB DKC63-71SS G16K DGVT2P G14R GT RIB DKC59-50SS D55VC77RIB G12W GT G07F DKC66-74SS P1479AM STXRIB P1197AMXT DKC60-87SS G07B A-EZ SS/RIB P1311AMXT DGVT2P P1257AMXT G10S EZ RIB VT2P/RIB SS/RIB SS/RIB D52VC91RIB DKC63-60SS SS/RIB VT2P G18D GT D56VC46RIB G15Z STXRIB VT3P/RIB G10T GT G09E EZ Mean LSD (P 0.10)

8 Table 3. Grain yield of the 44 hybrid entries grown under agronomic conditions of 32,000 plants acre -1, 60 lb N acre -1, and 30-inch row spacing at Champaign, IL in Rank Hybrid Grain yield Rank Hybrid Grain yield bu acre -1 bu acre -1 1 DKC60-87SS D56VC46RIB DGVT2P STXRIB VT2P/RIB DGVT2P DKC64-34SS DKC63-71SS DKC66-74SS RIB VT3P D54DC94RIB G14R GT STXRIB G10T GT G10S EZ STXRIB G07B A-EZ RIB VT2P VT2P/RIB SS/RIB DKC59-50SS P1197AMXT P1311AMXT SS/RIB P1257AMXT G09E EZ SS/RIB VT3P/RIB G12J A G18D GT G16K SS/RIB DKC63-60SS RIB P1479AM G11F A D55VC77RIB D52VC91RIB G12W GT G15Z SS/RIB G07F Mean LSD (P 0.10)

9 Table 4. Grain yield of the 44 hybrid entries grown under agronomic conditions of 32,000 plants acre -1, 280 lb N acre -1 and 30-inch row spacing at Champaign, IL in Rank Hybrid Grain yield Rank Hybrid Grain yield bu acre -1 bu acre VT2P/RIB P1479AM P1311AMXT VT3P P1197AMXT G16K DKC64-34SS G07B A-EZ DKC60-87SS G15Z G10T GT RIB STXRIB DGVT2P VT2P/RIB D55VC77RIB P1257AMXT G14R GT DKC66-74SS SS/RIB DGVT2P DKC63-71SS G12W GT G11F A VT3P/RIB G07F D54DC94RIB VT2P RIB D52VC91RIB DKC63-60SS SS/RIB RIB DKC59-50SS SS/RIB SS/RIB STXRIB G09E EZ G18D GT D56VC46RIB G12J A SS/RIB G10S EZ STXRIB Mean LSD (P 0.10)

10 Table 5. Grain yield of the 44 hybrid entries grown under agronomic conditions of 38,000 plants acre -1 at 280 lb N acre -1 and 30-inch row spacing at Champaign, IL in Rank Hybrid Grain yield Rank Hybrid Grain yield bu acre -1 bu acre -1 1 G10T GT DKC63-60SS DKC64-34SS P1479AM P1197AMXT VT3P/RIB DKC60-87SS DKC59-50SS DKC66-74SS G07F P1257AMXT G14R GT D54DC94RIB STXRIB G12W GT SS/RIB G18D GT SS/RIB G10S EZ G11F A VT2P/RIB G15Z DGVT2P RIB RIB SS/RIB P1311AMXT G09E EZ SS/RIB DKC63-71SS RIB G07B A-EZ G16K D55VC77RIB STXRIB VT2P DGVT2P SS/RIB VT2P/RIB D56VC46RIB VT3P D52VC91RIB G12J A STXRIB Mean LSD (P 0.10)

11 Table 6. Grain yield of the 44 hybrid entries grown under agronomic conditions of 44,000 plants acre -1 at 280 lb N acre -1 and 30-inch row spacing at Champaign, IL in Rank Hybrid Grain yield Rank Hybrid Grain yield bu acre -1 bu acre -1 1 G10T GT STXRIB P1197AMXT VT3P DKC64-34SS SS/RIB VT2P/RIB RIB G12W GT G12J A DKC60-87SS G15Z STXRIB G14R GT P1311AMXT G07B A-EZ P1257AMXT SS/RIB G16K G10S EZ G18D GT DKC59-50SS DKC66-74SS G07F D54DC94RIB VT2P DGVT2P VT3P/RIB VT2P/RIB DKC63-71SS P1479AM D55VC77RIB RIB G11F A DKC63-60SS G09E EZ STXRIB SS/RIB DGVT2P D56VC46RIB SS/RIB SS/RIB RIB D52VC91RIB Mean LSD (P 0.10)

12 Table 7. Grain yield of the 44 hybrid entries grown under agronomic conditions of 64,000 plants acre -1 at 280 lb N acre -1 and 20-inch row spacing at Champaign, IL in Rank Hybrid Grain yield Rank Hybrid Grain yield bu acre -1 bu acre -1 1 G10T GT SS/RIB DGVT2P SS/RIB DKC64-34SS G10S EZ G12W GT DKC59-50SS DKC60-87SS DKC63-71SS RIB G07B A-EZ P1479AM RIB DKC66-74SS SS/RIB P1197AMXT G16K STXRIB SS/RIB DKC63-60SS G14R GT G18D GT P1257AMXT DGVT2P D56VC46RIB VT2P/RIB D54DC94RIB RIB G15Z STXRIB VT3P G11F A STXRIB SS/RIB D55VC77RIB VT3P/RIB D52VC91RIB G07F P1311AMXT VT2P/RIB VT2P G12J A G09E EZ Mean LSD (P 0.10)

13 Table 8. Individual yield values of all hybrid entries (n = 44) grown under two levels of row spacing (30 and 20 inches), four levels of plant population (32,000, 38,000, 44,000, and 64,000 plants acre -1 ) and three levels of N supply (0, 60, and 280 lb N acre -1 ) at Champaign, IL in Trial means and phenotypic ranges (smallest and largest hybrid means) shown for comparison. Hybrids are sorted by company in 20 in 38,000 plts a -1 44,000 plts a -1 64,000 plts a -1 0 lb N 32,000 plts a 60 lb N 280 lb N 280 lb N 280 lb N bu acre Dynagro bu acre bu acre D52VC91RIB D54DC94RIB D55VC77RIB D56VC46RIB Monsanto STXRIB STXRIB STXRIB RIB RIB RIB DKC59-50SS DKC60-87SS DKC63-60SS DKC63-71SS DKC64-34SS DKC66-74SS Pioneer P1197AMXT P1257AMXT P1311AMXT P1479AM Syngenta G07B A-EZ G07F G09E EZ G10S EZ G10T GT G11F A G12J A G12W GT G14R GT G15Z G16K G18D GT Winfield 4644DGVT2P SS/RIB DGVT2P VT2P SS/RIB SS/RIB SS/RIB SS/RIB VT3P VT2P/RIB VT3P/RIB VT2P/RIB LSD (P 0.10) Mean Range

14 Table 9. Yield values averaged within seed companies under two levels of row spacing (30 and 20 inches), four levels of plant population (32,000, 38,000, 44,000 and 64,000 plants acre -1 ) and three levels of N supply (0, 60, and 280 lb N acre -1 ) at Champaign, IL in in 20 in 32,000 plts a -1 38,000 plts a -1 44,000 plts a -1 64,000 plts a -1 0 lb N 60 lb N 280 lb N 280 lb N 280 lb N bu acre bu acre bu acre Dyna-Gro Channel Stone DeKalb Pioneer Syngenta Winfield Figure 1. Yield response to different agronomic management practices for intermediate yield response to population (IntRTP, yield response between 32,000 and 38,000 plants acre -1 at 280 lb N acre -1 ), maximum yield response to plant population (MaxRTP, yield response between 38,000 and 44,000 plants acre -1 at 280 lb N acre -1 ), and the yield response to narrower row spacing (RTR, yield response between 30 inches at 44,000 plants acre -1 and 20 inches at 64,000 plants acre -1 at 280 lb N acre -1 ) at Champaign, IL 14

15 Yield Data - Yorkville, IL Table 10. Grain yield of the 44 hybrid entries grown under agronomic conditions of 32,000 plants acre -1, 0 lb N acre -1, and 30-inch row spacing at Yorkville, IL in Rank Hybrid Grain yield Rank Hybrid Grain yield bu acre -1 bu acre RIB DKC60-87SS RIB G10S EZ G12W GT G09E EZ DKC64-34SS SS/RIB G10T GT RIB STXRIB DKC59-50SS DKC63-60SS G12J A G14R GT P1257AMXT STXRIB G07F DKC66-74SS P1311AMXT P1479AM DGVT2P D54DC94RIB VT3P/RIB P1197AMXT D56VC46RIB VT2P/RIB G03H GT SS/RIB G11F A D52VC91RIB VT3P DKC63-71SS G07B A-EZ VT2P/RIB DGVT2P VT2P G06N D55VC77RIB G02W GT STXRIB SS/RIB SS/RIB SS/RIB Mean LSD (P 0.10)

16 Table 11. Grain yield of the 44 hybrid entries grown under agronomic conditions of 32,000 plants acre -1, 60 lb N acre -1, and 30-inch row spacing at Yorkville, IL in Rank Hybrid Grain yield Rank Hybrid Grain yield bu acre -1 bu acre -1 1 G10T GT DGVT2P VT2P/RIB SS/RIB RIB D52VC91RIB RIB G07F DKC64-34SS DKC63-71SS P1197AMXT G10S EZ G12W GT G14R GT VT3P/RIB VT2P/RIB STXRIB STXRIB D54DC94RIB D55VC77RIB STXRIB RIB DKC66-74SS SS/RIB DKC63-60SS VT2P G09E EZ G06N VT3P DKC60-87SS G12J A G07B A-EZ SS/RIB DKC59-50SS P1479AM P1257AMXT DGVT2P SS/RIB G11F A G03H GT P1311AMXT SS/RIB D56VC46RIB G02W GT Mean LSD (P 0.10)

17 Table 12. Grain yield of the 44 hybrid entries grown under agronomic conditions of 32,000 plants acre -1, 280 lb N acre -1, and 30-inch row spacing at Yorkville, IL in Rank Hybrid Grain yield Rank Hybrid Grain yield bu acre -1 bu acre VT2P/RIB G09E EZ G10T GT VT2P/RIB P1197AMXT D54DC94RIB DKC64-34SS DKC63-71SS VT3P/RIB SS/RIB RIB G14R GT G12W GT D56VC46RIB DKC66-74SS RIB RIB G11F A STXRIB DGVT2P G12J A DKC59-50SS DKC63-60SS P1311AMXT STXRIB G10S EZ DGVT2P STXRIB D55VC77RIB VT2P SS/RIB VT3P P1257AMXT G07B A-EZ D52VC91RIB G03H GT DKC60-87SS SS/RIB SS/RIB G06N P1479AM SS/RIB G07F G02W GT Mean LSD (P 0.10)

18 Table 13. Grain yield of the 44 hybrid entries grown under agronomic conditions of 38,000 plants acre -1 at 280 lb N acre -1 and 30-inch row spacing at Yorkville, IL in Rank Hybrid Grain yield Rank Hybrid Grain yield bu acre -1 bu acre VT2P/RIB SS/RIB P1197AMXT D52VC91RIB G10T GT RIB VT3P/RIB DGVT2P G12W GT G11F A DKC64-34SS G14R GT STXRIB DKC59-50SS RIB DKC63-71SS STXRIB G03H GT DKC66-74SS STXRIB P1257AMXT VT2P/RIB G12J A G07F SS/RIB D56VC46RIB SS/RIB VT3P D54DC94RIB G10S EZ P1479AM SS/RIB RIB SS/RIB DKC63-60SS P1311AMXT DKC60-87SS G06N G09E EZ G07B A-EZ D55VC77RIB VT2P DGVT2P G02W GT Mean LSD (P 0.10)

19 Table 14. Grain yield of the 44 hybrid entries grown under agronomic conditions of 44,000 plants acre -1 at 280 lb N acre -1 and 30-inch row spacing at Yorkville, IL in Rank Hybrid Grain yield Rank Hybrid Grain yield bu acre -1 bu acre -1 1 P1197AMXT SS/RIB VT2P/RIB G11F A RIB DKC59-50SS DKC66-74SS SS/RIB STXRIB DGVT2P STXRIB G09E EZ DKC64-34SS STXRIB G10T GT G14R GT G12W GT G03H GT RIB D54DC94RIB SS/RIB VT2P VT3P/RIB SS/RIB DKC63-60SS VT2P/RIB P1257AMXT SS/RIB G12J A G06N RIB DKC63-71SS D55VC77RIB G07B A-EZ G07F P1311AMXT DKC60-87SS G10S EZ D52VC91RIB G02W GT DGVT2P VT3P P1479AM D56VC46RIB Mean LSD (P 0.10)

20 Table 15. Grain yield of the 44 hybrid entries grown under agronomic conditions of 44,000 plants acre -1 at 280 lb N acre -1 and 20-inch row spacing at Yorkville, IL in Rank Hybrid Grain yield Rank Hybrid Grain yield bu acre -1 bu acre -1 1 G10T GT G11F A VT3P/RIB RIB P1197AMXT SS/RIB D54DC94RIB RIB DKC66-74SS DGVT2P VT2P/RIB DKC60-87SS DKC63-60SS D52VC91RIB DKC64-34SS STXRIB STXRIB SS/RIB DGVT2P D56VC46RIB G12W GT G14R GT G09E EZ G07B A-EZ RIB SS/RIB G12J A SS/RIB VT2P/RIB VT3P P1311AMXT D55VC77RIB DKC63-71SS G03H GT DKC59-50SS STXRIB SS/RIB G10S EZ P1479AM G06N G07F VT2P P1257AMXT G02W GT Mean LSD (P 0.10)

21 Table 16. Individual yield values of all hybrid entries (n = 44) grown under two levels of row spacing (30 and 20 inches), three levels of plant population (32,000, 38,000, and 44,000 plants acre -1 ) and three levels of N supply (0, 60, and 280 lb N acre -1 ) at Yorkville, IL in Trial means and phenotypic ranges (smallest and largest hybrid means) shown for comparison. Hybrids are sorted by company in 20 in 38,000 plts a -1 44,000 plts a -1 44,000 plts a -1 0 lb N 32,000 plts a 60 lb N 280 lb N 280 lb N 280 lb N bu acre Dynagro bu acre bu acre D52VC91RIB D54DC94RIB D55VC77RIB D56VC46RIB Monsanto STXRIB STXRIB STXRIB RIB RIB RIB DKC59-50SS DKC60-87SS DKC63-60SS DKC63-71SS DKC64-34SS DKC66-74SS Pioneer P1197AMXT P1257AMXT P1311AMXT P1479AM Syngenta G02W GT G03H GT G06N G07B A-EZ G07F G09E EZ G10S EZ G10T GT G11F A G12J A G12W GT G14R GT Winfield 4644DGVT2P SS/RIB DGVT2P VT2P SS/RIB SS/RIB SS/RIB SS/RIB VT3P VT2P/RIB VT3P/RIB VT2P/RIB LSD (P 0.10) Mean Range

22 Table 17. Yield values averaged within seed companies under two levels of row spacing (30 and 20 inches), three levels of plant population (32,000, 38,000, and 44,000 plants acre -1 ), and three levels of N supply (0, 60, and 280 lb N acre -1 ) at Yorkville, IL in ,000 plts a -1 38,000 plts a -1 44,000 plts a -1 44,000 plts a -1 0 lb N 60 lb N 280 lb N 280 lb N 280 lb N bu acre bu acre bu acre Dyna-Gro Channel Stone DeKalb Pioneer Syngenta Winfield Figure 2. Yield response to different agronomic management practices for intermediate yield response to population (IntRTP, yield response between 32,000 and 38,000 plants acre -1 at 280 lb N acre -1 ), maximum yield response to plant population (MaxRTP, yield response between 38,000 and 44,000 plants acre -1 at 280 lb N acre -1 ), and the yield response to narrower row spacing (RTR, yield response between 30 and 20 inches row spacing at 44,000 plants acre -1 and 280 lb N acre -1 ) at Yorkville, IL. 22

23 Yield Data - Harrisburg, IL Table 18. Grain yield of the 44 hybrid entries grown under agronomic conditions of 32,000 plants acre -1, 0 lb N acre -1, and 30-inch row spacing at Harrisburg, IL in Rank Hybrid Grain yield Rank Hybrid Grain yield bu acre -1 bu acre STXRIB VT2P DKC60-87SS G14R GT STXRIB D52VC91RIB G07F DKC59-50SS G10T GT G09E EZ G12W GT SS/RIB D54DC94RIB P1479AM DGVT2P RIB VT2P/RIB SS/RIB DKC63-60SS VT3P/RIB DKC64-34SS G15Z RIB G12J A D55VC77RIB STXRIB VT2P/RIB VT3P G10S EZ G18D GT DGVT2P P1197AMXT DKC66-74SS SS/RIB G11F A G16K RIB P1257AMXT D56VC46RIB P1311AMXT SS/RIB SS/RIB DKC63-71SS G07B A-EZ Mean 90.6 LSD (P 0.10)

24 Table 19. Grain yield of the 44 hybrid 3 entries grown under agronomic conditions of 32,000 plants acre - 1, 60 lb N acre -1, and 30-inch row spacing at Harrisburg, IL in Rank Hybrid Grain yield Rank Hybrid Grain yield bu acre -1 bu acre -1 1 DKC64-34SS D55VC77RIB STXRIB STXRIB STXRIB VT2P DGVT2P G09E EZ VT2P/RIB DKC59-50SS DKC60-87SS DKC63-71SS G10T GT SS/RIB VT2P/RIB G14R GT DKC66-74SS RIB D52VC91RIB DGVT2P RIB P1197AMXT VT3P/RIB SS/RIB RIB P1479AM G12W GT P1257AMXT G12J A SS/RIB G07F VT3P DKC63-60SS G15Z D56VC46RIB SS/RIB G11F A SS/RIB D54DC94RIB G16K G10S EZ P1311AMXT G18D GT G07B A-EZ Mean LSD (P 0.10)

25 Table 20. Grain yield of the 44 hybrid entries grown under agronomic conditions of 32,000 plants acre - 1, and 280 lb N acre -1, and 30-inch row spacing at Harrisburg, IL in Rank Hybrid Grain yield Rank Hybrid Grain yield bu acre -1 bu acre -1 1 DKC64-34SS D52VC91RIB G10T GT D56VC46RIB DKC60-87SS D55VC77RIB STXRIB G12W GT DGVT2P VT3P DKC66-74SS P1479AM VT2P/RIB G10S EZ RIB G09E EZ STXRIB G18D GT P1197AMXT SS/RIB VT3P/RIB SS/RIB RIB SS/RIB G07F VT2P DKC63-60SS G14R GT P1257AMXT G11F A D54DC94RIB SS/RIB G12J A G16K STXRIB G15Z P1311AMXT DKC59-50SS VT2P/RIB SS/RIB DKC63-71SS G07B A-EZ RIB DGVT2P Mean LSD (P 0.10)

26 Table 21. Grain yield of the 44 hybrid entries grown under agronomic conditions of 38,000 plants acre -1 at 280 lb N acre -1 and 30-inch row spacing at Harrisburg, IL in Rank Hybrid Grain yield Rank Hybrid Grain yield bu acre -1 bu acre -1 1 DKC64-34SS D55VC77RIB STXRIB P1257AMXT STXRIB P1311AMXT G10T GT G10S EZ DKC60-87SS G11F A VT2P/RIB D52VC91RIB DGVT2P SS/RIB RIB SS/RIB P1197AMXT VT2P VT2P/RIB SS/RIB RIB G14R GT DKC63-71SS SS/RIB DKC63-60SS G12W GT STXRIB G09E EZ DKC66-74SS DGVT2P D54DC94RIB G12J A RIB DKC59-50SS D56VC46RIB G18D GT VT3P/RIB G16K P1479AM G07B A-EZ G07F SS/RIB VT3P G15Z Mean LSD (P 0.10)

27 Table 22. Grain yield of the 44 hybrid entries grown under agronomic conditions of 44,000 plants acre -1 at 280 lb N acre -1 and 30-inch row spacing at Harrisburg, IL in Rank Hybrid Grain yield Rank Hybrid Grain yield bu acre -1 bu acre STXRIB SS/RIB DKC64-34SS RIB STXRIB VT2P DKC60-87SS P1479AM G10T GT D52VC91RIB DGVT2P SS/RIB DKC63-60SS G10S EZ RIB G11F A DKC66-74SS G12W GT RIB SS/RIB D54DC94RIB G14R GT VT3P/RIB P1257AMXT DKC63-71SS G09E EZ STXRIB G18D GT P1197AMXT DKC59-50SS D56VC46RIB P1311AMXT VT2P/RIB DGVT2P VT2P/RIB G16K VT3P G15Z SS/RIB G07B A-EZ G07F SS/RIB D55VC77RIB G12J A Mean LSD (P 0.10)

28 Table 23. Grain yield of the 44 hybrid entries grown under agronomic conditions of 44,000 plants acre -1 at 280 lb N acre -1 and 20-inch row spacing at Harrisburg, IL in Rank Hybrid Grain yield Rank Hybrid Grain yield bu acre -1 bu acre -1 1 G10T GT G12W GT G07F SS/RIB DKC63-60SS SS/RIB DKC66-74SS VT2P/RIB D54DC94RIB DKC63-71SS DGVT2P DGVT2P VT3P/RIB G09E EZ VT2P/RIB G18D GT P1197AMXT G12J A RIB P1311AMXT P1479AM SS/RIB STXRIB DKC59-50SS STXRIB G14R GT DKC64-34SS STXRIB D56VC46RIB P1257AMXT VT3P G10S EZ DKC60-87SS G15Z RIB D52VC91RIB D55VC77RIB G16K RIB SS/RIB G11F A G07B A-EZ SS/RIB VT2P Mean LSD (P 0.10)

29 Table 24. Individual yield values of all hybrid entries (n = 44) grown under two levels of row spacing (30 and 20 inches), three levels of plant population (32,000, 38,000, and 44,000 plants acre -1 ) and three levels of N supply (0, 60, and 280 lb N acre -1 ) at Harrisburg, IL in Trial means and phenotypic ranges (smallest and largest hybrid means) shown for comparison. Hybrids are sorted by company. 32,000 plts a in 20 in 38,000 plts a -1 44,000 plts a -1 44,000 plts a -1 0 lb N 60 lb N 280 lb N 280 lb N 280 lb N bu acre Dynagro bu acre bu acre D52VC91RIB D54DC94RIB D55VC77RIB D56VC46RIB Monsanto STXRIB STXRIB STXRIB RIB RIB RIB DKC59-50SS DKC60-87SS DKC63-60SS DKC63-71SS DKC64-34SS DKC66-74SS Pioneer P1197AMXT P1257AMXT P1311AMXT P1479AM Syngenta G07B A-EZ G07F G09E EZ G10S EZ G10T GT G11F A G12J A G12W GT G14R GT G15Z G16K G18D GT Winfield 4644DGVT2P SS/RIB DGVT2P VT2P SS/RIB SS/RIB SS/RIB SS/RIB VT3P VT2P/RIB VT3P/RIB VT2P/RIB LSD (P 0.10) Mean Range

30 Table 25. Yield values averaged within seed companies under two levels of row spacing (30 and 20 inches), three levels of plant population (32,000, 38,000, and 44,000 plants acre -1 ), and three levels of N supply (0, 60, and 280 lb N acre -1 ) at Harrisburg, IL in in 20 in 32,000 plts a -1 38,000 plts a -1 44,000 plts a -1 44,000 plts a -1 0 lb N 60 lb N 280 lb N 280 lb N 280 lb N bu acre bu acre bu acre Dyna-Gro Channel Stone DeKalb Pioneer Syngenta Winfield Figure 3. Yield response to different agronomic management practices for intermediate yield response to population (IntRTP, yield response between 32,000 and 38,000 plants acre -1 at 280 lb N acre -1 ), maximum yield response to plant population (MaxRTP, yield response between 38,000 and 44,000 plants acre -1 at 280 lb N acre -1 ), and the yield response to narrower row spacing (RTR, yield response between 30 and 20 inches row spacing at 44,000 plants acre -1 and 280 lb N acre -1 ) at Harrisburg, IL 30

31 Characterization of Workhorse and Racehorse Hybrids Environmental conditions in 2016 created different hybrid performances across the three locations of the trial. Overall average check plot yield (0 lb N acre -1 ) was 134.9, 216.1, and 90.6 bu acre -1 at Champaign, Yorkville, and Harrisburg, IL, respectively. High check plot yield at Yorkville was associated with high residual N, mineralized from soil organic matter. Overall average initial yield response to N was 82.5, 20.7, and 51.6 bu acre -1 and maximum yield response to N was 115.6, 27.5, and 89.8 bu acre -1 at Champaign, Yorkville, and Harrisburg, IL, respectively. The low yield response to N at Yorkville was associated with high check plot yield, while low check plot and low yield response to N at Harrisburg was associated with suboptimal yield environmental conditions during the growing season (high temperature and low soil moisture). Overall average intermediate yield response to plant population was 9.3, 0.8, and -1.7 bu acre -1 and maximum yield response to population was 0.5, -5.7, and 3.6 bu acre -1 for Champaign, Yorkville, and Harrisburg, respectively. Minimal yield response to increased plant population at Harrisburg indicates that under stressed conditions high plant density increases the intra-plant competition and decreases corn yield. On the other hand, overall average yield response to narrower row spacing was 17.4, and 12.2 bu acre -1 at Yorkville and Harrisburg, respectively. Narrower row spacing decreased inter-plant competition and increased individual plant yield under ultra-high plant density conditions in high and low yield environments (Yorkville and Harrisburg, respectively). Yield response to increased plant density and narrower row spacing (yield response between 30 inches row spacing at 44,000 plants acre -1 and 20 inches row spacing at 64,000 plants acre -1 ) was bu acre -1 at Champaign. Notably, approximately 75% of the tested hybrids did not tolerate high plant densities even under narrower row spacing conditions. Nonetheless, the only hybrid (G10T GT) at Champaign that exceeded 300 bu acre -1 was grown under 20 inches row spacing and 64,000 plants acre -1. Similarly to previous years, there was large genetic variation of corn hybrids in response to different agronomic conditions. The objective of the MYP trial is to identify the impact of the most important agronomic factors on grain yield for different corn genotypes and develop parameters that allow agronomists and farmers to better position their products. Workhorse and Racehorse indices will support agronomic decisions in order to express a hybrid s maximum yield potential using the recommended crop management system. The Racehorse index is composed of the intermediate and maximum yield response to plant population (IntRTP and MaxRTP), maximum yield response to N (RTN), and yield response to narrower row spacing (RTR) evaluations. The Workhorse index is constituted by the check plot yield (Check) and the initial yield response to N (InitN). Racehorse and Workhorse indices consider the variation and relationship of each parameter across environments and their contributions to observed yield increases. Using multivariate analysis, the relative weights for IntRTP, MaxRTP, RTN, RTR, Check, and InitN were generated. The objective of this trial is to develop indices that will be consistent to the genetic characteristic of each hybrid regardless of the year and location tested. Therefore, the relative weights were generated using the 2015 and 2016 data in the same analysis to better estimate the value of each 31

32 parameter (Table 26). Using the combined data, the relative weights for IntRTP, MaxRTP, RTN, RTR, Check, and InitN parameters were 0.104, 0.039, 0.615, 0.242, 0.735, and 0.260, respectively (Eq. 4 and 5). Parameter scores for each hybrid across locations are represented in Table 27. The calculation of a hybrid score for each location enables the understanding of the genetic by environment interaction for a specific parameter and hybrid. Racehorse index = 0.10 IntRTP MaxRTP RTN RTR [4] Workhorse index = 0.74 Check InitN [5] Table 26. Relative weights for IntRTP, MaxRTP, RTN, RTR, Check, and InitN generated for hybrids tested in 2015 and Total of 67 hybrids evaluated at Champaign, DeKalb, and Harrisburg in 2015 and Champaign, Yorkville, and Harrisburg in Year used for data analysis IntRTP MaxRTP RTN RTR Check InitN and

33 Table 27a. Scores for intermediate response to population (IntRTP), maximum response to plant population (MaxRTP), maximum yield response to N (RTN), response to narrower row spacing (RTR), initial response to N (InitN), and Check plot yield (Check) for Dyna-Gro and Monsanto hybrids at Champaign, Yorkville, and Harrisburg IL. IntRTP MaxRTP Champaign Yorkville Harrisburg RTN RTR * Check InitN IntRTP MaxRTP RTN RTR Check InitN IntRTP MaxRTP RTN RTR Check InitN CPS D52VC91RIB D54DC94RIB D55VC77RIB D56VC46RIB Monsanto STXRIB STXRIB STXRIB RIB RIB RIB DKC59-50SS DKC60-87SS DKC63-60SS DKC63-71SS DKC64-34SS DKC66-74SS *RTR at Champaign refers to the yield response between 30 inches row spacing at 44,000 plants acre -1 and 20 inches row spacing at 64,000 plants acre -1 and was not included in the Racehorse index analysis. 33

34 Table 27b. Scores for intermediate response to population (IntRTP), maximum response to plant population (MaxRTP), maximum yield response to N (RTN), response to narrower row spacing (RTR), initial response to N (InitN), and Check plot yield (Check) for Pioneer, Syngenta, and Winfield hybrids at Champaign, Yorkville, and Harrisburg IL. Champaign Yorkville Harrisburg IntRTP MaxRTP RTN RTR * Check InitN IntRTP MaxRTP RTN RTR Check InitN IntRTP MaxRTP RTN RTR Check InitN Pioneer P1197AMXT P1257AMXT P1311AMXT P1479AM Syngenta G02W GT G03H GT G06N G07B A-EZ G07F G09E EZ G10S EZ G10T GT G11F A G12J A G12W GT G14R GT G15Z G16K G18D GT Winfield 4644DGVT2P SS/RIB DGVT2P VT2P SS/RIB SS/RIB SS/RIB SS/RIB VT3P VT2P/RIB VT3P/RIB VT2P/RIB *RTR at Champaign refers to the yield response between 30 inches row spacing at 44,000 plants acre -1 and 20 inches row spacing at 64,000 plants acre -1 and was not included in the Racehorse index analysis. 34

35 Table 28. Average scores across seed brands for intermediate response to population (IntRTP), maximum response to plant population (MaxRTP), maximum yield response to N (RTN), response to narrower row spacing (RTR), initial response to N (InitN), and Check plot yield (Check) at Champaign, Yorkville, and Harrisburg IL. Champaign Yorkville Harrisburg IntRTP MaxRTP RTN RTR * Check InitN IntRTP MaxRTP RTN RTR Check InitN IntRTP MaxRTP RTN RTR Check InitN Dynagro Channel DeKalb Stone Pioneer Syngenta Winfield *RTR at Champaign refers to the yield response between 30 inches row spacing at 44,000 plants acre -1 and 20 inches row spacing at 64,000 plants acre -1 and was not included in the Racehorse index analysis. 35

36 Summary of Hybrids Agronomic Characteristics This section presents a brief summary for each hybrid. Scores for each hybrid (bar-graph figures) were generated using the combined data from all locations, which allows us to understand the overall response for each hybrid across different environments in CHANNEL: STXRIB High yield response to increased plant density at 30 inch row space. High tolerance to N loss, and low yield response to N fertilizer and narrower row spacing STXRIB Highest yielding hybrid from Channel in the trial. High yield potential and stable performance. Combines high Check Plot and high maximum yield response to N fertilizer STXRIB Average and stable performance across environments. Yield responsive to increased plant density. 36

37 CROPLAN 4644DGVT2P: Good yield response to increased population and to narrower row spacing. 4895SS/RIB: High maximum response to population, but low yield response to narrower row spacing. 5290DGVT2P: High yield and stable performance across environments. Combines high yield response to N fertilizer and narrower row spacing. High Racehorse index. 5887VT2P: High yield response to increased plant population, but poor tolerance to narrower row spacing. 37

38 6065SS/RIB: Average and stable performance across environments. Average yield response to increased plant population and to narrower row spacing. 6110SS/RIB: Low tolerance to N loss conditions. Average response to increased plant population and narrower row spacing. 6265SS/RIB: Low tolerance to N loss conditions, but above average response to initial N and increased population. 6594SS/RIB: Below average response to N and to increasing plant population. 38

39 6640SS/RIB: High yield response to initial N and intermediate plant population, but below average for other characters. 7087VT2P/RIB: Above average for tolerance to low N, but low yield response to increased plant population. 7927VT3P/RIB: Excellent yield response to N fertilizer and narrower row spacing, but low Check Plot score. The highest Racehorse index of the trial. 8621VT2P/RIB: Highest yielding hybrid for Croplan brand across locations. Versatile hybrid with high Racehorse and Workhorse indices. Good tolerance to low N conditions and good response to N fertilizer. 39

40 DEKALB DKC59-50SS Low yield response to N fertilizer, but above average yield response to increasing plant population and narrower row spacing. DKC60-87SS High Workhorse index. Combines high yield response to N fertilizer and high Check Plot score. DKC63-60SS Consistent high yield performance in narrower row spacing. Average performance under 30 inch row spacing. Tolerant to low N conditions, high yield response to narrower row spacing and high plant density. DKC63-71SS Above average response to narrower row spacing and tolerant to low N conditions. 40

41 DKC64-34SS Highest yielding hybrid for the DeKalb brand across treatments and environments. High yield performance and yield stability. High Check Plot score and Workhorse index. DKC66-74SS High yielding hybrid and stable performance across locations. Versatile hybrid with high Racehorse and Workhorse indices. DYNA-GRO: D52VC91RIB: Good yield response to N fertilizer and increased plant density, but average response to increasing plant population and poor tolerance to narrower row spacing. D55VC77RIB: Average response to most characters, but poor tolerance to narrower row spacing. 41

42 D54DC94RIB: Highest yielding hybrid for Dyna-Gro brand in the trial. Good yield response to increased plant density and narrower row spacing. High Check score, but below average response to N fertilizer. D56VC46RIB: High yield response to narrower row spacing and good tolerance to low N conditions. GOLDEN HARVEST G02W GT: Hybrid only tested at Yorkville. High yield response to intermediate plant population, but below average for most characters. G03H GT: Hybrid only tested at Yorkville. Poor tolerance to N loss and yield response to N fertilizer. High yield response to plant population. 42

43 G06N : Hybrid only tested at Yorkville. High yield response to initial N and high plant populations. Low Check Plot yield and tolerance to narrower row spacing. G07B A-EZ0: High yield response to maximum plant populations and N fertilizer. Low Check Plot yield. G07F : High yield response to narrower row spacing and to maximum plant population. G09E EZ0: Above average response to intermediate plant population. High yield response to N fertilizer, but low Check Plot score. 43

44 G10S EZ0: High yield response to intermediate plant population and Check Plot score. Below average response to N fertilizer. G10T GT: High yield performance and stability across environments. Highest yielding hybrid of the trial. Versatile hybrid with high Racehorse and Workhorse indices. G11F A: Above average for Check Plot score. High yield response to narrower row spacing and intermediate plant population. G12J A: High yield response to N fertilizer and narrower row spacing. High Racehorse index, but doesn t tolerate increased plant densities at 30 inch row spacing. 44

45 G12W GT: Combines high Check Plot and high yield response to narrower row spacing. High Workhorse index. G14R GT: High Workhorse index with high Check Plot score. Above average response to increased plant population (38,000 plants acre -1 ). G15Z : High yield response to maximum plant population, but low yield response to narrower row spacing. High yield response to N fertilizer. G16K : Low yield response to N fertilizer and narrower row spacing. High yield response to increased plant population. 45

46 G18D GT: Excellent yield response to N fertilizer, but low tolerance to N loss conditions. Above average response for increased plant population and narrower row spacing. High Racehorse index. PIONEER P1197AMXT: Highest yielding hybrid for Pioneer brand in the trial. High yield response to N fertilizer and increased plant density. High Racehorse index. P1257AMXT: High yield response to N fertilizer, but below average score for other characters. P1311AMXT: High yield response to N fertilizer. Low Check Plot score and low yield response to increased plant density. 46

47 P1479AM: Average and stable yield performance across environments. High yield response to intermediate plant population and narrower row spacing. STONE 6068RIB: High yield response to increased plant density. Above average response to increased plant population. Low yield performance under low N conditions. 6458RIB: Average and stable yield performance across environments. Excellent Check Plot score, but low yield response to N fertilizer. High Workhorse index. 6718RIB: Combines high Check Plot score and yield response to N fertilizer. High yield response to maximum plant population. High Workhorse index. 47