The relationship between corn (Zea mays L.) yield and plant height has been poorly documented in major corn production systems. This study was conducted to assess the relationship of corn yield with plant height under four major corn production systems at Milan, TN from 2008 through 2010. Six N treatments at rates of 0, 62, 123, 185, 247, and 308 kg N ha−1 with four replications were evaluated in a randomized complete block design in the following corn production systems: nonirrigated corn after corn, nonirrigated corn after soybean [Glycine max (L.) Merr.], nonirrigated corn after cotton [Gossypium hirsutum (L.)], and irrigated corn after soybean. The regression of corn yield with plant height was significant and positive at 6‐leaf growth stage (V6), 10‐leaf growth stage (V10), and 12‐leaf growth stage (V12), and mostly became stronger as plant growth progressed from V6 to V10 and to V12 under an exponential model in the four corn production systems for all 3 yr. In general, corn yield was strongly related with plant height measurements made at V10 and V12. Factors affecting the responses of plant height measured at V6, V10, and V12 or/and yield to the N treatments may have contributed to the variations of determination coeffient (R
2) values across years. In conclusion, corn yield may be predicted with plant height measurements collected during V10 to V12. This prediction provides a physiological basis for the utilization of high resolution plant height measurements to guide variable‐rate N applications within the field on corn at around V10 and to more accurately estimate yield for earlier grain marketing purposes.
Research on how land suitability affects yields and breakeven prices for switchgrass (Panicum virgatum L.) grown as a bioenergy crop is lacking for the U.S. Southeast. Data from a 3‐yr multilocation experiment at Milan, TN, were analyzed to determine the influence of soil drainage and landscape position on switchgrass yield and farm‐gate breakeven price. Plots were seeded in 2004 with ‘Alamo’ at 2.8, 5.6, 8.4, 11.2, and 14.0 kg ha−1 pure live seed (PLS). Plots were split in 2005 and N was applied at 0, 67, 134, and 201 kg N ha−1. Farm‐gate breakeven prices for 5‐ and 10‐yr production contracts were determined by calculating unit production costs from enterprise budgets that varied by input level and yield. Maximum yields occurred at 67 kg N ha−1 on well‐drained soils and at higher N levels on less‐well‐drained soils. Yield response to seeding rate (SR) was insignificant or small relative to other factors. Averaged across treatments, the well‐drained upland location suitable for row crops had the largest yield (17.7 Mg ha−1) and lowest breakeven price ($46 Mg−1) for a 10‐yr period. In contrast, the poorly drained flood plain location considered marginal yielded lowest (8.5 Mg ha−1) and had the highest breakeven price ($69 Mg−1). Breakeven prices were sensitive to yield, N price, and fuel price. Results suggest a lower breakeven price for switchgrass in the U.S. Southeast as compared with other U.S. regions, mainly due to high yields for the Alamo variety.
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